Defecation by Salpa thompsoni and its contribution to vertical flux in the Southern Ocean
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ORIGINAL PAPER
Defecation by Salpa thompsoni and its contribution to vertical flux in the Southern Ocean Brennan Phillips Æ Patricia Kremer Æ Laurence P. Madin
Received: 24 March 2008 / Accepted: 21 November 2008 / Published online: 16 December 2008 Ó Springer-Verlag 2008
Abstract Measurements of the defecation rate of Salpa thompsoni were made at several stations during two cruises west of the Antarctic Peninsula in 2004 and 2006. Rates were quantified in terms of number of pellets, pigment, carbon and nitrogen for a wide size range of both aggregate and solitary salps. Measured defecation rates were constant over several hours when salps were held at near-surface conditions from which they had been collected. The defecation rate per salp increased with both salp size and the ambient level of particulate organic matter (POM) in the upper water column. The weight-specific defecation rate ranged between 0.5 and 6% day-1 of salp body carbon, depending on the concentration of available particulate matter in the water. Carbon defecation rates were applied to biomass estimates of S. thompsoni to calculate daily carbon defecation rates for the populations sampled during the two cruises. Dense salp populations of over 400 mg C m-2 were calculated to produce about 20 mg C m-2 day-1, comparable to other major sources of vertical flux of organic material in the Southern Ocean. Measured sinking rates for salp fecal pellets indicated that the majority of this organic material could reach deep
Communicated by X. Irigoien. B. Phillips P. Kremer Department of Marine Sciences, University of Connecticut, Groton, CT, USA Present Address: B. Phillips (&) L. P. Madin Oceanographic Systems Laboratory, MS #10, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA e-mail: [email protected]
sediments within a few days, providing a fast and direct pathway for carbon to the deep ocean.
Introduction Salps (subphylum Urochordata, class Thaliacea) are pelagic tunicates found throughout the world’s oceans. Salpa thompsoni is the principal salp species in the Southern Ocean (Foxton 1966; Casareto and Nemoto 1986; Pakhomov et al. 1994). Salps are indiscriminate filter feeders, utilizing a pharyngeal mucus net to capture particles as water is pumped through the body (Madin and Diebel 1998). Therefore, they are assumed to ingest all particulate matter (both living and detrital) small enough to fit through their oral opening and large enough to be retained by the mucus net. This may include particles as small as 1–2 lm (Harbison and McAlister 1979; Kremer and Madin 1992; Bone et al. 2003). Measured ingestion rates of S. thompsoni, expressed as mg C ind.-1 day-1, have been estimated to be higher than any other Antarctic herbivore (Perissinotto and Pakhomov 1998). Salps produce large, dense fecal pellets that are enriched in carbon and nitrogen (as percent dry weight) compared to salp body composition (Andersen 1998). These pellets sink rapidly, and when salps are abundant they may play a significant role in the transport of particu
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