A recent study found that corals influence the microbial community surrounding them by both consuming them and facilitating microbial growth. See popular news articles here and here and a brief summary below.
The researchers used a lab experiment to test how the presence and absence of corals affected microbial communities present in seawater. When corals were placed in tanks, the researchers found a decrease in the microbial community (a result of grazing), especially in bacteria such as Rhodobacteraceae, Synechococcus, and SAR11. Once corals were removed from these tanks, the researchers found that microbial growth rates of Rhodobacteraceae, Synechococcus, and SAR11 were very rapid. This suggests that the microbes were able to grow well on something excreted or left by the corals in the tank. The researchers also found that nitrogen (N) remineralization occurred when corals were placed back into experimental tanks from which they were removed. This suggests the potential role of coral in N remineralization on coral reefs – a role sponges commonly take part in.
Sean P. McNally, Rachel J. Parsons, Alyson E. Santoro, Amy Apprill. Multifaceted impacts of the stony coralPorites astreoideson picoplankton abundance and community composition. Limnology and Oceanography, 2016; DOI: 10.1002/lno.10389