EDRIOASTEROID ENCRUSTATION PATTERNS: IS THERE A CORRELATION BETWEEN THECA SIZE AND SETTLEMENT LOCATION ON BRACHIOPOD SHELLS?

This study examines the spatial patterns of two species of edrioasteroids, Isorophusella incondita and Cryptogoleus chapmani, collected from the Verulam Formation in Gamebridge, Ontario, Canada in 1975. The edrioasteroids occupy strophomenid brachiopod shells, which provided a hard substrate for the edrioasteroids to reside above the ancient unconsolidated seabed. For this study, I investigated the spatial patterns of edrioasteroids upon these raised surfaces. Edrioasteroid settlement on the shells shows preferential settlement with 41% of Isorophusella incondita encrusting most frequently near the anterior margin, while specimens of Cryptogoleus chapmani show a preference for the central region of the shell (42.9%). It appeared that the majority of juvenile edrioasteroids (based upon size) were located near the brachiopod commissure, an area where small eddies would bring a greater amount of nutrients to the juvenile edrioasteroids, yet larger edrioasteroids resided nearer the topographic high of the shells. To determine if there is a correlation between theca size and settlement location, I noted edrioasteroid attachment site based upon a generalized brachiopod shell divided into a nine-sector grid following the method of Kelley (1988). I tested the coupled data using the Pearson Correlation Coefficient, which measures the strength of a linear association between two variables. With r-values of 0.28 for Cryptogoleus chapmani and -0.009 for Isorophusella incondita, I determined that no such correlation exists for the two species.