Zoology

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Larval fish assemblages of selected estuarine and coastal systems in Kwazulu-Natal, South Africa
(1996) Harris, Shael Anne; Cyrus, D.P.; Beckley, L.E.
This study focuses describing assemblages of fish larvae occurring in potential nursery habitats and elucidating the recruitment processes of fishes in the KwaZulu-Natal region. The composition, the degree of estuarine-association of all taxa, temporal and spatial abundance patterns, developmental stages and were examined in three large estuarine systems, a surf zone habitat and in the nearshore marine environment. In addition, two 24-h inlet studies were undertaken to ascertain diel patterns. Relationships between larval densities with environmental variables were also examined to gain insight into the possible causal mechanisms for the observed abundance patterns. Larval fish samples from Durban Harbour and Richards Bay Harbour were collected at top, mid and bottom depths in the dredged channel 100 to 200 m from the harbour entrance, over 13 and 12 month study periods, respectively. Larval fish from the St Lucia Estuary were collected over 12 months at a foxed station 4 km from the mouth. A total of 8 797 fish larvae, representing 64 families and 144 taxa, was collected in Durban Harbour. From Richards Bay Harbour, 105 taxa representing 53 families were collected from a total of 7 163 larvae. Larvae of the thorny anchovy, Stolephorus holodon, were very abundant in both harbours (32% and 10% of the total catch, respectively), with the blueline herring Herklotsichthys quadrimaculatus (30%) and an unidentified goby Gobiid 12 (9%) being dominant in Durban Harbour and in Richards Bay Harbour, respectively. Conversely, in the St Lucia Estuary, 51 590 larvae in total were collected represented by 85 taxa from 44 families. The river goby Glossogobius callidus (67%) and the estuarine roundherring Gilchristella aestuaria (19%) were the most dominant species. Larval fish in the surf zone were collected monthly, using a pushnet, at six stations up to 3 km north of the St Lucia Estuary mouth. To determine any diel patterns a 24-h study was also undertaken in the surf zone when the estuary mouth was closed. Far more larvae were collected during the 24-h study compared to the 12-month study: 13 731 larvae and 2 931 larvae, respectively. The larval assemblage was characterised by taxa in the families Sparidae, Haemulidae, Ambassidae, Tripterygiidae and Chanidae. The most abundant species were Pomadasys olivaceum, Ambassis sp., Rhabdosargus holnbi, Croilia mossambica and Chanos chanos. Fish larvae were also sampled in the adjacent nearshore coastal zone, from five stations in a transect up to 2.5 km offshore, and from two stations north and south of the St Lucia Estuary mouth. The assemblage consisted of 246 taxa representing 98 families from a total of 6 069 larvae. Larvae in the families Myctophidae and Tripterygiidae comprised 21% and 16% of the total catch, with the dominant species being an unidentified triplefin, Tripterygiid 1, and the lanternfish Benthosema fibulatum. The percentage contribution to total number of larvae of estuarine-associated fish species increased from "estuarine-habitat" (St Lucia Estuary) to "semi-estuarine habitat" (Richards Bay Harbour and the surf zone) to "marine-habitat" (Durban Harbour and the nearshore coastal zone). Species representative of each estuarine-association group were, for example: G.aestuaria, Thryssa vitrirostris and Rhabdosargus spp.-estuarine-dependent; S.holodon, C.mossambica smdAmbassis spp - partially estuarine-dependent; unidentified gobies (Gobiid 12 and Gobiid 27), unidentified tripleflns (Tripterygiid 1), Lampanyctus alatnst H.quadrimaculatus and Umbrina ronchus -estuarine-independent. In all study areas, different recruitment periods were evident for each estuarine-association group with peaks in abundance occurring in all four seasons. This was dependent upon the seasonality of the dominant species present in a particular study area. In the estuarine environments, young larvae (preflexion and flexion developmental stages) of estuarine-dependent species were moderately abundant whereas, old larvae (postflexion) and early juveniles of partially estuarine-dependent species predominated. The surf zone habitat was dominated by postflexion larvae (68% of total catch) of estuarine-associated species, with early juveniles of estuarine-independent species being prevalent in the 24-h study when the estuary mouth was closed (50%). In the nearshore coastal environment larvae of marine species not dependent of estuaries were mainly at the preflexion and flexion developmental stages (67% of the total catch). Stepwise regression statistics and multivariate analysis (classification and ordination) clearly indicated the importance of environmental factors in determining the structured of the larval fish assemblages. Furthermore, the correlations of larval densities with environmental variables was found to be species-specific. The most significant variable accounting for the observed distributional patterns of the fish larvae was turbidity (pw = 0.55 - weighted Spearmans rank correlation). However, the intercorrelations between all the environmental variables measured were also important in determining abundance patterns (e.g. pw = 0.48 for salinity + turbidity; pw = 0.41 for salinity + temperature + turbidity). Analyses of tidal exchange of fish larvae on flood and ebb tides, in Durban Harbour, Richards Bay Harbour and in the St Lucia Estuary mouth, indicated that selective tidal stream transport is a recruitment mechanism employed by certain species (e.g. Argyrosomus sp., Pomadasys commersonnii and Solea bleekeri) to enable retention in the estuarine habitat i.e. larval densities of these species were significantly higher on flood tides and in bottom waters (P < 0.05). In conclusion, results of the present study have indicated that diverse and dynamic larval fish assemblages are present in the estuarine and coastal systems on the KwaZulu-Natal coast. Larvae (mainly postflexion) of estuarine-associated fish species were abundant in all three estuarine systems and the surf zone suggesting that all these habitats function as nursery sites for particular species. Additional species-specific studies on larval stages of recreational and commercially important linefish species are needed in order to make management decisions regarding the conservation and exploitation of these species.
The benthos of the Siyaya estuary : species composition, density and distribution
(1996) Mackay, Christine Fiona; Cyrus, D.P.
