Date of Award

2013

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Department

Interdepartmental Program

First Advisor

David A. Bengtson

Abstract

The Atlantic silverside (Menidia menidia) is one of the numerically most abundant fish species in estuaries along the East Coast of North America, but its ecology during the first two weeks post-hatch has not been described. Therefore ecological investigations into appropriate sampling methods, preferred habitats, feeding ecology and growth of these larvae will contribute valuable information to our knowledge base for this species. The upper reaches of two Rhode Island, USA, estuaries, with differing levels of anthropogenic inputs, were the study sites for this project. Previous studies have shown that during early spring M. menidia adults ripen for spawning by feeding exclusively on zooplankton. The zooplankton community in Upper Point Judith Pond (UPJP) is dominated by polychaete larvae, indicating a eutrophic environment, whereas the Upper Pettaquamscutt River (UPR) is dominated by crustaceans, indicating a relatively pristine environment. To assess and describe the habitat ecology of M. menidia larvae during their first two weeks of life in the littoral zone, four goals were set: (1) determine depth distribution of M. menidia larvae from both estuaries: (2) assess abundance and distribution of M. menidia larvae between estuaries; (3) compare feeding habits of the larvae in the two estuaries through gut content analysis; (4) compare growth of larvae in the two estuaries via age-length relationships based on otolith analysis. Of the four sampling devices used to collect larvae, the circular quadrat, which sampled the land-water interface, the aquarium net, which sampled water from 0.3 – 0.4 m depth, and the small plankton net, which sampled water from 0.4 – 0.5 m depth collected many larvae. A large plankton net, which sampled water > 1 m depth, did not. This indicates that M. menidia larvae can be found from the shoreline interface to 0.5 m depth. Analysis of collection data indicated a zero-inflated Poisson distribution, suggesting a patchy distribution of larvae in the field. Gut content of larvae between estuaries differed markedly, with 76.2% of the larval diet at UPR consisting of copepod eggs and 72.5% of that at UPJP consisting of copepod nauplii. The slopes of the age-length regressions of the larvae between estuaries were not significantly different, indicating that growth rates did not differ. These results provide new information on the feeding habits, growth, and distribution of M. menidia during its first two weeks of life in the field.

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