Plankton communities are influenced, in part, by water exchange with adjacent estuarine and oceanic ecosystems. Reduced advective transport through tidal passes or with adjacent bay systems can affect chemical processes and biological interactions, such as nutrient cycling, phytoplankton abundance and productivity, community respiration, and zooplankton biovolume. The most threatened estuarine ecosystems are shallow, bar-built, microtidal estuaries with small water volumes and restricted connections through tidal passes and other water exchange points. This research explored spatio-temporal trends in plankton communities and the physicochemical environment in Mesquite Bay, Texas a microtidal, bar-built, subtropical estuary in the Gulf of Mexico. This research couples sampling at fixedstations for multiple physical and biological parameters with high-resolution spatial mapping of physicochemical parameters. Spatial trends were less in magnitude and affected fewer parameters in fixed station and spatial data. Two dimensional ordination plots indicated spatial heterogeneity with a more pronounced temporal trend affecting parameters including temperature, salinity as a function of inflow timing, and seasonal wind direction affecting primary production and zooplankton biovolume. Temperature was positively correlated with gross production and respiration rates during spring and late summer with sporadic positive and negative correlations with phytoplankton biomass. The timing and magnitude of freshwater inflow affected various physicochemical and biological parameters. Higher than 71-year inflow rates resulted in low salinity system wide, with spatial heterogeneity increasing over the course of the study, which was confirmed by spatial maps. Additionally, high inflow rates led to two periods of increased inorganic nutrients and dissolved organic matter. Low salinity periods coincided with persistence of higher turbidity, likely because of decreased sediment flocculation. Gross production was low at this time, and likely from light limitation. Additionally, wind magnitude and direction created spatial heterogeneity in turbidity levels and phytoplankton biomass. Zooplankton biovolume was highest during spring and late summer with high species diversity in total rotifers. Copepod biovolume and phytoplankton biomass were positively correlated. Other zooplankton taxonomic groups exhibited variable correlations with phytoplankton biomass and other taxonomic groups. Further long-term studies are needed to determine interactions of various components of trophic food-webs and account for interannual variability in all system parameters.

Hydrokinetic tidal power is a novel and emergent technology undergoing continuous advancement with much of the progress focused on large utility scale projects. This resource is potentially underutilized because much of the coastal United States, despite having substantial tidal currents, do not have the deep and wide environments required by most of the developing turbine technology. This dissertation includes a detailed characterization of the tidal hydrodynamics for Rose Dhu Island, Georgia used for a tidal energy resource assessment as well as a general feasibility study for tidal estuaries with extensive wetlands. For predictions and evaluation of the estuarine hydrodynamics, data from an existing numerical model of the estuary encompassing the island is utilized. Field measurements in close proximity to the island are used to calibrate the model as well as characterize local hydrodynamic features. After the model calibration, the simulation data is used to evaluate the hydrodynamics. Wetland dominated estuaries commonly have a high degree of non-linear distortion which govern the relative durations and strengths of the tidal stages and thus the overall hydrodynamics and incoming hydrokinetic energy. The Ogeechee Estuary is characterized as ebb dominant with peak ebb and flood volume fluxes near high tide as a result of the increased storage capacity of the wetlands. Lowering the average wetland elevation in the model decreased ebb dominance and quickened the transition from flood to ebb tide. Increased domain friction in the model removed energy from the system and reduced ebb dominance. Enhanced model marsh friction reduced lateral flooding of the wetlands as well as ebb dominance. Localized measurements surrounding the island are analyzed to determine a location near the southwest coast of the island as a hydrokinetic energy hotspot. A kinematic and dynamic analysis is performed using channel transect measurements to identify key physical processes behind the hotspot formation. The hotspot forms due to sub-critical flow acceleration over a singular bump in the topography. High streamwise momentum is further concentrated at the hotspot due to secondary circulation cells across the channel. Flood tide circulation is characterized by two co-rotating cells induced by channel curvature and delineated by the bump. Ebb circulation consists of two counter-rotating cells from flow confluence of two upstream channels. Once the hydrodynamics are understood, the theoretical and technical resource assessment of the island is completed. A sensitivity analysis of hydrokinetic energy and tidal distortion is performed on synthetic data. For a principle constituent and its first harmonic, distortion greatly changes as does the distribution of velocities and energy as the relative phase varies. While the theoretical energy remains consistent, the technical energy can greatly vary. This effect is reduced with the addition semi-lunar variation. Using a simplified analytical method, the maximum average channel power is estimated as 8.80 MW. For the hotspot it is estimated that there is 30.3 MWh available to capture yearly with an average power of 3.46 kW for a turbine with an area of 10 square meters. For the same turbine area with conservative efficiencies, the hotspot could provide a yearly technical energy of 10.9 MWh with an average power of 1.25kW for the island. Due to the complex localized hydrodynamics, both the theoretical and technical resource varies greatly across and along the channel. These considerations are more pertinent when performing a hydrokinetic energy resource assessment in a marsh estuary than for large scale bay-ocean exchange environments, the present industry focus.

