The zooplankton communities of the Mdloti and Mhlanga estuaries were studied over a 13-month period (March 2002-March 2003). Monthly daytime samples were collected from both estuaries at the lower, middle and upper reaches using a WP-2 net and a hyperbenthic sled. Throughout the study period, the Mdloti Estuary experienced nine breachings, while the Mhlanga experienced 16 such events. Significant differences in zooplankton abundance were observed between the two estuaries (F I, 73 = 5.2; P<0.05), with the Mdloti consistently exhibiting higher values than the Mhlanga. No significant differences were, however, observed in zooplankton biomass between the two estuaries (U = 634; P>0.05). At the Mdloti, zooplankton abundance ranged from 20 ind.m-3 to 5.4 x 106 ind.m-3 , while at the Mhlanga this ranged from 76 ind.m-3 to 2.0 x 105 ind.m-3 • Zooplankton biomass ranged from 0.08 mg.m-3 (OW) to 2010 mg.m-3 (OW) at the Mdloti, and from 0.18 mg.m-3 (OW) to 1210 mg.m-3 (OW) at the Mhlanga. A one-way ANOV A revealed significant differences in zooplankton abundance between the open and the closed phase, both at the Mdloti (FI, 30 = 59; P<0.05) 'and the Mhlanga (FI, 38 = 7.3; P<0.05), with the closed phase exhibiting consistently higher values than the open. Similarly, biomass was significantly higher during the closed than the open phase, both at the Mdloti (U= 16.5; P<O.OI) and the Mhlanga (U= 88, P<O.O 1). This pattern may be attributed to the stability achieved by these systems during periods of mouth closure, when the estuaries exhibit less freshwater input and a restricted exchange of water with the sea. At the Mdloti, zooplankton biomass (OW) was positively correlated to both phytoplankton (r= 0.36) and microphytobenthos biomass (r = 0.41). At the Mhlanga, zooplankton biomass (OW) was only positively correlated to phytoplankton biomass (r = 0.45) The most abundant taxa at the Mdloti during the open phase were Pseudodiaptomus hessei and copepod nauplii, each contributing 38% and 32% of the total stock, respectively. During the closed phase, however, rotifers were by far the dominant taxon, contributing 82% of the total zooplankton abundance. These were followed by cope pod nauplii with 16%. At the Mhlanga, the most abundant groups during the open phase were again the copepod nauplii (89%) and P. hessei (7 %), while the closed phase was dominated mainly by caridean larvae (39%) and copepod nauplii (26%). The dominance of P. hessei during the open phase of both estuaries may be attributed to the pioneering nature of this species. The dominance of rotifers at the Mdloti during the closed phase may have been due to the freshwater conditions that prevailed in this estuary as a result of prolonged mouth closure. The concentration of copepod nauplii increased dramatically 2-4 weeks after major rain events, possibly due to the hatching of dormant eggs in response to freshwater pulses. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2005.

