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    Rights statement: This is the peer reviewed version of the following article: Robinson, JPW, McDevitt‐Irwin, JM, Dajka, J‐C, et al. Habitat and fishing control grazing potential on coral reefs. Funct Ecol. 2019; 00: 1– 12. https://doi.org/10.1111/1365-2435.13457 which has been published in final form at https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.13457 This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.

    Accepted author manuscript, 759 KB, PDF document

    Embargo ends: 6/10/20

    Available under license: CC BY-NC: Creative Commons Attribution-NonCommercial 4.0 International License

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Habitat and fishing control grazing potential on coral reefs

Research output: Contribution to journalJournal article

E-pub ahead of print
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<mark>Journal publication date</mark>6/10/2019
<mark>Journal</mark>Functional Ecology
Publication statusE-pub ahead of print
Early online date6/10/19
Original languageEnglish

Abstract

Herbivory is a key process on coral reefs, which, through grazing of algae, can help sustain coral‐dominated states on frequently disturbed reefs and reverse macroalgal regime shifts on degraded ones.
Our understanding of herbivory on reefs is largely founded on feeding observations at small spatial scales, yet the biomass and structure of herbivore populations is more closely linked to processes which can be highly variable across large areas, such as benthic habitat turnover and fishing pressure. Though our understanding of spatiotemporal variation in grazer biomass is well developed, equivalent macroscale approaches to understanding bottom‐up and top‐down controls on herbivory are lacking.
Here, we integrate underwater survey data of fish abundances from four Indo‐Pacific island regions with herbivore feeding observations to estimate grazing rates for two herbivore functions, cropping (which controls turf algae) and scraping (which promotes coral settlement by clearing benthic substrate), for 72 coral reefs. By including a range of reef states, from coral to algal dominance and heavily fished to remote wilderness areas, we evaluate the influences of benthic habitat and fishing on the grazing rates of fish assemblages.
Cropping rates were primarily influenced by benthic condition, with cropping maximized on structurally complex reefs with high substratum availability and low macroalgal cover. Fishing was the primary driver of scraping function, with scraping rates depleted at most reefs relative to remote, unfished reefs, though scraping did increase with substratum availability and structural complexity.
Ultimately, benthic and fishing conditions influenced herbivore functioning through their effect on grazer biomass, which was tightly correlated to grazing rates. For a given level of biomass, we show that grazing rates are higher on reefs dominated by small‐bodied fishes, suggesting that grazing pressure is greatest when grazer size structure is truncated.
Stressors which cause coral declines and clear substrate for turf algae will likely stimulate increases in cropping rates, in both fished and protected areas. In contrast, scraping functions are already impaired at reefs inhabited by people, particularly where structural complexity has collapsed, indicating that restoration of these key processes will require scraper biomass to be rebuilt towards wilderness levels.

Bibliographic note

This is the peer reviewed version of the following article: Robinson, JPW, McDevitt‐Irwin, JM, Dajka, J‐C, et al. Habitat and fishing control grazing potential on coral reefs. Funct Ecol. 2019; 00: 1– 12. https://doi.org/10.1111/1365-2435.13457 which has been published in final form at https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.13457 This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.