This study describing the zoobenthos of the Siyaya Estuary is the result of data collection spanning three consecutive years (1992 - 1994). The investigation of the zoobenthic component of the estuary, forms part of a multidisciplinary study to monitor the effects of catchment rehabilitation. The abiotic and biotic characteristics of the estuary have been used as a tool to determine the effectiveness of improved management practices in the catchment. The response of the zoobenthos was first examined in 1983, and this showed 37 zoobenthic taxa with a strong marine/estuarine component. From 1992 to 1994, the zoobenthos was sampled on a seasonal basis at each of five sites along the length of the estuary. A total of 88 taxa representing four phyla were collected over three years. During 1992, 50 taxa were recorded in samples and the impression was of a wide faunal assemblage, with representatives from Nematoda, Annelida, Crustacea, Insecta, and Gastropoda. Five less taxa were recorded during 1993, although the faunal assemblage was still fairly wide with the inclusion of several more insect taxa. The greatest number of taxa were recorded during 1994. Of the 59 zoobenthic taxa, 40 represented the freshwater component. Over the three year period, few decapod invertebrates were sampled, the majority were primarily post prawn larvae. Results of this study have therefore shown that the number of taxa have increased. However, the majority of new taxa added to the total species list belong to the freshwater component of the zoobenthos. This is due to prolonged closure of the estuary mouth as a result of the prevailing drought conditions. A comparison of zoobenthic densities from the estuarine and freshwater components revealed that the estuarine component still dominated the benthos, and that this dominance decreased from 1992 to 1994. During 1992, the estuarine component constituted 97.2% of the total zoobenthos, while this decreased to 84.6% and 54.4% in 1993 and 1994, respectively. Of the overall mean density of 29 623 invertebrates m"2 calculated from the sum of five sites, on a seasonal basis over three years, 48.7% (J4 433 m"2) of the total was from 1992. Zoobenthic densities declined in 1993 and 1994, to 28.2% (8 340 m"2) and 23.1% (6 850 m"2) of the total for the three years. Zoobenthic densities were generally highest in winter, and lowest in autumn. However, a multifactor ANOVA showed that season alone was not a significant factor governing the increase or decrease of zoobenthic densities. The relict estuarine amphipods Granclidierella lignorum and Corophium triaenonyx, and the tanaid Apseudes digitalis were among the taxa dominating the benthos in all seasons. Various parameters were used to determine the physico-chemical condition of the estuary, and several were used as an input matrix to determine their effects on the distribution and abundance of the zoobenthos. Salinity, temperature, dissolved oxygen concentration, depth and turbidity were measured each year. In 1994, a more detailed water quality and sediment analysis was performed. A gradient of turbidity, salinity and oxygen existed from the upper to lower reaches of the estuary, and the substratum constituted medium sands in the lower reaches to detrital muds with silt patches in the upper reaches. The estuary became increasingly fresh over the study period, as salinity declined in the upper reaches from 6%o in 1992 to 0%o at the end of 1994. A suite of multivariate techniques involving classification and ordination methods revealed that sediment particle size was not the most important environmental factor determining species distributions. A combination of turbidity, dissolved oxygen, pH and the percentage organic content proved to be the most important effect of the environment, accounting for most of the variability in the distribution and abundance of the zoobenthos. On the basis of the results obtained, it is concluded that the effects of improved catchment management practices have had a positive effect on the ecology of the estuary, and particularly on the state of the zoobenthos. However, the prevailing drought conditions also had an effect on the benthos, in terms of a change in species composition from 1992 to 1994. Despite this, the estuarine taxa still dominate the estuarine benthic fauna.
Bioaccumalation of metals in mullet from Mhlathuze Estuary and the effect of Cu and Pb on the uptake kinetics,haematology and acid-base balance of Liza dumerelii.
(2001) Mzimela, Hendrick Mabutho Mduduzi; Wepener, V.; Cyrus, D.P.
Mhlathuze Estuary came into being when the original Richards Bay was divided into the northern part, which was dredged to form the habour and the southern part, which was reserved for the preservation of natural resources as a sanctuary. This sanctuary was however disturbed during development. The disturbance took the form of canalisation and redirection of Mhlathuze River and cutting of the new mouth after the berm wall was erected. These were drastic changes, which had a profound influence on the sanctuary (estuary). Resultant changes included siltation of the estuary and loss of water residence time. The construction of the harbour was in line and enhanced the increase of industries in the Richards Bay area. The industries manufacture a number of metal products and also utilise other metal ores in the manufacturing process. The high population growth and concentration of industries in the area have a potential to pollute the sanctuary and the nearby harbour. Research was undertaken to assess the amount of metal pollution in the Mhlathuze Estuary and their possible effects on the biota. In order for meaningful assessment of ecosystem health to be realised, the cause and also the effects of metals were investigated. Metals are non-biodegradable pollutants. Their persistence can result in them taken up by biota to concentrations far above ambient levels. This is termed bioaccumulation. The accumulation of metals in biota can result in stress, which can in turn induce changes in physiological parameters and other metabolic processes. The need to understand and predict the stress conditions, which metals will pose to fish, and extrapolate the effects of pollutants from laboratory to populations levels, have necessitated the search for physiological and biochemical indicators of health and sublethal toxicant effects. To determine the effects of these pollutants on the structure and functions of metabolic processes, it is important to monitor the bioaccumulation of such metals in the field and to expose the fish to environmental relevant concentrations of the same metal under controlled laboratory conditions. In this study, this was achieved by conducting field observation and sampling, that involved the collection of water, sediment, fish (Liza diimerelii), benthic invertebrates (Paratylodiplax blephariskios and Apsendes digitalis) and submerged macrophytes (Zostera capensis) and analysing for metal accumulation. Seven metals, i.e. Al, Cr. Cu, Fe, Mn, Pb and Zn were analysed in the abovementioned abiotic and biotic compartments following standard nitric/perchloric acid digestion techniques and using a Varian AA50 atomic absorption spectrophotometer. The study found elevated metal concentrations in the water and sediment samples from the Mhlathuze Estuary. High metal accumulation in water and tissues were found during summer months, which coincided with high rainfall and floods. The highest metal concentrations in the sediment were found during periods of low flow e.g. in winter and spring. A significant correlation was found between metals in water and fish liver tissue. Further significant correlations were recorded between metals in sediment and benthic invertebrates. Metals occur in nature as ions and compounds. In order to understand their effects on biota, the effects of metal mixtures have to be investigated. In a metal mixture, the effects of metals can be additive, synergistic or antagonistic. Laboratory investigations involved the determination of effects of copper (Cu), lead (Pb) and their mixture on the haematology and acid-base balance of a mullet species, Liza dumerelii. Changes in physiological parameters measured, must be directly affected by the exposure to a toxicant, and the changes must not be because of other factors such as handling stress. Experiments were, therefore conducted in controlled environmental conditions to maintain constant temperatures and photoperiods. Haematological and acid-base balance evaluation of fish blood provides valuable information concerning the response of fish to changes in the external media, and could be used to diagnose abnormal functioning of physiological mechanisms in fish. Haematological parameters measured were, red blood cell count (RBC), white blood cell count (WBC), haematocrit (Hct), haemoglobin (Hb), mean cell volume (MCV), mean cellular haemoglobin concentration (MCHC), mean cellular haemoglobin (MCH), blood glucose, and plasma lactate. Acid-base balance parameters measured were bicarbonate (HCO3"), pH, PC02, the plasma ions, sodium (Na), potassium (K), chloride (CI), and osmolality. In the study of the effects of metals on physiology, the combination of Cu and Pb was found to induce more physiological stress as compared to individual metals. Copper binds to ligands in the gill lammellae of fish where it can disrupt the Na and CI balance. Lead on the other hand inhibits delta aminolevulinic acid dehydratase, an enzyme responsible for haemoglobin synthesis thus decreasing the potential for red blood cells to carry oxygen. During stress the organism responds by either increasing or decreasing the particular parameter as a compensatory measure. The fish responded to the metal stress by increasing the RBC's, blood glucose concentration and haemoglobin. This was an attempt by the fish to increase the respiration potential, which was decreased by both the disruption of gill lamellae by Cu, and the inhibition of haemoglobin synthesis by Pb. Bicarbonates and PCO2 levels were also increased. The HC03" increase was probably due to increase in lactic acid that acidified the blood or, it was caused by the B -adregenic stimulation of red blood cells, which also slows the process of CO? elirnination from the blood. The amount of metal accumulation in the Mhlathuze Estuary raises some concerns. While previous studies of metal accumulation in the water, sediment and fish from the Mhlathuze Estuary are comparable to this study, there seems to be a gradual increase in the amounts of metals from both the biotic and abiotic components of the Mhlathuze Estuary. The existence of metals in the water bodies as individual metals or as mixtures, as it was also shown in the study, has an effect on the physiology of the fish communities.
Invertebrate plankton assemblages in the surf zones of St. Lucia and Mhlathuze Estuaries, KwaZulu-Natal, South Africa
(2002) Buthelezi, Philokuhle Patrick; Owen, R.K.; Cyrus, D.P.
