Zoology

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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
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.
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.
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.

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