Macroalgae exhibit diverse responses to human disturbances on coral reefs

Cannon, Sara E. and Donner, Simon D. and Liu, Angela and González Espinosa, Pedro C. and Baird, Andrew H. and Baum, Julia K. and Bauman, Andrew G. and Beger, Maria and Benkwitt, Cassandra E. and Birt, Matthew J. and Chancerelle, Yannick and Cinner, Joshua E. and Crane, Nicole L. and Denis, Vianney and Depczynski, Martial and Fadli, Nur and Fenner, Douglas and Fulton, Christopher J. and Golbuu, Yimnang and Graham, Nicholas A. J. and Guest, James and Harrison, Hugo B. and Hobbs, Jean‐Paul A. and Hoey, Andrew S. and Holmes, Thomas H. and Houk, Peter and Januchowski‐Hartley, Fraser A. and Jompa, Jamaluddin and Kuo, Chao‐Yang and Limmon, Gino Valentino and Lin, Yuting V. and McClanahan, Timothy R. and Muenzel, Dominic and Paddack, Michelle J. and Planes, Serge and Pratchett, Morgan S. and Radford, Ben and Reimer, James Davis and Richards, Zoe T. and Ross, Claire L. and Rulmal, John and Sommer, Brigitte and Williams, Gareth J. and Wilson, Shaun K. (2023) Macroalgae exhibit diverse responses to human disturbances on coral reefs. Global Change Biology, 29 (12). pp. 3318-3330. ISSN 1354-1013

Abstract

Scientists and managers rely on indicator taxa such as coral and macroalgal cover to evaluate the effects of human disturbance on coral reefs, often assuming a universally positive relationship between local human disturbance and macroalgae. Despite evidence that macroalgae respond to local stressors in diverse ways, there have been few efforts to evaluate relationships between specific macroalgae taxa and local human‐driven disturbance. Using genus‐level monitoring data from 1205 sites in the Indian and Pacific Oceans, we assess whether macroalgae percent cover correlates with local human disturbance while accounting for factors that could obscure or confound relationships. Assessing macroalgae at genus level revealed that no genera were positively correlated with all human disturbance metrics. Instead, we found relationships between the division or genera of algae and specific human disturbances that were not detectable when pooling taxa into a single functional category, which is common to many analyses. The convention to use percent cover of macroalgae as an indication of local human disturbance therefore likely obscures signatures of local anthropogenic threats to reefs. Our limited understanding of relationships between human disturbance, macroalgae taxa, and their responses to human disturbances impedes the ability to diagnose and respond appropriately to these threats.