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 6 l h - 1 ml - 1 biovolume. Maximum displacement volumes of salps measured were 5.7 l m - 2 in 1986 and 1.6 l 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 C m - 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.