This study described the surf zone invertebrate plankton assemblages of the exposed sandy beaches adjacent to the St Lucia and the Mhlathuze estuaries. The broad aims of this study were to identify the invertebrate plankton assemblages, to describe these in terms of species composition, abundance and spatio-temporal changes, and to relate these communities to adjacent estuarine fauna. Physico-chemical variables which influenced the community structure were investigated. Samples previously collected at St Lucia between February 1992 and January 1993 by Harris (1996) were used. Additional sampling was carried out monthly from November 1998 until October 1999 in the Mhlathuze surf zone during the day and night Invertebrate assemblages in the surf zones described in this study were compared with their adjacent estuaries to investigate the relationship between these habitats.. tn total, 171 taxa were collected from both systems. Total abundances ranged from Q.31 to 1570 and 0.17 to 106 individuals/m3 at the St Lucia and Mhlathuze surf zones respectively. Plankton and bentho-planktonic organisms belonging to different taxonomic types formed the major component of the assemblages in the St Lucia and Mhlathuze surf zones. The surf zone invertebrate communities were mainly dominated by crustaceans, with the mysids Gastrosaccus spp. and brachyurans (megalopae) dominating the taxa at St Lucia and the Mhlathuze estuaries respectively. Collectively copepods dominated the boioplanktonic forms. Other commonly abundant hotoplankton included siphonophores, chaetognaths, dadocerans and medusae. The meroplankton composed of polychaetes and decapod larvae which dominated this group. Decapod larvae included pagurid, brachyuran and shrimp-like forms. Benthoplanktonic crustaceans sampled from these surf zones included surf zone/beach mysids of the genus Gastrosaccus, the isopod Grolana spp. and amphipods. Classification and ordination analyses revealed distinct day and night communities, with less seasonal and spatial (site) differences. Nine and eight fauna! assemblages separated on basis of season were identified at St Lucia and the Mhlathuze respectively. At St. Lucia four day assemblages were identified: (i) the day summer/autumn assemblage characterised by the dominance of calanoids, brachyuran megalopae and zoeae, penaekt prawns, the copepod Corycaeus sp.; (it) the day summer assemblage characterised calanoids, Sagitta sp., Lucifer sp., brachyuran megalopae and Gastrosaccus spp.; (iii) the day autumn/winter characterised by Sagitta sp., calanoids, and Oro/ana spp.; (iv) the day spring assemblage characterised calanoids, Sagitta sp., Gastrosaccus spp. brachyuran megalopae, Lucifer sp. and penaeid prawns. Within the night community five assemblages were distinguished: (i) the night summer assemblage characterised by Gastrosaccus spp., Grolana spp., brachyuran megalopae and zoeae, calanoids and cumaceans; (ii) the night autumn assemblage dominated by Gastrosaccus spp., calanoids, Grolana spp., brachyuran megalopae, and Sagitta sp.; (iii) the night autumn/winter assemblage characterised by the dominance of Grolana spp., calanoids, Gastrosaccus spp. and brachyuran megalopae; (iv) the night spring assemblage characterised by Gastrosaccus spp., calanoids, and Grolana spp.; (v) the night spring/autumn assemblage characterised by the dominance of calanoids, Grolana spp., and brachyuran megalopae. In the Mhlathuze surf zone, the day community was formed by four assemblages which included: (i) the Mhlathuze day summer/autumn assemblage dominated by brachyuran megalopae and zoeae, ctenophores, and calanoids; 00 me Mhlathuze day winter assemblage characterised by the dominance of calanoids, ctenophores and brachyuran megalopae; (iii*) the Mhlathuze day winter/spring assemblage characterised by calanoids, siphonophores and Sagitta sp.; (tv) the Mhlathuze day spring/summer characterised by brachyuran megalopae, Grolana spp. and Gastrosaccus spp. Within the night community at the Mhlathuze, four assemblages were identified which included: (i) the Mhlathuze night summer assemblage characterised by the dominance of brachyuran megalopae, Grolana spp., and calanoids; (ii) the Mhlathuze night autumn assemblage characterised by the dominance of Grolana spp., brachyuran megalopae, Gastrosaccus spp. and ctenophores; (iii) the Mhlathuze night spring/summer assemblage characterised by brachyuran megalopae, Grolana spp. and calanoids; (iv) the Mhlathuze night winter/spring assemblage characterised by the dominance of calanoids, brachyuran megalopae, Gastrosaccus spp. and Grolana spp. Assemblages in these surf zones showed diverse invertebrate plankton taxa which originated from different habitats such as intertidai and offshore marine environments and nearby estuaries. The significant differences recorded between day and night communities were attributable to the nocturnal activity of many crustacean bentho-planktonic groups including beach/surf zone mysids, isopods and decapod larvae in the St Lucia and Mhlathuze surf zones. At St Lucia, significant differences were found between summer and winter communities, while at the Mhlathuze significant differences were recorded between seasonal groups. With respect to site, there were no significant differences recorded at St Lucia and Mhlathuze. This indicated that there was no apparent accumulation of planktonic invertebrates in the surf zone near the estuary mouths. Significant differences were also recorded between the St Lucia and Mhlathuze surf zones in terms of their community structure, abundance and diversity where higher densities were recorded at the St Lucia estuary. These results reflected differences in physical processes and conditions that the St Lucia and Mhlathuze surf zone communities were exposed to. These included currents, the extent of freshwater input from the estuary, wind-dri ven-wa ve action, temperature, salinity and turbidity. Significant differences between the St Lucia and Mhlathuze communities were also ascribed to a dry period (1992/93) at St Lucia compared with the Mhlathuze which was sampled during a wet period (1998/99). However, salinity and temperature were the most influential physico-chemical factors structuring the two communities. Although variables such as salinity and longshore currents may have influenced the surf zone communities, distinct temperature-related, seasonal patterns occurred with decreased densities in winter. A comparison of surf zone plankton recorded in this study with estuarine communities indicated the existence of a faunal relationship between the surf zones and estuaries of the St Lucia and Mhlathuze systems. Densities of common taxa were slightly higher in the surf zone than in the estuaries, emphasising the importance of these surf zones as habitats rather than being used as a transient area between the estuary and offshore environments. The St Lucia and Mhlathuze surf zones were important to many faunal groups which included the mysid Gastrosaccus spp., brachyurarts (megalopae and zoeae), the isopod Orolana, copepods and chaetognaths. However, during present study it was difficult to demonstrate the utilization of these surf zones as nursery grounds due to the use of 500 mesh which precluded the collection some larval stages. It is therefore recommended that more detailed research be conducted with smaller mesh nets such as 60 ^im in these surf zones to better understand the importance of surf zone ecosystems.
Habitat utilisation by juvenile fishes in Mhlathuze Estuary and Richards Bay Habour
(2002) Weerts, Steven Paul; Cyrus, D.P.
