Biological and environmental interactions drive disparate patterns of succession for biofilm bacteria and reef invertebrates
The persistence of coral reef ecosystems relies on the successful settlement and recruitment of stony corals and other benthic invertebrate species. This process is known to be moderated by complex environmental and biological factors, including cues from biofilm-associated bacteria, which determine where larvae choose to settle and influence post-settlement survival. Consequently, this process plays a key role in shaping the structure of benthic reef communities and becomes more important as reefs re-populate following increasingly frequent disturbances. The connections between the environment, biofilms, and communities of benthic eukaryotes are highly interactive but are rarely studied outside of controlled experimental systems, which do not reflect the natural complexity of reef ecosystems. To better understand the processes shaping settlement and succession of biofilms and benthic eukaryotes in situ, including stony corals specifically, bacterial and eukaryotic community diversity and composition were tracked on settlement tiles placed on the reef for seven months. Both seasonality and succession impacted the communities, but microenvironmental conditions associated with the top and bottom tile surfaces were most important for driving community composition, with minimal influence of larger scale site-level environmental characteristics. The development of the biofilm and eukaryotic communities followed distinct successional trajectories, suggesting that different biological processes are involved in structuring communities from different domains. These results help us to better understand the biotic and abiotic factors shaping the development of benthic biofilm and eukaryotic communities and the connections between them, while providing insight into reef resilience and recovery in the face of ongoing environmental disturbances.