Microphytobenthos (MPB) generally dominates total autotrophic biomass in temporarily open/closed estuaries (TOCEs) of South Africa. A comparative study of MPB biomass was undertaken in two KwaZulu-Natal TOCEs, the Mdloti and the Mhlanga. Both estuaries receive different volumes of treated sewage waters. The Mdloti receives 8 ML.d-1, while the Mhlanga receives 20 ML.d-1, resulting in a capping flow of 0.092 and 0.23 m3.s-1, respectively. Through these effluents, eutrophication is enhanced and periods of mouth opening are also increased and prolonged, particularly at the Mhlanga. The aim of this study was to investigate fluctuations in MPB biomass in the Mdloti and the Mhlanga systems, with emphasis on freshwater flow and the alternation of closed and open phases. Sediment samples for MPB biomass were collected on a monthly basis, between March 2002 and March 2003, in the lower (mouth), middle, and upper (head) reaches of the two estuaries. MPB biomass ranged from 1.33 to 391 mg chI a m-2 and from 1.7 to 313 mg chI a m-2 in the Mdloti and the Mhlanga, respectively. A I-way ANOVA revealed no significant differences in MPB chI a concentrations between the two estuaries for the entire data set (Fl, 76 =1.48, P > 0.05). At the Mdloti, MPB biomass varied considerably, with values ranging from 1.33 to 131 mg chI a m-2 during the open phase, and from 18 to 391 mg chI a m-2 during the closed phase. A Mann-Whitney U test confirmed the high significance of these differences between open and closed phases (U= 29, P < 0.001). At the Mhlanga, MPB biomass ranged from 7.0 to 313 mg chI a m-2 during the open phase, and from 1.7 to 267 mg chI a m-2 during the closed phase. Unlike what was observed at the Mdloti, the higher MPB values at the Mhlanga were not always associated with the closed mouth state. In relation to key physico-chemical and biological factors, grazing pressure exerted by the zooplankton community appeared to have played a major role in controlling MPB biomass. Zooplankton biomass was consistently and positively correlated to MPB biomass throughout the study period both at the Mdloti (r = 0040, P < 0.001) and at the Mhlanga (r = 0.33, p < 0.05). Unlike what was shown in previous studies, light attenuation was not significantly correlated with MPB biomass during the period ofthe study, either at the Mdloti or the Mhlanga. These results show that the opening and closing of the mouth play a key role on the MPB biomass of both estuaries. The Mdloti seems to function as a typical TOCE, with prolonged open and closed phases. The Mhlanga, on the other hand, lacks a prolonged closed phase. This, in turn, affects its entire trophic structure and functioning. / Thesis (M.Sc.)-University of KwaZulu- Natal, 2004.

Estuaries in South Africa are important nursery areas for the juveniles of many fish species. The condition of many of these systems has, however, deteriorated as a result of degradation caused by urban, industrial and agricultural development. An assessment of the role of harbours, particularly in KwaZulu Natal, as nursery grounds has therefore become an important issue. Durban Bay has undergone considerable changes since the mid-1800s and further developments are proposed. If these developments continue, they will result in the loss of large areas of the sandbanks, but Portnet has recognised the need to integrate environmental considerations into future port developments and operations. It was the overall aim of this study to establish the nature of the association of the juveniles of four common fish species viz. Pomadasys commersonnii, Gerres filamentosus, Liza dumerilii and Leiognathus equula with these sandbanks and, thereby assess the impact of their removal. It was found that all species were abundant on the sandbanks and that the diets of P. commersonnii, G. fiiamentosus and L. equuia were very similar, consisting primarily of bivalve siphon tips, benthic crustaceans and polychaetes. The respective contributions of each food type to the diet varied with species. The diet of L. dumerilii differed from that of the other three species, consisting primarily of benthic floc, foraminiferans, ostracods and sponge spicules. Despite differences in selectivity, it was concluded, from studies of the benthos in the harbour, that all four species, irrespective of size, were feeding on these sandbanks, as opposed to in the channels, throughout the year. Removal of the sandbanks for the construction of a new pier would, thus, result in the elimination of important feeding grounds for the juveniles of these four species. / Thesis (M.Sc.)-University of Natal, 1994.

