Graduation Year

2009

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Marine Science

Major Professor

Joseph Torres, Ph.D.

Keywords

C: N-cycling, Trichodesmium, Macrosetella, Oncaea, Microzooplankton

Abstract

Zooplankton were sampled on a monthly basis at the Bermuda Atlantic Time-series Study (BATS) site from January 1995 to December 1999. Samples were collected using a 1-m², 200 µm mesh net. The net sampled the water column in an oblique manner from the surface to a mean depth of 200 m. One day and one night tow from each cruise was examined microscopically to determine the community structure of the non-calanoid copepods. In addition, a three year set of nighttime samples were examined taken by 0.5-m², 20 and 35 µm mesh nets (1995-1996 and 1997, respectively) towed obliquely to 150 m. The dominant orders in terms of overall abundance were the Cyclopoida and Poecilostomatoida. The cyclopoid genus, Oithona, was most abundant followed by the Poecilostomatoid family, Oncaeidae, and the genera Farranula and Corycaeus. Harpacticoids, although common, were about an order of magnitude less abundant and were dominated by Macrosetella gracilis.

Representatives of the Mormonilloida and Siphonostomatoida also were frequently encountered, although in much lower numbers. Overall, pronounced seasonal signals were noted; highest abundances occurred during spring and lowest during winter. However, abundance of some groups peaked either in the fall or winter, with lowest abundance in spring or summer. Miraciid copepods are estimated to consume an overall average of 359 µg C m?² d?¹ and regenerate 55 µg N m?² d?¹ derived from Trichodesmium at BATS. Highest grazing and regeneration rates were found in late summer through fall and early winter and lowest in spring and early summer. The ecological consequences of miraciid copepod feeding on Trichodesmium are discussed. The 20-35 µm net samples revealed an astonishing abundance of non-copepod species, some totally missed and others woefully under-sampled by the 200 µm net.

At least four species of oncaeid copepods and the harpacticoid copepod Microsetella norvegica were found in abundances that were more than an order of magnitude higher than the corresponding numbers of non-calanoid copepods sampled by the 200 µm net. The role of all non-calanoid copepods, from both net systems, in C and N dynamics at BATS is analyzed and discussed along with the sex-ratios of most identified species.

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