Pressurizing System for Observation of Marine Zooplankton

Planktonic animals occur from the surface to the sea bottom and they are exposed to hydrostatic pressure throughout their lifetime. A hydrostatic pressure apparatus integrating ideas of past apparatuses was developed to investigate effects of hydrostatic pressure on marine zooplankton. The pressure apparatus system is composed of a peristaltic pump, a pressure chamber, a specimen holder which is placed in the pressure chamber, a temperature-controlled bath, a CCD camera, a monitor and a video-recorder. This hydrostatic pressure apparatus made it possible (1) to incubate at a constant temperature by connecting it with a temperature-controlled bath, (2) to observe live zooplankton through a window, (3) to increase pressure gradually from 1 to 150 atm and (4) to continually record the behavior of specimens by using a CCD camera and a video-recorder. Effects of hydrostatic pressure on the egg of the marine zooplankton, were examined using the newly designed hydrostatic pressure apparatus. The apparatus is practical for experiments using a wide size range of specimens, from eggs to adult size of mesozooplankton (100-10000 mum size range). In present study, egg development time of planktonic copepod was examined; C. sinicus is the dominant zooplankton community in the coastal area of Japan. The egg development time at different experimental pressure conditions (1, 10, 50 and 100 atm) were similar to that at 1 atm. The hatching success of C. sinicus eggs at 1 atm was generally higher than 80 % within the temperature range from 5 to 25degC. At higher pressure conditions of 10, 50 and 100 atm, highly significant decreases in egg hatching success of C. sinicus occurred as pressure increased. Thus, hydrostatic pressure does not inhibit egg development but egg hatching of C. sinicus.