Salp-falls in the Tasman Sea: A major food input to deep-sea benthos

Abstract

Large, fast-sinking carcasses (food-falls) are an important source of nutrition to deepsea benthic communities. In 2007 and 2009, mass depositions of the salp Thetys vagina were observed on the Tasman Sea floor between 200 and 2500 m depth, where benthic crustaceans were observed feeding on them. Analysis of a long-term (1981 to 2011) trawl survey database determined that salp biomass (wet weight, WW) in the eastern Tasman Sea regularly exceeds 100 t km-3 yr-1, with biomasses as high as 734 t km-3 recorded in a single trawl. With fast sinking rates, salp fluxes to the seafloor occur year-round. Salps, like jellyfish, have been considered to be of low nutritional value; however, biochemical analyses revealed that T. vagina has a carbon (31% dry weight, DW) and energy (11.00 kJ g-1 DW) content more similar to that of phytoplankton blooms, copepods and fish than to that of jellyfish, with which they are often grouped. The deposition of the mean yearly biomass (4.81 t km-2 WW) of salps recorded from the trawl database in the Tasman Sea represents a 330% increase to the carbon input normally estimated for this region. Given their abundance, rapid export to the seabed and high nutritional value, salp carcasses are likely to be a significant input of carbon to benthic food webs, which, until now, has been largely overlooked. © 2013 The authors.