Preferential consumption of benthic cyanobacterial mats by Caribbean parrotfishes

Cyanobacteria are ubiquitous on coral reefs and perform important ecosystem functions. Benthic cyanobacterial mats (BCMs) have become increasingly abundant on degraded reefs. While epilithic and endolithic benthic cyanobacteria are the primary trophic resource for many parrotfishes, mat-forming benthic cyanobacteria are generally considered unpalatable to reef fishes. Regardless, recent studies have documented substantial grazing of BCMs by reef fishes, including parrotfishes. Here, we observed foraging in five Caribbean parrotfishes on the fringing coral reefs of Bonaire, Netherlands, to investigate BCM consumption relative to other benthic substrates. All species overwhelmingly targeted reef substrates composed of algal turfs and crustose coralline algae, which are typically associated with epilithic and endolithic microalgal and cyanobacterial communities. Additionally, three species preferentially consumed BCMs. As such, our work is consistent with and provides direct evidence supporting the recently proposed trophic role for parrotfishes as microphages. Contrasting observations of reef fishes avoiding substrates dominated by BCMs on other reefs suggests variation in the palatability of BCMs to grazing reef fishes, or species-specific differences in preference for these potentially nutritional trophic resources.