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MEPS prepress abstract   -  DOI:

The neglected role of omnivore fish in the overgrazing of Mediterranean rocky reefs

Orestis Papadakis*, Konstantinos Tsirintanis, Vasiliki Lioupa, Stelios Katsanevakis

*Corresponding author:

ABSTRACT: Whereas sea urchins are considered as the most important grazers in Mediterranean shallow sublittoral rocky reef ecosystems, fish can also have an important role in overgrazing and the reduction of habitat complexity. In this study, the trophic behavior of fish was recorded when providing access on experimental surfaces with increased macroalgal biomass and associated benthic fauna, created by herbivore exclusion cages. After a sufficient period for substantial algal growth, the cages were removed and the activity of fish on these surfaces was recorded for three hours, by an automated photographic camera system. Control surfaces with no restriction on grazers, were defined on similar substrates for comparison. To quantify the effects of fish feeding activity on macroalgal coverage, photographic samples were taken, immediately after the opening of the cages and after each 3-hr camera recording. The response of fish when the cages were removed was immediate and intense. Feeding activity by 13 different fish species was recorded in total, of which the most frequent were the omnivores Diplodus vulgaris, Coris julis, Thalassoma pavo and much less the herbivore Sarpa salpa. The coverage of erect algae substantially decreased in the experimental surfaces due to fish feeding activity. The algae were either directly consumed by the fish, or cut off when feeding on macroinvertebrates. It is concluded that in addition to grazing by herbivores, fish of higher trophic levels can also significantly affect macroalgal assemblages and restrict the recovery of erect algae in overgrazed reefs where prey is scarce.