One of the most recognised values of tidal salt marshes is the ecosystem service they provide as natural sinks for contaminants such as metals. This study examines net accumulation of metals (As, Cr, Cu, Hg, Ni, Pb, Zn and V) over a 5-yr period, from 1997 to 2002, in surface sediments of salt marshes in the Bay of Fundy, Canada. Metal accumulation has been measured in seven sites that extend from outer to inner Bay and in low and high marsh areas within each site. Overall, sediment metal concentrations are at or near their natural levels. Concentrations of metals show variability among marshes but are not significantly different between low and high marsh. Concentrations of As, Hg, Pb and V appear to be influenced by anthropogenic inputs. Calculated sediment loading rates for these metals generally showed gradients of increased loading from outer to inner Bay. Variability in sediment deposition rate is the driving force behind this spatial pattern. Results of this study suggest that the value of salt marshes as a sink for metals may be enhanced by high sedimentation rates.

No description available.

This thesis documents eight estuaries that are situated on the northern coastline of KwaZulu-Natal viz.: St Lucia, Mfolozi, Zinkwazi, Mvoti, Mngeni and those of the South i.e. Isipingo, Manzimtoti and Mkomazi. The documentation is aimed at undertaking a holistic approach on estuaries of KwaZulu-Natal approximately 10% and determines the influence of anthropogenic and natural impacts upon their health status. The study has also analysed selected sample estuaries of KZN in terms of their general natural characteristics, looked at the morphological features, riparian vegetation and land use directly from site visits and from aerial photographys, and determined the influence of anthropogenic and natural impacts in the estuaries. It also assessed the health status of the estuaries, proposed appropriate management strategies and reviewed the current status of estuaries in KZN / southern Africa. The researcher employed quantitative approach as a viable and the most relevant method where a holistic approach has been used. This was achieved through the execution of various techniques. For instance, reconnaissance survey was conducted including the usage of aerial photographys and topographical maps. Data was also collected using the YSI 6920 model. The study was also undertaken in order to determine whether the KwaZulu-Natal estuaries were still having a nursery function, which appeared to be losing when considering both primary and secondary activities that took place in the catchment areas. All of these estuaries were under a severe stress and pressure through natural and anthropogenic phenomenon. They were all suffering and gradually getting contaminated and depleted through anthropogenic activities that took place uncontrolled in their catchmenmt areas. Findings also show humans as the main culprits for estuarine contamination and degradation. It was discovered that about 84.2% of the catchment areas within the study area was human occupied. Their suffering differed as it depended on the extent in which catchment areas were utilized. Where anthropogenic activities took place alarmingly, estuaries also suffered a great deal. This posed a challenge to ecologists, hydrologist and environmentalists generally, and to physical geographers specifically since they regard estuaries as very important for their nursery functions and ecological balances. Mfolozi and St Lucia estuaries were found to be little affected from direct anthropogenic effects. Pollutants accumulating in the systems may have come from farmlands in the north of the Mfolozi and from the town of St Lucia in the case of the St Lucia estuary. However, more negative effects were clearly due to excessive sedimentation. The study has revealed that the Mfolozi mouth position had been artificially relocated on several occasions since 1952 by human intervention in the system. In these situations, the Mfolozi mouth may be located between one and two kilometres south of the St-Lucia mouth. Two estuaries, Mvoti in the north and Isipingo in the south were found to be the most affected water bodies by human activities occurring in the catchment areas and this has led to them having unhealthy water status. It was found that through anthropogenic interference, there were changes in the nature of runoff and water quality that was attributed to industrial pollution, runoff from agricultural activities, sewage effluent and the runoff from urban areas. There is evidence of extremely poor catchment management practices as proved by the poor state of many estuaries along the KwaZulu-Natal coast. The study recommended that for the important future well being of these estuaries, various tiers of catchment management authority must be put in place by the Department of Water Affairs and Forestry. The local authorities must proactively manage land uses and anthropogenic activities on and around the estuaries in order to minimise potential impacts on the systems. / Thesis (Ph.D.)-University of KwaZulu-Natal, 2008.

