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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.

During 1973 data was collected to analyze the seasonal variations of the tidal dynamics, water quality and sediments of the Alsea Estuary. A summary of historical information with a list of all known alterations to the estuary was made. A complete physical description, including the geographical setting and mixing classification of the estuary, was done. Times of high and low water and tidal ranges at three locations were measured. Tide measurements made at Waldport indicated that the published tide predictions for that location were reliable. At a location upstream of the estuary embayment noticeable damping of the tidal wave amplitude was detected during periods of high river flow and high tidal range. High water lag times were found to decrease during periods of high river flow, but low water lag times were unaffected by river flow. The tide motion was found to be a damped, partially standing wave, which altered its behavior according to the volume of water in the estuary. The high and low tide water quality parameters of salinity, temperature, dissolved oxygen, turbidity and pH were measured at 10 to 18 locations during each season to determine any seasonal changes in them. The parameters at a given location were found to be a function of river flow and tidal range. Winter and summer sediment samples were analyzed for grain size distribution, volatile solids and porosity. The sediments from the main channel exhibited characteristics of a high velocity regime and those of the north channel, a low velocity regime. / Graduation date: 1975

vii, 97 leaves : ill., maps ; 28 cm Notes Typescript Thesis (M.S.)--University of Oregon, 1985 Includes vita and abstract Bibliography: leaves 92-97 Another copy on microfilm is located in Archives

ix, 62 leaves : ill. ; 29 cm Notes Typescript Thesis (M.S.)--University of Oregon, 1987 Includes vita and abstract Bibliography: leaves 59-62 Another copy on microfilm is located in Archives

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 45-47). / Rhithropanopeus harrisii is an introduced Atlantic crab in Coos Bay, Oregon. In Coos Bay, it occurs only in the uppermost estuary where salinities are seasonally low (<1 0/00). Rhithropanopeus occurs at higher salinities in its native range, and tolerates higher salinities in the laboratory. A native crab, Hemigrapsus oregoneos1s, occurs in the estuary, but not as far up into the oligohaline and freshwater zones as Rb1tbcopanopeus. In laboratory experiments, adult Hem1grapsus consume juvenile Rhithropanopeus. Hemjgrapsus is significantly more aggressive than Rhithropanopeus. The absence of juvenile Rhithropanopeus at field sites where both species occur suggests that field interactions may be occurring. Taken together, these results and observations suggest that there may be a dynamic zone in the estuary where the distribution of Rhithropanopeus is restricted by Heroigrapsus. Rhithropanopeus may find a refuge from Hemigrapsus in the oligohaline-freshwater Zones of the estuary, such that Hemigrapsus may be exerting selective pressure on the Rhithropanopeus population favoring freshwater adapted individuals.

