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To resolve biogeographic limits and patterns on the east coast of Africa, the presence/absence and quantitative biomass data were collected from 55 shallow subtidal reefs along 4,800 km of coastline (5.2°-31.1°S). Multivariate analysis of distributions, trophic structure and biomass revealed two distinct marine provinces, the Tropical Indo-West Pacific and Subtropical Natal, with a transitional overlap (of ca. 120 km) located between Leven Point and Kosi Mouth on north-east South Africa. This region of overlap was one of three bioregions revealed by post hoc analyses. Biomass was unexpectedly highest in the tropics. 'Auto-heterotrophs' (species with autotrophic symbionts such as corals and clams), deposit feeders and grazers contributed significantly more biomass to the Tropical Indo-West Pacific Bioregion, whereas filter feeders dominated the Subtropical Natal Bioregion. 'Autoheterotrophs' declined with latitude while filter feeders increased; soft corals made a defining contribution in the overlap bioregion. Possible underlying causes of these patterns include productivity, nutrient levels, riverine input, light penetration and temperature., Introduction A principal concept of marine biogeography is that organisms are associated with specific aquatic regions that are separated by physical and biological barriers from other such regions (Golikov et [...]

On the basis of 16-yr satellite time series (1987 2003) of sea surface temperature (SST) and using univariate and multivariate statistical techniques, we quantified patterns of fluctuation in oceanographic conditions, as well as their spatial structure along the coasts of South Africa and Chile between 29.0 [degrees] and 34.5[degrees]S. Since variations in environmental conditions over multiple timescales are driven by oceanographic-atmospheric processes modulated by coastal morphology, all of which affect in different ways coastal organisms, we hypothesized that dynamic properties of the environment contribute to characteristic patterns on rocky intertidal biomass structure across upwelling ecosystems. Although long-term mean temperatures were similar between coasts, the relative importance of annual, semiannual, intraseasonal, and high-frequency SST fluctuations differed; South Africa is more strongly pulsed over shorter timescales. Similar spatial discontinuities in thermal regimes were observed, with changes at about 32[degrees]S. Multivariate summaries of benthic community structure derived from functional group biomasses revealed striking differences between South Africa and Chile, as well as between regions north and south of 3[degrees]S within each ecosystem. Between-continent and regional-scale differences in community structure were largely unrelated to mean SST, but correlated with the different measures of temporal variance in SST. For all functional groups, as well as aggregate measures of benthic community composition, the weekly to annual SST fluctuations explained large fractions (>35%) of biological variability. Results highlight the importance of quantifying the temporal variance of regimes of hydrographic conditions since multispecies assemblages are expected to respond in different ways to the driving oceanographic processes behind these fluctuations.

We evaluated the effects of marine iguanas, sally lightfoot crabs, and fish on rocky-shore sessile organisms at two sites at Santa Cruz Island, Galapagos Islands, Ecuador, for 3-5 years during and after the 1997-1998 El Nino, using exclusion cages to separate the effects. Plots exposed to natural grazing were dominated either by encrusting algae or by red algal turf and articulated corallines. Algae fluctuated in response to El Nino in the following way. During an early phase, crustose Gymnogongrus and/or red algal turf were dominant. In the heart of El Nino, grazers had limited effects on algal cover but influenced algal sizes substantially. Most algae (particularly edible forms) were scarce or declined, although warm-water ephemeral species (notably Giffordia mitchelliae) flourished, increasing diversity and overgrowing crusts. Iguana mortalities were high, and crab densities low. When normal conditions returned, warm-water ephemerals declined, crab densities rose, and grazers had significant but site-specific effects on algae. At one site, any combination of grazers diminished most erect species, reducing diversity and restoring dominance of competitively inferior grazer-resistant crusts. At a second site, only the combined effect of all grazers had this effect. Laboratory experiments confirmed that crabs could control erect algae and promote crustose forms, and crustose Gymnogongrus developed into an erect form in the absence of crabs. Differences between sites and large-scale temporal changes associated with El Nino indicate that tropical shores are not all as constant in time and space as previously suggested. Mobile grazers did affect algal communities, but over the period of our observations far greater effects were attributable to intersite differences and temporal shifts in oceanographic conditions. El Nino events reduce nutrients, intensify wave action, and raise sea levels, affecting food availability for intertidal herbivores and their influence on benthic algae. Thus, the dramatic transformations of communities during El Nino presage the impacts of global climate change. Key words: algae; bottom-up top-down effects; climate change; ENSO; Galdpagos Islands; grazing; rocky shores.

Much current research on community ecology concerns indirect effects, cascading trophic interactions, and the role of top-down vs. bottom-up processes, as well as subsidization of matter and energy between different systems. We addressed all these topics by exploring interactions between the urchin Parechinus angulosus and both recruits and juveniles of the abalone Haliotis midae, in the light of the fact that juvenile abalone shelter beneath the urchins. In field experiments at six sites, urchins were eliminated from removal plots to determine the degree to which juvenile abalone (individuals 3-35 mm in length) depend upon urchins. Comparisons were made with undisturbed and disturbance-control plots. We hypothesized that after removal of urchins: (1) there would be an immediate decline of juvenile abalone, since they are intimately associated with the urchins; (2) abalone recruits (recent settlers Key words: abalone; bottom-up effects; commensalism; Haliotis midae; indirect effects; kelp; Parechinus angulosus; subsidization; trophic interactions; urchins.

