| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1982 Zooplankton samples were collected with the MOCNESS (Multiple Opening/ Closing Net and Environmental Sensing System) on six cruises in the western North Atlantic Ocean during the period from August 1975 to November 1977 as part of the study of the biology, physics, and chemistry of Gulf Stream cold core rings. The physical, chemical and biological properties of the Slope Water to the North of the Gulf Stream differ substantially from the properties of the Northern Sargasso Sea to the south. The purpose of this thesis was to identify the horizontal, vertical and seasonal abundance patterns of chaetognaths in this region and to relate these patterns to environmental conditions. Twenty one chaetognath species were identified, of which eighteen were abundant enough for analysis of the spatial and temporal abundance patterns. The most important sources of sampling error in this study were mesh selection and avoidance, which bias the abundance estimates, and patchiness and subsampling, which add variability to the abundance estimates. The 0.333 mm mesh of the MOCNESS does not appear to sample individuals of any of the species less than 6 mm in length very well. Avoidance appears to be a problem only for the larger individuals (>20 mm) of the larger species. Variability due to small scale patchiness was less for this study than for many previous studies, and this may have been due either to the location of the tows in presumably less variable open ocean regions or to the increased volume of water filtered relative to previous studies. Subsampling with the Folsom plankton sample splitter introduced more variability than predicted by the binomial distribution, and for some species the subsampling variability was greater than that due to patchiness. In spite of these sources of variability, significant spatial and temporal ...
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