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Browsing Zoology by Author "Vivier, L."
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- ItemThe 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.
- ItemEffect 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.
- ItemThe 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.
- ItemThe 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.
- ItemSpatial 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).