Population structure and fecundity of two species of grapsid crabs (Brachyura, Grapsidae) that inhabit the oyster reefs of western Taiwan

This study on carcinological aspects of oyster farming was carried out at the coast of Yunlin County, Taiwan, for a period of 25 months from July 2012 to July 2014. The space formed by the clustering of the oyster shells provides a habitat for at least eight species of crabs. Nanosesarma minutum was the dominant species (73.7% or n = 18 753) with an average of 59.5 ± 30.6 individuals/string/month, while the average monthly rate of ovigerous females was 12.6 ± 13.0%, and the average number of eggs per berried female was 1510.8 ± 1018.7 eggs/individual. Hemigrapsus penicillatus was the second dominant species (23.9% or n = 6074) with an average of 17.4 ± 17.1 individuals/string/month; here, the average monthly rate of ovigerous female crabs was 4.6 ± 9.0, and the average number of eggs of a berried female was 3073.4 ± 2167.5 eggs/individual.