Distribution, Growth and Production of Nephtys Hombergii and N. Assimilis (Polychaeta: Nephtyidae) in Benthic Communities of the North Sea
Abstract:The polychaetes Nephtys hombergii and N. assimilis are morphologically similar species, usually considered together under the name N. hombergii. Both species were present in benthic samples collected in the North Sea by the R/V Dana in 1951 and 1952. N. hombergii (s.s.) occurred most frequently in clayey sand (4.1 worms·m−2) or sandy clay (4.7 worms·m−2) sediments, mainly in water depths greater than 40 m. N. assimilis was most abundant in muddy sand (5.1 worms·m−2), particularly around the Dogger Bank; in the deeper parts of its range it also occurred with N. hombergii. The maximum body width of both species was about 7 mm; maximum body length was estimated at 150 mm in N. hombergii, and measured at 100 mm in N. assimilis. Life spans, estimated from size modes and by the analysis of growth rings in the jaws, were 7 years in N. hombergii, 9 years in N. assimilis, implying estimated annual production:biomass ratios of 1.11 and 0.93 respectively. The mean biomass of N. hombergii and N. assimilis on the Dogger Bank was estimated to be 0.22 and 0.85 g·m−2 respectively; for North Sea areas other than the Dogger Bank, 0.40 and 0.56 g·m−2. Production by N. hombergii and N. assimilis on the Dogger Bank was estimated to be 0.25 and 0.79 g wet weight·m−2·yr−1 respectively, or about 20% of a previous estimate for the two species combined; for areas other than the Dogger Bank, the corresponding values were 0.44 and 0.52 g·m−2·yr−1. The food requirements of the five Nephtys species known from the Dogger Bank are estimated to be 32.9 g·m−2·yr−1, or four times the previous estimate of production by non-nephtyid polychaetes (8.1 g·m−2·yr−1). A re-evaluation of benthic polychaete production on the Dogger Bank is required.
Document Type: Research Article
Publication date: 1991-03-01
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