BORING BRACHIOPODS FROM BRAZIL

Brachiopods have a fossil record extending hundreds of millions of years, and have been important players in marine communities for much of the Phanerozoic. While small marine organisms, they provide a basis for studies on colonization and paleocommunities that can be applied at larger scales, and so benefit our understanding of more complex systems. This study evaluates 144 randomly selected brachial (dorsal) valves of the rhynchonelliform brachiopod Bouchardia rosea collected from a depth of 15.5 m at Ilha Grande, Rio de Janeiro state, Brazil. Previous work on pedicle (ventral) valves collected from the same species and location indicated a high frequency of repair scars associated with borings of the spionid Polydora, indicating biotic interactions with live hosts and supporting preferential orientation of the valve margin towards prevailing currents. Comparison of these results to data from the brachial valve allows testing for differences in encrustation and bioerosion frequency and abundance, and to evaluate the role of surface area in host colonization. Dimensional measurements of length, width, and height were collected on the brachial valves and were found to range from 8mm to 15mm in length, with encrustation data and surface area data gathered for each valve. By looking at these components, it is possible to determine if there are preferred locations or size classes for sclerobionts colonizing brachiopod shells. While most brachiopods are colonized post-mortem, there is some evidence that not all organisms colonize at this stage, but during the host’s life as well. Repair scars have been interpreted as evidence that spionid polychaetes may colonize living brachiopods and the brachiopods respond by secreting calcite. Because these borings may occur during the host’s life, they may influence the later colonization of the shell.