Carbon-14 measurements of community and size- fractionated production in continental shelf waters of the Agulhas Bank (South Africa) are presented. Auxiliary measurements included chlorophyll α, nitrate concentrations and thermal profiling of the water column. During the winter and spring surveys, the mixed layer extended deeper than the euphotic zone, with nitrate and phytoplankton biomass being evenly distributed through the euphotic zone. Production maxima occurred at the 40 - 90 % surface irradiance light depths, with some evidence of surface photoinhibition. All surveys during summer months (December - March) showed a thermally stratified euphotic zone (ZeuO.5%/Zm = 1.1 - 2.2), with a well deformed nitracline within the thermocline. A subsurface chlorophyll maximum closely associated with the region of maximum nitrate gradient (3 - 10 % surface irradiance) was typical of summer measurements. Subsurface chlorophyll α concentrations were lower in western Agulhas Bank waters (0.5- 6 μg.l⁻¹) than in eastern Agulhas Bank waters (l- 15 μg.l⁻¹). Highest subsurface chlorophyll α concentrations (15- 40 μg.l⁻¹) were measured during the late summer survey (March 1986) at the Alhard Banks station in a strongly stratified water column. For profiles showing a very well developed subsurface chlorophyll maximum, the production maximum occurred at or slightly shallower than the depth of the chlorophyll maximum. In western Agulhas Bank waters, during surveys when a shallow (<30m) thermocline persisted, production maxima at 90 and 100% surface irradiance intensities were frequently observed. Integrated production values ranged between 70 and 1390 mgC.m⁻².h⁻¹. Minimum areal production rates were observed during winter (July), whilst maximum rates were measured during late summer (March). High euphotic zone production was also measured during the spring survey in western Agulhas Bank waters (347 mgC.m⁻².h⁻¹), associated with the stabilising of the water column after winter mixing. The <15 μm size-fraction was observed to account for much of total production (62-97%) during conditions of deep mixing in winter and a deep upper mixed layer during summer. During the spring survey and those surveys where a shallow (<35m) thermocline persisted, production was predominantly by the netplankton > 15 μm size-fraction (60- 87 %). Periods of enhanced netplankton growth may be crucial for the sustaining of the large biomass of spawning anchovy present in western Agulhas Bank waters. Vertical profiles, the subsurface chlorophyll and production maximum and size-fractionated production measurements are discussed with relevance to the control of phytoplankton production and potential trophic fluxes in Agulhas Bank waters.

The African penguin Spheniscus demersus is a seabird endemic to the south-western coast of Africa and can be found in three main breeding localities; southern Namibia, the Western Cape and Algoa Bay, Eastern Cape, South Africa. The African penguin has been listed as Endangered since 2010, having experienced a decline in population of more than 50% over the past three generations. This study was conducted at the breeding colony on Robben Island, South Africa, and examined two factors that have the potential to affect breeding success of African penguins; body mass at the onset of breeding and the suitability of various nest types to mitigate changing climatic conditions. Body mass was measured by recording weights using an automated weighing scale set up in front of a nest. Weights were taken at the start of breeding of each penguin in a breeding pair and these weights were compared to the number of chicks fledged, fledging period, hatching success, clutch size, and chick fledging weight. Hatching success, clutch size, and fledging weight were not influenced by the mass of either parent. There was a trend of shorter fledging periods as the mass of the heavier parent increased. The greatest effect was from the body mass of the lighter parent on the number of chicks that fledged from the nest; as the mass of the lightest adult increased, more chicks were fledged. If the lighter adult weighed below 2 kg there were always no chicks at the nest that fledged. This suggests evidence for a carry-over effect of body mass from the time before breeding starts into the breeding season, and highlights the importance of food availability for African penguins on a global scale, and not just a local one. The proportion of nest failures of six nest types (vegetation, open, natural burrow, building, wooden nest box, and artificial fibreglass burrow) at the incubation and chick-rearing stage were compared to rainfall and maximum temperature.