Estuaries in South Africa are important nursery areas for many fish species, but this role has been threatened by habitat degradation due to anthropogenic impacts, especially in KwaZulu-Natal systems. This has emphasised the importance of harbours in the province for juvenile estuarine fishes, but as areas of ongoing development the future ecological value of harbours is not guaranteed. Descriptions of shallow water estuarine habitats and an assessment of their utilisation by juvenile fishes is important if fish stocks are to be effectively managed for conservation purposes, and recreational and subsistence fisheries. The aim of this study was to investigate assemblages of juvenile fishes associated with a range of habitats in Mhlathuze Estuary and the adjacent Richards Bay Harbour. Habitats in these systems are typical of those in permanently open KwaZulu-Natal estuaries, and by virtue of their size they bestow considerable conservation status on the estuary and the harbour. Fish ranging from postlarval to adult were sampled using a fine-mesh seine net. Endemic and conservation worthy species, as well as fishes valued in recreational and subsistence fisheries were recorded in both systems. Distinct assemblages of fishes were associated with different habitats. Differences in species compositions were largely due to habitat structure rather than the influences of physico-chemical variables. Eelgrass, Zostera capensis, is an important nursery for many fishes not found in other habitats. Presently in KwaZulu-Natal Zostera only occurs in Mhlathuze Estuary and St Lucia. Fish diversity in several other systems where it historically occurred may now be limited by its absence. Deep access channels, clear waters and an abundance of prey items render the harbour an attractive foraging ground for piscivorous fishes. Mangroves in this system play an important role as predation refugia for high densities of small fishes. Other habitats in both systems, including mudflats and sandbanks were also important. Many species showed a high preference for only one habitat type and the loss of any habitat in the estuary or the harbour would reduce biodiversity and the value of these systems as nursery areas. Comparison of fishes associated with structurally similar habitats in different systems indicated that physico-chemical variables do influence the role of habitat in estuarine ecosystems. Sandbanks in the clear waters of the harbour supported different assemblages of fishes from sandbanks in the more turbid estuary. This could be related to turbidity preferences of selected species as well as higher predation threat in the harbour. Mangroves in both systems also supported different fish communities, probably also as a result of different predation risk and therefore indirectly attributable to turbidity differences in the two systems. Results from this study highlight the conservation importance of the systems studied. Whilst it is probable that a multitude of species-specific responses to physical and biological factors influence fish assemblages associated with different habitats, results are broadly applicable to other KwaZulu-Natal estuaries. The distinct roles of structurally different habitats, and the influence of physico-chemical conditions, in the nursery function to different fish assemblages, illustrate the need for clearly stated management objectives at a provincial level.
The macrobenthos of the Mlalazi estuary: KwaZulu-Natal
(2002) Mabaso, Samkelisiwe Hlengiwe; Vivier, L.; Owen, R.K.
The Mlalazi estuary situated in the Mlalazi Nature Reserve is regarded as one of the least spoiled estuaries on the KwaZuIu-Natal coast, with the relatively unspoilt character being enhanced by the location of the estuary in a marine protected area (MPA). Available information of the biota of the estuary is, however, limited to one ecological study undertaken by Hill (1966). A survey, conducted by the Coastal Research Unit of Zululand for the purpose of a masters study, of the benthic community was initiated during the period 1989-1991 but unfortunately was never written up or published. Additional sampling in the Mlalazi estuary was carried out from August 1999 to July 2000 at the same six sites where the 1989-1991 samples were collected, with the addition of site 7 in the mouth region. A prawn farm was established in 1992 approximately 500 m from and adjacent to the middle reaches of the estuary. Concern has been expressed about water being discharged into the estuary from the prawn farm since this represents a source of anthropogenic disturbance. This study focused on describing the water quality and macrobenthos of the Mlalazi estuary during the 1989-1991 and 1999-2000 sampling periods. The community structure, temporal and spatial abundance patterns of the two sampling periods were examined A relationship between the observed community patterns and environmental variables was also determined to find the possible causes for the observed abundance patterns. Since no study has been done on the potential impact of the prawn farm on the biotic community of the estuary, comparison of the 1989-1991 (pre-prawn farm period) and 1999-2000 (post prawn farm period) sampling periods attempted to correlate the prawn farm activities to changes in community patterns of the two periods. The physico-chemical results indicated high concentrations of nutrients (nitrates, nitrites, orthophosphates, total phosphates) during the two sampling periods. Since there were no major industries and the prawn farm was not yet established during the 1989-1991 sampling period, high nutrient concentrations were suspected to be due to agricultural runoff. The high nutrient load during the 1999-2000 sampling period indicated the prawn farm as the source. This is because high concentration of these nutrients were recorded at the prawn farm outlet and at Site 3, which is the site closest to the prawn farm outlet, compared to the rest of the sites. The results of the biotic analysis indicated that the biotic community of both periods was disturbed to some degree with the 1989-1991 period indicating that it was more disturbed than the 1999-2000 sampling period. The 1989-1991 period was characterised by a reduced number of taxa (28) and was dominated by highly abundant opportunistic species such as Prionospio and capitellid polychaetes. The 1999-2000 period recorded 36 taxa but was also dominated by highly abundant Prionospio spp Multivariate analysis (classification and ordination) indicated the importance of environmental factors in determining the structure of biotic communities for both the sampling periods. The significant variable accounting for the observed distributional patterns of the biotic community in 1989-1991 was the median particle diameter (pw = 0.505) whereas in the 1999-2000 sampling period it was salinity (pw - 0.292). However a combination of environmental factors played an important role in determining the observed biotic patterns. A combination of salinity, oxygen, turbidity, depth and median particle size was responsible for distribution of the benthic fauna during the 1989-1991 period. During the 1999-2000 sampling period, salinity and organic content formed a combination most responsible for the biotic patterns observed. Even though the above results indicated that organism abundance and distribution were largely determined by physical factors, the chemical results did indicate that large amounts of nutrients in the estuary are being discharged from the prawn farm. The impact on the estuary and the organisms inhabiting it may not be apparent at this stage but there is a concern that continuous discharge of such a high nutrient load may affect the estuary in future. A monitoring program should therefore be initiated with this study being used as a baseline from which references can be made.
Macrobenthic community and ecotoxicological status of the Nhlabane Estuary
(2010) Vivier, Leon; Cyrus, D.P.