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.

Acanthopagrus berda is an estuarine-dependent fish species which is widespread in the tropical Indo-Pacific. In South Africa, it is particularly abundant in the three large northern KwaZulu-Natal estuarine systems, namely Kosi Bay, St Lucia and Richards Bay. In these systems, A. berda is harvested by a variety of methods, including traditional fish traps, gillnets and hook and line. The importance of A. berda to the different fisheries was evaluated by analysing all the available monitoring data specific to catches in these three systems. A. berda was found to be one of the five most important species taken in both the gill net and recreational fisheries at Kosi Bay and St Lucia. It was less important in the marine-dominated Richards Bay system. Catches were generally seasonal, with trends in catch per unit effort (cpue) for A. berda related to annual spawning migrations. The long-term trend in cpue for this species in the Kosi recreational fishery showed a disturbing downward trend. Ages of A. berda specimens caught in northern KwaZulu-Natal estuaries were determined by examining whole otoliths. Age estimates were validated by marginal zone analysis and oxytetracycline labelling, which indicated that opaque deposition occurs primarily from September to November each year. The reproducibility of age estimates was described by a coefficient of variation of 10%. The special von Bertalanffy growth curve was found to best describe the growth of A. berda. The parameters of the von Bertalanffy growth curve indicated that A. berda in northern KwaZulu-Natal is slow growing, attaining at least 16 years of age. The age and growth parameters and mortality estimates from catch curves were used to complete a per-recruit stock assessment of the species. The results of the spawning biomass per-recruit model using different ages of first capture indicate that A. berda is at 47% to 55% of its unfished level. Although these results may indicate that A. berda in northern KwaZulu-Natal is not at present overexploited, longevity coupled with late maturation, sex change, estuarine dependency, increasing catches of A. berda and poor monitoring give cause for concern for the continued sustainable use of this species in northern KwaZulu-Natal. / Thesis (M.Sc.)-University of Natal, Durban, 2001.

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.

Various aspects of metabolism and physiology were investigated during the ontogeny of yellowtail kingfish (Seriola lalandi), a fish of growing aquaculture importance in both New Zealand and other countries. Incubation experiments between 18-24°C showed that developing eggs and larvae were heavily influenced by temperature. It appeared that at warmer temperatures larvae hatched smaller but grew on the yolk sac, whereas at cooler temperatures larvae grew inside the chorion. Oxygen consumption data supported this, with a negative correlation found between total embryonic oxygen consumption and temperature. A mechanism was proposed to explain the differential effect of temperature on ontogeny and growth. Like other marine fish with pelagic eggs, yellowtail kingfish were found to be heavily reliant on free amino acids as a source of energy. At 23°C the pattern of substrate utilisation in eggs was considerably different from that at 17-21°C, indicating that 23°C exceeded the tolerance for normal development. Inter-individual aggression by large individuals was associated with the development of size heterogeneity in juveniles. Although this aggression also affected the survival of smaller juveniles, it was not the primary agent of much of the mortality that occurs during this phase, as many of these individuals were on a degenerate developmental trajectory. Yellowtail kingfish fingerlings used for ongrowing were robust to the stressors imposed by live transport. The ontogenetic development of metabolic rate from 0.6 mg-2.2 kg did not follow the same scaling exponent as that observed for mammalian models of allometry, and has implications for interspecific studies of mass-dependent metabolism.