Reproductive patterns and population characteristics in five deep-water pandalid shrimps in the Western Mediterranean along a depth gradient (150-1100 m)

Reproductive patterns and populations characteristics of 5 deep-water pandalid shrimp species of the genus Plesionika (Decapoda: Caridea) were studied between 150 and 1100 m depth in the Western Mediterranean Sea over the period 1991 to 1994, including monthly samples taken from November 1992 to October 1993. With the aim of establishing interspecific relationships among reproductive biology and population characteristics 2831 individuals of Plesionjka hetel-oca~pus, 1787 of P edwardsl, 1601 of P. gigliolii, 3888 of P. martia and 928 of P acanthonotus were analysed. Results show an Increasing seasonality in reproductive periods from the shallowest species, P heterocarpus (distributed between 82 and 699 m depth) with ovigerous females present throughout the year, to the deepest species, P acanthonotus (distributed between 165 and 1550 m) with ovigerous females present only In late spring and early sumlner months. A possible link was hypothez~sed between deep-water pandalid shrimp breeding period and sinking particulate matter from primary production. A significant decrease in relative brood size (number of eggs per 'standard' 20 mm carapace length female) with increasing depth distribution of each species was found. No significant relationship between egg size and depth distribution was apparent. In 4 of the 5 species studied a differential depth distribution based on sex-ratio and intraspecific size composition by depth was found. The only species where no significant trend was found in sex-ratio by depth, P. acanthonotus, did not show differences in size composition by depth. A slight interspecific size overlap was observed. Sex-ratio and size composition by depth distribution are discussed in the light of trophic and reproductive behaviour of each species.