Parasitism is accepted as being an essential driver in the organization of biological communities. However, although there are estimated to be more parasitic than free-living organisms, parasites have been largely neglected from ecological studies and we have a relatively limited understanding of their trophic ecology. Hence, in order to incorporate parasites into food-web models and ecological studies, basic trophic interactions between parasites and their hosts need to be assessed. Here, I investigated host-parasite interactions using stable isotope analyses on a broad range of marine fish hosts and their associated copepod and monogenean gill parasites. The study also provides insight into the gill parasite diversity of a number of host species from South African marine waters. Seventeen species of fish hosts, ranging from lower to upper trophic levels, were collected from South African waters in 2015 and 2016 during surveys conducted by the Department of Agriculture, Forestry and Fisheries from South African waters. These host species were; Thunnus albacares, Thunnus maccoyii, Thunnus alalunga, Thunnus obesus, Isurus oxyrinchus, Prionace glauca, Xiphius gladius, Brama brama, Thyrsites atun, Seriola lalandi, Sarda sarda, Genypterus capensis, Merluccius paradoxus, Merluccius capensis, Lampanyctodes hectoris, Sardinops sagax and Trachurus capensis. The head region, gills and operculae from a total of 1513 fish were examined and any ectoparasites removed, identified down to the lowest taxonomic level possible, and counted. A total of 32 parasite taxa, comprising 20 copepods and 12 monogenean species, were recorded. Two new host records and 15 new geographic records for South Africa were catalogued. The new host records are Mazocraes sp. infecting T. atun, and Caligus dakari infecting T. capensis. The new locality records consist of Euryphorus brachypterus recovered from T. alalunga and T. obesus, Pseudocycnus appendiculatus recovered from T. albacares, T. alalunga and T. obesus, Hexostoma sp. recovered from T. albacares and T. obesus, Nasicola klawei recovered from T. albacares and T. obesus, Tristoma adcoccineum recovered from X. gladius, Eobrachiella elegans and two species from the genus Parabrachiella recovered from S. lalandi and Anthocotyle merlucci recovered from M. paradoxus and M. capensis. These new records have substantially contributed to the known parasite biodiversity within the South African marine environment. Host-parasite interactions between 15 species of fish host and their copepod and monogenean gill parasites were investigated by means of stable isotope analysis. Host white muscle tissue, host gill tissue and parasite samples were analysed for their carbon and nitrogen isotopic signatures. Results indicated that δ¹⁵N is tissue-specific, with host white muscle tissue showing significantly greater enrichment in ¹⁵N compared to host gill tissue (n =60; Z=5.66843; p<0.00001), and as gill tissue is what the parasites are presumably feeding on, host gill tissue was therefore selected as the most appropriate proxy.

Abstract Several questions pertaining to the marine communities at the Prince Edward Islands are addressed. Firstly, the nature of the 'island-mass effect', and the cause of the frequently recorded diatom blooms in the area are examined. It had been suggested that the cause of the blooms is related to the presence of a Taylor Column-induced, low density, stationary eddy which stabilises the water column. On a cruise in April/May 1989, temperature, salinity, nutrients, chlorophyll and primary production were measured at 90 stations in a large grid centred on the islands. These, together with data collected on previous cruises, are used to show that the repeated occurrence of diatom blooms was not a result of nutrient enhancement. No evidence for light-limitation of phytoplankton was found. The evidence and theoretical basis which was used to predict the existence of a Taylor Column is questioned. An alternative hypothesis for explaining the blooms is presented. It is argued that these local blooms are simply the result of seeding by a dormant stock of diatom resting spores from the shallow sediments around the islands. This hypothesis hinges on three observations: (1) the blooms occur only over shallow sediments and are not a feature of the open ocean, (2) the species Chaetoceros radicans has been responsible for the bloom each time the cells were identified, and (3) C. radicans forms a rapidly sinking, heavily silicified, resting spore.

Bibliography: pages 143-160. / The objective of this thesis is to describe the composition and distributional variation of, and environmental factors influencing, the bottom canopy assemblages in a southern African kelp community at Cape Hangklip, Western Cape, South Africa. A detailed collection of intertidal and subtidal marine macroalgal species from the Cape Hangklip area, a site centrally located in the south coast/west coast overlap, yielded a list of 201 species (26 Chlorophyta, 24 Phaeophyta, 150 Rhodophyta). The list of taxa .included four new records for southern Africa (Aphanocladia cf. skottsbergii, Audouinella endophytica, Centroceras distichum and Grate/oupia doryphora), five undescribed species (Antithamnion sp., Colaconema sp.,, Erythrocladia sp., Erythrog/ossum sp. and Pterosiphonia sp.) and one rhodophyte of uncertain affinity (cf. Ceramiaceae indet.), probably representing a new genus in the Ceramiaceae.

The habitat associations between the caridean shrimp Nauticaris marionis and sessile epibenthic assemblages and substratum types of the Sub-Antarctic Prince Edward Islands were investigated. Twenty five stations, varying in substratum type, depth and location on the shelf and slope around the islands were sampled photographically with a towed benthic camera sled. At each station the substratum type was classified, sessile epibenthic cover was quantified through the use of digital quadrats and shrimp density was estimated. Results add to the broadly described distribution patterns of N. marionis by identifying specifically the habitat characteristics they generally utilize. The distribution of N. marionis was found to be influenced by a combination of substratum and sessile epibenthic assemblages, but not substratum type alone. Shrimp inhabited stations with >50 % biogenic cover on mud and gravel substrata, but were not found at stations with rocky-sand or rocky-mud substrata. Their distribution appears to also be influenced by depth, as shrimp were only found within a depth range of 50 - 160 m in this study. A strong correlation was found between N. marionis density and depth. Shrimp were found both inshore around the islands, and on the relatively shallow saddle between the islands. In comparison with previous studies, N. marionis was found at similar, if not higher, densities in this study, although they occupied a narrower depth range.

