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The Chaetognatha Community of the Agulhas Current: Its Structure and Related Properties
Author(s) -
Stone James H.
Publication year - 1969
Publication title -
ecological monographs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.254
H-Index - 156
eISSN - 1557-7015
pISSN - 0012-9615
DOI - 10.2307/1942355
Subject(s) - hydrography , abundance (ecology) , ecology , oceanography , community structure , geography , group (periodic table) , zooplankton , biology , geology , chemistry , organic chemistry
An objective technique was used to identify and study related groups of chaetognath species from the Southwest Indian Ocean off the coast of the Republic of South Africa. Groups or community—type data agreed with, corroborated, and extended the scope of data on single species, multiple species and hydrographic conditions. The most representative groups were from the data of the N70V—nets which formed 3 groups. The 1st (or main) group was composed of 9 species and was distributed as a unit almost solely in the upper 200 meters of oceanic waters, and occurred in neritic waters only when > 1 to 2 species were absent. This agrees with and corroborates individual species data as each was, according to its distribution and abundance, a resident of the general ocean and each showed, except 3 species found predominantly in deeper waters, a positive correlation with the flow—pattern of the Agulhas current. The 2nd (or associate) group of 3 species was found 61% of the time at mixed—water stations, the best of these being located along a line where mixing between neritic waters and the Agulhas current was most likely to occur. Hydrographic data gave no indication of the latter. The 3rd group was made up of 1 oceanic— species which was distinctive by virtue of its vertical distribution; it was a mesoplanktonic beast, inhabiting water >200 m in depth. Species fecundity correlated quite well with each group and its distribution, in that neritic individuals of only one species of the 1st (main) group contained significantly more eggs than corresponding oceanic individuals whereas neritic individuals of all 3 species of the 2nd (associate) group contained significantly more eggs than corresponding oceanic individuals. This evidence suggests that the species of each group were reacting similarly to their environment and that fecundity is a suitable index to hydrographic conditions. Despite the close similarity of chaetognath species in regard to their habitats and niches considerable overlap existed among the species as a result of differences in their horizontal and vertical distributions, in their abundances, in their size relationships, in food diversity which apparently allows for some specialization in feeding but not in a rigid manner, and finally in structural aspects of the food chain itself as 2 of the larger species appeared to function as 2nd—order carnivores.