Invasive, non-indigenous corals in a tropical rocky shore environment: No evidence for generalist predation

Abstract

The biological invasion of rocky shore communities modifies species composition and the interaction between community elements. Two species, Tubastraea coccinea Lesson, 1829 and Tubastraea tagusensis Wells, 1982 have been identified as non-indigenous and invasive to the tropical rocky shores of southeast Brazil. The aim of the current study was to investigate predator–prey interactions between a guild of native potential generalist predators and the non-indigenous corals using total exclusion and partial cages versus controls on a tropical rocky shore in the southwest Atlantic. Despite generalist predators being present in natural densities on the experimental system and substantial settlement occurring during the 2year study (average density of Tubastraea spp. was 11.29 ind. 240cm−2) no significant differences were found in density or size of corals between treatments. Dominant groups in the accompanying biological community (ABC) were encrusting calcareous and turf algae, the sponge Iotrochota sp. and barnacles but ABC height and biomass and sediment mass did not differ between treatments. Due to transport and invasion of new communities these corals are thought to have escaped from predation despite a diverse suite of native potential generalist predators. Both corals have been shown to possess bioactive chemicals which predatory fish avoid and this would seem to be the mechanism of predator avoidance. The successful invasion by Tubastraea spp. in the southwest Atlantic is at least in part due to highly reduced (or nil) predation compared to the native range.