Dynamics and productivity of two populations of the benthic tube-dwelling amphipodAmpelisca brevicornis(Costa) in Helgoland Bight

Abstract

Population dynamics of the amphipod Ampelisca brevicornis were investigated from 1969 to 1972 at two sublittoral (28 m) fine sand stations. Juveniles appear between the end of July and the end of September; they reach maturity in the following year. Females propagate once. Numerical abundance and biomass (up to 2.8 g wet weight per m²) are highest from October to December. In winter the population density is low, and a further decrease occurs in spring. Biomass values between June and August are below 0.3 g per m². Productivity was calculated on the basis of monthly abundance and biomass figures, and on the basis of monthly size class distributions. The second procedure gives somewhat higher values: a mean annual biomass of about 1 g wet weight per m², an annual production of about 4 g per m² , and a turnover ratio of about 4. Of the annual production 60–70 % is consumed in October, November and December, 15–23% in May, and only 8–22 % during the remaining 8 months of the year. A turnover rate of about 4 is rather high among sublittoral benthic invertebrates. Since 1969 wastes containing sulfuric acid and ferrous sulfate from a titanium dioxide plant have been dumped in the area investigated. No significant influence of these wastes upon biomass values could be detected.