Antagonistic effects of seawalls and urban sedimentation on epilithic algal matrix (EAM)-feeding fishes

Abstract

Marine urbanisation often results in the proliferation of artificial coastal defences and heavy sedimentation, adversely impacting coral reef systems in tropical coastal cities. Knowledge of how motile organisms, such as reef fish, respond to novel human-made habitats and high sedimentation is limited. Here, we examine the role of sloping granite seawalls in supporting reef fishes that utilise the epilithic algal matrix (EAM) as a food resource. We surveyed fish assemblages and feeding activities on seawalls and reef flats, and conducted a field experiment to examine the effects of sediment on EAM feeding rates. Seawalls and reef flats supported distinct fish assemblage composition with significantly greater feeding activity on seawalls. However, reduced feeding activity on EAM with elevated sediment loads suggests that urban sedimentation may limit the utility of this novel feeding ground for nearshore communities. These findings illustrate the complexities and interactive effects of anthropogenic changes driven by coastal urbanisation.