Intertidal Food Webs in Rocky Shores: Topology and Energetics

Abstract

The study of food webs is a very important topic in order to understand the dynamics and stability of communities. We studied the food webs structure and energy balance of some tide pools from a rocky shore of Mar del Plata (Argentina). Food webs were drawn, and connectivity, proportion of different trophic species, and the link-richness regression slope were determined. Photosynthesis and respiration rates of several species were also measured. All the topological measures were calculated with and without sediments/detritus as potential energy sources. The proportion of basal species and the connectivity were greater when detritus were included; proportion of intermediate species lowed significantly with detritus inclusion. There were no differences between seasons, but sampling sites did show differences. Proportion of top species and connectivity did not show differences in any case. Some discrepancies were found with respect to the theoretical expected values of the food web properties: the proportion of basal species was significantly higher and the intermediate species proportion significantly smaller than the theoretical ones. Slope of the L-S regression was near 2 and the fit was improved when detritus was included. Mesograzers showed higher respiratory rates in spring and green algae higher photosynthetic rates in autumn. Considering the entire intertidal zone, anemone and mussels were the most important oxygen consumers. The intertidal zone works as a source of production with P/R ratio greater than one.