CLEARANCE OF PICOPLANKTON-SIZED PARTICLES AND FORMATION OF RAPIDLY SINKING AGGREGATES BY THE PTEROPOD, LIMACINA-RETROVERSA

Findings from experiments showed that the web-feeding euthecosomatous pteropod, Limacina retroversa, can produce rapidly sinking, mucous agg regates. It is suggested that, by adhesion, these aggregates scavenged picoplankton-sized particles, which were thus effectively cleared fro m the medium. In contrast, Calanus finmarchicus was not able to clear these particles in our experiments. Sedimentation velocities of 10 agg regates measured in vivo were up to 1000 m day(-1), with an average of similar to 300 m day(-1) (not including two aggregates with neutral b uoyancy). Mean velocities measured for feces of C. finmarchicus, Calan us hyperboreus and Thysanoessa sp. were considerably lower. We suggest that the sedimentation of L. retroversa aggregates was the source of mucous flocs collected in sediment traps (Bathmann et al., Deep-Sea Re s., 38, 1341-1360, 1991) and at the sea floor at 1200 m depth in the s outhern Norwegian Sea. This process may be an important mediator of se dimentation to the deep sea, when these pteropods are present in surfa ce waters in large abundance.