Population Structure and Relative Growth of the Marbled Crab (Pachygrapsus marmoratus) in the Aegean Sea (Turkey)

Abstract

Although crab Pachygrapsus marmoratus, is one of the common species in the intertidal zones of the Aegean coasts of Turkey, its’ population structure has not been investigated to date. This study aimed to provide information on population characteristics of Pachygrapsus marmoratus, including the sex ratio, size distribution, spawning period, relative growth and catch per unit effort (CPUE). The samples were collected by hand monthly between January 2018 and December 2018, from the rocky shores of Izmir, Turkey. The results indicated that males were dominant except for the months of July, August and September. The CW (carapace width) of female and male crabs ranged from 5.5 to 36.0 mm and 5.5 to 40.0 mm, respectively. The berried (egg-carrying) females were found in May, June and July and their CW varied from 13.0 to 27.0 mm. Only 0.8% of the P. marmoratus population was shown to be infected with the parasite Sacculina sp. The CPUE of P. marmoratus significantly changed monthly and there was a significant correlation between the CPUE and seawater temperature. Concerning the relative growth, the carapace width-cheliped length relationship in males and carapace width-abdomen width relationship in females showed positive allometry. Males were significantly heavier in comparison to females of the same size. Future survey designs would need to investigate whether spatial differences in the population characteristics and size at maturity occur in the Aegean coasts of Turkey.