Drifting oyster larvae often survive by fastening their shells to those of preceding generations, making shell aggregates. Many other permanently sedentary organisms also attach themselves to oyster shells; thus arise oyster shell communities, in which we may find bacteria, diatoms, red, green and brown algae, protozoans, sponges, hydroids, actinians, bryozoa, pelecypods and ascidians as fixed permanent dwellers.
Andrews, E. A.. 1944. "Folliculinids on oyster shells." Journal of Marine Research 5, (3). https://elischolar.library.yale.edu/journal_of_marine_research/614