Oceanographers traditionally use plankton nets to quantify zooplankton population characteristics. In the last decade new approaches using in situ (i.e. under natural conditions) video have demonstrated that new and affordable technology would allow biologists to quickly assess zooplankton vertical and horizontal distributions and abundance. These techniques would, in turn, speed up the process between sample collection and analysis, as traditional methods require long hours of manual sorting of plankton samples and identification of plankton species. Specifically, a digital imaging system would allow scientists to record digitally onto a computer, which could process the data in real-time via image-recognition software. Moreover, in situ imaging would enable very high resolution sampling, and, therefore, mapping of the horizontal and vertical distribution of zooplankters as well as provide in situ realizations of their natural behaviors. Nets generally provide dead or dying individuals that are often hard to recognize due to net-inflicted damage. To date, however, imaging systems have been limited in the volume of water being sampled, thereby limiting the utility to quantifying highly abundant, small zooplankton like copepods, but not ichthyoplankton.
With the recent advances in digital imaging and data storage technologies, a very high-resolution imaging system can be assembled for use on small towed, undulating vehicles. Combined with special lighting techniques, large volumes of water can be imaged at very high resolution. The system proposed by the PIs is composed of a very high resolution monochrome line scan digital camera (8000 pixels @ 18,600 scans per second) facing a laser-illumination device which creates a shadow image of any organism passing in front of the field of view of the instrument. The images gathered are transferred to an onboard computer which processes the images in real-time to select Regions of Interest (ROI) then stored onto a high throughput disc array. The whole unit can be mounted onto a small towed platform enabling an undulating motion (i.e. yoyo) for detailed vertical profiling of the water column as it is towed behind the ship.
This system will have major impact on ichthyoplankton studies. Besides reducing costs associated with the labor of sample processing, this instrument would enable major advances in our knowledge of the processes influencing the distribution of mesoplankton, as well as provide insight to their natural behavior and interactions with their environment. Increased spatial and vertical resolution would nearly match that available with other means of environmental sampling (e.g. CTD, Fluorometry, ADCP). Utilizing this system in areas of high frontal activity could resolve hypotheses concerning frontal dynamics with unprecedented clarity. Examination of food distribution and trophic impacts of larval fish will be enhanced. Tracking eggs and larvae from specific spawning events would be possible with this system. Finally, where biological specimens are required, this camera system could easily be attached to the net frame to take concurrent digital and specimen samples.
