Trophic structure of rocky intertidal communities response to wave action and implications for energy flow

Abstract

The influence of physical factors on the trophic structure of rocky intertidal communities in the Cape of Good Hope was investigated by examining species composition and biomass on shores subject to different conditions of substratum, sea temperature and wave exposure. Biomass of herbivores on shores with an unstable substratum was particularly high while the sessile filter-feeders and algae were impoverished, but actual rock type did not affect trophic structure. Sea temperature influenced species composition but not trophic structure which was most strongly affected by the degree of wave exposure. Exposure influenced both vertical distribution of biomass and trophic composition of total biomass. Total biomass showed a simple decrease upshore on sheltered shores but the pattern was more complex with greater exposure. Filter-feeders, carnivores and omnivores all exhibited significantly higher biornass under exposed conditions. Consequently the balance between consumers and primary producers shifted, implying alterations in the net balance between importation and exportation of production between these communities and the inshore marine system. The addition of huge filter-feeder components to the intertidal system resulted in significantly higher total biomass under exposed conditions. This allows the importation of production from the water column to a community in which consumers exhibit considerably higher standing crops than primary producers. Benthic carnivores exhibited a positive correlation with filter-feeder biomass. It is therefore suggested that domination of exposed shores by sessile filter-feeders and of sheltered shores by algae and mobile herbivores may explain divergent views in the literature on the relative importance of competition and disturbance/predation to community structure on rocky shores.

Effect of wave exposure on growth and mortality rates of the mussel Perna perna: bottom-up regulation of intertidal populations

“…Bustamente et al (1995) showed that densities of limpet populations on the west coast depended on the rate of kelp input. In this study we found that growth rates of mussels are affected by wave action (presumably as this dictates rates of food supply), and it has previously been shown that predator biomass in South Africa is correlated with filter-feeder biomass (McQuaid & Branch 1985, see also Menge 1992. Both filter-feeder and total animal biomass are significantly higher on exposed than sheltered shores (McQuaid & Branch 1985), and this may indicate the importance of energy subsidies into the system through the medium of wave action.…”

“…In this study we found that growth rates of mussels are affected by wave action (presumably as this dictates rates of food supply), and it has previously been shown that predator biomass in South Africa is correlated with filter-feeder biomass (McQuaid & Branch 1985, see also Menge 1992. Both filter-feeder and total animal biomass are significantly higher on exposed than sheltered shores (McQuaid & Branch 1985), and this may indicate the importance of energy subsidies into the system through the medium of wave action. Higher growth rates on exposed shores also provide a mechanism which can explain the shift in dominance between filter-feeders on exposed shores and algae on sheltered shores recorded for the South African coast (McQuaid & Branch 1985).…”

Effects of wave exposure on the sublittoral distribution of blue mussels Mytilus edulis ina heterogeneous archipelago

“…Large waves also dislodge sessile organisms living on exposed rocky shores, leading to altered size distributions, redistribution of individuals or increased mortality (Alvarado & Castilla 1996, Hunt & Scheibling 2001. Wave exposure may affect the distribution and abundance of individual species, species interactions and entire rocky shore communities (McQuaid & Branch 1985, Menge & Branch 2001, Hammond & Griffiths 2004. Sessile ABSTRACT: Exposure to wave action is an important factor determining the distribution and abundance of marine species on rocky shores.…”

Interactive roles of mesograzers and current flow in survival of kelps

“…Menge (1978a,b) and Peterson (1979) found a negative relationship between wave exposure and the importance of consumers in structuring the intertidal in the northwestern Atlantic, but Robles (Robles & Robb 1993, Robles 1997 found the opposite when examining lobster predation in southern California. Negative correlations between wave exposure and consumer effect have been observed for tropical urchins (Foster 1987) and temperate urchins (Kawamata 1998), while no relationship was observed between exposure and herbivory in South African intertidal structure (McQuaid & Branch 1985).…”