Fiddler crab burrow morphology:: How do burrow dimensions and bioturbative activities compare in sympatric populations of Uca vocans (Linnaeus, 1758) and U-annulipes (H. Milne!Edwards, 1837)?

Dimensions of crab burrows were compared in two sympatric populations of fiddler crabs, Uca vocans and U. annulipes, to determine interspecies variation. Nine dimensions of burrow architecture were defined from 62 complete burrow casts of U. vocans: burrow diameter, BD; burrow volume, BV; total burrow depth, TBD; burrow neck height, BNH; curved burrow length, CBL; horizontal length, HL; chamber diameter, CD; angle between descending neck of burrow and the substrate surface, P; angle between the bend in the burrow and the perpendicular, theta. None of the nine dimensions of burrow architecture showed any difference between sexes. Six out of seven linear burrow dimensions differed significantly among crabs in the three size classes recognized; BNH did not differ among small, medium, and large-sized crabs. Regardless of species, larger-sized crabs dug larger entrances and resided in more voluminous burrows. The architecture of the burrows in the two sympatric populations is rather similar: the only significant difference is that Uca vocans had wider BDs than U. annulipes. This could be due to the difference in carapace proportions of the two species: adult specimens of U. vocans have significantly larger carapace length to width ratios than those of U. annulipes. Comparisons of between the two species showed that the descent slopes of the burrows were similar, indicating that there is no evidence to suggest that burrows of fiddler crabs in sandy habitats have steeper descent slopes than those in muddy habitats. The mean volume of sediment excavated by U. vocans per m(2), though not significantly greater than that of U. annulipes, suggests that U vocans is potentially a more active agent of sediment re-working than its sympatric species in this lagoon.