The annual biomass of fish caught from estuaries in South Africa is currently estimated at over 24,800 tons. These estuarine fishes are caught by over 73,000 fishers, most of them recreational. Annual income derived from South Africa’s total estuarine fishery was worth approximately R430,000,000 in 1997. There is increasing concern that unless our estuarine fisheries are effectively managed, we will not be able to sustain these benefits into the future. Two factors that contribute to inadequate management of the estuarine fisheries in South Africa are a lack of data on which to base management decisions, and the lack of indicators by which to assess trends towards sustainability. The main aims of this study were to provide a description of the Kowie estuary fishery, identify suitable indicators of sustainability for this fishery, and assess its sustainability. Boat-based and shore-based roving creel surveys were carried out on the Kowie estuary between July 2000 and June 2001; 1,091 interviews were conducted with linefishers, and 277 interviews with bait collectors. In the boat-based interviews, data were collected on fisher demographics, fishing site, fishing method, choice of bait, fishing duration and catch statistics. In the shore-based surveys, additional data were collected from shore-based linefishers and bait collectors on their perceptions, attitudes, and knowledge of fishery regulations. Total annual fishing effort on the Kowie estuary was estimated at 30,952 angler hours (SD=154); 84% of it recreational, and the rest subsistence. Most fishing occurred during December and January, and decreased during winter, especially June and July. The annual yield of fish from the estuary was estimated at 16,240 fish (SD=667) or 5.99 tons (SD=0.81). By number, recreational anglers caught 69% of the annual catch. Three species dominated the catch by number: Rhabdosargus holubi (62%), Pomadasys commersonnii (17%) and Argyrosomus japonicus (7%). By mass, the dominant species caught were Argyrosomus japonicus (60%) and Pomadasys commersonnii (19%). Overall catch rate on the estuary was 0.57 fish.ang.⁻¹h⁻¹ (SD=0.24), or 0.298 kg ang.⁻¹h⁻¹ (SD=0.31). Overall catch rate by number was highest in the subsistence sector at 1.13 fish.ang.⁻¹h⁻¹(SD=0.70), while the boat-based recreational sector recorded the highest overall catch rate by mass (0.427 kg.ang.⁻¹h⁻¹, SD=0.625). Argyrosomus japonicus had the highest overall catch rate by mass on the estuary (0.496 kg ang.⁻¹h⁻¹), and Rhabdosargus holubi the highest overall catch rate by number (1.233 fish.ang.⁻¹h⁻¹). Only 19% of the catch of R. holubi was above the minimum legal size, while the estimates for P. commersonnii and A. japonicus were 21% and 25%, respectively. The annual number of bait collecting outings on the estuary was estimated at 2,889, of which 75% were subsistence. The highest numbers of bait collecting outings were recorded in December and April. The Bay of Biscay was the most popular site for bait collecting. A total of five invertebrate species were collected from the estuary to be used as bait, of which the mud prawn Upogebia africana was the dominant species. Total annual number of mud prawns collected from the estuary was estimated at 260,648; of which 41% was collected by subsistence bait collectors. Thirteen indicators were selected to assess sustainability in three fishery sectors on the Kowie estuary: namely, the shore-based recreational linefishery, the subsistence linefishery and the subsistence bait fishery. Social sustainability was evaluated on the basis of the use fishery resources to fulfil Maslow's basic human needs of food and employment, safety and security, affiliation, self-esteem and selfactualisation. Indicators of ecosystem sustainability assessed the productivity, diversity, disturbance and degree of water quality in the estuary. Institutional sustainability was assessed on the basis that management systems in the fishery should be results-oriented, consent-based, truth-seeking and adaptable. Data on indicator performance was collected during the shore-based roving creel survey, and from published literature. Arbitrarily set reference points were used to assess indicator performance, which was graded on a scale from 1 (indicating minimum probability of sustainability) to 4 (indicating maximum probability of sustainability). Sustainability was illustrated with the aid of amoeba plots. Overall sustainability was low in all three fishery sectors investigated. Nine of the 13 indicators in the shore-based recreational fishery performed poorly, while 11 of 13 in the subsistence line fishery, and 10 of 13 in the subsistence bait fishery, performed poorly. In all three fishery sectors all four selected indicators of institutional sustainability performed poorly. The probability of social sustainability was higher in the shore-based recreational line fishery, where the performance of two of the five selected indicators was very good. The probability of ecological sustainability was lowest in the shore-based recreational linefishery, while in the subsistence linefishery only one selected indicator performed very well. Recommendations made towards assessing sustainability in small-scale estuarine fisheries include the formulation of national policy for assessing sustainability in fisheries, the involvement of fishers in the assessment process, use of fisher perceptions where data gaps exist, and the use of research results to guide future management decisions. Management changes recommended for the Kowie estuary fishery include the formulation of an effective and integrated management plan, identification of the key stakeholders in the fishery, inclusion of fishers in management, the protection of the estuary’s Zostera capensis beds, and the establishment of a programme to increase research and monitoring in the fishery.

Temporarily open/closed estuaries (TOCEs) are unpredictable environments that change in response to mouth condition, which is influenced by freshwater flooding or sea storm surges. The aim of the study was to determine whether macrophyte phenology in a TOCE was event driven rather than cyclically predictable and if it differed from permanently open estuaries (POEs). Macrophyte growth and flowering phenology in response to environmental conditions was investigated in the East Kleinemonde Estuary (TOCE) and the Kowie Estuary (POE) along the eastern coastline of South Africa. The lack of freshwater flooding due to low rainfall coupled with several overwash events resulted in a prolonged period of mouth closure from September 2008 to the end of this study period in 2010. This in turn caused the inundation of the supratidal and intertidal habitats, high water level (> 1.57 m amsl) and high salinity (30 - 42 ppt) in the TOCE. Principle Components Analysis showed that high water level and reduced sediments were the most significant environmental factors affecting macrophyte phenology. Macrophyte phenology in the POE was primarily driven by temperature, sediment redox potential and salinity. The saline high water level and reduced sediment significantly reduced macrophyte cover in all habitats in the TOCE. Macrophytes in the POE maintained high cover abundance due to seasonal re-growth compared to the TOCE where cover declined over the sampling period due to the high water level. Subsequent to water level dropping by as little as 11 - 20 cm in the TOCE, the intertidal species Sarcocornia tegetaria and Salicornia meyeriana completed their life-cycles and produced viable seeds within four and three months of germinating respectively. In contrast, the Sarcocornia hybrid and S. meyeriana in the POE took longer to complete their life-cycles, namely seven and nine months respectively, while S. tegataria did not germinate in situ but reproduced vegetatively despite producing seed. In the TOCE, the submerged species Ruppia cirrhosa and Chara vulgaris completed their life-cycles within five and three months and produced a maximum of 26 242 and 196 998 seeds m-2 respectively. Due to high water level and prolonged inundation, the reproductive periods were shorter for the intertidal and reed and sedge species in the TOCE compared to the POE. Seed output during the two reproduction periods varied between the two estuaries. Sarcocornia decumbens and S. tegetaria produced a substantially higher number of seeds in the TOCE compared to the POE, namely 0 - 102 847 versus 20 661 - 48 576 seeds m-²; and 7 001 - 45 542 versus 1 587 – 16 958 seeds m-² respectively. Seed output in the TOCE was significantly higher in S. tegetaria during the second reproduction period despite the significantly lower plant cover, which may be a function of the stressful environment in the TOCE. Seed production of S. meyeriana was significantly higher in the POE compared to the TOCE, with 264 224 - 640 292 compared with 24 050 - 27 643 seeds m-², due to higher plant cover in the POE. The research suggests that macrophyte phenology in the TOCE was significantly influenced by mouth condition. Further, macrophytes were able to demonstrate considerable phenotypic plasticity in response to changing and unfavourable environmental conditions. These data can be used in mouth management plans and freshwater requirement studies in TOCEs to ensure that macrophytes can complete their life-cycles and produce viable seeds for the safeguarding of habitat persistence and ecological processes. In impacted estuaries where artificial mouth opening is practised and the macrophytes have been severely degraded or extirpated, management should ensure that the intertidal and supratidal habitats are not inundated during peak flowering and seed production periods i.e. late spring to early autumn (November to March).

