SS3.15 Physical Forcing and Pelagic-Benthic Interactions in Aquatic Systems
Date: Thursday, June 13, 2002
Location: Poster Session - VCC
 
UhdenHA, Darling Marine Center, Walpole, USA, heather.uhden@umit.maine.edu
Shellito, S, M, Darling Marine Center, Walpole, USA, Shellito@maine.edu
Jumars, P, A, Darling Marine Center, Walpole, USA, Jumars@maine.edu
 
FIRST UP, LAST DOWN: USING ACOUSTICS TO RESOLVE NIGHTLY EXCURSIONS OF HYPERBENTHOS
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Light as a cue for diel vertical migration is investigated using TAPS, an acoustic instrument that measures backscatter intensity vertically through the water-column at six frequencies from 265 to 3000 kHz. Light data are modeled from ac-9 profiles of water absorption and attenuation at nine wavelengths from 412 to 715 nm using Hydrolight(TM). Absorption and scattering vary depending on time of tide and season. Timing of migration correlates with spectral irradiance and PAR within the water column, focusing on wavelengths near 515 nm - the peak sensitivity estimated for one abundant migrating zooplankter, Neomysis americana (Herman 1962). Size distributions of migrators are investigated based on the predator-evasion hypothesis (Zaret and Suffern 1976) under the theory that contrast between organisms and the water background is lessened as light levels decrease during twilight, which shades them from visual predators. Thus small zooplankton should initiate migration at slightly higher light intensities than large zooplankton, remain near the surface longer, and return to the benthos later (DeRobertis, Jaffe, and Ohman 2000). On strongly moonlit nights, all migrators should stay away from the surface.