Effects of turf algae on recruitment and juvenile survival of gorgonian corals

Abstract

During the last 2 decades, the widespread temperate gorgonian Eunicella singularis has been among the species most affected by climate-induced mortalities. Recruitment and juvenile survival play crucial roles in the recovery process of this species, but turf algae may affect these early life history processes. We investigated the effects of turf algae on recruitment and juvenile survival of E. singularis using in situ turf-removal and turf-exposure experiments. The experiments were performed at a depth of 15 to 20 m off the island of Menorca (Balearic Islands, NW Mediterranean Sea) between April 2008 and July 2009. The turf-removal experiment indicated that exposure to turf algae caused up to a 5-fold reduction in the recruitment of the gorgonian species. The turf-exposure experiment revealed that transplanted juveniles exposed to turf algae overgrowth lost biomass and exhibited a threefold increase in juvenile mortality. These results demonstrate the negative effects that turf algae can exert on early stages of gorgonian species; in turn, this may affect their recovery capacity and population dynamics. Given that most Mediterranean invasive algae form a persistent turf, an increase in turf algae abundance may exacerbate these negative effects.