Sensor Technology for Zooplankton Assessment

The composition and structure of marine food webs and it's variation in space and time influence the quality and quantity of carbon exported from surface water, the concentration of inorganic nutrients, and the elemental ratios of particulate and dissolved pools in the ocean. Marine phytoplankton, microzooplankton and larger zooplankton important to the biological pump, range over several orders of magnitude in size, occur over widely varying vertical and horizontal scales, exhibit different behaviors (e.g., vertical migration), and may occur seasonally or episodically. Consequently, assessing the efficiency and variability of the biological pump remains a major challenge. Two different sensor systems used to assess the abundance and distribution of marine biota will be described. The first approach uses a split-beam digital echo sounder system and the second approach uses a high-speed digital line scan imaging system. The merits, limitations, and recent developments of these systems will be presented. Although hardware and software used to assess marine biota have improved significantly during the last few decades, researchers still face serious technical issues in relating the detected image or signal to a biologically useful measure. Recommendations from a recent workshop on sensor technology are discussed.