Relating Modern Holothurian Burrows to Environmental Conditions and the Study of Nearshore Paleoenvironments

Holothurians have a patchy fossil record extending from the Middle Cambrian to the Holocene. Determining their local and global distribution through time is difficult due to the poor preservation of their soft-anatomy. In the modern, holothurians are abundant on the sea floor in tropical and subtropical environments. Several holothurian taxa are burrowers that produce shallow feeding and dwelling structures. Ichnofossils are the preserved remains of burrows which provide in situ paleoenvironmental and paleoecological information by recording the behaviors of organisms in response to their environment. Neoichnological experiments conducted on soft-bodied organisms such as holothurians allow for the observation of modern burrowing behaviors in a laboratory or natural setting. These data can then be used for the interpretation of ichnofossils produced by organisms that have a poor preservation potential.

In this neoichnological experiment, the burrowing behaviors and burrow morphologies of Thyonella gemmata, a mud-burrowing holothurian from the shallow waters of the northern Gulf of Mexico, were studied in a laboratory setting. The first goal of the experiment was to observe the burrowing behavior of T. gemmata and to describe the architectural and surficial morphology of the resulting biogenic structures by examining resin casts and box cores of evacuated burrows. The second goal was to associate variations in the morphology of the biogenic structures with specific environmental conditions. Three aspects of the holothurians environment were altered in separate experiments: sediment size, water temperature, and salinity.

By studying the burrow morphologies produced under the three experimental environmental parameters, the burrows can be compared with ichnofossils from nearshore paleoenvironments to determine if holothurians were present as well as paleoenvironmental conditions. This study provides a means of interpreting sediment consistency, fluctuations in water temperature and salinity, and proximity to the shoreline providing another tool to aid in understanding nearshore paleoenvironments.