A majority of the research on sea turtle vision focuses on the turtle's ability to perceive shapes, colors and brightness cues on land. However, aerial vision is a minor component of the visual ability of sea turtles, potentially used only when surfacing to breathe, while basking, and during female reproductive activities. For my doctoral dissertation, I examined the aquatic visual acuity of juvenile loggerhead sea turtles (Caretta caretta) by investigating the morphology of the eye, the electrophysiology of response to stimuli, and the behavior to specific stimuli. For the morphological experiments, eyes were obtained from loggerheads, euthanized due to injury, and histological techniques were used to identify both cell types as well as regionization of cell densities. For the collection of electrophysiological responses from healthy juvenile loggerheads, testing was performed using a water-filled goggle and subdermal platinum electrodes implanted over the optic nerve and contralateral optic tectum. Stimuli were flickering black and white gratings. Visual evoked potentials (VEPs) were collected using an averaging computer and thresholds were measured from the recordings. Finally, for the psychophysical study, loggerheads were trained, in a 500-gallon tank, to discriminate between a vertical grating and a 50% gray panel using positive reinforcement. Thresholds were then recorded from incrementally smaller gratings. These data, from the three techniques used in this study, suggest that vision does play an integral role in the juvenile loggerhead's perception of its surroundings. Higher concentrations of cone photoreceptors and ganglion cells were found in the dorsal region of the eye, indicating an area centralis. Furthermore, the cone and rod photoreceptor densities throughout the eye suggest that this animal is capable of both visual acuity and sensitivity. Acuity threshold, measured from the VEP recordings, was approximately 5.4 minutes of arc for all turtles tested. Moreover, the psychophysical experiment measured an acuity threshold of 12.9 minutes of arc. The regionalization of acuity in the dorsal hemisphere of the eyes as well as the acuity threshold levels recorded for juvenile loggerhead sea turtle suggests that loggerheads are using vision for foraging, predator avoidance, territory selection and defense, and other basic behaviors in their aquatic surroundings.

No description available.

Traditional measurements of phytoplankton N uptake have been confounded by bacterial retention on filters used in 15N uptake studies, and such methodological obstacles have limited our understanding of phytoplankton-bacterial interactions regarding N cycling. In this research, uptake of various inorganic and organic N substrates by phytoplankton and bacteria was measured in several marine ecosystems using two distinct approaches: size fractionation into phytoplankton and bacterial size classes, and flow cytometric (FCM) sorting of autotrophic cells. Comprehensive assessments of N uptake dynamics were conducted in Chesapeake Bay, the Mid-Atlantic Bight, and Raunefjord, Norway, with supplementary data collected from the York River, Virginia and the Gulf of Mexico. In Chesapeake Bay, the composition of the dissolved N pool shifted from being dominated by dissolved inorganic N (DIN) in the upper bay to mostly dissolved organic N (DON) in the lower bay. Accordingly, phytoplankton nitrate uptake was highest near the head, whereas uptake of urea and dissolved free amino acids generally increased southward. Nonetheless, ammonium was the dominant form of N used by phytoplankton and bacteria throughout the bay. In the Mid-Atlantic Bight, the surface layer was devoid of DIN but ambient urea concentrations were relatively high and this organic substrate supported a large majority of total measured N uptake. The dissolved N pool in the bottom water consisted of about two-thirds DIN, with ammonium contributing most to total uptake. Bacteria were especially active in the bottom water and contributed over half of the total DIN uptake, and there was evidence of bacterial urea uptake in the surface water. In Raunefjord, a mesocosm approach was used to examine N uptake by a bloom of colonial Phaeocystis as well as the competition between phytoplankton and bacteria for limited N resources. Despite amending with nitrate, ammonium was the primary N form supporting the bloom. In the unfertilized mesocosm, bacteria were responsible for about half the urea uptake, most of the DFAA uptake, and at least a third of DIN uptake. Overall, total dissolved N concentrations and total N uptake decreased from estuarine to oceanic waters, although uptake rates were highly variable within each ecosystem. The reduced N forms, ammonium and urea, were most important to phytoplankton N nutrition, and contrary to traditional belief, urea at times played an important role in bacterial N uptake. With respect to methodological approaches, traditional filtration resulted in significant overestimation of phytoplankton N uptake due to the inclusion of, and 15N enrichment in, bacterial biomass retained on filters. This research represents the first comprehensive assessment of phytoplankton-specific N uptake across various ecosystems. It highlights not only the need for careful qualification of uptake rates measured using traditional approaches, but also the potential application of FCM sorting to more detailed examination of N uptake by phytoplankton in general, but also by specific taxa in various marine ecosystems.

No description available.