HYDROGRAPHIC REGIME PREFERENCES OF BURROWING COASTAL DECAPODS (CARDISOMA/DISCOPLAX): PALEOENVIRONMENTAL IMPLICATIONS

As an integral part of assessing the reliability of a (paleo) sea-level indicator, the tidal range of a particular coastal setting dictates variations in high-tide elevation (neap-spring difference) and the full amplitude of the resulting data envelope. For unconventional indicators, such as burrows of some land crab genera that require the presence of water in a basal chamber, regional tidal fluctuations affect their habitat preferences and landward dampening of the tidally controlled water table (transfer function). Based on published reports and recent field data from the Bahamas, this study represents the first assessment of the global distribution and hydrographic regime for all four species of Cardisoma, as well as three Cardisoma species now synonymized within Discoplax. These decapod genera are distributed along continental and insular coastlines of all three tropical oceans, with some extending into subtropical biotopes. At least 90% of sites inhabited by Cardisoma spp. are in low-microtidal settings (mean tidal range: 0.2-1.0 m). Whereas many open-ocean microtidal coasts are characterized by high wave energy, these crustaceans prefer relatively calm bay margins and mangrove coasts. Such environmental conditions are consistent with their ecological requirement for a reservoir of saline water within the burrow, thereby avoiding long-term submergence or desiccation. Our findings further support the utility of hydration-related biogenic structures produced by these brachyurans as potential water-level indicators and as diagnostic attributes of low-energy microtidal depositional settings.