An Ecophysiological Study of the Meiofauna of the Swartkops Estuary

As part of a larger project, a number of physical and chemical features of two beaches in the Swartkops Estuary near Port Elizabeth were monitored over a period of fourteen months. These features included temperature, nitrogen, chlorophyll a, oxygen and salinity. In addition measurements were made of particle size, porosity, permeability and desiccation. It was found that environmental conditions were most severe at the higher tidal levels as well as in the upper reaches of the estuary. Nitrogen and chlorophyll a varied greatly from month to month and the usefulness of such determinations as indicators of available food is questioned. The interstitial environment was found to be greatly influenced by the presence of sand prawns (Callianassa kraussi). It is suggested that burrowing macrofauna, particularly those forms with burrows extending from the surface, have profound effects on the physical and chemical conditions in beaches and mud flats

Seasonal fluctuations in the vertical distribution of meiofauna in estuarine sediments

The vertical distribution of meiofauna in estuarine sand and mud sediments was  investigated over a period of fourteen months. Statistically significant differences were found between fluctuations of meiofauna inhabiting different depth zones in the top 20 cm of the sediment. The shallow populations are affected more drastically during rimes of adverse conditions but they have the ability to respond rapidly to favourable  conditions. It is concluded that a combination of physiological adaptation and changes in species composition, rather than seasonal vertical migrations, are responsible for the observed patterns

Epibenthic Algal Production in the Swartkops Estuary

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Diurnal vertical migrations of meiofauna in an estuarine sand flat

Diurnal vertical migrations of meiofauna were observed in an estuarine sand flat and these were related primarily to desiccation and temperature. The migrations, which occurred in the top 10 cm of the sediment, had a mean range of 5 cm and were most strongly exhibited by the interstitial flatworms, polychaetes and oligochaetes, followed by the nematodes and harpacticoid copepods. It is concluded that vertical migrations are restricted to areas experiencing some degree of desiccation and would not be significant in waterlogged areas such as mud flats

Recovery and recruitment of the brown mussel, Perna perna (L.), in Transkei: implications for management

The brown mussel Perna perna, has been an important food resource for indigenous inhabitants of the Transkei coast for centuries. The impoverished state of mussel stocks in this region and major differences in lowshore community structure between exploited and protected areas, have been ascribed to the ever-increasing explOitation of this species. In spite of this there has been no effective management of this resource owing to political and logistical problems related to law-enforcement, and misconceptions concerning the resilience of P. perna and the interspecific interactions which govern its recovery. Our present understanding of the ecological impacts of exploitation, and of the potential for recovery, is based on a series of studies and observations made over the last 15 years. These studies have shown that algae usually replace mussels following disturbance and that recovery may take more than eight years. As mussels tend to recruit preferentially into existing mussel beds, exploitation not only affects reproductive output but also reduces the preferred habitat. Recruitment onto both natural and artificial substrata is extremely low, even in marine reserves where standing stock is considerably higher than in exploited areas. Under these conditions stock enhancement in conjunction with rotational cropping may be the best management strategy.S Afr. J. Zool. 1997,32(4

An Ecophysiological Study of the Meiofauna of the Swartkops Estuary

Environmental correlations with mean, as well as seasonal, distribution and abundance of the meiofauna in two exposed beaches in the Swartkops Estuary, near Port Elizabeth, were elucidated. Population densities showed a direct relationship with particle size. Consequent on this, oxygen appeared to be the controlling factor although desiccation played a role in the intertidal distribution of meiofauna in sandy areas. Seasonal fluctuations in numbers were characterized by peaks occurring in spring and autumn. Variations of temperature and oxygen were found to be responsible for this pattern. The presence of the sand prawn Callianassa kraussi affected both vertical penetration and seasonal fluctuation of the meiofauna. Since fluctuation in nitrogen and chlorophyll a content of the substrate bore little relationship to the fluctuation of the meiofauna, it is concluded that food is not limiting in these areas. Biomass determinations revealed that nematodes, which were the dominant taxon, weighed 0,42 μg individual mean ash-free dry mass and harpacticoid copepods 0,47 μg. On this basis the standing crop biomass was 0,40 μm2 in the sandy areas and 0,07 g/m2 in the muddier areas, both to a depth of 20 cm

An ecophysiological study of the Meiofauna of the Swartkops Estuary: 3. Partition of benthic oxygen consumption and the relative importance of the Meiofauna

