Chaetognath ecology in relation to hydrographic conditions in the Australian sector of the Antarctic Ocean

Abstract

Chaetognath ecology in relation to hydrographic conditions was investigated during austral summer in the Antarctic Ocean with two cruises conducted seven years apart. Time series samples were collected at a total of five stations along 140_E in the region of the Antarctic Divergence (AD). The numerically dominant species was Eukrohnia hamata, averaging over 80% of the collected specimens. This species was most abundant north of the AD where bi-modal distribution was common. No species displayed regular diel vertical migration nor were their vertical distribution restricted by hydrographic clines. Breeding of E. hamata appeared unaffected by water conditions-the same maturity stages were present in similar percentages across the water masses. Vertical segregation of size classes among E. hamata was clearest north of the AD in a more stratified water column. In other locations, the size classes overlapped considerably; this is likely due to physical forcing from mixing water. Feeding activity of E. hamata was lowest within the AD and increased both north and south on the edges of the front. Feeding activity appeared continuous with no recognizable diel pattern. E. hamata containing prey items were smaller north of the AD compared to the south, suggesting two separate populations. The percentage of predators with food in their gut was much larger in this study than previously reported work. Often times nearly 50% of the E. hamata collected had highly digested contents in the posterior of the gut