ROLE OF HALICRYPTUS-SPINULOSUS (PRIAPULIDA) IN STRUCTURING MEIOFAUNA AND SETTLING MACROFAUNA

Priapulids are potentially important in structuring soft-bottom commun ities in temperate and arctic regions, and this study is a first attem pt to evaluate their importance in zoobenthic communities. Halicryptus spinulosus is an important component of the zoobenthos of the norther n Baltic Sea. It is competitive in harsh environmental conditions as i t can withstand hypoxia and hydrogen sulphide. The natural food select ion of H. spinulosus consists mainly of detritus (62 to 68 % of the st omach contents) and 10 infaunal categories (the amphipod A Monoporeia affinis and other crustaceans being most frequent). The effects of H. spinulosus on both meio- and macrofauna were studied experimentally. S ignificant negative effects were found for both meiofauna (nematodes a nd total abundance) and macrofauna (Manayunkia aestuarina, oligochaete s and total abundance). The effects on recruitment (mainly larval Maco ma balthica) were also significant. In the field, total abundance and the number of nematodes were also significantly reduced by the presenc e of H. spinulosus. The effects of H. spinulosus on other fauna is sug gested to be a consequence of predation in combination with disturbanc e.