BIOSTRATINOMIC INVESTIGATION OF HORSESHOE CRAB (LIMULUS POLYPHEMUS) DEATH ASSEMBLAGES AFTER HURRICANE IRENE

Ongoing monitoring of horseshoe crab (HSC) death assemblages has allowed for a detailed look at the impact of Hurricane Irene on Limulus polyphemus at Wallops Island, Virginia. Assemblages containing both entire molts and carcasses have demonstrated high proportion of juvenile/young adult molts in late summer assemblages compared to other times of the year. The presence of entire molts in storm assemblages (including those produced by Irene in August 2011) indicates that molting episodes were clustered near storm events. Thus, if HSC’s were actively molting prior to or during Hurricane Irene, then surviving individuals may have been subject to storm-influenced deformities as their carapaces hardened. Compared to previous investigations where deformity rates were relatively low (<1 deformity per 100 specimens), trips in October, and December 2011 have shown increased rates of deformities in HSC assemblages (~ 10 per 116 specimens). The most common deformation has been observed as asymmetries in the spiny frill at the rear of opisthosomas. Other deformations were noted in the shape of the prosoma and telson although these were rarer. Statistical analysis is ongoing to assess rates of deformation from previous samples. Future sampling will focus on recovery of new samples that may also contain Hurricane Irene-influenced mortality. Biostratinomic investigations like this provide for comparison to arthropod fossil assemblages where non-symmetrical deformities are most often attributed to post-depositional processes. Although premature to declare conclusively, this study suggests some of these non-symmetrical deformities may be result of storm-influenced deformation on living, molting populations of arthropods.