The Nhlabane Estuary is a small temporary open/closed estuary along the Northern KwaZulu-Natal coastline, 40 km north of Richards Bay. Historically, the Nhlabane Estuary formed the tidally influenced lower reaches of the Nhlabane coastal lake system, but in 1978, its connection with the coastal lake was permanently severed by the construction of a weir across the upper end of the estuary. The weir altered the natural flushing regime of the estuary, resulting in the estuary mouth often remaining closed for a number of years. Dune mining operations around the estuary raised concerns about trace metal concentrations in the estuary. This study was initiated following concerns about the ecological integrity of the estuary in relation to reduced freshwater input into the system and its effect on the macrobenthic community, as well as the potential trace metal contamination of the estuary water, sediment and biota due to mining activities. The study aimed to describe the macrobenthic community of the Nhlabane Estuary during the post-drought period 1996-1999, to assess the ecotoxicological status of the Nhlabane Estuary in relation to dune mining activities and to determine the suitability of two resident amphipod species, Corophium triaenonyx and Grandidierella lignorum, as potential test organisms for sediment toxicity testing in estuarine environments. Quarterly samples of the benthos, water and sediment were collected at six sites in the estuary over the period 1996-1999. Physical water quality parameters were measured in situ at each sampling station. At the start of the study, the estuary showed a highly stressed benthic community characterized by low species richness and densities, caused by a combination of a naturally occurring drought event exacerbated by anthropogenically induced lack of freshwater input into the system. The number of taxa and benthic densities increased significantly after the mouth was breached. The 32 macrobenthic taxa recorded during the four year study period were dominated by estuarine crustaceans, notably the two amphipods amphipods, C. triaenonyx and G. lignorum, and the polychaetes Ceratonereis keiskamma, Desdemona ornata and Prionospio sexoculata and the tanaid Apseudes digitalis. Multivariate analysis showed a marked temporal change in the benthic community, reflected in significant changes in the number of taxa, density, species richness and species diversity during the 1996-1996 study period. This represented a recovery in the Nhlabane Estuary benthic following the extended period of mouth closure during the 1992-1995 drought. Trace metal concentrations in the Nhlabane Estuary water, sediment and invertebrate tissues were consistently lower than in regional anthropogenically influenced estuaries. Normalization of Nhlabane Estuary sediment metal concentrations to background concentrations for uncontaminated KwaZulu- Natal coastal areas showed the system to be uncontaminated, with dune mining not being the cause of pollution in the system. Trace metal concentrations in the two amphipod species, G. lignorum and C. triaenonyx, also compared favorably with that found in similar species, providing further evidence of the relatively uncontaminated conditions in the system. Amphipods are commonly utilized throughout the world to test the toxicity of potentially contaminated sediments in marine and estuarine environments, because they are ecologically relevant, are sensitive to sediment contaminants and are suitable for laboratory experimentation. Laboratory studies with cadmium, zinc and copper to test the suitability of the two local amphipod species, Grandidierella lignorum and Corophium triaenonyx as test organisms in sediment toxicity tests, showed that both species accumulated Cu and Zn in their bodies in relation to increasing concentrations of the metals in the sediment. The ability to accumulate trace metals during exposure to contaminated sediments is one of the primary requirements in sediment bioassay test organisms, and results from this study have clearly shown both species to be sensitive to and accumulate bioavailable Cu and Zn in sediment. Lack of estuarine management means that estuaries in South Africa have been subjected to increasing pressure, both indirectly from the effects of catchment utilization, which affect their water supply, and directly from the increasingly industrial and residential development along the coastal zone. As a result, many South African estuaries have become functionally degraded, which has resulted in a loss of species. The Nhlabane system is located in a forestry dominated catchment, so the system is subjected to limited industrial and residential encroachment and organic and inorganic chemical contamination. Results from this study showed that trace metal concentrations in the water and sediment were low and within environmentally acceptable levels. Construction of the Nhlabane weir, however, deprived the Nhlabane Estuary of adequate freshwater and altered the natural flushing regime. The functioning of the estuary and the state of its biotic communities are largely dependent on the maintenance of the estuarine-marine link, which in turn are directly related to freshwater input from the lake. In an Estuarine Flow Requirement (EFR) study, which forms part of the RDM based Ecological Reserve Determination process for aquatic ecosystems in South Africa, water allocations were determined to maintain the ecological integrity of the Nhlabane Estuary. The EFR study recommended that during droughts the system be permitted to close for a year, but that this was only acceptable 1 year in 3. The recommended environmental flows for the estuary have not been implemented by DWAF and no allocation of water is allowed for the Reserve for the estuary. As such, abstraction of water from the lake is still causing water levels in the lake to be consistently below overflow levels. Results from this study showed that the Nhlabane Estuary, once regarded as one of the most pristine estuaries along our coastline, has been adversely affected by impoundment of the lake to the point where it ceases to be a functional estuary for periods of time extending over a number of years. Although this study has shown that the ecotoxicological condition of the estuary is generally good, the system is hydrologically stressed due to freshwater deprivation. There is currently no management plan for the estuary that can address these issues. Based on this, the following key issues should be addressed if the future ecological functioning of the Nhlabane Estuary is to be ensured: It is imperative that the Ecological Reserve for the estuary be implemented, as this will ensure that freshwater allocations for the estuary be adhered to. A management plan should be designed and implemented for the estuary by MCM in which all stakeholders are represented. Management of the estuary should incorporate not only the estuarine environment, but also be directed at a catchment level. A monitoring program consisting of key ecological components, which should complement the existing database and investigate long-term temporal and spatial changes in important biotic communities in the estuary, should be regarded as a priority. The Nhlabane Estuary should be considered to be of high conservation importance as it is one of the few estuaries along the coastline that is not adversely affected by industrial development, other than dune mining, in its catchment. Motivation for the Nhlabane Estuary to be made a Estuarine Conservation Areas (ECAs) should be considered.
The diet of selected benthic feeding fish in the Mfolozi-Msunduzi system, KwaZulu-Natal
(University of Zululand, 2011) Nhleko, Jabulile Blessed Busisiwe; Cyrus, D.P.; Vivier, L.
The St Lucia estuarine system is considered to be the largest nursery area for estuarine-associated marine fish in southern Africa. The prolonged mouth closure due to regional droughts has resulted in large declines in its fish and prawn communities with deleterious consequences for regional marine populations, especially those that require estuaries for completion of their life cycle. Mouth closure of the St Lucia system contributed to a renewed interest in the St Lucia-Mfolozi System link, particularly the importance of the Mfolozi system in terms of its role as a refuge and alternative nursery area for species which cannot recruit into the closed St Lucia system when the Mfolozi remains open. The Mfolozi-Msunduzi estuarine system is the closest open estuary to St Lucia but there is a paucity of data on the ecological functioning of the system. Studies on the benthos of the Mfolozi-Msunduzi estuarine system have found it to be impoverished but large numbers of benthic feeding fish are present in the system at times. This raised the question: if the zoobenthic community is impoverished and high numbers of benthic feeding fish are nevertheless present in the system, then what are these fish feeding on? The stomach contents of 961 fish of 15 different species collected between August 2008 and March 2010 using seine and gill nets were examined. Of these 15 species, only six were caught in sufficient numbers for gut analysis. The six species that were used in the analysis were Leiognathus equula, Acanthopagrus berda, Glossogobius giurus, Ambassis ambassis, Ambassis gymnocephalus and Ambassis natalensis. Four methods were used for stomach content analysis, namely Frequency of occurrence, Numerical occurrence, Points (Proportional Volumetric) analysis and Index of Relative Importance (IRI). It was found that the diet of L. equula was dominated by the copepod, P. stuhlmanni, with the macrobenthos contributing <0.5% to the overall diet of the species. Similarly, the diet of A. berda was dominated by P. stuhlmanni, with the benthic fauna contributing <1.5% to the diet. The dominant prey in the diet of G. giurus was Glossogobius sp, while the only benthic species that was fed on was the crab P. blephariskios, which contributed not more than 0.3% to the overall diet of the species. A large proportion of the Ambassids (A. ambassis, A. gymnocephalus and A. natalensis) had empty stomachs, whilst most of those that contained food had stomachs < 30% full, based on the Points determination method. The diet of all three Ambassid species was dominated by P. stuhlmanni, with A. gymnocephalus feeding only on the copepod. The total contribution of the benthic fauna found in the diet of A. ambassis was <30% and <1% in A. natalensis. Copepods dominated the diets of the majority of the species examined, indicating that in the Mfolozi system, zooplankton rather than benthic organisms are being fed on. This tends to tie in with the impoverished state of the benthic fauna. The results of this study indicate that only those species capable of adapting their diets to whatever is available and abundant to feed on will be able to survive in the Mfolozi-Msunduzi system.
Spatial and temporal distribution of the benthos in the Mfolozi-Msunduzi Estuary, KwaZulu – Natal
(2012) Ngqulana, Sibusisiwe Gloria; Cyrus, D.P.; Vivier, L.
