Periodic swarms of the salp Salpa aspera in the Slope Water off the NE United States:: Biovolume, vertical migration, grazing, and vertical flux

Sampling during four summers over a twenty-seven year period has documented dense populations of Salpa aspera in the Slope Water south of New England, northeastern United States. The salps demonstrated a strong pattern of diel vertical migration, moving to depth (mostly 600-800 m) during the day and aggregating in the epipelagic (< 100 m) at night. Filtration rates determined from both gut pigment analysis and direct feeding experiments indicated that both the aggregate and solitary stages filtered water at rates ranging from 0.5 to 61 h(-1) ml(-1) biovolume. Maximum displacement volumes of salps measured were 5.71 m(-2) in 1986 and 1.61 m(-2) in 1993. Depending on the year, the sampled salp populations were calculated to clear between 8 and 74% of the upper 50 m during each 8 h night. Total fecal output for the same populations was estimated to be between 5 and 91 mg Cm-2 night(-1). These results, and other observations, suggest this region is a salp hot spot, with swarms of S. aspera developing seasonally on a frequent basis. (c) 2006 Published by Elsevier Ltd.