Declines in rock-lobster (Jasus lalandii) growth have prompted a re-assessment of their diet, for which we employed an immunological approach (enzyme-linked immunosorbent assay, ELISA). Antisera were raised against 26 prey species, and their specificity was determined using ELISA. Antibody-binding was compared using Western blots. The antisera showed high specificity to undigested prey with cross-reactions among antisera being reduced to < 4%. However, cross-reactivity increased to 49% when tested against digested prey, with some antisera even failing to recognise homologous prey. Sodium dodecylsulphate (SDS) gel electrophoresis demonstrated that excess rock-lobster digestive enzymes prevented the identification of digested prey by ELISA. However, 'inhibition ELISA' (modified ELISA) did demonstrate species-specific proteins in the digested extracts and could be used to identify digested prey accurately. Nevertheless, the problem of enzyme interference has to be solved before large-scale screening of rock-lobster diets by ELISA is feasible.

The study demonstrates that monochrome video photography technique generates reliable data, comparable to those from scuba dives, on the population of preys available to lobsters. The camera method is more economical.

Dense populations of patellid limpets characterize the mid- to low-intertidal communities of the southwestern rocky shores of South Africa. Patella argenvillei and P. granatina reach average densities up to 200/[m.sup.2], representing in some cases [approximate] 10-13 kg/[m.sup.2] of whole wet biomass, and attain sizes up to 100-mm shell length. Traditionally these limpets have been regarded as generalized grazers, but in fact they have highly specialized feeding mechanisms. P. granatina is found primarily on the mid- to low shore of sheltered boulder-bays, while P. argenvillei forms a conspicuous monospecific belt low on semiexposed shores in association with adjacent kelp beds. Both species are the dominant occupiers of space in their respective habitats. We have investigated the main pathways and supply of food necessary to maintain limpet biomasses as high as this. Epilithic micro- and macroalgae and the kelps Ecklonia maxima and Laminaria pallida are common sources of food for these two limpet species. Gut contents show that kelp represents [is greater than] 50% of the total diet of both species. An abundant source of food is provided to P. granatina by drifting kelp and seaweed debris, and to P. argenvillei by nearby attached kelp plants, which they actively prune. Differences in the timing and method of feeding exist. P. granatina captures drifting kelp and seaweeds while underwater during incoming and outgoing tides, and P. argenvillei prunes the fronds of nearby attached kelp plants during the rising tide. P. argenvillei feeds collectively, several individuals sharing a piece of kelp trapped by a single limpet. This overcomes the intraspecific competition normally experienced in high density limpet populations, and the maximum size of P. argenvillei rises with density. P. granatina does not feed collectively and its maximum size declines with density. An experimental exclusion of kelp from the limpets' diets resulted in significantly increased mortality and a reduction in body mass. Subtidal production of kelp fronds subsidizes populations of both limpet species and is vital to the maintenance of their remarkably high biomasses. Supplied with a superabundance of food, both species achieve such high 'packing' that primary space becomes their limiting factor. The trophic subsidy provided by kelps has important secondary consequences since the dense limpet populations powerfully influence intertidal community structure and function., Key words: biomass; drift;food web; intertidal; kelps; limpets; South Africa; subsidy; subtidal; trophic. INTRODUCTION Interactions between grazers and plants are of major importance in many marine benthic food webs (see [...]

The idea that plant polyphenols act as digestibility-reducing compounds is well entrenched. This hypothesis has recently been countered with the proposal that the presence of surfactants in the gu fluids of herbivores may preclude the digestibility-reducing effects of plant polyphenols. We examined three marine isopods, three limpets, and a rock lobster, and established that surfactant are present in the digestive fluids of all of these organisms. However, further determinations of the efficacy with which these surfactants can prevent the complexation of proteins by brown-algal polyphenols in vitro revealed substantial differences between species. Moreover, in cases where the surfactants were ineffective, polyphenols reduced in vitro digestibility in a dose-dependent manner. We therefore conclude that the presence of gut surfactants does not necessarily preclude protein precipitation by polyphenols in vivo. Thus polyphenols might still be regarded as digestability-reducing compounds, since gut surfactants only counter these effects in some cases. Key words: brown algae; chemical defenses; digestibility-reducing; gut surfactants; herbivory; polyphenols.

Abstract: Algal blooms commonly occur along the South African west coast. In March 1994 a dense bloom developed within St Helena Bay. Its subsequent decay caused near-shore hypoxia and elevated hydrogen sulphide levels, leading to it being termed a ‘black tide’. The bloom caused immediate massive intertidal mortalities (95% reduction of biomass), significant changes in community structure, and declines in richness and diversity. Only four taxa were not diminished: ephemeral algae, the gastropod Afrolittorina knysnaensis, the anemone Bunodactis reynaudi and the false limpet Siphonaria capensis. This limpet species subsequently increased at impacted sites relative to controls, probably reflecting reduced competition from other grazers. Ephemeral algae flourished during early recolonisation while grazers were depleted, but declined as grazers re-established. Manipulative experiments demonstrated that grazers do have this capability. Perennial algae also flourished, but lagged behind ephemerals, possibly contributing to their decline. Predators took longest to recover. Differences in the responses of species reflect differing tolerances, zonation patterns and biological interactions. Communities at control sites remained unchanged over the four-year study, and those exposed to a low intensity of the bloom were little affected, but communities exposed to its full intensity failed to recover fully within four years. Increasing frequency of harmful algal blooms along the west coast of South Africa could, therefore, significantly alter rocky-shore communities if intervals between bloom events become shorter than recovery times. [Copyright &y& Elsevier]