DISTRIBUTION AND MAINTENANCE OF A LANICE CONCHILEGA ASSOCIATION IN THE WESER ESTUARY (FRG), WITH SPECIAL REFERENCE TO THE SUSPENSION—FEEDING BEHAVIOUR OF LANICE CONCHILEGA

ABSTRACT The distribution of the polychaete Lanice conchilega (Pallas) was investigated in 1976 at about 150 stations in the outer part of the Weser Estuary (FRG). Special attention was given to a well-defined area (Nautical Buoys ‘L’, ‘K’ and ‘J’) where, at least since 1963, very high population densities of L. conchilega have been maintained. Over the past 14 years, L. conchilega was the numerically dominant species in this area, associated with the passive suspension-feeding anthozoan Sagartia troglodytes Price. The interactions between these two dominant species are discussed with respect to food availability and competition for food. The density of L. conchilega in this area amounted to 20,000 individuals/m 2 (= 1090 g dry meat wt), and the density of s. troglodytes to 700 individuals/m 2 (= 108 g dry meat wt). The highest density of s. troglodytes (1010 individuals/m 2 ), however, was found in the adjacent sand-coral area which has been included in the present investigations. These high population densities may be maintained by strong tidal currents (up to 1 m/sec) supplying a high energy input of (1) primary benthic production (diatoms) from large tidal flats surrounding 2/3 of the research area, and of (2) precipitated planktonic organisms from the open sea. From the high population densities of L. conchilega observed (grazing area: 0.5 cm 2 /animal), it is unlikely that L. conchilega engages solely in surface-deposit-feeding. Laboratory experiments revealed that in addition to surface-deposit-feeding, suspension-feeding plays a very important role in the nutrition of this polychaete. The suspension-feeding experiments showed that the amount of food ingested, expressed in percentages of body wt (dry tissue wt), increases from 3.9 to 35.7% with decreasing body size. Such values agree well with those obtained for highly specialized obligatory filter-feeders. Thus, the final explanation of the high population density is based on the high amounts of suspended matter and the ability of L. conchilega to utilize alternative sources of food.