Crabs are conspicuous inhabitants of temperate salt marshes and tropical mangroves and interact with their environment through several processes. However, detailed information on crab community processes is absent for most South African estuaries and nearshore coastal regions. This study evaluated the primary producers supporting crab species in the salt marsh dominated Swartkops estuary and the mangrove Mngazana estuary. Various methods estimating crab abundances were also assessed in different microhabitats and the larval distribution of crabs in the coastal zone was also investigated. Various methods for estimating crab abundance have been employed in the past, each with its inherent biases. The microhabitat of a mangrove forest in Australia was structurally altered by the manipulation of the litter, pneumatophores and the associated algae. These alterations did not affect the behavioural activity or the numbers of crabs recorded in any of the experimental treatments by either visual counts or pitfall traps. However, the number of crabs caught in the pitfall traps differed between the sites. Species-specific behaviour which was not investigated in this study may bias crab abundance estimates when using pitfall traps and therefore requires further investigation. Benthic consumers inhabiting shallow coastal environments may ultimately have the origin of their nutrition in a number of possible sources. Isotopic and gut content analysis of Thalamita crenata and juvenile Scylla serrata in the Mngazana estuary in South Africa revealed that these two portunids are able to share a habitat by resource partitioning. Differences were noted for species-specific utilization of primary producers not only between seasons within a site, but also between sites. This highlighted the use of locally produced primary producers sustaining food webs in estuaries. Mangrove production in the Mngazana estuary is very important and contributes to most of the carbon in the underlying sediments in the mangrove forest. However, the relatively large number of species and biomass encountered in this estuary may also be attributed to the fact that the different species are able to exploit of a number of different resources. The variation in stable isotope analysis of the different crab species throughout the estuary indicated that these crabs able to occupy the same habitat by feeding on a number of different resources and may preferentially select for a specific primary producer. A stable isotope of crabs in the salt marsh Swartkops estuary indicated that the dominant primary producer sustaining crab communities may even take place on a relatively smallscale. Sesarma catenata found at the inner marsh site recorded more depleted carbon signatures than those encountered in the other sites approximately 100 m away, and reflected signatures similar to the locally-encountered inner marsh plants. The relatively enriched nitrogen signatures of the anthropogenically-impacted Swartkops estuary is an indication of extensive inputs due to urbanization and industrialization, in contrast to the relatively pristine Mngazana estuary which exhibited low nitrogen signatures. Emphasis has been placed on the abiotic component of the exchange of nutrients and energy, although living organisms may also be transported, both actively and passively, between ecosystems. Little variation in either species composition or abundance was found between seasons for the larval distribution of brachyuran crabs on the east coast of South Africa. Due to the lack of published larval descriptions, larvae could not be identified to species level and it was therefore not possible to identify whether the larvae were hatched or spawned in an estuary or in a marine environment, or whether the larvae originated in the northern tropical regions. Frequent wind-reversals which are common in this region may retain larvae close inshore and supply the southern temperate locations with larvae from the northern locations. In conclusion, this study has shown that in highly productive systems with a number of potential primary producers, the crabs that inhabit the estuary show a marked diversity in resource utilization which could potentially allow a number of closely related species to occupy different trophic levels. This study also highlights the importance of locally produced sources in an estuary, which may occur on very small scales and this needs to be factored in with the design of any future stable isotope studies of this nature.

Zooplankton populations in the St. Johns River Estuary ranged from 3,000/m3 to 20,000/m3 during monthly collections from September, 1973 to August, 1974. Acartia tonsa Dana was the dominant organism throughout the year, except for spring blooms of Balanus sp. nauplii in the lower estuary and summer occurrences of Eubosmin tubins in the upper estuary. With these two exceptions, species composition, and community structure were similar throughout the estuary, year round. A patchy distribution of the zooplankton caused high replicate sample variation which made it difficult to detect small population variations. Salinity appeared to have the greatest effect on the distribution and abundance of zooplankton within the estuary. Population numbers were sufficiently low to suggest that zooplankton were not the major component of secondary production.