Occurrence and variation in the depth of burrows of mangrove crabs around a tropical creek in Nigeria

Abstract

Mangrove crabs are active burrowers in intertidal sediments of wetland, living beneath drifts and high-tide marks in lagoon shores in many parts of the world. The occurrence, distribution and burrow depths and diameters of the mangrove crabs, Cardisoma armatum and Goniopsis pelii collected from a mangrove wetland of the Lagos Lagoon were investigated between February and July, 2017. Burrows were counted biweekly on permanent square plots marked out in the six stations, while the appearance of new burrows as well as disappearance of old burrows, depths and diameters were recorded. C. armatum was present in all the study sites with a total of 848 specimens and occurred throughout the study period, while G. pelli with a total of 115 specimens occurred in two study sites and during the wet season only. Species ratio was 1: 0.37 while the Chisquared value at 1 d.f and 5 % significant level was 557.93. The depth of the crab burrows across the stations ranged from 16.65 – 33.47 cm with diameter ranging between 4.0 – 6.40 cm. Crab burrows, its occurrence and distribution were observed to be affected by natural and anthropogenic factors. There was a rapid decline in burrows in the month of April when rainfall seized and anthropogenic factors like noise, refuse dumping and construction works also played major roles in determining the dispersion of burrows. Therefore, mangrove crabs and their burrows are greatly influenced by both abiotic and biotic factors.

Keywords: Cardisoma armatum, Goniopsis pelii, Mangrove wetland, Burrow, Depth and width, Occurrence, Distribution