Biology of the Southern Ocean tunicate Salpa thompsoni: latitudinal variability in demography and life cycle

Evgeny A. Pakhomov^1,2

¹Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC, V6T 1Z4, Canada. E-mail: epakhomov@eos.ubc.ca

²Department of Zoology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa

Abstract

The pelagic tunicate Salpa thompsoni is recognized as one of the most important metazoan filter feeders of the Southern Ocean. Under specific conditions, this species is known to undergo an explosive population development out competing other zooplankton species and dramatically influencing the regional downward biogenic carbon flux. Despite S. thompsoni is well adapted to an unproductive, low Antarctic (45-60°S) oceanic realm, it has been repeatedly sighted in the areas previously occupied by the Antarctic krill Euphausia superba. This postulates that the southward shift in the salp distribution over the last half a century in the Southern Ocean might have occurred. In the light of possible climate change, it is critical to understand changes in the salp life cycle if modelers aim to assess the salp contribution to the Southern Ocean biological pump. Expending southward, salp populations could be exposed to the lower than the species tolerance lever water temperatures, which may negatively impact their developmental rates. The research investigating S. thompsoni development dynamics over the wide geographical range indicates that the southward expansion of salps may be associated with the dramatic decrease in their ability to complete their life cycle at high latitudes. Furthermore, elevated particle concentrations, which are relatively normal within the Marginal Ice Zone, may lead salp populations to a collapse. Based on the date set collected between 1993 and 2005, the paper will summarize latitudinal changes in the biology of S. thompsoni.

STATUS UPDATE:
Title and abstract received on 06/06/05.