Diver presence increases egg predation on a nesting damselfish

Abstract

Scuba diving is a form of ecotourism that has demonstrably negative impacts on benthic sessile organisms through diver-induced mechanical damage, but we know relatively less about the direct and indirect impacts of divers on fishes and the communities they live in. Damselfishes (Pomacentridae) are an ideal model to study to understand the effects of human presence on fish behavior because they are common, often territorial and exclusively demersal egg spawners. We experimentally studied the short-term effect of diver presence on egg-guarding behavior of a damselfish, the sergeant major, Abudefduf saxatilis. We found that the mere presence of a scuba diver changed the short-term behavior of sergeant majors during their reproductive phase, which resulted in a 92% increase in the frequency of opportunistic predation on their eggs. Identifying the consequences of this human-driven trophic interaction will allow us to evaluate its ecological importance and, if important, guide management efforts to mitigate human impacts.