x, 120 leaves : ill. ; 28 cm Typescript Thesis (Ph.D.)--University of Oregon Includes vita and abstract Bibliography: leaves 113-120 Another copy on microfilm is located in Archives University of Oregon theses, Dept. of Biology, Ph.D., 1982

Behavioural responses of the colour forms of Carcinus maenas to salinity variation were investigated, and related to their physiology and distribution in an estuary. Red males, characterised by a thicker carapace were unable to survive in as low salinities as green males; this was reflected in their poorer osmoregulatory capabilities. Haemolymph osmolality and ion concentrations of red crabs decreased at a faster rate and reached lower levels than in green crabs. Haemolymph osmolality and choice behaviour did not vary with size. In the tidally mixed estuary male and female crabs occurred in roughly similar proportions. Most were green and generally smaller than their open shore counterparts. Migration out of the estuary in winter was reversed in late spring. Differences in salinity tolerance of red and green crabs were reflected in salinity preference behaviour. Green crabs persisted longer in the lowest range of salinities tested, especially if a shelter was available. Prior acclimation affected the timing of choice behaviour; the lower the salinity of acclimation the faster the time of exit from the lowest range of salinities tested, and vice versa. Estuarine green crabs exhibited endogenous locomotor activity of circatidal periodicity and were less responsive to episodes of low salinity than open shore red and green crabs. Constant low salinity initiated a rhythm of circatidal periodicity in arhythmic red and green crabs; red crabs reacted faster and were more active upon salinity change than green crabs. The amount of locomotor activity induced after prior acclimation was similar within each acclimation salinity tested. Carcinus detected salinity variation by responding to the concentrations of Na and Cl in seawater, and was able to differentiate between salinities separated by as little as 0.5ppt., - General physiological changes appear to occur before behavioural responses are mediated; they probably act as cues for the behavioural responses, which appear not to be triggered by specific receptors. Behavioural and physiological responses combing to enhance, the survivability of crabs in changing salinities.

Estuaries worldwide are being subjected to various degrees of catchment degradation, which is having severe consequences on the integrity of these aquatic ecosystems and their ability to function properly. This thesis investigated the relationship between catchment land-cover and estuarine health in four temporarily open/closed estuarine systems (TOCEs) in South Africa, namely the Groot Brak, East Kleinemonde, Mdloti and Tongati. GIS techniques were employed to delineate catchments, lower sections of catchments, 1 km and 100 m buffer zones, and to quantify the extent of land-cover classes present within these delineations. Anthropogenic activities outlined by the Department of Water Affairs and Forestry (DWAF) Resource Directed Measures (RDM) studies and their associated land-cover classes were described. The possible links between catchment and buffer zone land-cover class composition and health of the estuaries were explored. Results indicated that there was a relationship between catchment and estuarine health within the Coastal Protection Zone (CPZ) (1 km and 100 m) buffers, but not at a broader catchment level. Out of natural, urban built-up and cultivation land-cover classes, natural land was determined to be the best predictor of estuarine health within the CPZs. A method of rapidly assessing South African TOCE condition was applied and could be used to prioritise these estuaries for rehabilitation and/or conservation.

The Knysna estuary system, on the south coast of South Africa, was sampled for zooplankton over period of one year. All species were recorded and an attempt was made at relating the distribution of populations to physical factors within the estuary. Over 50 species were identified. Pseudodiaptomus hessei, Acartia(Paracartia) longipatella and A.(Acartiella) natalensis were the dominant copepods in the upper estuary. Paracalanus spp. were dominant near the mouth. Zooplankton distribution was found to be related to tidal exchange. The zooplankton displayed a seasonal cycle of abundance, with maximum numbers occuring during summer. P. hessei displayed no pronounced seasonal cycle in abundance. Its abundance was strongly related to freshwater inflow. Seasonal succession was evident between A. natalensis, the summer dominant, and A. longipatella, the winter dominant. The controlling factors for this cyclical dominance were not clear. Diel vertical migration behaviour was shown to various degrees by virtually all zooplankton populations. The stimulus for this behaviour could not be definitely identified.

Thesis (Ph.D.). / Written for the Dept. of Geography. Title from title page of PDF (viewed 2008/08/04). Includes bibliographical references.

Thesis (MSc)--University of Stellenbosch, 2007 / Bibliography. Also available via the Internet.

Thesis (Ph.D. (Zoology & Entomology)) - Rhodes University, 2009.

Thesis (M. Sc. (Ichthyology and Fisheries Science))--Rhodes University, 2006.

Thesis (Ph.D. (Ichthyology and Fisheries Science)) - Rhodes University, 2007.

This investigation had three major objectives; firstly to document the estuarine fishes from several poorly studied Eastern Cape estuaries, secondly, to identify similarities and differences in the fish communities from permanently open and intermittently open estuaries, and thirdly, to establish which physico-chemical or environmental variables are responsible for the structuring of these communities. The study area incorporated 10 estuaries along a 70 km long stretch of the Eastern Cape coastline between the towns of Seafield (33° 32' 42" S, 27° 03' 05" E) in the south-east and Hamburg (33° 16' 45" S, 27° 29' 50" E) in the north-west. The systems investigated included two permanently open estuaries and eight intermittently open systems of varying sizes. Overall fish abundance and species richness in the study area revealed no significant seasonal variation. A contrast between open and closed estuaries was evident in the dominance of species from different estuarine dependence categories. Open estuaries comprised mainly category Ib, lla and IIb species, with a high proportion of category IV species. Closed estuaries were dominated by category IIa species, with few category IV species represented. Clear longitudinal trends in relative abundance were demonstrated for individual species. Margalefs species richness index for seine net catches, and a combination of the seine and gill net data, were significantly correlated with catchment size, mean annual runoff, estuarine area and linear length. Fish assemblages in the permanently open and intermittently open estuaries were significantly different (p<0.001) when analysed on a community and density basis. Similarly, the communities in large and small intermittently open estuaries differed significantly on a community (p=0.01) and density basis (p<0.001). These differences where caused by changes in abundance of the dominant estuarine resident and marine migrant species. The environmental variable that was dominant in accounting for these differences was the estuary mouth status. Estuarine resident species had smaller overall body lengths when compared with the marine migrant species. In addition, the estuarine resident species had smaller modal size classes in the closed estuaries when compared with the open estuaries. These differences may be linked to the foraging strategies of the species, as well as food availability and different levels of predation in the different estuary types. The marine migrant species did not show any trends in this respect although the closed systems had the largest individuals for all four dominant marine species. This finding may be linked to the inability of these species to breed in closed estuaries, thus channelling reproductive energy resources into somatic growth. In addition, prolonged periods of mouth closure prevent the emigration of large individuals back to the sea. Otter trawling was conducted in fiye estuaries and captured mostly demersal species. The otter trawl data confirmed the seine net community analysis, with significantly different communities identified in the permanently open and intermittently open estuaries (p=0.02), as well as in the small and large intermittently open estuaries (p=0.03). The environmental variables responsible for these community differences were mouth status and variables associated with estuarine size. The identification of estuary mouth status by this study as the most influential environmental factor is compounded by this "ariable affecting or being indicative of numerous other physico-chemical features. The large differences in the fish communities in different estuary types indicate the importance of each estuary type to various species. This should be taken into account before allowing any form of commercial fishing in these important nursery areas.