TH-234 AND PB-210 EVIDENCE FOR RAPID INGESTION OF SETTLING PARTICLES BY MOBILE EPIBENTHIC MEGAFAUNA IN THE ABYSSAL NE PACIFIC

Particle-scavenged Th-234 and Pb-210 can be used to trace the fate of particulate matter reaching the deep-sea floor. We used this technique to demonstrate rapid ingestion of particles arriving at the sea floor (at a depth of 4,100 m) by mobile epibenthic holothuroids (Abyssocucu mis abyssorum and Oneirophanta mutabilis). Excess Th-234 and Pb-210 ac tivities of sediment trap material, detrital aggregates from the sea f loor, and animal gut contents all were similar while activities of sur face sediments (top 0-5 mm) were considerably lower. A simple calculat ion using the excess Pb-210 concentration of two potential food source s, sediment trap material and surface sediments, shows that similar to 91% of gut content material of A. abyssorum must have come from mater ial similar to that found in the sediment trap cups. By setting the se diment trap material as age 0, apparent ages of <0-20 d, >100 d, and 1 2-13 d were estimated for the aggregates, surface sediments, and A. ab yssorum guts, respectively. The population of A. abyssorum at this sit e could potentially process 0.2-4% of the vertical mass flux (m(-2) d( -1)) during the high particle flux period between June and October 199 4. The percentage of vertical flux processed could be substantially gr eater when all of the mobile epibenthic megafauna species are consider ed.