Notes: Abstract Cool nutrient rich waters combined with a rocky coastline extending infratidally make the west coast of South Africa well suited to growth of kelp species. The kelp bed community is compared with the main kelp beds studied elsewhere (Nova Scotia, W. Europe, California). All these areas have cool, nutrient-rich water but the Benguela region differs in that large swells prevail. This paper deals with the determination of faunal and algal boundaries in these kelp beds (composed mainly ofEcklonia maxima andLaminaria pallida), as well as their biomass, in order to build a descriptive model of the food web. The main components of a site representative of the variable kelp beds on the west coast of the Cape Peninsula (Oudekraal) have been identified and quantified in terms of ash-free dry weight and Joules. The study covered an area from the rocky intertidal zone to the rock/sand interface found at a depth of 20 m. The site was divided into different areas (offshore, intermediate, inshore), and these were subdivided into depth zones of 4 m to show up any differences with depth. Different sampling techniques using SCUBA were combined to cover a wide range of organisms in the survey. Horizontal and vertical surfaces were differentiated. Kelp holdfasts were removed as a sampling unit for the infauna study. The distribution data of the organisms, other than kelp, were studied by means of multivariate methods which confirmed the division into inshore, mediate and offshore associations. Differences in faunal and floral composition could be detected between horizontal and vertical surfaces. Kelp biomass data showed high average standing crop in the inshore and mediate locality compared to the low offshore values. Maximum standing crop values, however, were not reduced. Mechanisms regulating the kelp bed structure are discussed. In the inshore and intermediate areas, algal biomass is much higher than animal biomass. A fact emerging from the data is that there is relatively little biomass of grazers; the major primary consumers are filter feeders. Problems of turnover rates are mentioned and an energy flow diagram for the area is proposed and its validity discussed.

Notes: Abstract Four of the most abundant gorgonian species from the southwestern Cape waters, Eunicella papillosa (Esper, 1797), E. alba (Esper, 1797), E. tricoronata Velimirov, 1971 and Lophogorgia flamea (Ellis and Solander, 1786) were analysed for Ca and Mg by atomic absorption spectroscopy (AAS) and ethylenediaminetetraacetate (EDTA) titration. The total mineral content in the peripheral tissues, excluding the axial skeleton, expressed as the sum of CaCO3 and MgCO3 of dry matter was between 65.5 and 83.5%. The mineral content varied in different growth regions and all specimens showed a higher degree of mineralization at the base than at the branch tips. The MgCO3 concentration varied with genus and species and was between 9 and 11 mol %. The variation of the MgCO3 concentration within different growth regions of the same species was small and generally did not exceed 0.8 mol %. From the branch to the stem, CaCO3 and total mineral content was found to increase. The CaCO3:MgCO3 rations in different growth regions of all species indicated that the composition of the mesoskeleton with regard to the relative concentration of CaCO3 and MgCO3 is constant throughout the animal. Mineralogically, the mesoskeleton consists of high magnesian calcite as identified by X-ray diffraction. MgCO3 concentrations determined by the peak shift method and by AAS were in fair agreement. The MgCO3 data in gorgonian samples from the cold Atlantic Ocean and the warmer Indian Ocean show a linear relationship between water temperature and MgCO3 concentration already demonstrated by Chave (1954). However, our data were consistently lower by 1 to 2% than expected.

Notes: Abstract This paper presents the results of a preliminary study on the uptake of 45Ca in the mesoskeleton of the gorgonian Eunicella papillosa (Octocorallia). Hourly seawater aliquots over 12 h periods displayed considerable fluctuations of activity with time, reflecting a disappearance and reappearance of tracer during the experiment. Analysis of total coenenchyme mass showed an initial rapid but fluctuating uptake of tracer and a progressive decrease with time. Distinct differences in the calcification rate of specific growth regions of the coral were detected, the rate being higher in branch tips than in lower branch regions. Chase experiments on colonies previously incubated for 24 h revealed that up to 45% of the tracer taken up during labelling were returned to the seawater. A comparison of the tracer content of the coenenchyme and the calcite spicules revealed that up to 70% of the calcium taken up remained in the coral tissue. Quantification of isotopic exchange phenomena with dead corals and isolated spicules emphasized the importance of the live coral tissue as a barrier and regulator of Ca uptake. The results are discussed in the light of the limitations of radioisotope techniques for the determination of calcification rates, and an attempt to compare rates with data in the literature is made.