Composition, abundance and distribution of holoplanktonic polychaetes within the Strait of Magellan (southern America) in austral summer

This study enlarge the knowledge on species composition, distribution and community structure of pelagic polychaetes on the basis of finely stratified spatial sampling representing austral summer conditions in the Strait of Magellan. Zooplankton samples were collected in late austral summer 1995. A total of 56,489 pelagic polychaete specimens were collected. Eight holopelagic polychaete taxa were recorded in addition to Spionidae and Terebellidae larvae and reproductive stolons of Autolytinae. Pelagobia longicirrata (Lopadorhynchidae) was the most abundant species, representing about 96 % (54,092 specimens, 184.6 ind. 100 m-3) of all individuals, followed by Tomopteris planktonis (Tomopteridae) at 3 % (1,725 specimens, 5.9 ind. 100 m-3). The longest measured individuals belonged to T. planktonis, which also showed the largest size range, whereas the smallest individuals belonged to P. longicirrata. Spatial distribution of polychaetes in terms of abundance was not related to bottom depth, but rather the number of taxa was lower in the central part of the Strait. P. longicirrata and T. planktonis were negatively related to chlorophyll a. In addition, the first was negatively related to temperature instead the second was positively affected by salinity. Polychaetes were widely distributed in both epi- and mesopelagic realms, whereas they were almost absent above 80 m depth. Both of the most abundant species were concentrated in the deepest layers sampled (below 100 m) throughout day and night hours without showing any specific migratory behavior.