Female reproductive success in artificial sponges in Paracerceis sculpta (Holmes) (Crustacea: Isopoda)

Paracerceis sculpta (Holmes), a sphaeromatid isopod crustacean, breeds in the spongocoels of intertidal sponges (Leucetta losangelensis de Laubenfels) in the northern Gulf of California. In the laboratory, P. sculpta adults readily colonize and inhabit artificial sponges constructed of a synthetic polymer (FHP-3000). To examine the effect of artificial sponges on female fecundity, I compared the numbers of live mancas and undeveloped embryos produced by females that had completed their gestations (1) without sponges in 225 ml cups, (2) within artificial sponges at densities of one, three and five females per sponge, and (3) within natural sponges in the field. Females that completed their gestations in 225 ml cups released the most live mancas, whereas females that completed their gestations in the field released the fewest live mancas. Although differences among female groups in numbers of undeveloped embryos were found, the majority of females in all groups produced no undeveloped progeny, thus the significance of these differences is uncertain. There were no differences in numbers of live mancas released, or in numbers of undeveloped embryos remaining in the brood pouches among females that completed their gestations in artificial sponges at different densities. Thus, neither female aggregation nor gestation in artificial sponges appear to deleteriously affect female fecundity. These results corroborate earlier experiments indicating that artificial sponges provide suitable substitute reproductive habitat for laboratory studies of P. sculpta, and suggest that selection in other contexts (perhaps predation) maintains the tendency for females to complete their gestations in protected locations.