PRELIMINARY OBSERVATIONS FROM A WOOD BIOEROSION EXPERIMENT IN MARINE AND MARGINAL MARINE SETTINGS, MOBILE BAY AREA, ALABAMA

Previous studies of wood substrates in modern and ancient marine and marginal marine environments indicate that an array of bioerosion structures may result from inhabitation by wood-boring bivalves (teredinids and pholadids), as well as by various worms and crustaceans. In order to better assess the potential of using suites of bioerosion structures in fossil wood substrates to evaluate the physical and chemical conditions that prevailed during emplacement, a neoichnological experiment has been initiated in areas surrounding Dauphin Island, situated between Mobile Bay, Alabama, and the Gulf of Mexico. This experiment is designed to test several related hypotheses: wood-inhabiting invertebrates and the character and distribution of their biogenic structures vary as a function of: (1) time for colonization; (2) environmental setting and conditions; (3) position of the wood (on the seafloor vs. suspended in the water column); (4) type of wood; and (5) wood freshness/degradation state. Forty (40) logs have been attached to each of five specially constructed PVC cages and submerged at five shallow-water deployment sites characterized by different environmental conditions (e.g., hydrodynamic energy, bottom-sediment type). Each cage holds ten strands of 4 logs each; five strands rest on the bottom and five strands are suspended in the water column. Each log strand contains one each of dead pine, recently living pine, dead oak, and recently living oak, all debarked along half of their lengths. Two log strands, one in contact with the bottom and one suspended in the water column, were retrieved from each locality after 1.5 and 3 months; additional recoveries are scheduled for 6, 9, and 12 months. Bioerosion features are being examined via CT scan imaging. Observations made to date on logs recovered after 1.5 months indicate that, although encrusting organisms (bryozoans, cirripeds, algae, tunicates, decapods, etc.) vary among sites, teredinid bivalves are the main bioeroders at all localities. Teredinids show clear preference for dead wood. However, thus far, results have yet to indicate preference for oak versus pine, barked vs. debarked, or bottom vs. suspended substrates. Additional trends may become apparent upon analysis of logs recovered throughout the remaining period of the experiment.