Measurements of plankton distribution in the ocean using submersible holography

A submersible holography system for in situ recordings of the spatial distribution of plankton has been developed and deployed. The system utilizes a ruby laser with an in-line recording configuration and has a sample volume of 732 ml. The reconstructed images have a resolution ranging from 10-20 mu m for spherical particles and 3 mu m for linear particles that lie within 100 mm from the film. Reconstructed volumes from holograms recorded during two recent deployments in the Strait of Georgia are scanned to obtain focused images of the particles, their position, size and orientation. The particles are also classified to several groups based on their morphological characteristics. The holograms include a set recorded during a 15 min vertical transect of the top 30 m of the water column. Along with the holograms, the data include records of depth, temperature, salinity, dissolved oxygen and optical transmissivity. The results show substantial variations in population makeup between layers spaced a short distance apart, particle concentration maxima at and near a pycnocline and evidence of zooplankton migration. A predominant horizontal diatom orientation is indicated in the region of peak diatom concentration. Individual holograms show clustering within different classes of plankton.