Madin¹, Laurence P., Erich F. Horgan¹ and Patricia Kremer²

¹Woods Hole Oceanographic Instittution, Woods Hole, MA 02543, E-mail: lmadin@whoi.edu, Tel: 508-289-2739, Fax: 508-457-2134, ²University of Connecticut, Groton, CT

Salp blooms in the Mid Atlantic Bight: the FedEx of flux?

Transport of particulate material from the surface to deeper waters depends to a large extent on ingestion by zooplankton and higher consumers. An efficient biological mechanism to transport such material would be a grazer that feeds rapidly and indiscriminately on a wide range of particles, compacts them into large and rapidly sinking fecal pellets, and accelerates the process by diel migration into the mesopelagic. Ideally they would also leave huge masses of sinking carcasses when the population dies. To be truly effective, such a consumer should occur in high population densities over large areas, and have a life cycle that coincides with spring and summer growth of phytoplankton. In June and September 2002 we mapped dense populations of the salp Salpa aspera in the Mid-Atlantic Bight. Extending from northern Virginia to Bear Seamount, bounded westerly by the shelf break and on the east by the Gulf Stream, the population covered an estimated 100,000 km². At night, salps were in the top 50 m at densities up to 60m^-3. They migrated daily as deep as 800 m. Our measurements showed the population was capable of filtering up to 7% of the water in the top 50 m in 8 h every night, producing 5.5mg Cm^-2 of fecal matter. The fecal pellets sink at about 1000 md^-1. The functional and life history characteristics of salps make them ideal consumers and transporters of particulates to deeper layers of the ocean. Large blooms like this one can locally dominate zooplankton communities and vertical flux.