Structure and trophic organization of subtidal fish assemblages on the northern Chilean coast: the effect of habitat complexity

A series of local factors such as substrate structure, presence or absence of kelp forests and environmental variables play an important role in deter mining both the diversity and abundance of temperate reef fish assemblages. The presence of kelp forests has been shown to increase structural complex ity, available shelter, and prey availability in the reef environment. This , in turn, may affect the structural organization of the fish assemblage. I n this study, the diversity, abundance and trophic patterns of subtidal fis h assemblages at 2 localities off the northern Chilean coast were analyzed. These localities differ markedly in their spatial structure: the subtidal substratum at Caleta Errazuriz is characterized by a sloping bedrock with l arge rocks and boulders and a kelp forest, while at Carrizal Bajo it consis ts of a sharply declining bedrock with few boulders and isolated kelp stand s, We hypothesized that structurally highly complex habitats would exhibit higher diversity, abundance and a more complex trophic organization in term s of more functional groups and guilds of reef fish assemblages than less s tructured environments. Contrary to our hypothesis, we found similar specie s diversity and fish abundance at both localities. However, there were clea r differences in species dominance, number of functional groups and trophic guilds. There were also marked differences in the trophic webs between loc alities, In the presence of kelp forest, both carnivores and omnivores cons umed mainly benthic prey inhabiting the understory canopy, while in its abs ence carnivores fed on pelagic prey in the water column. Therefore, a more complex spatial structure would seem to support a more complex trophic orga nization with a greater degree of connectivity, as well as interaction betw een the species in a reef fish assemblage.