Scientia Marina, Vol 71, No 1 (2007)

Spatial distribution, density, and relative growth of Microphrys bicornutus (Latreille, 1826) (Brachyura: Majidae) in five biotopes in a Thalassia complex

Carlos A. Carmona-Suárez
Centro de Ecología, Instituto Venezolano de Investigaciones Científicas (IVIC), Caracas, Venezuela, Bolivarian Republic of


Spatial distribution, population density, number of ovigerous females, and relative growth of Microphrys bicornutus were studied in an extremely shallow Thalassia complex (Buchuaco- Venezuela). Monthly sampling was undertaken in 5 different biotopes (zones) (July 1988 to December 1990). Zone 3 (coral rubble) was the least populated by M. bicornutus. The highest densities were found in Zones 1 (coral rubble and macro algae) and 4 (Thalassia and calcareous algae). Crab size ranged between 1.86 and 35.40 mm (carapace length). The largest mean size was found in Zones 2 and 5, and the smallest in Zone 1. The least mean percentage of ovigerous females was found in Zone 3, and the highest in Zone 5. There were strong temporal fluctuations, with the absence of ovigerous females in the first months of each year. The biometric data showed that pre-pubertal males ranged from 1.80 to 24.20 mm carapace length, and post-pubertals from 15.16 to 26.15. Pre-pubertal females ranged from 3.16 to 20.25 and post-pubertals from 8.84 to 21.85. Zone 3 was the most inadequate biotope for M. bicornutus, as it had the lowest density and the least mean percentage of ovigerous females. Zone 4 was the most appropriate biotope. Temporal absence of ovigerous females and the small sizes of the crabs in Buchuaco could be due to extreme environmental conditions.  


Crustacea; Brachyura; spider crabs; Microphrys bicornutus; spatial distribution; population density; relative growth

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