Mesoscale spatial distribution of chaetognaths along hydrographic gradients in the South Scotia Sea (Antarctica)

Mesoscale distribution of chaetognaths in the South Scotia Sea was studied in January 1994. Three transects lice margin to Elephant Island, (ice margi n to the Weddell-Scotia Confluence, and the Drake Passage) and a station gr id in the East Bransfield Strait were laid out, seeking the greatest possib le heterogeneity in hydrographic conditions. Six species were collected, wi th the most abundant species, Eukrohnia hamata, accounting for 83% of the t otal number of individuals, followed by Sagitta gazellae (9.7%). High spati al variability was observed both along the transects and over the mesoscale station grid. The station grid allowed two assemblages to be distinguished on the basis of species abundance and demographic population structure. Bo th assemblages were distributed through areas with distinct hydrographic ch aracteristics. Use of a smaller sampling scale and a more detailed definiti on of development stages than in earlier studies revealed a higher level of spatial heterogeneity than previously suggested for chaetognaths in the So uthern Ocean.