Accuracy Accommodation Of Optical Plankton Counter And Its Application In Measuring The Size Distribution Characters Of Several Domestic Zooplankton Species

In marine ecological research, it's crucial to observe the composition and biomass of the plankton in an ecosystem, especially for the zooplankton observation.Several methods have been developed for the zooplankton observation, the OPC is one of the successful instruments. Optical Plankton Counter(OPC) is a new type instrument, which capable of counting and sizing zooplankton rapidly, continuously and easily in the larger spatial scales. When the OPC is used synchronously with other sensors as a single deployable instrument package, it can provide reasonably detailed spatial resolution of the interaction between plankton and the physical structure of their habitat. A brief summary on the design principle, research status and advantages of the OPC was described, the current problems and application trends of the OPC was discussed. OPC-1L, the laboratory version of the OPC, can count and size zooplankton rapidly, simply and easily in the lab, and can offer valuable information in a lot of aspects, such as counting single species, describing size distributions and estimating biomass of copepods community. In the OPC usage, the shape of the zooplankton, the density of the sample and the flow passing the counter tube and air bubble occurred in the flute flow all will affect the measure accuracy. In this study, the relationship between the accuracy and the shape of the animal, the relationship between the accuracy and the measure speed and how to prevent the air bubble occurrence were discussed. The bubble can be removed by the modification of the circulation system. Coincidence also can be controlled effectively when sampling speed keep at a certainty scope. Coincidence ratio maintain less than 5% and 2% when Dmax(maximum sampling speed)keep at 11 and 7 ind/s respectively. Through the research of connection between bodily form(L/W) and accuracy, adjusting sampling speed according to bodily form(L/W)of target species will make OPC-1L to achieve 98%number accuracy and 95%ESD( Equivalent Spherical Diameter)mean accuracy. The OPC is now used for the time series research of zooplankton in our laboratory. ESD reflects the size of organism, and different species has different size spectrum. And the size spectrum theory based on the concept of ESD can express the dynamic changes of marine ecosystem and the common structure of marine food web briefly. As a result, it is urgent to determine ESD mean and distribution of dominant species in target sea area while investigating it's characters of structure and alteration. And OPC has overwhelming advantages in determine this parameter. Recurring to OPC-1L, in this paper, we measure four dominant species in different size class, including Euphausia pacifica, Calanus sinicus, Acartia bifilosa and Megalopa larva. Their size spectrums settle the foundation for extracting the information of dominant species in target sea area. It appears that the OPC offers a promising solution to the zooplanktong counting, especially for the long term observation and sample analysis.