A high proportion of South Africa’s temporarily open/closed estuaries (TOCEs) occur along the coast of KwaZulu-Natal. Mouth breaching events have major impacts on the biological processes of an estuary, resulting in depletion of zooplankton via flushing and sediment scouring. Mouth closure, usually within weeks of a breaching event, initiates a new phase of stable physical conditions, leading to biological recovery. Therefore, the aim of this investigation was: (1) to monitor the recovery of zooplankton abundance and biomass following a breaching event in the Mdloti Estuary; (2) to compare the spatial and temporal patterns in zooplankton distribution in the lower (mouth), middle and upper reaches (head) of the Mdloti Estuary in terms of abundance and biomass just before, during and after a mouth breaching event; and (3) to determine the key environmental variables influencing zooplankton abundance and biomass during such a breaching event. The zooplankton community of the Mdloti Estuary was studied over a 3-month period (27 January to 26 April 2004). The estuary was artificially breached on 12 February 2004, due to a fish kill, and closed again naturally on 18 March 2004. Samples were collected twice a week in the lower, middle and upper reaches using a WP-2 net and an epibenthic sled. Upon breaching, 98% of zooplankton biomass was lost through sediment scouring and flushing. During the open phase, zooplankton biomass showed a temporary recovery, but due to continual sediment scouring and flushing, this was not sustained. One-way ANOVA revealed a significant difference in total zooplankton abundance and biomass between phases (d.f.2, 59 = 55.0; p < 0.001; d.f.2, 59 = 15.51; p < 0.001). ANCOVA revealed significant differences between zooplankton abundance and biomass (d.f.0.05;2,56=2.97, p = 0.05) at the different estuarine reaches (d.f.0.05;2,56=5.51, p < 0.01) . In both cases, the lower reaches recovered quicker than the middle and upper reaches. Thirty-five taxa were identified during the study, with only 10 contributing more than 1% of the total abundance or biomass. For the overall study, P. hessei was the dominant species, accounting for 42% of the total abundance and 58% of the total biomass. Keratella sp. 1 accounted for 17% and 11% of the total abundance and total biomass, respectively, while harpacticoid copepodites and Acartia natalensis contributed 11% and 10% to the total zooplankton abundance and 3% and 7% to the total zooplankton biomass, respectively. Pre-breaching levels of zooplankton were reached only 9 days after the closure of the mouth, during the recovery phase (mean 1.1 x 105 ± 6.5 x 104 SD ind.m3 and 2.4 x 102 ± 1.6 x 102 SD mg.m3). Zooplankton abundance and biomass reached a peak in the lower reaches after 19 days, in the upper reaches after 28 days and in the middle reaches after 35 days. The zooplankton biomass decreased slightly, but stabilised for the duration of the study. During the study the state of the mouth was primarily responsible for regulating the zooplankton abundance and biomass. However, the zooplankton in the different reaches did not recover in synchrony after mouth re-closure because abiotic factors and food availability were different in the three estuarine reaches. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.

Estuaries are complex ecosystems, typified by remarkable fluctuations in environmental conditions. In addition to this natural variability, stochastic events and anthropogenic influences effect change at different spatial and temporal scales. Macrozoobenthic invertebrates are preferable biological indicators because of their sensitivity to variations in habitat quality. This thesis describes inherent changes in the macrozoobenthos of temporarily open/closed estuaries (TOCEs) in KwaZulu-Natal, ‘change’ as measured in spatial and temporal community differences using various community metrics, namely species composition, abundance and diversity. Standard and widely published quantitative sampling techniques were employed, with simultaneous measurements of ambient physico-chemical conditions, including sediment characteristics. The thesis is in three parts. Regional distributions and long-term decadal-type changes in macrozoobenthic community structure were determined for 31 TOCEs using historical data (1998/9) compared with more recently collected data (2009/10). Results showed that, although of the same estuary type, the macrozoobenthic communities of these estuaries differed significantly. Furthermore, community composition did not reflect a north to south progression of predominantly tropical species to predominantly warm-temperate species. In the last decade, the macrozoobenthos of these systems had indeed changed (in composition, abundance and/or diversity), the scale of change within each estuary being estuary-dependent. The recolonisation of two urban and non-urban estuaries by macrozoobenthos following a stochastic flood disturbance was investigated, describing the short-term community changes during the recovery process. Differential recolonisation patterns were attributed to inherent differences in community composition and not to the influence of urbanisation. Recolonisation was marked by distinct changes