A. Errhif et al., COMPOSITION AND COMMUNITY STRUCTURE OF PELAGIC COPEPODS IN THE INDIANSECTOR OF THE ANTARCTIC OCEAN DURING THE END OF THE AUSTRAL SUMMER, Polar biology, 17(5), 1997, pp. 418-430
The present paper describes latitudinal and vertical changes in the co
mposition, abundance and diversity of copepods in the Indian sector of
the Antarctic Ocean, during the end of austral summer along a transec
t on 66 degrees 30'E between 43 and 62 degrees S, within three layers
(600-0, 200-0, 100-0 m). Highest copepod densities were noted in the c
entral part of the transect, between the Antarctic Divergence and the
Antarctic Convergence, with a maximum in the Antarctic Divergence zone
, particularly in the upper levels of the water column. A total number
of 80 copepod species were identified over the entire survey area. Th
e south end and the central part of the transect comprised a small num
ber of species. North of the Antarctic Convergence, this number increa
sed markedly with the progressive disappearence of those species chara
cteristic of Antarctic waters and their replacement by temperate and s
ubtropical species. Generally, small copepods, particularly Oithona si
milis, Oithona frigida and Ctenocalanus citer, dominated in numbers in
both Antarctic and sub-Antarctic areas. The contribution of large spe
cies to total copepod numbers was much lower, with Calanus simillimus
in the central part of the transect, Pleuromamma borealis in the subtr
opical zone and Calanus propinquus in the southern part. Correspondenc
e analysis showed a marked latitudinal gradient in population structur
e with four groups of samples and species corresponding to four latitu
dinal zones. Community structure (species richness, relative dominance
index, evenness, Shannon species diversity index) and species abundan
ce patterns (as rank-frequency diagrams) suggested that the maturity a
nd species richness increased gradually from south to north. A low div
ersity index and evenness were observed in the area of the Antarctic D
ivergence, whereas the convergence zone showed high diversity and even
ness. Conversely, the frontal zone showed high diversity and evenness.
Distribution appeared unrelated to chlorophyll concentrations and on
the large scale was related to the hydrologic characteristics.