On the spatial distribution and nearest neighbor distance between particles in the water column determined from in situ holographic measurements

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Abstract
A film-based holography system was used in conjunction with instrumentation that detected bioluminescent thin layers to record the spatial distribution of zooplankton and their prey in the Gulf of Maine, USA. The holocamera and instruments were mounted on the Johnson Sea Link (JSL) in a setup that minimized the disturbance to the sample volume. More than 143 holograms were automatically scanned to provide focused images of 5000–10 000 particles and their three-dimensional coordinates in each 894 cm3 sample. The reconstructed volumes provided clear images of intermingling copepods species, nauplii, Pseudonitzschia diatoms and particles in the 10 μm–5 mm size range. Spatial analysis of the nearest neighbor distance (NND) of the smallest particles showed a random distribution, but detritus particles showed small-scale clustering in regions below the pycnocline. A detritus maximum, found several meters below the pycnocline, at 20–30 m, was determined to be caused by fecal pellets in various stages of degradation. This region also contained elevated concentrations of calanoids, cyclopoids and harpacticoids. In one third of the cases, the harpacticoids, Aegisthus sp, were attached to detritus.