Decoupling linked coral and fish trait structure

Abstract

In coral reef systems, increasingly frequent, severe climate change-driven disturbances are responsible for declines in vulnerable species, and a reorganisation of assemblages. Whilst these changes will certainly elicit shifts in ecosystem functioning, how trait distributions and cross-taxon interactions are altered remains largely unmeasured, hampering our ability to predict functional shifts and target management actions to support reef health and recovery. We quantify trait distributions and interactions between habitat-engineering corals affected by a coral-bleaching mortality and associated fished reef fish assemblages. First, we assess changes in the proportional contributions of different traits pre- vs. post-disturbance. We then quantify changes in the trait associations that underpin cross-taxon interactions, and test relationships between coral and fish traits. The effects of reef type and survey atoll on coral trait structure are most influential, and there is a subtle temporal shift over the survey period. The trait structure of the fish assemblage remains stable. This suggests a simplification of the coral assemblage as vulnerable species disappear. The stability of the fish trait assemblage could indicate a lagged response, limited reliance on coral habitat, influence of other drivers or relative resilience. However, when examining traits of both taxa together, we discover that associations between individual coral and fish traits break down over time. We find reduced co-structure between the assemblages’ trait distributions, altering the associations between taxa. Our study signals weakened associations of fishes with their habitat as coral assemblages degrade with climate change, potentially disrupting the ecosystem functions that support services of coral reefs.