Possible control of acute outbreaks of a marine fungal pathogen by nominally herbivorous tropical reef fish

B P Neal,N N Price,T Warrender,T M Work,B Honisch,G J Williams

doi:10.1007/s00442-020-04697-7

B P Neal, N N Price + Show 4 more

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https://doi.org/10.1007/s00442-020-04697-7

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Abstract

Primary producers in terrestrial and marine systems can be affected by fungal pathogens threatening the provision of critical ecosystem services. Crustose coralline algae (CCA) are ecologically important members of tropical reef systems and are impacted by coralline fungal disease (CFD) which manifests as overgrowth of the CCA crust by fungal lesions causing partial to complete mortality of the CCA host. No natural controls for CFD have been identified, but nominally herbivorous fish could play a role by consuming pathogenic fungi. We documented preferential grazing on fungal lesions by adults of six common reef-dwelling species of herbivorous Acanthuridae and Labridae, (surgeonfish and parrotfish) which collectively demonstrated an ~ 80-fold higher grazing rate on fungal lesions relative to their proportionate benthic coverage, and a preference for lesions over other palatable substrata (e.g. live scleractinian coral, CCA, or algae). Furthermore, we recorded a ~ 600% increase in live CFD lesion size over an approximately 2-week period when grazing by herbivorous fish was experimentally excluded suggesting that herbivorous reef fish could control CFD progression by directly reducing biomass of the fungal pathogen. Removal rates may be sufficient to allow CCA to recover from infection and explain historically observed natural waning behaviour after an outbreak. Thus, in addition to their well-known role as determinants of macroalgal overgrowth of reefs, herbivorous fish could thus also be important in control of diseases affecting crustose coralline algae that stabilize the foundation of coral reef substrata.

Highlights

Primary producers form the foundations of terrestrial and aquatic ecosystems and serve as habitat and food for a plethora of organisms, but disease can threaten the provision of Communicated by Deron E
While fungi are known to comprise a large fraction of plant pathogens in terrestrial ecosystems (Agrios 2005), less is known about the prevalence, interactions, and the dynamics of fungal infections of primary producers in marine environments (Amend et al 2012; Worden et al 2015; Scholz et al 2016)
For herbivorous fish feeding observations, we focused on three species of Acanthuridae (Acanthurus nigricans, Ctenochaetus cyanocheilus, and Ctenochaetus marginatus) and three scarine labrids (Scarus frenatus, Scarus oviceps, and Chlorurus spilurus)

Summary

Introduction

Primary producers form the foundations of terrestrial and aquatic ecosystems and serve as habitat and food for a plethora of organisms, but disease can threaten the provision of Communicated by Deron E. Loss of plant hosts due to fungal infections can have important ecological and economic ramifications in terrestrial systems (Oerke 2006). While fungi are known to comprise a large fraction of plant pathogens in terrestrial ecosystems (Agrios 2005), less is known about the prevalence, interactions, and the dynamics of fungal infections of primary producers in marine environments (Amend et al 2012; Worden et al 2015; Scholz et al 2016). One important group of marine primary producers affected by disease, including by fungal pathogens, is the crustose coralline algae (CCA)

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