Life-history characteristics of two sympatric thalassinidean shrimps, Neotrypaea californiensis and Upogebia pugettensis, with implications for oyster culture

An investigation of the life-history characteristics of 2 thalassinid shrimps (Neotrypaea californiensis and Upogebia pugettensis) on intertidal mud hats in Willapa Bay, Washington (U.S.A.), revealed substantial differences. Both species are viewed as pests by the oyster industry due to their ability to disturb sediments. The density of Neotrypaea was always higher than that of Upogebia in the undisturbed populations sampled, and burrow opening-shrimp density relationships differed between species (1.2 burrow openings shrimp(-1) in Neotrypaea and 1.5 openings shrimp(-1) in Upogebia). Differences were also noted in growth rate (2-3-mm CL yr(-1) for Neotrypaea versus 4-5-mm CL yr(-1) for Upogebia), size at maturity, and sexual dimorphism. Male and female claw size diverged immediately in juvenile Upogebia (4-5-mm CL, <1 yr old), but not until sexual maturation in Neotrypaea (9-10-mm CL, almost 2 yr old). Average fecundity was higher for Upogebia (7,100 eggs) than Neotrypaea (3,900 eggs) and we found a distinct difference in the seasonal reproductive cycle of the 2 species of shrimps. Neotrypaea were ovigerous from April through August and Upogebia were ovigerous from October through May. Seasonal timing of postlarval recruitment was correspondingly offset; Neotrypaea recruited to the estuary from late summer through early fall (August-October). while Upogebia recruited in spring (April-June). The seasonal difference in timing of recruitment of these shrimps to the estuary has important implications for shrimp-control programs and oyster-culture practices which are currently not being considered. Control operations occur in July before settlement of postlarvae of Neotrypaea, enabling this species to rapidly reinfest oyster-culture areas.