Evaluation of in situ Silhouette Photography in Investigations of Estuarine Zooplankton and Ichthyoplankton
Trials of a paired-net towing frame fitted with a submersible 35-mm camera system were conducted in Chesapeake Bay in 1989–1990 to 1) demonstrate the use and efficiency of in situ silhouette photography in studies of estuarine zooplankton and ichthyoplankton; 2) determine the taxonomic potential of in situ silhouette photography in several estuarine habitats; and 3) compare estimates of plankton density from in situ silhouette photographs with concurrent preserved net collections. Time required to split, sort and enumerate plankton in preserved samples was 2–75 h per sample longer than the time required to view and enumerate silhouettes on film. Ninety-four taxa (or different ontogenetic stages of the same taxon) were identified on film. Of these, 55% were classified to genus or species. The camera-net system failed to detect 16 of 31 rare or uncommon categories of zooplankton at one or more stations. Abundance estimates of two gelatinous forms (ctenophores and doliolids) were provided by the camera but these taxa could not be counted or were absent in paired, preserved collections. There were no detectable differences in estimates of abundance provided by the camera and the paired, preserved collection for hydromedusae, polychaete larvae, marine and some freshwater Cladocera, cyprid stages of barnacles, larval stomatopods, caridean and some brachyuran zoeae, megalopae, and fish eggs. Differences in plankton density estimated by the camera and the paired net were significant for some freshwater cladocera, gastropod larvae, some brachyuran zoeae, mysids, and chaetognaths. Statistical results were mixed, depending upon locality, for copepods, naupliar stages of barnacles, and fish larvae. For all categories of planktonic taxa that differed significantly from net collections, in situ photography provided lower density estimates than the net. Underestimation was partly attributed to the poor photographic qualities of some taxa and stalling of plankton along the sides of the camera net.
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Document Type: Research Article
Publication date: 01 May 1993
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