Responses of coral reef wrasse assemblages to disturbance and marine reserve protection on the Great Barrier Reef

Abstract

Coral reefs are periodically impacted by disturbance events that reduce live coral cover and habitat complexity, with concomitant effects on fish assemblage structure. While the density of some fish species may increase following coral loss, most species decline. Determining which species are ‘winners’ and ‘losers’ following disturbances is fundamental to inform projections of future reef community structure, biodiversity, and productivity. Here, we analyse a long-term (2006–2018), spatially extensive (≈ 700 km) ‘natural experiment’ in which the responses of 11 wrasse taxa to acute disturbance events and no-take marine reserve (NTMR) protection were quantified on fringing coral reefs in the Palm (18°34′ S, 146°29′ E), Whitsunday (20°08′ S, 148°56′ E), and Keppel Island (23°10′ S, 150°57′ E) groups, Great Barrier Reef, Australia. The responses of wrasse densities to benthic habitat change were taxa specific and temporally consistent. Disturbance-mediated reductions in live hard coral cover and/or habitat complexity resulted in density declines for Hemigymnus melapterus, Hemigymnus fasciatus, Cheilinus fasciatus, Labroides spp., Oxycheilinus digramma, and Thalassoma spp. Conversely, Halichoeres spp. densities correlated positively with increased relative cover of sand and rubble, while Stethojulis spp., Anampses spp., Epibulus insidiator, and Bodianus spp. displayed variable responses to habitat changes. No wrasses exhibited an NTMR effect and predator density, irrespective of NTMR status, only influenced five taxa across all island groups. The lack of NTMR effects and variable top-down predator effects suggest that taxa-specific benthic habitat associations were the predominant drivers of wrasse densities on inshore GBR reefs.