LIFE-HISTORY CHARACTERISTICS OF 2 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 intert idal mud hats in Willapa Bay, Washington (U.S.A.), revealed substantia l 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 bet ween species (1.2 burrow openings shrimp(-1) in Neotrypaea and 1.5 ope nings shrimp(-1) in Upogebia). Differences were also noted in growth r ate (2-3-mm CL yr(-1) for Neotrypaea versus 4-5-mm CL yr(-1) for Upoge bia), size at maturity, and sexual dimorphism. Male and female claw si ze diverged immediately in juvenile Upogebia (4-5-mm CL, <1 yr old), b ut not until sexual maturation in Neotrypaea (9-10-mm CL, almost 2 yr old). Average fecundity was higher for Upogebia (7,100 eggs) than Neot rypaea (3,900 eggs) and we found a distinct difference in the seasonal reproductive cycle of the 2 species of shrimps. Neotrypaea were ovige rous from April through August and Upogebia were ovigerous from Octobe r through May. Seasonal timing of postlarval recruitment was correspon dingly offset; Neotrypaea recruited to the estuary from late summer th rough early fall (August-October). while Upogebia recruited in spring (April-June). The seasonal difference in timing of recruitment of thes e shrimps to the estuary has important implications for shrimp-control programs and oyster-culture practices which are currently not being c onsidered. Control operations occur in July before settlement of postl arvae of Neotrypaea, enabling this species to rapidly reinfest oyster- culture areas.