REPRODUCTIVE PATTERNS AND POPULATION CHARACTERISTICS IN 5 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) we re studied between 150 and 1100 m depth in the Western Mediterranean S ea over the period 1991 to 1994, including monthly samples taken from November 1992 to October 1993. With the aim of establishing interspeci fic relationships among reproductive biology and population characteri stics 2831 individuals of Plesionika heterocarpus, 1787 of P. edwardsi , 1601 of P. gigliolii, 3888 of P. martia and 928 of P. acanthonotus w ere analysed. Results show an increasing seasonality in reproductive p eriods from the shallowest species, P. heterocarpus (distributed betwe en 82 and 699 m depth) with ovigerous females present throughout the y ear, to the deepest species, P. acanthonotus (distributed between 165 and 1550 m) with ovigerous females present only in late spring and ear ly summer months. A possible link was hypothezised between deep-water pandalid shrimp breeding period and sinking particulate matter from pr imary production. A significant decrease in relative brood size (numbe r of eggs per 'standard' 20 mm carapace length female) with increasing depth distribution of each species was found. No significant relation ship between egg size and depth distribution was apparent. In 4 of the 5 species studied a differential depth distribution based on sex-rati o and intraspecific size composition by depth was found. The only spec ies where no significant trend was found in sex-ratio by depth, P. aca nthonotus, did not show differences in size composition by depth. A sl ight interspecific size overlap was observed. Sex-ratio and size compo sition by depth distribution are discussed in the light of trophic and reproductive behaviour of each species.