The objectives of the study were to describe the subtidal component of the invertebrate benthic fauna and to investigate spatial and temporal distribution of the fauna. Samples were collected quarterly in 2009 to investigate seasonal patterns of the benthos of the system. Another aim of this study was to determine the benthic biomass of the Mfolozi – Msunduzi estuarine system. Results indicated that 23 taxa were recorded in 2009 with 18 and 15 taxa in the Mfolozi and Msunduzi Estuary, respectively. The most abundant species were the burrowing ocypodid crab Paratylodiplax blephariskios and the polychaete Dendronereis arborifera. These were followed by the polychaetes Ceratonereis sp., Prionospio sexoculata and the amphipods Corophium triaenonyx. Freshwater taxa, such as Simuliidae, Baetidae, Chironomidae and Ecnomidae were recorded in the upper reaches of the Mfolozi Estuary during summer, this was due to the area being dominated by freshwater inflow. No significant differences (p<0.05) were found between sampling seasons and between sampling sites with regard to the mean number of taxa, mean densities (N.m-2), species richness (D), species evenness (J') and species diversity (H'). The cluster and MDS ordination showed that the benthic fauna of the system could be separated into three most important clusters, the first of which comprised mostly of the Msunduzi sites, indicating that seasonal changes did not influence the community structure of the Msunduzi Estuary. the second group comprised mostly of the Mfolozi winter (June and August) samples while the third group comprised the Mfolozi summer (March and November) samples and this clearly showed that seasonal changes played a major role in structuring the benthic community in the Mfolozi Estuary. The SIMPER results indicated that P. blephariskios and D. arborifera were the taxa most responsible for structuring the benthic community in both the Mfolozi and Msunduzi Estuaries. BIOENV showed that the single variable most responsible for structuring the benthic assemblage in the system was sediment particle size, followed by sediment sorting coefficient and temperature. The best combination of environmental factors which played a role in the distribution and abundance of benthos were temperature, sediment particle size and the sorting coefficient. These results showed that sediment characteristics combined with natural seasonal variability (temperature), played the most important role in structuring the benthic community of the Mfolozi – Msunduzi system. In terms of biomass, P. blephariskios was the greatest contributor to the benthic biomass of the system, followed by D. arborifera. The mean benthic biomass at the Mfolozi sites was very low, with highest values recorded at the mouth of the system, while the highest mean benthic biomass at the Msunduzi sites was recorded at sites MS2 and MS1, while the biomass of the remaining sites was less than 50 mg.m-2. Seasonal variations were evident in the Mfolozi – Msunduzi system, with very low biomass of 1883 mg.m-2 dry weight in March, while the highest biomass was recorded in June (16827 mg.m-2 dry weight). The biomass decreased in August (13412 mg.m-2 dry weight) and again in November (12660 mg.m-2 dry weight).
Effect of dietary protein level, feeding frequency and amount of food offered on growth and gastric evacuation of Oreochromis mossambicus fry
(University of Zululand, 2012) Luthada, Rendani Winnie; Jerling, H.L.
Excess protein in fish diet may be wasteful and unnecessarily expensive. Furthermore, when fish are fed insufficiently or excessively, their growth or feed efficiency may decrease, resulting in increasing production costs and water quality deterioration. Therefore this study was conducted to determine the optimum dietary protein level, feeding frequency and feeding rate on growth, gastric and intestinal evacuation of O. mossambicus fry under hatchery conditions, in order to reduce the production costs while optimizing growth rate. Diets contained 20%, 30%, 35%, 40% and 45% protein levels, feeding frequency of once, twice, thrice, four times and five times per day and feeding rates of 10%, 15%, 20%, 25% and 30% body weight per day were tested in separated experiments conducted in a temperature and light cycle controlled environmental room. The results indicated that both dietary protein level and feeding frequency had a significant effect on weight gain, specific growth rate and gross food conversion ratio (ANOVA, P<0.05) but not survival rate (ANOVA, P>0.05). Feeding rate had a significant effect on weight gain and gross food conversion ratio (ANOVA, P<0.05) but not on specific growth rate and survival rate (ANOVA, P>0.05). A diet containing 30% protein level, feeding frequency of four times per day and 15% of the fry body weight per day were the optimal levels obtained from the growth experiments. Dietary protein level had a significant effect on gastric and intestinal evacuation (ANOVA, P<0.05); feeding frequency had a significant effect on intestinal evacuation rate and time (ANOVA, p<0.05) only but not on gastric evacuation rate and time (ANOVA, P>0.05), while feeding rate had no significant effect on both gastric and intestinal evacuation rate and time (ANOVA, P>0.05). The optimum levels obtained in gastric and intestinal evacuation are 40% dietary protein level, feeding frequency of twice per day and a feeding rate of 15% body weight per day.
The Mzingazi gauging weir and its effects on the fish and macrocrustacean communities of Lake Mzingazi
(University of Zululand, 2012) Moloi, Puleng Cathrine; Vivier, L.; Cyrus, D.P.
Lake Mzingazi is a freshwater coastal lake in Richards Bay, KwaZulu-Natal. Because of ongoing industrial and residential developments in the Richards Bay area, the need for potable water increased and led to the construction of a weir across the outlet of Lake Mzingazi. The first weir on this historically estuarine lake was built in 1955, after which it was raised several times to satisfy the increasing demand for water. Due to potential salt-water intrusion via groundwater from the saline Mzingazi River into the lake, another weir, namely the Saltwater Barrier, was built 1.4 km downstream of Lake Mzingazi to limit saltwater intrusion into the lake. The Mzingazi weir largely prevented the migration of fish and crustaceans between the marine/estuarine environment and the freshwater environment. In 2005-2006, the DWA designed and constructed a new and improved gauging crump weir across the lake outlet, which included a pool and weir fishway to allow the migration of fauna in and out of the lake. The fishway was aimed at allowing euryhaline fish species to migrate out to sea to spawn and back to the lake to complete their life cycle since Lake Mzingazi historically served as an important nursery habitat for juveniles of a number of euryhaline fish species. Monitoring of the fishway was required to assess the efficiency of the design, and if necessary, to modify flow conditions to meet the requirements of migrating fauna. This study aimed firstly at monitoring the operation and efficiency of the Mzingazi fishway and secondly, at monitoring its effect on the fish community of Lake Mzingazi. In order to assess the operation and efficiency of the Mzingazi fishway, the fish and macroinvertebrate fauna were sampled at six locations in the Mzingazi system, i.e at the Saltwater Barrier, in the upper Mzingazi River, at the entrance to the fishway, in the fishway pools, at the fishway exit and in the lake immediately above the fishway. The fishway was sampled over two days on a monthly basis over the period August 2007 to July 2008, using funnel traps, dip nets and a small seine net. In order to monitor the effect of the fishway on the lake fish community, seasonal sampling in the lake was conducted for a period of two years, from August 2007 to June 2009, using seine and gill nets. A total of 3 288 fish, representing 29 species, were recorded throughout the study. Of these 29 species, 20 species were able to locate and enter the fishway. The fishway was found to allow passage for 17 fish species between the estuary and the lake. The dominant species that managed successfully to migrate through the fishway were Myxus capensis, Glossogobius callidus and Eleotris fusca, making up 77% of the total catch. The fish migrating through the fishway included five marine species, five estuarine resident species, six freshwater species and one unclassified Gobiid larvae sp. Abstract The Mzingazi gauging weir and its effects on the fish and macrocrustacean communities of Lake Mzingazi ii A total of 8 188 macrocrustacea representing eleven species were also recorded in the Mzingazi system, of which seven prawn and one crab species were able to locate and enter the fishway. The fishway provided migratory passage for seven prawn species, these being dominated by Macrobrachium equidens, Caridina nilotica and Caridina indistincta respectively, together making up 97.6% to the total catch. This study proved that the fishway was effective and efficient for upstream migration of the target species. The design of the fishway was found to create suitable hydraulic conditions for migration of juvenile and sub-adult fish (10 to < 100 mm SL) and for macrocrustacea (3 to < 26 mm CL). Peak upstream migration of fish through the fishway occurred in August, September, October and December, which coincides with the peak recruitment period of most estuarine and marine spawning species. Peak migration and species abundance of both fish and macrocrustaceans were found to be a natural effect of seasonal recruitment and breeding, which was indirectly driven by seasonal temperature variations. The fish community of Lake Mzingazi during the study comprised 16 species, which included four marine species, five estuarine resident species and seven freshwater species. The community was dominated by freshwater species such as Oreochromis mossambicus and Tilapia rendalli and estuarine species such as Glossogobius callidus and Gilchristella aestuaria. The operation of the Mzingazi fishway was found to be causing a gradual change in the lake fish community by re-introducing euryhaline fish species into the freshwater coastal lake. The following important recommendations were made. Firstly, further long-term monitoring of the fishway and the lake fish community is required to validate the absence of previously recorded euryhaline species and to determine the long-term effect of the fishway on the fish and macrocrustacean community. Secondly, the operation of the fishway is entirely dependent on water levels in the lake and ongoing water abstraction for domestic and industrial purposes often results in the water level in the lake being drawn below the overflow level of 3.0 masml. For this reason, the Department of Water Affairs should limit abstraction from the lake so that there is sufficient water allocated to allow the fishway to operate. The water level should never be drawn below the minimum level of 3.0 mamsl, at which the fishway can still operate.
