GIANT AGGREGATES - IMPORTANCE AS MICROBIAL CENTERS AND AGENTS OF MATERIAL FLUX IN THE MESOPELAGIC ZONE

By using a remotely operated vehicle (ROV), we studied large mucous ag gregates produced by the larvacean Bathochordaeus in Monterey Bay, Cal ifornia. These fragile structures or ''houses,'' cannot be sampled by typical water or net collecting devices, and Likely represent a class of cosmopolitan, widely spaced aggregates in subsurface waters. ROV sa mples allowed us to determine the contribution of the aggregate-associ ated communities to populations of microorganisms at depths of 100-500 m. Because the giant houses only average similar to 1 per 100 m(3), t hey harbor <1% of the microorganisms in the water, although they are l ocally enriched. However, once abandoned, houses may play a significan t role in transporting materials and organisms to depth. Flux calculat ions indicate they may seasonally account for 11-100% of some classes of sinking materials at 500 m. These calculations are based on house-f lux contributions predicted from house age (estimated), house abundanc e (ROV measured), and particle flux (measured by a nearby sediment tra p). Based on our ROV observations of spatial and temporal characterist ics of the giant aggregates, we calculate the probability that sedimen t traps collect the correct number of sinking aggregates. Our results suggest that rare particles, such as large aggregates and some sarcodi nes and pteropods, may be undersampled by commonly used, small sedimen t traps. Furthermore, the predictably infrequent capture of such compa ratively rare particles can lead to erroneous interpretations of tempo ral or spatial patterns in the flux of material through the upper ocea n.