Mei Sato

Date of Award

12-2006

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Oceanography

Advisor

Peter A. Jumars

Second Committee Member

David W. Townsend

Third Committee Member

Lee Karp-Boss

Abstract

Field observations of emergence events by epibenthic animals were conducted with two Tracor Acoustic Profiling Systems (TAPS) in the Damariscotta River estuary, Maine, in fall 2005 and summer 2006. Spectral analysis revealed that periodic temporal variability of the acoustic signals was concentrated at four periods. One was the solar day (24 h) and the other three were lunar tidal periods of 25.82 (diurnal or Oi), 12.42 (semidiurnal or M2) and 6.21 h (half the semidiurnal period). The mysid Neomysis americana showed strong nocturnal migration patterns of water-column activity during its peak summer emergence season, regulated by the diel cycle. Toward the end of the emergence season in fall, however, as phytoplankton standing stocks waned, the dominant rhythm regulating their behavior shifted from a diel to semidiurnal. The timing of mysid abundance peaks in the fall coincided with low slack tides near the surface, but with maximal flood tidal speed near the bottom, providing a plausible mechanism of retention and selective tidal stream transport within the estuary, respectively. Behaviors of smaller organisms, most likely dominated by copepods, were regulated by both M2 and half of M2 components. The phase difference between the acoustic backscatter and the tidal currents suggests that the signal results from smaller organisms emerging into the water column, instead of resuspension of sediment by tidal currents. The timing of their emergence varies depending on TAPS frequency, suggesting emergence by several species. Changes in the magnitudes of each frequency component in the power spectrum can be related to ontogenetic changes in behavior of mysids, intensity of tides, and seasonal food availability. This study suggests the multiple emergence events may affect the degree of benthic-pelagic coupling and reveals the mechanism of previously observed phenomenon (midnight sinking and dawn ascent) by increased sampling resolution.

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