TEMPORAL PERSISTENCE OF COPEPOD SPECIES GROUPS IN THE GULF-STREAM

The distributions of 22 copepod types (18 species and the copepodite stage V of four of the species) across a transect of the Gulf Stream near Cape Hatteras, NC, sampled in May 1983 with a MOCNESS, were analyzed and compared with the distributions found on a similar transect sampled in September 1982. Copepod species distributions followed physical characteristics closely and were similar for the two sampling times. Species were found in discrete environments, and species distributions changed across the Stream with changing physical properties. Most of the copepod types (18) were placed into four distributional groups using recurrent group analysis, cluster analysis, and examination of species distributions. The September and May transects were analyzed independently, yet virtually the same groups resulted, implying that these species groups are consistent over time and suggesting that a persistent community structure may be a general feature of the Gulf Stream. The distributions of the species groups were associated with physical properties across the Gulf Stream, with little overlap between group environments. In both September and May cross-stream trends in integrated abundances of two of the species groups followed the patterns expected if continuous cross-stream mixing processes had occurred. Cold-water species had higher abundances at the northern stations, with abundances decreasing across the Stream to the south. Warm-water species abundances followed the opposite pattern (high abundances on the Sargasso Sea side of the Stream and lower abundances on the northern side). Certain species or species groups may be reliable indicators of water type and could be used as tracers of water mass mixing across the Gulf Stream.