Abstract
Coral reef resilience is greatly influenced by herbivory. There is a need to identify key fish species fulfilling this critical function in biogeographically distinct regions. This experimental in situ study investigated fish herbivory in coral reefs of the lower Gulf of Thailand characterized by a considerably low herbivorous fish biomass and diversity, but high live coral and low macroalgal cover. This provided an intriguing situation for macroalgal browsing research. Visual census techniques assessed the abundance of local herbivorous fish species, and filmed single-choice assays using the macroalga Turbinaria evaluated mass-standardized bites (ms-bites) and biomass removal. Multiple-choice assays offering four locally abundant macroalgae identified specific biomass removal and ms-bites to uncover selection and avoidance patterns of observed fish species. The rabbitfish Siganusvirgatus constituted only 39% of herbivore biomass but accounted for 90% of ms-bites. In multiple-choice assays, fishes took most (61%) bites on Sargassum, followed by Padina (28%) and Turbinaria (11%), while Lobophora was avoided. S. virgatus exhibited the most generalized browsing pattern of all species observed. Coinciding with recent studies, our findings suggest that S. virgatus plays a key functional role in reefs characterized by low diversity of herbivores and low functional redundancy.
Highlights
Published: 13 March 2021Coral reefs constitute the taxonomically most diverse ecosystems on earth [1]
The removal of morphologically and chemically defended mature macroalgae is limited to the functional group of macroalgal browsers [1,7]
Chronic drivers such as overfishing and nutrient pollution can lead to transitional states, with turf-dominated reefs eventually developing into reefs dominated by macroalgae [8,9], but recent literature suggests that turf can constitute a stable regime in itself [10,11,12]
Summary
Published: 13 March 2021Coral reefs constitute the taxonomically most diverse ecosystems on earth [1]. It is well established that herbivorous fishes play a key role ensuring the continued functioning of reef systems, in the face of negative impacts, due to their ability to remove algae, one of the main competitors of corals [2,4,5,6]. The removal of morphologically and chemically defended mature macroalgae is limited to the functional group of macroalgal browsers [1,7]. Chronic drivers such as overfishing and nutrient pollution can lead to transitional states, with turf-dominated reefs eventually developing into reefs dominated by macroalgae [8,9], but recent literature suggests that turf can constitute a stable regime in itself [10,11,12]. Macroalgae can outgrow feeding pressure when grazing is low, thereby reducing coral settlement, recruitment [13,14]
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