Complex food webs of tropical intertidal rocky shores (SE Brazil) – An isotopic perspective

Abstract

Knowledge on food web structure, trophic links and energy pathways is essential for the understanding of complex and highly biodiverse tropical ecosystems. Emerging issues related to global change and species invasions call for an urgent advance on this topic. Isotopic analyses were applied to the tropical intertidal rocky shores of Southeastern Brazil, with the aim of 1) describing the general food web structure, 2) estimating food web length, 3) estimating the trophic level of the secondary consumers, and 4) their dependence on different energy pathways. An exceptionally high number of food web nodes (71) was analysed. The maximum trophic level (TL) was 3.3, similarly to what has been previously reported for temperate rocky intertidal ecosystems. Fish were the dominant top consumers (TL > 2.0), along with an important number of gastropods and crustaceans (both crabs and shrimp). Primary consumers were mostly crabs, gastropods and bivalves. Two invasive crustaceans were found among the top consumers, the Japanese peppermint shrimp, Lysmata lipkei (TL = 3.0), and the Indo-Pacific swimming crab, Charybdis hellerii (TL = 2.3). Among the primary consumers, one invasive bivalve was found, Isognomon bicolor. Mixing models showed that the top consumers depend mostly on the macroalgal and pelagic energy pathways. The food web currently established has low dependence on the benthic pathway. Given the important increase in precipitation predicted for this region and the increment in detritus it incurs, this food web is likely to suffer important alterations in the future.