Variation in the reproductive status, larval occurrence and recruitment in an estuarine population of Marenzelleria viridis (Polychaeta: Spionidae)

Abstract

Since its immigration in 1985, the spionid polychaete Marenzelleria viridis (Verrill, 1873) has become a major element of the fauna in the Darss-Zingst Bodden Chain, a tideless estuary-like coastal water of the southern Baltic. High abundances of the pelagic larvae were found in this area in autumn.

The reproduction of M. viridis was investigated from March 1992 to April 1995 at an inner station (salinity 2–6%) and an outer station (salinity 4–12%) of the estuary. Adult animals were collected once a month and the reproductive stage was ascertained. Plankton samples were taken twice a week during the spawning season, and the pelagic larvae were counted. The recruitment of juvenile worms was observed by benthos samples. Gametogenesis began in May, and the animals reached maturity at the end of September in 1992, but gametogenesis lasted one month longer in 1993 and 1994. Maximum larval densities were highest in 1992 (about 22*10⁶ ind./m³), reached 1*10⁶ ind./m³ in 1993 and 314,000 ind./m³ in 1994. In 1994 the salinity was unusually low and few larvae reached metamorphosis (16 to 17-setiger stage) in 1994. Recruitment started in mid-October and juveniles were most abundant in 1993. Also spatial differences in the proportion of spawning animals and larval density were observed.

The way of successful colonization of the oligohaline regions of the estuary is discussed.