Abstract
Habitat degradation can affect trophic ecology by differentially affecting specialist and generalist species, and the number and type of interspecific relationships. However, the effects of habitat degradation on the trophic ecology of coral reefs have received limited attention. We compared the trophic structure and food chain length between two shallow Caribbean coral reefs similar in size and close to each other: one dominated by live coral and the other by macroalgae (i.e., degraded). We subjected samples of basal carbon sources (particulate organic matter and algae) and the same 48 species of consumers (invertebrates and fishes) from both reefs to stable isotope analyses, and determined the trophic position of consumers and relative importance of various carbon sources for herbivores, omnivores, and carnivores. We found that both reefs had similar food chain length and trophic structure, but different trophic pathways. On the coral-dominated reef, turf algae and epiphytes were the most important carbon source for all consumer categories, whereas on the degraded reef, particulate organic matter was a major carbon source for carnivores. Our results suggest that the trophic structure of the communities associated with these reefs is robust enough to adjust to conditions of degradation.
Highlights
One of most evident effects of habitat loss and degradation in terrestrial and aquatic ecosystems is a decline in the diversity of ecological communities via changes on species abundance and richness[1,2]
Whereas the overall range of δ15N values was very similar on both reefs, the range in δ13C values was wider on Bonanza than on Limones (Fig. 3, Supplementary Table S1)
In only eight of the 48 consumer species the trophic positions (TP) varied significantly with reef. Five of these species had a higher TP on Bonanza, whereas three had a higher TP on Limones
Summary
One of most evident effects of habitat loss and degradation in terrestrial and aquatic ecosystems is a decline in the diversity of ecological communities via changes on species abundance and richness[1,2]. Coral reef degradation is already affecting community structure by changing diversity and abundance of species[16,17] as well as ecosystem functioning and services[18,19]. As occurs with terrestrial species, coral reef specialists are expected to be more affected than generalists by reef degradation[21,22,23], further altering the food webs[16]. Food-chain length is an important descriptor of community structure and ecosystem functioning[24,25]. At the global scale, food chain length showed weak or no relationships with ecosystem size[28], probably because environmental variables interact in complex ways to structure a community and may affect metrics of food web structure other than food chain length[29]
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