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The current status of marine alien species along the South African coast is reviewed and the ecological and economic impacts of these invasions are discussed. In all, 10 confirmed extant alien and 22 cryptogenic species are recorded from the region. All 10 alien species support well-established populations and the majority of these remain restricted in distribution to sheltered bays, estuaries and harbours. Only one species, the Mediterranean mussel Mytilus galloprovincialis, has spread extensively along the coast and caused significant ecological impacts. These include the competitive displacement of indigenous species and a dramatic increase in intertidal mussel biomass. These changes have also increased available habitat for many infaunal species and resulted in enhanced food supply for intertidal predators. Considerable economic benefits have also resulted from this invasion because M. galloprovincialis forms the basis of the South African mussel culture industry.

The structure of rocky intertidal communities may be influenced by large-scale patterns of productivity. In this study we examine the in situ rates of production by intertidal epilithic microalgae (chlorophyll a production per unit area per month), intertidal nutrient concentrations (nitrates, nitrites, phosphates and silicates), and standing stocks of different functional-form groups of macroalgae around the South African coast, and their relationships to consumer biomass. Clear gradients of in situ intertidal primary production and nutrient concentrations were recorded around the South African coast, values being highest on the west coast, intermediate on the south and lowest on the east coast. Primary production by intertidal epilithic microalgae was correlated with nutrient availability and could also be related to nearshore phytoplankton production. The dominance patterns of different functional forms of macroalgae changed around the coast, with foliose algae prevalent on the west coast and coralline algae on the east coast. However, overall macroalgal standing stocks did not reflect the productivity gradient, being equally high on the east and west coasts, and low in the south. Positive relationships existed between the average biomass of intertidal intertebrate consumers (grazers and filter-feeders) and intertidal productivity, although only the grazers were directly "connected" to in situ production by epilithic intertidal microalgae. The maximum body size of a widely distributed limpet, Patella granularis, was also positively correlated with level of in situ primary production. The maximal values of biomass attained by intertidal filter-feeders were not related to intertidal primary production, and were relatively constant around the coast. At a local scale, filter-feeder biomass is known to be strongly influenced by wave action. This implies that the local-scale water movements over-ride any effects that large-scale gradients of primary production may have on filter-feeders. The large-scale gradient in intertidal productivity around the coast is thus strongly linked with grazer biomass and individual body size, but any effect it has on filter-feeder biomass seems subsidiary to the local effects of wave action.

The origins (autochthonous or allochthonous) and pathways of organic matter in various marine communities were investigated in the vicinity of the sub-Antarctic Prince Edward Islands using stable-isotope analysis. Four major assemblages, comprising zooplankton, kelp-associated species, inter-island and nearshore benthos, were considered. Despite consumers exhibiting a predictable enrichment in δ 13 C and δ 15 N with trophic position, only the zooplankton community displayed distinct trophic levels. The benthic and the kelp-associated communities showed trophic continua. Both pelagic (zooplankton) and benthic inter-island communities ultimately derived their diets from phytoplankton (associated with surface-water POM). However, planktonic grazers fed primarily on allochthonous nano-and pico-plankton, while inter-island benthos seemed to rely mostly on microphytoplankton derived from autochthonous blooms. In contrast, kelp-associated animals derived a high proportion of their diet from kelp. The nearshore benthic community had an intermediate position between kelp-associated and inter-island communities. While POM was of primary importance, kelp-derived organic matter accounted on average for > 30% of the nearshore animals' diet. Findings of the present study indicate for the first time that autochthonous sources of organic matter (e.g. kelp-derived and microphytoplankton blooms), are important components of the diets of all but the zooplankton community at the sub-Antarctic Prince Edward Islands.

The universal temperature-dependence model (UTD) of the metabolic theory of ecology (MTE) proposes that temperature controls mass-scaled, whole-animal resting metabolic rate according to the first principles of physics (Boltzmann kinetics). Controversy surrounds the model's implication of a mechanistic basis for metabolism that excludes the effects of adaptive regulation, and it is unclear how this would apply to organisms that live in fringe environments and typically show considerable metabolic adaptation. We explored thermal scaling of metabolism in a rocky-shore eulittoral-fringe snail (Echinolittorina malaccana) that experiences constrained energy gain and fluctuating high temperatures (between 258C and approximately 508C) during prolonged emersion (weeks). In contrast to the prediction of the UTD model, metabolic rate was often negatively related to temperature over a benign range (30 -408C), the relationship depending on (i) the temperature range, (ii) the degree of metabolic depression (related to the quiescent period), and (iii) whether snails were isolated within their shells. Apparent activation energies (E) varied between 0.05 and 20.43 eV, deviating excessively from the UTD's predicted range of between 0.6 and 0.7 eV. The lowering of metabolism when heated should improve energy conservation in a high-temperature environment and challenges both the theory's generality and its mechanistic basis.