An experimental evaluation of macroalgal consumption and selectivity by nominally herbivorous fishes on subtropical rocky reefs

Herbivory is of great importance to reef system dynamics and structures because of the role primary consumers play in shaping benthic communities at various scales. In this work, the consumption and the feeding selectivity of the fish assemblage towards a set of macroalgae was evaluated through remotely filmed multiple-choice feeding assays. Macroalgal species showed a variable susceptibility to consumption, with Spyridia hypnoides and Amphiroa sp. being the most consumed and Plocamium brasiliense and Codium intertextum the least consumed among the 11 options. Eighteen herbivorous and omnivorous fish species were recorded taking bites from the feeding trial and only six were responsible for about 90% of the total number of mass standardized bites. Nominally herbivorous species (mainly Sparisoma tuiupiranga and Acanthurus chirurgus), as well as omnivorous species like Stephanolepis hispidus and Diplodus argenteus, were important in terms of macroalgal consumption. These observed patterns are likely to be driven by different food processing modes employed by fishes and nutritional and defensive properties of algae. Moreover, these results evidence a great potential for macroalgae consumption on subtropical rocky reefs and suggest the existence of elements of both redundancy and complementarity on macroalgal selectivity by herbivorous and omnivorous fishes in these environments.