Epibionts on Turbinaria ornata, a secondary foundational macroalga on coral reefs, provide diverse trophic support to fishes

A persistent green macroalgal mat shifts ecological functioning and composition of associated species on an Eastern Tropical Pacific coral reef

Global evidence of phase shifts to alternate community types is of particular concern because these new communities can provide fundamentally different and often novel ecosystem functions and services compared to the original community. Shifts of a diverse range of marine communities to dominance by green macroalgal mats have occurred worldwide, making it critical to understand their emerging functions and roles. We observed a green algal mat on two reefs in the Eastern Tropical Pacific, with one persisting for >10 years on a reef with stable herbivore populations and no known sources of anthropogenic nutrients. These mats supported a more speciose macroalgal community with fewer taxa present in the adjacent coral community and facilitated growth of an associated understory macroalgal species by reducing herbivory pressure and possibly enhancing nutrient supplies within the mat community state. These results demonstrate a weakening in the processes controlling reef community structure as a result of the shift in composition associated with the macroalgal mat, creating a positive feedback supporting mat persistence. These novel ecosystem functions generated by this alternate community state illustrate the importance of further research on community shifts, which will become increasingly common in the Anthropocene.

TESTING THE CONCEPTUAL AND OPERATIONAL UNDERPINNINGS OF HERBIVORY ASSAYS: DOES VARIATION IN PREDICTABILITY OF RESOURCES, ASSAY DESIGN, AND DEPLOYMENT METHOD AFFECT OUTCOMES?

Herbivory assays are a valuable tool used by ecologists to understand many of the patterns and processes affecting herbivory, a widely recognized driving force in marine communities. However, methods vary substantially among studies in both design and operation, and the effect of these differences has yet to be evaluated. We assessed the effects of several key components of assay design on estimates of herbivory to offer four recommendations. First, we found assays out-planted on sequential days in both predictable and random locations within a 60m² site experienced temporal increases in herbivory by an increasingly diverse assemblage of fishes. Thus, we strongly advise against placing herbivory assays in the same site over a series of days. Second, we found while the amount of biomass consumed in assays was density dependent, the percent loss was not. Thus, we recommend researchers report percent consumption because this metric is robust to differences in biomass offered and will facilitate comparisons across studies. Third, we found associational effects, where proximity of species of differing palatabilities impacted estimates of herbivory rate on one or both species, but these impacts were not consistent across species or sites. Thus, we recommend the effect of association be directly tested for multi specie herbivory assays. Fourth, we found no effect of attachment method on estimates of herbivory rate and recommend researchers continue to use the attachment method in which they are most confident. We hope our experimental results prove useful in the future when designing, conducting, and interpreting herbivory assays.