EFFECT OF THE SPIONID POLYCHAETE BOCCARDIA-SYRTIS ON THE DISTRIBUTIONAND SURVIVAL OF JUVENILE MACOMONA-LILIANA (BIVALVIA, TELLINACEA)

The tellinid bivalve Macomona liliana (Iredale) occurs at relatively l ow densities on a sandbank (Te Tau bank) in Manukau Harbour, New Zeala nd. Te Tau bank is dominated by polychaetes, including the tube-buildi ng spionid Boccardia syrtis (Rainer). Juvenile M. liliana are known to disperse as post-settlement juveniles by byssus-drifting. Laboratory experiments were conducted to assess whether the low abundance of M. l iliana on Te Tau bank was due to the presence of B. syrtis, or to some reaction to the sediment itself. In particular, we examined how juven ile M. liliana survived after exposure to Te Tau bank sediments with a nd without the spionid tube-mat for 1 mo in still-water conditions, an d how they responded when given a choice of different sediment/tube-ma t treatments in moving water. Juvenile hi. liliana did not appear to h ave a strong aversion to settling and burrowing: in sediments from Te Tau bank. Sediments without the tube-mat did not adversely affect the survivorship of the bivalves, but survival was significantly lower amo ngst the B. syrtis tube-mat. In the presence of a current, the juvenil e bivalves settled in Te Tau bank sediments without a tube-mat, but av oided settling amongst live B. syrtis. An artificial tube-mat enhanced settlement. Avoidance of live B. syrtis appears to be an avoidance of the worms themselves rather than a response to the physical presence of their tubes.