DISSOLUTION OF ECHINOID OSSICLES IN THE GULF OF MEXICO: RESULTS FROM A LONG-TERM EXPERIMENTAL TAPHONOMIC STUDY

A potential biproduct of climate change is increased acidification of the oceans, which may have a significant impact on the global carbon cycle, sedimentation rates, and ecology of marine organisms. Echinoderm ossicles are composed of high-Mg calcite, are major components of sea floor sediment, and thus are useful to determine rates of dissolution.

The Shelf and Slope Experimental Taphonomy Initiative is a long-term study of the taphonomic processes acting on a variety of organisms in various environments in the Gulf of Mexico. Echinoids (Echinometra and Eucidaris) were placed in 30 localities on the shelf and slope of the Gulf of Mexico in 1993. Multiple replicate samples composed of mesh bags containing echinoids were attached to PVC Pipe and placed on the ocean floor. Echinoids were recovered in 1995, 2001, and 2006 and the skeletal elements (test, lantern, and spines) were taphonomically characterized immediately post-collection based on the level of dissolution of their skeletal elements. Following characterization, samples were submerged in 70% ethanol and stored in a controlled environment. Subsequently, the density of the skeletal elements in the samples were compared to control echinoids maintained frozen since 1993. The current study focuses on samples recovered in 2001 and 2006 from ten sites that represent various environments, depths, and locations across the Gulf.

The 8-year samples recovered in 2001, showed few signs of dissolution or a decrease in density. However, the samples recovered five years later in 2006 showed a significant increase in the qualitative characterization of dissolution in both the test and Aristotle’s Lantern, though the level of dissolution is greater on the test. Levels of dissolution varied between sites, but 9 out of 10 sites showed an increase in average taphonomic score. Preliminary results showed that density decreased by approximently 10% on average in the Aristotle’s lantern between 2001 to 2006. Though these rates of dissolution are likely too low to be detrimental to living echinoids, the results indicate that significant levels of dissolution are occurring over a decadal time scale. These trends will be further examined by measuring changes in density in the spines and test along with characterization of dissolution features in a SEM analysis.