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Checkley, DM, Davis RE, Herman AW, Jackson GA, Beanlands B, Regier LA.  2008.  Assessing plankton and other particles in situ with the SOLOPC. Limnology and Oceanography. 53:2123-2136.   10.4319/lo.2008.53.5_part_2.2123   AbstractWebsite

We combined a Sounding Oceanographic Lagrangian Observer float with a Laser Optical Plankton Counter (LOPC) and a fluorometer to make an autonomous biological profiler, the SOLOPC. The instrument senses plankton and other particles over a size range of 100 mm to 1 cm in profiles to 300 m in depth and sends data ashore via satellite. Objects sensed by the LOPC include aggregates and zooplankton, the larger of which can be distinguished from one another by their transparency. We hypothesized that the diel production of particles and their loss by sinking and grazing are reflected in the change of the particle distribution. We present data from four deployments of the SOLOPC off California. Particle volume was maximal at the base of the surface mixed layer and correlated with chlorophyll a fluorescence. In a 3-d deployment in 2005, particle volume was greatest in the early evening and smallest in the morning, and average particle size increased with depth. Eigenvector analysis of the particle volume distribution as a function of diameter for each of the deployments yielded size peaks characteristic of planktonic crustaceans. Ship-based measurements showed that the abundance of opaque particles of 1.1-1.7 mm equivalent spherical diameter was positively correlated with copepods of this size and simultaneously collected in nets. This relationship was used with SOLOPC data to estimate the distribution of large copepods, which were most abundant beneath the depth of maximal particle flux, estimated from particle size and published sinking rates. Our data are consistent with a model with diel production of particles and their loss by sinking and grazing.

Checkley, DM, Uye S, Dagg MJ, Mullin MM, Omori M, Onbe T, Zhu MY.  1992.  Diel variation of the zooplankton and its environment at neritic stations in the Inland Sea of Japan and the north-west Gulf of Mexico. Journal of Plankton Research. 14:1-40.   10.1093/plankt/14.1.1   AbstractWebsite

Diel variations in the zooplankton and its environment were investigated at two, contrasting neritic stations. The first (BG-1), in the Inland Sea of Japan, was mixed and eutrophic, while the second (GM-1), in the north-west Gulf of Mexico, was stratified and oligotrophic. Intensive studies were conducted at each station in late summer for 2-3 days. Dissolved nutrients and the particulate matter were evenly distributed in time and space at BG-1, but were variable, and often maximal at depth in a nepheloid layer, at GM-1. For each station, approximately 20 categories of zooplankton were enumerated in samples collected with a plankton pump and retained on approximately 100-mu-m mesh filters, In general, the zooplankton at BG-1 exhibited little diel variation in abundance and distribution. By contrast, most types of zooplankton at GM-1 performed diel vertical migrations, though primarily within the lower half of the water column between the thermocline and nepheloid layer. Significantly, similar taxa and stages did not always behave similarly in these two, differing environments, nor did the zooplankton at GM-1 tend to aggregate at the depths of maximal particle abundance or primary productivity. We suggest that studies of diel variation of the distribution and abundance of the zooplankton often require more intense sampling, in time and space, in environments which are stratified rather than mixed.