Never Trust a Copepod-Some Observations on Their Behavior in the Canadian Arctic

Considerable variation has been observed in behavior of copepod populations in the high arctic in different years, particularly with respect to their vertical distribution, responses to light and utilization of food resources. Pseudocalanus frequently aggregated in dense concentrations under fast ice in May 1984 and their distribution seemed to be regulated largely by speed and direction of tidal currents. In subsequent years, dense, near-ice concentrations have been rare and transient. During the spring of 1986, six 32-h studies of copepod distribution under the ice and deeper in the water column were carried out at weekly intervals to sample both spring- and neap-tidal conditions. Simultaneous measurements of current speed and direction were also made. There was no obvious relationship between their behavior and tide, but unlike previous years, there was regular diel migration into the near ice zone in the evening regardless of current speed. Their response to food was also less dramatic in 1986 compared with 1984, as shown by lower short-term feeding rates, and accumulations of gut pigment. Nearby open water and higher concentrations of phytoplankton in the water column in the spring of 1986 are probably contributing factors to observed behavioral differences.