FECUNDITY AND REPRODUCTIVE OUTPUT OF PISIDIA-LONGICORNIS (DECAPODA, ANOMURA) IN THE RIA-DE-AROUSA (GALICIA, NW SPAIN)

Pisidia longicornis is a small anomuran crab that constitutes the domi nant component of the epifauna of mussel rafts in the Ria de Arousa (N W Spain). This species forms isolated postlarval populations on the ro pes used in the culture, experiencing a wide range of environmental co nditions, both spatially and seasonally. This paper studies the fecund ity (egg size and number per brood) of P. longicornis in the inner and outer areas of the ria at 5 and 10 m depth over a yearly cycle. The f ecundity of this species is highly variable (ranging from 10 to over 1 443 eggs per brood), and it is primarily determined by carapace width, CW (P < 0.05 for most of the samples, with slopes of the allometric r elation ranging between 2.38 and 4.48, and > 3 in most of cases). Spat ial differences were due partially to changes in body size; in the out er area (mean CW 4.9 mm), the number of eggs per brood was 265 +/- 225 (mean +/- SD), and in the inner area with larger specimens (mean CW 6 .1 mm), fecundity was higher (600 +/- 373 eggs). Egg volume in the out er station (0.025 mm(3) +/- 0.005) was higher than in the inner statio n (0.023 mm(3) +/- 0.005) and slightly larger at 10 m deep (0.025 mm(3 ) +/- 0.005) than at 5 m (0.023 mm(3) +/- 0.004). In the outer ria are a, where the food availability, density and growth are higher, the rep roductive output (defined as number of eggs x egg size) corrected for body size, was higher than in the inner station. Both parameters relat ed to reproductive output exhibited significant temporal variability. During the main breeding period there was an increase in number of egg s per brood and a decrease in egg volume from January to March-April. This seasonal change in the reproductive strategy is associated with t he increase in planktonic production in spring. P. longicornis shows a great plasticity in reproductive output, both seasonally (within a po pulation) as well as spatially (between populations), that is hypothes ized as an adaptative strategy to the spatial and temporal variations in the environment, and especially food abundance for planktonic larva e.