Bacterial shifts associated with coral-macroalgal competition in the Caribbean Sea

Abstract

Present-day coral reefs are impacted by frequent disturbance and increasing global stressors, which provide an environment that supports the growth of alternative dominants, such as macroalgae, sponges, and tunicates, rather than stony corals. Competitively damaging inter -actions arise between macroalgae and reef-building corals that can involve chemical, physical, and microbial mechanisms. Using 16S rRNA denaturing gradient gel electrophoresis (DGGE), amplicon sequencing, and multivariate analyses, we examined coral-and algae-associated bac -terial assemblages along interaction gradients between the common Caribbean stony corals Montastraea faveolata and Porites astreoides and the benthic macroalgae Halimeda opuntia and Dictyota menstrualis. Benthic surveys were conducted in 3 Caribbean locations, and interactions were sampled for bacterial analyses. Both macroalgae were capable of inducing shifts in coralassociated bacteria to an assemblage that more closely resembled macroalgal-associated bacteria. Overall, M. faveolata-associated bacteria were more significantly affected by macroalgal competitors than were P. astreoides-associated bacteria at all sites. Bacteria associated with M. faveolata corals changed during >83% of interactions, even when samples were taken 5 cm away from competing macroalgae. Detectable shifts in coral-associated bacteria at all sampling sites suggest that macroalgae play a large role in coral holobiont health. The degree to which coral species maintain stable microbial assemblages in the face of environmental fluctuations and competitive stress may indicate specific species and coral reefs that have the capacity to resist perturbations and those that may need additional protection in the future. © Inter-Research 2013.