Life History and Productivity of the Phoxocephalid Amphipod Rhepoxynius Abronius (Barnard)

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Abstract
Rhepoxynius abronius (Barnard) (Amphipoda: Phoxocephalidae) is a predominantly subtidal species of the North American Pacific coast. It is also found sub- and intertidally within the polyhaline region of estuaries of Oregon and Washington. Within the Yaquina Bay estuary, Oregon, R. abronius is an annual species producing one or two broods per year. Recruitment occurs over an extended period from mid to late winter through summer. Mortality was 20-25% per month during mid to late spring through fall, and was low in winter through early spring. Mortality may be largely due to predation. Mortality of males appears higher than that of females during the reproductive season. The annual range in biomass was 40– 180 mg ash-free dry weight (AFDW)/0.5 m2, averaging 104 mg AFDW/0.5 m2. Secondary production was 160-216 mg AFDW/0.5 m2/yr and the annual ratio of production to mean biomass was 1.54-2.08. Production and the production: biomass ratio are similar to values reported for other marine amphipods with one or fewer generations per year.