Salinity tolerance and osmoregulation in several subtropical decapods
(University of Zululand, 2012) Khanyile, Sithembele Nikeziwe; Newman, B.K.
This study investigated salinity tolerances and osmoregulatory strategies of several subtropical brachyuran mangrove crabs and an anomuran prawn, with particular reference to Uca vocans, Uca urvillei, Uca chlorophthalmus, Uca annulipes, Dotilla fenestrata, Macrophthalmus depressus, Macrophthalmus grandidieri, Metopograpsus thukuhar, Chiromantes eulimene and Callianassa kraussi. All species investigated were either directly exposed or acclimated to salinities between 0-75 and their tolerance to these salinities and osmoregulatory strategies monitored over a 4 day period. Other experiments conducted included an investigation of the time dependant responses of species following direct transfer to various salinities, and for one species also the influence of temperature on salinity tolerance and osmoregulatory strategy. All the species were shown to be euryhaline, as would be expected for species inhabiting an estuarine environment. However, the degree of euryhalinity varied between species. The general salinity range they could tolerate was between 0-55, but species like U. annulipes, D. fenestrata, C. eulimene and C. kraussi tolerated salinity as high as 65. Direct exposure was shown to be more stressful than acclimation, especially in low and high salinities. Out of seven species that were directly exposed and acclimated, C. eulimene was the only species able to tolerate freshwater (salinity 0) following direct exposure. All crab species followed an osmoregulation strategy by hyper-regulating at low salinities and hypo-regulating at higher salinities. The hyper-regulatory ability of most species was stronger than the hypo-regulatory ability, as this was shown by the hemolymph osmolality line which was much closer to the isosmotic line at salinities above the isosmotic point and also by the lower osmotic capacity (OC) at comparable salinity differences below and above the isosmotic point. Callianass kraussi osmoregulated at salinities lower than 25 and osmoconformed at salinities above 25. All Uca species investigated were able to tolerate direct transfer to freshwater for up to eight hours without experiencing any mortality. All specimens of U. vocans, which occurs lowest in the intertidal zone, died within 24 hours of exposure. All U. urvillei died within two days of exposure. Uca annulipes, which lives in the highest region of the intertidal zone, was the most tolerant to rapid freshwater exposure, with 70% of crabs surviving up to 72 hours. Uca annulipes regulated its hemolymph osmolality more efficiently than U. urvillei and U. vocans, which live on the lower level of the intertidal zone. The ability of Uca crabs to survive as well as regulate their hemolymph osmolality when directly transferred to freshwater was closely linked to the level they occupy in the intertidal zone. The third part of this study looked at the influence of temperature on the salinity tolerance and osmoregulation of C. eulimene. Temperatures between 14-22oC had no effect on salinity tolerance or osmoregulatory capability of C. eulimene at salinities between 0-45. Exposure of C. eulimene to lowered temperatures had no effect on the salinity tolerance and osmoregulation capacity of this species. Lower temperatures do not inhibit the distribution of this species from South and West Coast of Africa.
Effect of salinity and environmental changes on the fish community of the St Lucia Estuarine System with focus on the salinity tolerance of Oreochromis mossambicus (Mozambique Tilapia)
(University of Zululand, 2014) Schutte, Quintin; Vivier, L.; Cyrus, D.P.
St Lucia, the largest estuarine lake system in Africa, has been closed since 2002, except for a brief opening in 2007 caused by Cyclone Gamede. Mouth opening in 2007 was preceded by five years of low lake levels and hypersaline conditions which greatly reduced marine fish species diversity. Regardless of this, the freshwater tilapia, Oreochromis mossambicus has been found in abundance in all parts of the system. This indicates that O. mossambicus is capable of surviving hypersaline conditions when no other fish species can. Mouth opening in 2007 caused the system to partially fill marine salinities were restored and also allowed for recruitment of marine species back into the system. Following re-closure in August 2007, salinities in North Lake became hypersaline during 2009-2010. In 2012, a “beach channel” was dug to re-connect the St Lucia Narrows to the Mfolozi-Msunduzi Estuary, allowing water to enter the system and provide access to the ocean for recruitment of marine species. The study investigated the effect of salinity and environmental changes on the fish community structure of the St Lucia system during periods of mouth closure as well as after opening of the new beach channels connecting St Lucia to the Mfolozi system.Sampling was conducted from May 2008-Nov 2014 at six sites in the St Lucia system using small (10m) and large (70m) seine nets and CPUE’s were calculated for each site as the number of fish caught per meter of net, per haul. Fish were identified measured and returned to the system. The salinity tolerance of O. mossambicus from St. Lucia was also investigated under laboratory conditions. Acclimation of O. mossambicus was done at salinity intervals of five with a 96 hour exposure trial to test for survival. Spatial changes in the fish community were driven by the salinity gradient across the system, while temporal changes coincided with major changes in the salinity state of the system. Marine species dominated in terms of species number but freshwater and estuarine species dominated the fish abundance, notably O.mossambicus and Ambassis ambassis. Prior to opening of the beach channel, the number of species decreased from 51 in 2008 to 37 in 2011. The abundance of marine species decreased by >75%as the system became progressively more hypersaline and the closed mouth limited recruitment. Opening of the beach channel caused a decline in salinities and allowed for 12 marine species top re-enter the system in limited numbers. Oreochromis mossambicus was the most abundant species in the system, accounting for 48.8% of the catch between 200-2014 and dominating the fish assemblage in salinities between 30-90 (highest recorded salinity). Estuarine species were dominant in salinities between 0-20, while marine species dominated the fish assemblage in salinities between 20-30. In the laboratory, the salinity tolerance of O.mossambicus was found to be 0-105, with >70% survival in 105. Freshwater deprivation and mouth closure had the biggest impact on the fish assemblage and a regular more extensive connection to the ocean is therefore, needed to maintain healthy fish populations in Lake St Lucia and off-shore marine populations.
Acute and chronic toxicity of copper and zinc and environmental tolerances to the estuarine amphipod, melita zeylanica
(University of Zululand, 2015) Mofokeng, Refilwe P.; Vivier, L.; Cyrus, D. P.
