2014 Volume 61 Issue 1 Pages 65-71
An individual zooplankter behaves in response to its environment. If we look closely into the vertical distribution of zooplankton, we can find a species-specific pattern of vertical distribution. In other words, plankton specifically have favorite conditions within their environment. This preference may differ between species and even between developmental stages of a single species. So far, population dynamics of zooplankton have been investigated in both neritic and oceanic waters. The dynamics is attributable to the sum of the fate and behavior of each plankter; therefore, measurement of the vertical and horizontal distributions of zooplankton together with environmental properties should be more fruitful than spatially-averaged measurements. Modern technologies to measure the fine scale vertical distributions of zooplankton are introduced to monitor the spatial distributions and temporal fluctuations of zooplankton. We here target small-sized copepods, which play a pivotal role in aquatic ecosystems, considering their ubiquity in both neritic and oceanic waters. Here we propose two methods to achieve fine scale measurements of zooplankton: a new apparatus that employs bellows to sample plankton; and a digital holographic imaging device. Our devices can detect a range of sizes of targeted planktonic organisms of 300 µm to 1 mm. The detection limit of zooplankton population density is set as low as 1 ind. L-1 The maximum spatial resolution is less than 1 m in our devices.
