WOOD BIOEROSION IMPLANT EXPERIMENT, MOBILE BAY AREA, ALABAMA: AN UPDATE

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 worms and crustaceans. In order to assess the potential of using suites of bioerosion structures in fossil wood substrates to evaluate the conditions that prevailed during emplacement, a neoichnological experiment was initiated in the Mobile Bay area, Alabama. The experiment is designed to test several related hypotheses: wood-inhabiting invertebrates and 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 PVC cages and submerged at five shallow-water deployment sites characterized by different environmental conditions. 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, 3, 6, and 9 months; a 12-month recovery is scheduled for March 2018. Bioerosion features are being examined via CT scan imaging. Observations made to date indicate that, although encrusting organisms (bryozoans, cirripeds, algae, tunicates, decapods, etc.) vary among sites, teredinid bivalves are the main bioeroders at all localities. Thus far, results demonstrate clear differences in colonization among the different wood types deployed. Teredinids show clear preference for dead wood over recently living wood, for the debarked portions of logs, and demonstrate selectivity of pine over oak regardless of taphonomic state. Logs on the seafloor are significantly more bioeroded than those suspended in the water column. Differences among the five implant sites are more difficult to decipher, particularly because components of several cages were destroyed during Hurricane Nate.