Owing to economic growth and their geographic positioning, harbours and estuarine ecosystems have been considerably accelerated development around them over the past years. This has in turn induced excessive stress on these systems. Due to elevated metal deposition from surrounding industries, toxic metal concentrations are often evident in these systems as sediments tend to accumulate metals. Toxicity tests are essential in predicting the effects of contaminated water and sediments on biota. Acute bioassays refer to short term bioassay with mortality as an end-point, while chronic bioassays often take longer with sub-lethal end-points including growth and fecundity. In the past, acute toxicity tests were often reported as they were easier to conduct and generally more affordable than chronic tests. Chronic bioassays, however, are more relevant as chronic exposures are most likely to occur in the environment and they have higher sensitivity to metals sediment toxicity tests are often preferred over water-only tests, as metals tend to bind to sediment over prolonged periods of time , therefore, they provide a time-integrated measure of metal accumulation within estuarine ecosystems. Due to their high metal toxicity, environmental tolerance, abundance, as well as ease to handle in the laboratory, amphipod bioassays are used worldwide in toxicity testing. In this study acute and chronic toxicity bioassays were undertaken with the aim to determine the suitability of Melita zeylanica as an estuarine benchmark toxicity test organism in sub-tropical ecosystems. Melita zeylanica amphipods were collected in Mzingazi Canal, Richards Bay Harbour, and cultured in climate control chambers in aerated culture trays. Exposure experiments of M. zeylanica to Copper (Cu) and Zinc (Zn) were conducted at 25⁰C and a salinity of 25 using a 6 by 5 grid. The LC₅₀ EC₅₀ as well as metal concentrations in tissue and sediment were determined following a microwave digestion method, while an ICP-MS was used for metal analysis of sediment and tissue concentrations. An overview on amphipod toxicity bioassays using Cu and Zn over the past 10 years (2003-2013) was conducted with the aim to report on chronic toxicity publications during the past decade. General sensitivity of amphipods to Cu and Zn as well as the frequency of use of various endpoints (fecundity, accumulation, growth and behaviour) were reported. Results of the overview suggested that amphipods are generally more sensitive to Cu than Zn. Corophium volutator, however, showed a lower LC₅₀ value for Zn (10.03 µg/g-1) than that of Cu (26.07 µg/g-1). Fecundity was the most reported endpoint with C. volutator being the most used amphipod over the past ten years. It was concluded, however that no one amphipod species can represent all amphipod species as amphipods tend to adapt deferentially to their immediate environment. A Cadmium (Cd) reference toxicity test is often used as a method of standardising interlaboratory results as it is non-essential in organisms. A Cd 96hr static water-only reference test was used in this study to determine relevant toxicity of M. zeylanica as compared to other amphipods. This study also evaluated the median lethal concentrations (LC₅₀) of ammonia on M. zeylanica during a static 96hr sediment toxicity bioassay. Survival of M. zeylanica across a broad range of salinity (5-40) was also determined during 96hr bioassay. The Cd water-only tolerance test showed that M. zeylanica sensitivity to metals is comparable to that of other amphipods, with LC₅₀ of 1.17 µg/g-1 a Melita zeylanica was found to be more sensitive to ammonia as compared to other studies with a LC₅₀ of 17 µg/g-1 a Melita zeylanica however, was found to be tolerant to a wide range of salinities (5-40) but intolerant to freshwater. A 10-day acute sediment toxicity test with mortality as an endpoint and a 28 day chronic sediment toxicity test, with growth and fecundity as end-points, were conducted. Following the acute toxicity test, LC₅₀ values for Zn and Cu were found to be 9.15 and 11.76 µg/g-1 with LC₉₀ values of 238.5 and 78.6 showing that M. zeylanica is more sensitive to Cu at high concentrations. Tissue metal levels showed that M. zeylanica is able to accumulate both Zn and Cu in relation to sediment concentrations. This finding demonstrated that M. zeylanica is potentially a good biomonitor organism, as the ability to accumulate metals is one of the key requirements that qualify organisms as toxicity organisms the chronic bioassay showed that both Zn and Cu affected fecundity of M. zeylanica. Amphipods were, however, found to be more sensitive to Cu compared to Zn. EC₅₀ values of 2.7 and 0.8 µg/g-1 were recorded for Zn and Cu, respectively. Amphipod growth was also inversely correlated to Cu concentration. South Africa has experienced accelerated growth in its economy over the past decade which has resulted in increased demand for cargo container handling capacity throughout South African ports. Richards Bay Harbour is currently the largest deep-water port in South Africa, used primarily for the export of coal. Furthermore, there have been proposals to expand the port over the next 40 years, resulting in 5 times increase in its surface area. In order to test the suitability of M. zeylanica as a bio-indicator of estuarine contaminated sediments in South Africa, a field validation study was conducted in Richards Bay Harbour with sediment samples being collected from 9 sites. Samples were analysed for aluminium (AI) Arsenic (As), Cd, Cu, Iron (Fe) Mercury (Hg) Nickel (Ni), (Pb) and (Zn) concentrations. Metal concentrations recorded at the Bulk terminal. Metal concentrations were found to be within standard quality guidelines as stipulated by the Department of Water Affairs as well as the Australian sediment guidelines. The data from this study was compared with historical data to identify contaminated areas. Elevated Zn concentrations within the harbour were contrary to historical data, as a result Polycyclic chlorine biphenyls (PCB) and Polycyclic Aromatic Hydrocarbons (PAH) analysis was conducted to identify or eliminate oil-spill as a potential reason for the high Zn concentration. Metal accumulation in M. zeylanica following exposure to sediments showed that M. zeylanica is a good accumulator of metal, particularly for As, Cr, and Hg. When compared to other amphipods widely used in toxicity bioassays, M. zeylanica was found to accumulate metals to comparable concentrations. A range of 5-59 µg/g-1 and 98-227 µg/g-1 were recorded for Cu and Zn, higher than that of Melita matilda (140 µg/g-1 Zn), a closely associated species. Richards Bay Harbour is of high ecological and economic importance as it serves as both a fully functional estuarine ecosystem and is also one of the busiest ports in South Africa. Richards Bay Harbour as an estuarine environment has already been put under immense pressure with increased cargo handling over the past ten years. Plans to expand the harbour will also result in re-suspension of metal causing secondary metal contamination, which may contribute to loss of organisms and thus hinder the role of the harbour as an ecosystem. Although several toxicity and biomonitoring studies have been conducted on the harbour, no Estuarine Management Plan (EMP) has been put in place to Richards Bay Harbour as yet. EMP should, therefore, be urgently designed and implemented, with all stakeholders accommodated. National Sediment Quality Guidelines (SQG’s) should also be implemented as different areas do not necessarily react in the same manner, therefore, the use of international SQG’s would not be entirely appropriate. In terms of Estuarine Ecological Biodiversity, Richards Bay Harbour is Classified as a category C estuary, according to the National Water Act; no estuarine system should be allowed to degrade below D-class. The intended development of Richards Bay Harbour will, potentially, result in deterioration of the ecological integrity of the harbour. An EMP is thus of high importance within the harbour given the divergent roles of Richards Bay Harbour as both an estuarine ecosystem and a large cargo handling port. Although, M. zeylanica was found to be sensitive to ammonia, it was overall, found to be a good accumulator of metal, relatively easy to handle in the laboratory tolerant to a wide salinity range and it was found in abundance in the Mzingazi Canal. Furthermore, accumulation of metals within amphipods did reflect sediment metal concentrations, particularly for Zn and Cu, following the 10-day toxicity bioassays. The findings of the study, thus suggest that M. zeylanica can and can be recommended as a suitable bio-monitor species in South African and can be recommended as a suitable bio-monitor species ins South African coastal waters.
The use of biotic indices to assess the effect of fish farming in Richards Bay Harbour
(University of Zululand, 2023) Nzama, Sazi Fortune; Vivier, Leon; De Fortier, An

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