The microbial community of coral reefs: biofilm composition on artificial substrates under different environmental conditions

Artificial reefs are used as tools for the restoration of degrading coral reefs by providing new settlement substrates. The initial recruitment process consists of the formation of microbial biofilms shortly after deployment. The aim of the present study is to compare biofilm composition and development on artificial substrates at two different coral-reef sites. These locations differ in their environmental conditions, including their level of anthropogenic impact. Substrate and seawater samples were collected four times during the first 6 months after deployment, using a new methodology termed ‘tab-by-tab’. DNA was extracted, sequenced, and sorted for both prokaryotic (16s) and eukaryotic (18s) genes. No difference was found between the planktonic communities in the water, yet significant differences were observed in the biofilm communities on the structures at the two sites. Moreover, differences were recorded in coral recruitment rates, which are known to be affected by biofilm composition. Our findings suggest a potential role of environmental conditions in the early biofilm stages (first few months), which in turn may impact the succession and development of coral-reef communities and the success of artificial reefs as restoration tools.