Annual Variations in Length of Copepods in the Sargasso Sea off Bermuda

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Abstract
Measurements of cephalothorax length were made on 5 spp. of oceanic copepods from 30 samples collected from Jan. 1958 through Aug. 1959 by oblique hauls from 500 m to the surface with a 3/4-m plankton net with No. 2 mesh at Station "S" in approximately 1550 fathoms of water in the NW Sargasso Sea. Pleuromamma piseki, P. abdominalis and P. xiphias all showed similar seasonal variations in length, but the latter occurred infrequently. Lengths of P. piseki and P. abdominalis followed the phytoplankton cycle, being maximal at times of major flowering. Simple and partial correlation coefficients, calculated between the mean lengths of these 2 spp. and the mean surface temperatures and mean chlorophyll a of the month preceding each measurement, showed that the quantity of phytoplankton present during development was an important factor related to the length variations of these spp. (r 0.866 for P. abdominalis, 0.795 for P. piseki), but there was no significant relation between lengths and temperature. Females of Lucicutia flavicornis and Haloptilus longicornis did not exhibit an annual cycle of length variations similar to that of the Pleuromamma spp., although considerable variations in length were noted, and no correlation was found between the lengths and either the temperature or the chlorophyll. These spp. may feed selectively on some unmeasured fraction of the plankton, such as the nannoplankton, or on particulate organic matter.