in community structure, with the recovery trajectory being interrupted by localised disturbances (e.g. change of mouth state). Species indicative of the observed spatial and temporal community changes were examined for similarities in habitat association and trophic characteristics. The species that were representative of these KwaZulu-Natal TOCEs were identified and included common and highly abundant generalists of varying trophic groups. In conclusion, the present findings illustrated the effectiveness of using macrozoobenthic communities to depict ‘change’ over multiple temporal and spatial scales. This also supports their usefulness as a study group in environmental monitoring and detecting the loss of ecological functioning and biodiversity in estuaries in the long- and short-term. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

ln this study the exploitation of the fish fauna of the Kosi estuarine system by man and natural predators is described and estimates made of the off-take and its species composition. The most important human exploitation, that by the traditional Zulu fish traps, was monitored over a four year period and the data collected were used to give an insight into the marine fish populations of the system. All the physical parameters, which it was thought could influence the migrations of fish, were monitored and correlations between these and the daily and monthly fish trap catches were used to interpret fish movements into and out of the system. Reasons for the annual migrations and day to day movements of fish were investigated. In order to establish relative off-takes by local fishermen and sport anglers fish were tagged inside the system and the recovery rates by the various fishing methods were used to calculate estimates of the percentage off-takes of these principal human exploitation methods. These data were also used to obtain estimates of the population sizes of the major marine fish species inside the system. Catch data were used to indicate the levels of estuarine dependence of these species. Where possible comparable data from other areas were used to indicate whether or not similar trends in catch abundance were obvious. The ecological and economic importance of the Kosi system is discussed and its value to the local inhabitants stressed. Competition between the various fishing techniques is described and recommendations are made concerning future fish exploitation. Natural predation rates are also discussed and levels compared with those of other systems. The fish food resources of the systems are considered in the light of recently declining salinities, destruction of swamp forests and increasing numbers of hippopotami. The implications of these changing factors are discussed as is their impact on the Kosi Bay fisheries. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.

The vegetation of the Mgeni Estuary, Mhlanga Estuary and Mdloti Estuary was analysed according to the Braun-Blanquet phytosociological method using quadrats of 4m2 and 25m2 in area placed subjectively and the Point-Centred Quarter method with points chosen whilst traversing. A classification of plant communities is given. These are described floristically and related to habitat variables. Indicator species of the climatic climax of coast forest occur within the study area. The absence of coast forest is ascribed to low altitude, tidal inundation and the consequent effect of salinity, basal inundation resulting in a high water-table and the influence of man. The floodplain of the Mgeni Estuary is dominated by mangrove vegetation comprising mainly Bruguiera gymnorrhiza and Avicennia marina whereas vegetation established on Athlone Island is dominated by mesophytic thicket comprising mainly Schinus terebinthifolius, Lantana camara, Chromolaena odorata and Cardiospermum grandiflorum. The floodplain of the Mhlanga Estuary is dominated by Phragmites australis. The shores of the Mdloti Estuary are dominated by Barringtonia racemosa, Phragmites australis and Echinochloa pyramidalis. Major differences in vegetation patterns of the three systems are related primarily to the differences in the open nature of the river mouths. This is controlled mainly by river flow and longshore drift. Differences in vegetation patterns within an estuary are dependent on differences in tolerances to salinity, basal inundation and shade, together with variations in altitude and edaphic factors and competition between species. Generally soils of Mgeni Estuary had higher contents of small sized fractions, bulk densities, reserve acidities, organic matter, salts and exchangeable bases and lower pH than soils at Mhlanga Estuary and Mdloti Estuary. Differences exist between mangrove and non-mangrove soils at Mgeni Estuary and differences between the non- mangrove soils at the three study sites. Major differences in soil characteristics are as a result of differences in tidal inundation, geogenetic parameters and biotic factors. Information on topography, hydrology, geology, climatic factors, biotic factors and historical background of the area is given. A check-list of vascular plants is included. The work is illustrated by 44 figures. / Thesis (M.Sc.)-University of Durban-Westville, 1986.

