SHELL SIZE AND SCLEROBIONT COLONIZATION: AREA EFFECTS ON ENCRUSTATION AND BORING FREQUENCY, ABUNDANCE, DIVERSITY AND RECRUITMENT IN HARD-SUBSTRATE COMMUNITIES

Sclerobionts (organisms colonizing the skeletal remains of others, such as boring and encrusting organisms) record paleocommunity relationships with extraordinary spatial and temporal resolution, and thus may provide a great deal of paleoenvironmental information. However, meaningful comparisons between different study areas, host species and environmental conditions require an understanding of the controls on frequency, abundance and diversity on the development of hard-substrate assemblages. In this study we measure and evaluate sclerobiont colonization of the rhynchonelliform brachiopod Bouchardia rosea collected from 15.5 m water depth at Ilha Grande, RJ, Brazil. Dimensional measurements (maximum length, width and height) were collected for 581 ventral (pedicle) valves ranging from 6 mm to 18 mm in length, and a surface area model was constructed for comparison using measurements from specimens of known size. While encrustation frequency only increases marginally, mean sclerobiont abundance per valve appears to increase linearly with surface area, and mean diversity per valve increases logarithmically as a function of either area or abundance. Sclerobiont diversity distributions for any given size class do not deviate significantly from Poisson distributions, as expected for randomly distributed, independent events. By contrast, abundance distributions for all larger valves show significant deviation from a Poisson model, reflecting the impact of larval recruitment. Most colonization occurs after the death of the host, but live-host colonization by Polydora skews endobiont and epibiont diversity distributions in a recognizable manner. The strong role of surface area on host colonization, in contrast to the lack of host-age effect on sclerobiont assemblages observed previously, reinforces the view that host colonization occurs rapidly and that sclerobiont assemblages preserve communities capable of ecological interaction. However, these results indicate that surface area measurements are critical for evaluating sclerobiont assemblages and comparing communities colonizing different species or in differing locations.