Effects of invasive sun corals on habitat structural complexity mediate reef trophic pathways

Abstract

Biological invasions have modified habitat structure, forcing changes in ecosystem functions. Structural complexity modulates diversity and trophic pathways, but the roles of invasive species in mediating coral reef habitat attributes and trophic effects are poorly understood. We investigated the influence of invasive corals on reef structural complexity and their implications on reef fish trophic structure. To assess habitat complexity and trophic relationships, we used a digital probe to map reef rugosity and characterized benthic cover and fish abundances by video and visual estimates. We calculated a coral skeleton complexity index (for individual invasive and native colonies) by building high-resolution three-dimensional models with photogrammetry techniques. The study was conducted between February 2018 and March 2019 in Cascos Reef, located on the east coast of Brazil. We reveal that the complex morphology of the invasive coral Tubastraea spp. skeleton had a significant positive effect on reef rugosity, contributing to substrate complexity at a sub-metric scale. However, this likely did not promote reef fish diversity but altered the assemblage structure patterns, demonstrated by a negative relationship between coral colony complexity index and abundance of trophic groups such as roving herbivores and omnivores and a positive relationship with planktivores. Thus, our findings support that habitat attribute modification promoted by invasive corals can influence the benthos-fish dynamic, promoting some fish groups to the detriment of others, with pervasive implications for ecosystem functions. Global changes are increasing invasions worldwide, enhancing the need for effective policies for regulation and management to ensure human well-being and ecosystem services.