Pell, T.J., McClure, E.C., Emslie, M.J., and Hoey, A.S. (2024) Limited susceptibility of Lobophora to browsing fishes on inshore reefs of the Great Barrier Reef. Coral Reefs, 43. pp. 5-17.

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Abstract

Increases in the frequency, intensity and/or diversity of disturbances affecting coral reefs are leading to concerns; some reefs will be overgrown by macroalgae. While numerous studies, particularly in the Pacific, have used macroalgal assays to quantify the rates and agents of herbivory of Sargassum, little is known of the capacity of reef fishes to reduce biomass of Lobophora, a common alga in macroalgal-dominated areas. The aim of this study was to determine the relative palatability of Lobophora to local herbivorous assemblages across two inshore reefs (Havannah Island and Orpheus Island) in the central Great Barrier Reef (GBR), Australia. Multiple choice macroalgal assays were deployed on the reef crest on each reef to determine the relative palatability of three macroalgae taxa: Lobophora, Sargassum and Padina. Additional Lobophora-only assays were deployed on the reef crest at Orpheus Island. Overall, the average reduction in macroalgal biomass was greater at Orpheus Island (25.3 g/3 h, pooled across macroalgae taxa) compared to Havannah Island (5.0 g/3 h), with the reduction in Lobophora biomass (0.3–1.5 g/3 h) being significantly lower than Sargassum (4.7–19.1 g/3 h) at both reefs. The reduction in Lobophora biomass at Orpheus Island was consistently low, whether presented in multiple choice (1.5 g/3 h) or Lobophora-only assays (1.7 g/3 h). Video observations revealed that four species of herbivorous fish (Kyphosis vaigiensis, Naso unicornis, Siganus doliatus, and Siganus canaliculatus) were responsible for the majority of the bites recorded on algae. Despite differences in the relative importance of these four species between islands, all four species took more bites from the Sargassum than Lobophora. The limited susceptibility of adult Lobophora to local herbivorous fish assemblages over short (3 h) temporal scales may play a role in the persistence of Lobophora-dominated areas on inshore reefs of the GBR. Future investigations over longer temporal scales and under different contexts are required to fully assess the susceptibility of Lobophora to herbivores.

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