Webber, Kelsey, Fabricius, Katharina, Wilson, Shaun K., and Hoey, Andrew S. (2024) The influence of Sargassum biomass and thallus density on the recruitment of coral reef fishes. Coral Reefs, 43. pp. 687-699.

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Abstract

A habitat’s structural complexity is a key determinant of the recruitment and composition of associated communities. While the influence of the physical structure of corals on coral reef fish recruitment is well studied, the significance of other benthic components, like macroalgae, remains unclear. We used experimental patches of the canopy-forming macroalga Sargassum to assess the influence of macroalgal complexity, which was manipulated by altering thallus density and biomass, on coral reef fish recruitment. We established twenty-five 75 × 75 cm patches on the reef flat of Orpheus Island, (inshore, central Great Barrier Reef) during austral summer. Patches were randomly divided into five treatments of varying Sargassum thallus density (3–9 thalli) and/or biomass (177–779 g per patch) and surveyed daily for recruiting fishes for 18 d. We recorded 35 fish species recruiting to our patches, with Sargassum biomass having the greatest influence on fish recruits’ abundance and species richness. Comparisons between treatments with equal thallus density but varying biomass revealed a positive association between Sargassum biomass and fish species richness and abundance (up to ~ 2.5-fold differences). Additionally, treatments with similar total Sargassum biomass but different density revealed a negative relationship between density and fish species richness and abundance (20–30% reduction). These positive associations with Sargassum thallus biomass suggest that recruiting fishes favour the fine-scale complexity of intra-thallus spaces, rather than the larger, inter-thallus gaps. This study highlights that fine-scales of complexity within tropical macroalgal beds may influence the reef fish recruitment value of these often-underappreciated areas.

Item ID:	85850
Item Type:	Article (Research - C1)
ISSN:	1432-0975
Copyright Information:	© The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Funders:	Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies (CE)
Date Deposited:	17 Jun 2025 02:03
FoR Codes:	31 BIOLOGICAL SCIENCES > 3103 Ecology > 310305 Marine and estuarine ecology (incl. marine ichthyology) @ 100%
SEO Codes:	28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280111 Expanding knowledge in the environmental sciences @ 100%
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