Cavity-Dwelling Sponges in a Southern Caribbean Coral Reef and Their Paleontological Implications

The cryptobiontic (cavity-dwelling) sponges from 32 growth framework reef cavities were collected over the depth range 12 m to 43 m along the leeward side of Bonaire, Netherlands Antilles. The resulting sample of 1,245 specimens comprised 92 species, which showed a peak in species diversity at about 18 m depth. Of the 79 species that show significant restriction of their depth ranges in this study, most are known elsewhere to have different or greater depth ranges. However, 17 cryptobiontic sponge species in Bonaire appear to be depth restricted. This suggests that there may be a depth zonation of some cryptobiontic sponges, and opens up the possibility that with more study, cryptobiontic sponges may be of some use in ancient reefs as a paleoenvironmental tool. The presence of 10 species of endolithic sponge over a broad depth range shows that sponge bioerosion in the cavities is widespread, although it does not appear to be intensive. Based upon the amount of preservable skeletal material produced by sponges in these reef cavities, it appears that as much as 97% of the cryptobiontic sponge sample would be lost during fossilization, leading to the conclusion that the fossil record of cryptobiontic sponges may be a very poor representation of their actual importance in fossil reef cavity systems