Estuarine studies worldwide have shown that sediment disturbance effects on the macrobenthos are reIated to the nature and scale of the disturbance. Decreased species densities, diversity and richness have been found where the substratum and current patterns have been altered either by direct removal or by the creation of channels . Sediment disturbance in the St. Lucia Narrows has occurred through dredging, beam trawling and episodic floods. The Narrows, a meandering tidal channel approximately 21 km long linking the st Lucia Lakes to the sea, were dredged between 1952 and 1971 to provide a greater flow of seawater to the lakes during periods of low lake levels. A canal was cut through land from the Mfolosi River to the Narrows in an attempt to ameliorate hypersaline conditions in the Lakes, but was never commissioned. Beam trawling has formed the basis of a prawn bait fishery since the 1930's. The bait boats trawl on the mudflats over the entire Narrows on a daily basis and often churn the substratum with their propellers. The objectives of this study were to determine the effects of dredging, a once-off large scale disturbance, and beam trawling, a frequent small scale disturbance, on the macrobenthos of the Narrows. Studies in 1983 and 1984 showed that the dredged channel was impoverished compared with the adjacent mudflat, and that the Link Canal was devoid of benthos. In 1988 species densities, especially of polychaetes, were found to be lower in areas open to beam trawling than in adjacent closed areas. The dredged channel during the present study was again impoverished compared with the adjacent mudflats. The three most abundant species occurring on the mudflats, the crab Tylodiplax blephariskios, the amphipod Victoriopsia chilkensis and capitellid polychaetes, were recorded at densities an order of magnitude lower in the channel than on the mudflats. The substratum in the channel was generally sandier than the mudflats, and this condition appeared to be maintained by the scouring action of tidal currents. It was calculated that the creation of the dredged channel had reduced the standing benthic biomass in the Narrows by a minimum of approximately 20%. The Link Canal was colonised by the three major mud flat species , but at densities an order of magnitude lower than the mudflats. Beam trawling of experimental sites at monthly and 6-monthly intervals on muddy and sandy substrata in the Narrows between July 1989 and July 1990 did not appear to have a negative effect on the benthos. The coverage of the bait boats was calculated to be comparable to the trawling effort in this study, and suggested that the bait fishery is not having a detrimental effect on the benthos. It was concluded that the macrobenthos in the Narrows represented a pioneering community characteristic of estuaries, either not affected by, or able to recover from small scale and episodic disturbances provided that there was no long term habitat modification. / Thesis (M.Sc.)-University of Natal, Durban, 1992.

South African estuaries have high biodiversity value and provide many benefits to society, including food, real estate, a place for recreation and economic enterprise. However, they are facing growing human pressures such as urban encroachment, development in river catchments and interference in hydrological cycles. This dissertation provides an exploratory study of the environmental history of the Mgeni River Estuary, KwaZulu-Natal in an attempt to improve the understanding of the forces that drive environmental change. Through the application of the techniques and methodologies of environmental history, it explores the dynamics, characteristics and impacts of human interaction with the Mgeni River Estuary over time. It focuses on the emergence of a capitalist! industrial society in the twentieth century as this period has been characterised by the most significant environmental alteration and degradation. With the aid of the techniques and methodologies employed, the study highlights a complexity of natural and human events that have altered the estuary over time. Comparative analysis of aerial photographs between 1937 and 1996 reveals that physical changes to the estuary were linked to prevalent social and economic activities. The study describes cultural beliefs, modes of resource use and the political economy as significant and interwoven factors that facilitate environmentally intrusive activities. The study has provided insights into the complexity of factors that influence the rate and extent of change of an estuarine system. It concludes that to improve the understanding of the causes of environmental change, it is necessary to look further than the physical impacts on the environment to the attitudes and beliefs that underlie them. While the solutions to the problems facing the Mgeni River Estuary are not easily at hand, such analysis should assist policy makers and managers in finding a way to initiate more sustainable estuarine development in the future. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.