LARVAL POLYCHAETES ARE STRONGLY ASSOCIATED WITH MARINE SNOW

The association of larval polychaetes with marine snow was investigate d (1) with SCUBA to sample marine snow in the field and (2) in laborat ory experiments. The field sampling took place in the Atlantic Ocean o ff Charleston, South Carolina, USA (3 sample dates) and in the Pacific Ocean at 2 locations around the San Juan Islands, Washington, USA (7 sample dates). On all of the sample dates marine snow was present and abundant (range 1 to 63 agg. l(-1)). Larval polychaetes were significa ntly concentrated on aggregates on 7 of the 10 sample dates. Larval po lychaetes from 12 families were present in the plankton samples of whi ch 10 families were found associated with aggregates. On average, 16% (SD = 22%) of all larval polychaetes were on aggregates. Precompetent and competent larval polychaetes made up 84 and 16% respectively of th e larval polkchaetes in the plankton. On average 20% of all precompete nt polychaete larvae were on aggregates. In contrast, competent polych aete larvae were strongly associated with aggregates with 80% of the c ompetent larval polychaetes on aggregates. Laboratory experiments usin g 4 polychaete species and laboratory-made marine snow also found that larval polychaetes were concentrated on aggregates. In a vertical flu me, observations were made on the behavior of larval polychaetes follo wing contact with aggregates. Upon contacting marine snow, larval poly chaetes crawled into or over the surface of aggregates for several min utes before swimming away. These field and laboratory observations sug gest that a precompetent polychaete larva might spend about 5 h d(-1) visiting aggregates and that during a day it may visit about 90 aggreg ates. Competent larval polychaetes may spend >19 h d(-1) on aggregates . Polychaete larvae visiting or residing on aggregates may be feeding on the aggregate microbial community. Further, the vertical flux and, perhaps, benthic deposition of larvae residing in aggregates is due to the sinking of the marine snow. Clearly, marine snow is an important component of the environment for many types of polychaete larvae and a daptations to Life in aggregates may have played a role in the evoluti on of polychaete larval traits.