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Contributed Talk

Session: : Communities: Disturbance And Recovery 4

COS 77-3 - Macroalgae exhibit diverse responses to human disturbances on coral reefs

Tuesday, August 8, 2023
10:30 AM – 10:45 AM PDT
Location: B113
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 1,205 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.

Our analyses test the hypothesis that macroalgae percent cover is correlated with local human disturbance when accounting for additional environmental factors that might have confounded the findings in previous studies. For all sites and within five biogeographic realms, we determined the suite of human disturbance and environmental variables that best explain the genus-level macroalgae communities via canonical correspondence analysis (CCA) and stepwise ordination. Next, we fit permutational analysis of variance (PERMANOVA) models to estimate the effects of each variable on macroalgal communities. We then used Similarity Percentage Analysis (SIMPER) to determine the taxa driving differences across biogeographic realms. Finally, we fit linear mixed effects models (LMMs) to identify the relationship between local human disturbance and the individual common macroalgae genera and their divisions (red, green, brown).

Assessing macroalgae at genus level revealed that no genera were positively correlated with all human disturbance metrics. Instead, we found relationships with the Division or Genera of algae and specific human disturbances more often than when pooling taxa into a single functional category, which is common to many analyses. The percent of macroalgae cover convention 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.