Elevated feeding rates of fishes within octocoral canopies on Caribbean reefs
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Elevated feeding rates of fishes within octocoral canopies on Caribbean reefs G. Tsounis1
•
M. A. Steele1 • P. J. Edmunds1
Received: 7 September 2019 / Accepted: 26 May 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Increasing abundance of arborescent octocorals (often referred to as gorgonians) on Caribbean reefs raises the question of whether habitat structure provided by octocorals can mediate a transition between coral- and algal- dominated states by increasing fish abundance and herbivory. This study tested the hypotheses that feeding rates and densities of demersal reef fishes are affected by the habitat structure provided by dense octocoral communities. Surveys of fishes on coral reefs in St John, US Virgin Islands, found 1.7-fold higher densities, and 2.4-fold higher feeding rates within versus outside of dense octocoral canopies. This difference, however, was only seen at sites with octocoral densities [ 8 colonies m-2. Furthemore, the proximity of octocoral colonies to fish had an effect on the grazing rate of key herbivores (surgeonfishes and parrotfishes), with a 53% higher feeding rate (1.90 ± 0.11 bites min-1 m-2) near octocorals (\ 20 or 30 cm, depending on the site) versus farther from them (1.24 ± 0.09 bites min-1 m-2). Finally, within the canopy of dense octocoral communities (17 colonies m-2), reef fishes fed at a rate that was 2.2-fold higher within the community than at the edge of the community that faced an adjacent sand patch. Fish abundance, however, was not uniformly higher within versus at the edge of the octocoral
Topic Editor Andrew Hoey
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00338-020-01963-1) contains supplementary material, which is available to authorized users. & G. Tsounis [email protected] 1
Department of Biology, California State University, 18111 Nordhoff Street, Northridge, CA 91330-8303, USA
community, as ecotone specialists such as gobiids, blennioids, ostraciids, holocentrids, labrids, and pomacentrids were 1.3—2.3 times more abundant at the edge. In contrast, other taxa of demersal fishes, notably herbivores, were twice as abundant within octocoral communities than at the edges. Together, these results reveal an association between habitat structure created by octocorals on shallow reefs and increased feeding rates of demersal fishes (including those of herbivores). The potential of octocorals to increase herbivory that could mediate stony coral recovery is therefore worthy of further study. Keywords Grazing impacts Restoration Ecosystem engineers Ecosystem services Canopy effect Gorgonian Fish nursery Caribbean Habitat-structure
Introduction Arborescent benthic organisms (sensu Jackson 1979) such as corals are among the most effective of ecosystem engineers (sensu Jones et al. 1994) due to the large size and great quantity of the physical habitat structure they potentially can provide. Habitat structure affects the behavior of fishes on coral reefs
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