Benthic oxygen demand was measured by dark and light bottle technique at two beaches in the Swartkops estuary, near Port Elizabeth. Respiration of nematodes was measured by polarographic micro-rcspirometer technique. Secondary production was 82 g C/m2/y in sandy areas and 863 g C/m2/y in muddy areas rich in the prawn Callianassa kraussi. Meiofauna production was 1,72 g C/m2/y in sand and 0,24 g C/m2/y in mud. The meiofauna] contribution to secondary production was 2,1% and 0,03% for these two areas respectively. The largest proportion of secondary production was due to micro-organisms: 92% in sand and 73,5% in mud. Macrofauna accounted for 5,75% and 24,4%. It is concluded that meiofauna in these exposed sand and mud flat areas is not quantitatively important, but the qualitative importance may be considerable

Quantitative extraction of Meiofauna: A comparison of two methods

Two methods for the quantitative extraction of meiofauna from natural sandy sediments were investigated and compared: Cobb's decanting and sieving technique and the Oostenbrink elutriator. Both techniques were more efficient with pre-fixed samples than with fresh samples. The results indicated that elutriation is the more reliable method due to its low variability, 7,5% for nematodes and 8,4% for harpacticoids and  mystacocarids compared to 11,2% and 29,0% respectively in the case of decantation. However, with samples containing 3 000 to 5 000 animals per 200 cc, decantation yielded 25% more animals than elutriation

Defining fishers in the South African context: subsistence, artisanal and small-scale commercial sectors

Evolution of a new policy for the management of marine fisheries in South Africa led to the Marine Living Resources Act of 1998 (MLRA). Among other innovations, this requires that management strategies be developed for subsistence fisheries. As a prerequisite, definitions and criteria are needed to identify and distinguish them. To achieve this, the Chief Director of Marine & Coastal Management (MCM), the authority responsible for managing marine fisheries, appointed a Subsistence Fisheries Task Group (SFTG) to make recommendations about definitions and modes of management. The process involved successive surveys and consultations with fishing communities, communication with MCM, and a national workshop of all participants. This led to consensus about the following definition: Subsistence fishers are poor people who personally harvest marine resources as a source of food or to sell them to meet the basic needs of food security; they operate on or near to the shore or in estuaries, live in close proximity to the resource, consume or sell the resources locally, use low-technology gear (often as part of a long-standing community-based or cultural practice), and the kinds of resources they harvest generate only sufficient returns to meet the basic needs of food security. This definition builds on the facts that existing subsistence fisheries are usually: (1) local operations; (2) customary, traditional or cultural; (3) undertaken for personal or family use; (4) primarily for nutritional needs (though excess resources may be sold to ensure food security); (5) based on minimal technology; and (6) undertaken by people with low cash incomes. They are specifically non-commercial and non-recreational. The definition was designed to allow protection of the rights of these people and sustainability of the resources. While developing this definition, it became obvious that the definition of “commercial fishing” in the MLRA is also inadequate, and a new definition was developed. Commercial fisheries span a wide spectrum, and the SFTG defined “small-scale commercial fishers” as a distinct component that has not received adequate attention, and for whom specific management plans need to be developed. They are distinguished by living on or close to the coast, having a history of involvement with fishing, being personally involved in hands-on day-to-day running of their enterprises, operating with limited amounts of capital investment and low levels of technology, and employing small numbers of people.Keywords: defining subsistence, fisheries management, subsistence fishersAfrican Journal of Marine Science 2002, 24: 475–48

Assessment of resource availability and sustainability for subsistence fishers in South Africa, with a review of resource management procedures

The availability of resources and their suitability for subsistence and small-scale commercial fishers in South Africa were assessed and appropriate options for the management of resources recommended. Assessment of current resource utilization and recommendations for future subsistence and/or small-scale commercial use were based on information gathered during a nationwide survey of 144 subsistence fishing communities in South Africa and a review of relevant published and unpublished literature. Current patterns of resource use in three regions of the coast (West, South and East coasts) revealed that most true subsistence fisheries occur in the eastern half of the country. These fisheries are primarily focused on invertebrate species found on intertidal rocky shores and sandy beaches, or in estuaries. Fish are harvested by rod or handline, netting or traditional fishing methods (fishtraps, spearing, baited baskets). No “new” or previously underutilized resources were identified as suitable for subsistence fishing in any of the three regions. The potential for several new small-scale commercial fisheries was identified, but the need to retain certain resources for subsistence fisheries (rather than converting them to small-scale commercial fisheries) was evident in certain areas. Resources with high commercial value were not considered suitable for subsistence fishing, but rather for the introduction of small-scale commercial fisheries. The overall management strategy for the subsistence sector, which is currently in the process of being developed, must ensure sufficient flexibility to be able to take into account regional and site-specific requirements. It will also need to develop co-management structures, protect traditional fishing practices, avoid user conflict and provide for no-take areas, all within the framework of sustainable resource utilization.Keywords: estuarine resources, fisheries management, intertidal resources, subsistence fisheries, subtidal resourcesAfrican Journal of Marine Science 2002, 24: 489–50