Experimental Studies of the Survival of Zooplankton: Effects of Net Capture and Artificial Control of Population Densities

摘要

Field and laboratory experiments were performed to determine the effects of capture, transportation and various conditions of crowding in an artificial environment on the survival of zooplanktonic organisms. Mortality due to net capture was estimated to be 36 percent. Results indicate that this mortality can be significantly reduced by (1) using a net with a large mouth diameter (e.g., 1 meter), (2) restricting duration of each net tow to 4-5 minutes, and (3) towing at speeds not exceeding 3 knots. Experimental data suggest that a concentration equivalent to 18.6 x 10 to the 7th power per cu m is highly detrimental to their survival but at concentrations equivalent to 2, 4, and 6 10 to the 6th power/cu m the ability of the zooplankton to survive is good and appears to be independent of concentration. At a concentration of 10 to the 4th power/m3 survival decreases only slightly over an 8-day period. As was expected, between-sample variability was relatively high. The data suggest that this variability can be reduced by (1) judicious choice of the sampling site and time of year (2) conducting all net towing at the same speed, in the same direction and at the same depth and (3) when samples are collected on different days they should be taken on the same stage of the tide.