Description of planktonic polychaete larvae from Terre Adelie and the RossSea (Antarctica)

An analysis was carried out on 51 samples from 32 stations, obtained during the I.C.O.T.A, cruise between 18 January 1996 and 7 February 1996 in the P ointe Geologie Archipelago, Terre Adelie, and on samples obtained by 2 sedi ment traps deployed in the Ross Sea, within the framework of the Italian C. L.I.M.A. Project. These samples showed the unexpected presence of numerous larvae of benthic marine invertebrates. In addition, larvae from the Ross S ea were examined. Seven phyla with complex life-cycles and at least 18 spec ies of benthic polychaetes were represented. Morphological descriptions by scanning electron microscopy of the most frequent larvae and identification of larval types are provided. Descriptions from the literature of larvae c ollected in the Antarctic Peninsula were used for comparison. Morphological descriptions do not always lead to identification at the species level; ho wever, these descriptions are indispensable for establishing the geographic distribution of larvae. It has been demonstrated that indirect identificat ion methods relying on the premise that the benthic fauna is entirely known and that sampled larvae belong only to species already known through their benthic adult stage may lead to obvious absurdities. As an ecological cons equence, Thorson's rule, according to which indirect development should not be represented and direct development should be dominant at high latitudes , is not supported by our data. A short comparison of the local reproductiv e pattern with a subantarctic area, the Kerguelen Archipelago, strongly sug gests that the absence of planktonic development in this area cannot be exp lained by Thorson's rule. This rule has been invalidated in more austral zo nes: the prevalent reproductive pattern in the Kerguelen Archipelago is lin ked to the very marked advective strength of water flow.