J. Donnelly1, J.J. Torres1, T.T. Sutton1, C. Simoniello1, M. Grigsby1, J. Bellucci1, S. Burghart1, and T. Bailey2
1College of Marine Science, USF, 140 Seventh Avenue South,
St. Petersburg, FL 33701
2Indian River Community College, Mueller Campus, 6155 College Lane, Vero Beach, FL 32966
The fish fauna of the Southern Ocean is comprised of two elements, an oceanic fauna comprised of midwater fish families found throughout the world ocean and an endemic fauna associated with the shelf and slope of the continent and outlying islands. The pelagic fish fauna of the shelf regions is of considerable interest. Apex predators such as seals and penguins feed in the upper 500 m and include fishes in their diet. In addition, fishes are potentially important predators of krill and zooplankton. The 500 m average depth of the water column associated with the Antarctic continental shelf would not exclude the oceanic species from being present based on depth alone, so on an a priori basis a mix of oceanic and endemic species would be expected, particularly at the shelf break. We examined the pelagic fish communities of the eastern Ross Sea, including the continental shelf region, and compared them to those found on the western Antarctic Peninsula (WAP) shelf. Thirty six midwater trawls were taken in the Ross Sea, including 22 MOCNESS tows, and thirty two MOCNESS trawls were taken on the WAP shelf. We found a profound difference between the two systems. Representatives of the classical midwater fauna, e.g., the myctophids and bathylagids were present in both systems seaward of the shelf break, but there the resemblance ended. The midwater families were found throughout the study region on the WAP shelf, including the fjord regions near the continent. In contrast, the midwater families stopped abruptly at the shelf break in the eastern Ross Sea. The most obvious difference between the two systems is the temperature structure of the water column, which is uniformly cold (approximately -2oC) from surface to bottom on the Ross Sea shelf and warm (approximately 1oC) on the WAP shelf. It is tempting to conclude that temperature is excluding the oceanic species, but other factors are likely to play an important role as well. What is clear is that the character of the pelagic fish fauna between the two regions is quite different.