INFLUENCE OF THE CAPE COD CANAL ON THE HYDROGRAPHY AND ON THE COPEPODS IN BUZZARDS BAY AND CAPE COD BAY, MASSACHUSETTS. I. HYDROGRAPHY AND DISTRIBUTION OF COPEPODS1

Abstract

Seventeen hydrographic (temperature and salinity) surveys and plankton collections were made from June 1959 to May 1961. In the summer, there is a thermocline in both Buzzards Bay and Cape Cod Bay, with complete mixing of the water in the canal itself. With a westerly tidal flow, the colder water of Cape Cod Bay enters the canal but scarcely penetrates as far as the northern end of Buzzards Bay. When the tide runs to the east, the warmer water from Buzzards Bay moves toward Cape Cod Bay but does not extend far out into it. In winter, horizontal and vertical temperature differences almost entirely disappear throughout the area. In general, a relatively high salinity is found in Cape Cod Bay and at the southern stations in Buzzards Bay, with less saline “canal” water separating them.Calanus finmarchicus, an inhabitant of Cape Cod Bay, does not propagate in Buzzards Bay. Since this species is abundant between 4 and 9C and is scarce above 18 or below 3C, the high temperature in Buzzards Bay is presumably one of the important factors limiting its distribution. Temperatures above 20C appear to be harmful to Pseudocalanus minutus, since it disappears from the warm water of Buzzards Bay in summer. Likewise, Acartia clausi disappears completely from Buzzards Bay in summer and is scarce there in early fall, since temperatures above 18C are probably unfavorable. On the contrary, Labidocera aestiva is found abundantly only in Buzzards Bay at temperatures above 20C, but it is scarce at lower temperatures. Acartia tonsa occurs throughout the year in Buzzards Bay, but it is absent from Cape Cod Bay in winter. The temperature‐salinity characteristics indicate that temperatures of around 20C are more favorable to A. tonsa than are lower ones. Pseudodiaptomus coronatus is limited to the less saline “canal” water throughout the year. Hence, salinity may chiefly restrict its distribution. The length‐distribution analyses of A. tonsa and A. clausi suggest that both temperature and food supply are important in determining their size variations. Thus, temperature, salinity, and the amount of food available seem to be environmental factors important to the species selected for study. Laboratory experiments should clarify these relationships.