Seasonal and temporal variations in population dynamics of the Carcinus maenas (L.): the effect of an extreme drought event in a southern European estuary

Abstract

The temporal and spatial variability in population dynamics of the European crab Carcinus maenas (L.) was studied between June 2003 and September 2007 in the Mondego estuary. An extreme climate event (extreme drought) occurred in 2004 and 2005 with a low freshwater flow discharge into the estuary, leading to an increase in salinity. Juveniles' recruitment was continuous throughout each year with a high proportion of young recruits being recorded in the spring of 2005. The proportion of green crabs clearly increased from the mouth to the upstream areas and the proportion of crabs actually in moult followed the same pattern. Parasitization by the endoparasitic barnacle, Sacculina carcini was observed, principally at the mouth of the estuary. The C. maenas population showed a regular size–frequency distribution and structure for both sexes during the study. Secondary production (P) of C. maenas estimated for the 4-year study period was different between years though, P/B ratios were similar during the whole study period. During the drought period, catches of the crab recruits were higher, particularly in the spring, probably due to the increase in salinity, which emphasizes the importance of these extreme events in controlling the abundances of coastal populations.