Abstract
Herbivory is an important process in the general structuring of coral reef benthic communities. However, evidence of its ability to control coral reef benthic cyanobacterial mats, which have recently proliferated on reefs worldwide, remains ambivalent. Here, we report that the French Angelfish (Pomacanthus paru), Striped Parrotfish (Scarus iseri), Rock Beauty (Holacanthus tricolor), Ocean Surgeonfish (Acanthurus bahianus), Blue Parrotfish (Scarus coeruleus), and Atlantic Blue Tang (Acanthurus coeruleus) consume benthic cyanobacterial mats on coral reefs in Bonaire, Netherlands. We documented the foraging patterns of P. paru and S. iseri, and found that benthic cyanobacterial mats comprised 36.7% ± 5.8% and 15.0% ± 1.53% (mean ± standard error) of the total bites taken by P. paru and S. iseri respectively. This magnitude of consumption suggests that grazing by reef fishes may represent a potentially important, but previously undocumented, top-down control on benthic cyanobacterial mats on Caribbean reefs.
Highlights
Biodiversity of Caribbean coral reefs has decreased substantially following coral losses over the past half century, threatening overall reef function[1,2,3,4,5]
Decadal-scale surveys reveal that benthic cyanobacterial mat cover increased from 0.1% to 22.2% of the substrata on Caribbean coral reefs from 1973–2013, while coral, crustose coralline algal, and even macroalgal cover have decreased[10]
P. paru primarily targeted both benthic cyanobacterial mats and epilithic algal matrix (EAM; defined in methods), with sponges, gorgonians, fleshy macroalgae, and sediment all representing minor components of the total bites taken across all substrata (Fig. 2a)
Summary
Biodiversity of Caribbean coral reefs has decreased substantially following coral losses over the past half century, threatening overall reef function[1,2,3,4,5]. The high levels of nitrogen fixation associated with benthic cyanobacterial mats[11] and their net release of dissolved organic carbon[23] could amplify macroalgal cover on coral reefs, promote pathogenic bacterial expansion, and generate feedbacks that maintain reefs in degraded states[24]. One species of large-bodied reef fish in the Pacific, Bolbometopon muricatum (Green Humphead Parrotfish), has been previously observed grazing on mat-forming cyanobacteria[29]; no large-bodied herbivores have been documented to consume cyanobacterial mats on Caribbean coral reefs. We observed the following 6 different reef fishes grazing on benthic cyanobacterial mats on the fringing coral reefs off the island of Bonaire, Netherlands: French Angelfish (Pomacanthus paru), Striped Parrotfish (Scarus iseri), Rock Beauty (Holacanthus tricolor), Ocean Surgeonfish (Acanthurus bahianus), Blue Parrotfish (Scarus coeruleus), and Atlantic Blue Tang (Acanthurus coeruleus; Fig. 1). We focused on two of these, P. paru and S. iseri,
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