Production and life history of a deposit-feeding polychaete in an atypical environment

Abstract

The deposit-feeding opheliid polychaete Euzonus mucronata (Treadwell) is abundant in an environment atypical of deposit feeders, a high-energy sand beach. Its annual production was estimated from a life-history study of an Oregon, U.S.A. study population. Recruitment occurred over 1–2 months in early summer and varied greatly between years, leading to substantial interannual variations in productivity. Although adults were restricted to a sharply delineated, narrow band in the upper intertidal, juveniles settled both within and below this band. Juveniles settling below the band grew slower than those within the band and were absent by three months after recruitment. Individuals lived for up to two years and spawned in their first and second years. There is some evidence of increased mortality of adults just before the arrival of recruits, possibly due to reproductive stress. Few two-year-old individuals remained after spawning. Production estimates (ash-free dry weight) of 21·3, 47·4 and 7·8 g m −1 year −1 were obtained for 0–1 year old individuals and 35·8 and 58·3 g m −1 year −1 for 1–2 year old individuals, respectively. Ratios of production to biomass were higher for 0–1 year old individuals than for 1–2 year old individuals. Total annual production was comparable to that of deposit-feeding macrofauna in fine sediment. Over a 2 yr period, the population ratio of annual production to mean biomass was 1·73. If this ratio is typical of E. mucronata, the production of this species can be similar to the production of filter feeders, the normally dominant macrofauna of other high-energy sand beaches.