Allelopathic effects on the sun-coral invasion: facilitation, inhibition and patterns of local biodiversity

Abstract

In spite of growing concerns about the invasion of the sun-coral Tubastraea coccinea along the tropical Southwestern Atlantic, the biological interactions mediating this species’ establishment and spread are largely unknown. Here, we identified species associations with T. coccinea by comparing community structure between invaded and non-invaded areas at Buzios Island, SP, Brazil. We also investigated effects of chemical cues from representative benthic species on sun-coral larval performance in the laboratory and quantified the density of sun-coral recruits across different microhabitats in the field. Field surveys showed that the invasion of the sun-coral is more intense at reef areas of higher species richness and diversity, putting at risk a higher number of native species than anticipated and suggesting that local richness offers little resistance to invasion. Highest density of T. coccinea recruits observed on the least bioactive encrusting corallines suggests this taxonomic group may constitute doorways to the establishment of this coral. In contrast, field patterns of sun-coral colonies and recruits, as well as laboratory trials, suggest that cnidarian-dominated habitats represent obstacles to the sun-coral invasion. Thus, while areas dominated by the snowflake coral Carijoa riisei—which showed the greatest negative allelopathic effect on T. coccinea—likely provide resistance to the invader spreading, areas covered by encrusting coralline algae and ‘barren substrates’ probably facilitate its establishment. Because these latter, less-structured microhabitats often prevail after disturbance, damage assessment following human-mediated impacts should include detection and control of sun-coral populations.