CHARACTERISTICS, DISTRIBUTION PATTERNS, AND IMPLICATIONS FOR ICHNOLOGY OF MODERN BURROWS OF UCA (LEPTUCA) SPECIOSA, SAN SALVADOR ISLAND, BAHAMAS

摘要

Fiddler crabs (Brachyura: Ocypodidae: Uca) are important bioturbators globally in protected tropical and temperate marine intertidal to supratidal, muddy to sandy environments. Their burrow distribution patterns vary with specific substrate. The study area is a saltwort (Salicornia virginica) meadow in a high intertidal to supratidal zone bordered by mangroves on the northern end of Pigeon Creek, a slightly hypersaline lagoon on San Salvador Island. Here the mostly carbonate sand substrate is heavily burrowed by Uca (Leptuca) speciosa (Ives, 1891). Three micro-habitats were differentiated according to variations in vegetation cover and depth to groundwater, as follows: 1) a meadow wetland, commonly flooded during spring high tides and with dense, luxuriant S. virginica and intermediate substrate firmness values, which has the highest density of burrows and the widest range of burrow diameters with mid-range values in burrow depth and length - maintaining the best conditions for fiddler crabs that include individuals of different ages; 2) dryland with slightly more subaerial elevation and sparse vegetation with the highest substrate firmness values and lowest density of burrows, the burrows being deeper, longer, and exhibiting the lowest range of diameters - with less favorable burrowing conditions for only fully mature adults; 3) wetland with sparse vegetation in the high intertidal zone with lowest firmness values, lowest number of burrows, smallest burrow diameters, and shallowest and shortest burrows - favoring colonization mainly by juveniles. If burrows similar to those of this study were preserved as trace fossils, they should be assigned to the ichnospecies Psilonichnus tubiformis Fursich, 1981. When ichnological features such as burrow densities and dimensions, along with sedimentological and stratigraphical data, are taken into account in ways similar to those of this neoichnological study, interpretations of paleoenvironmental conditions and burrowing crab paleopopulation distributions could be significantly improved.