UBC Theses and Dissertations
Active carbon transport and feeding ecology of pelagic decapods in the North Pacific Subtropical Gyre Podeswa, Yasha
Pelagic decapods were collected during two cruises in the central North Pacific Subtropical Gyre (NPSG): in 2011 depth stratified samples with a MOCNESS-10 (10 m² Multiple Opening/Closing Net and Environmental Sensing System) were carried out at two stations to the west and north of the Hawaiian island of Oahu (21°20.6'N, 158°16.4'W and 22°45'N, 158°00'W), and in 2004 samples were collected using three different micronekton sampling gears in the shallow backscattering layer (SSL) and deep backscattering layer (DSL) off the southwest coast of Hawaii. A total of 40 decapod taxa were identified. Amongst the 22 species with sufficient representation, three migration classes were identified: full migrators (6 species); partial migrators (13 species); and non-migrators (3 species). Using measured local temperature profiles along with published models of respiration, excretion and mortality, the individual and total active downward carbon flux was calculated. From the 2004 samples, diets of nine pelagic decapod species were established through stomach content analysis. It was found that decapod diet varied not only with size, but also with taxonomy. All decapods fed more in the SSL at night than in the DSL during the day or night. However, decapods did not feed entirely at night in the SSL, a common assumption made in previous estimates of active flux for a wide variety of organisms. Instead, feeding in the DSL was equal to 9.67 – 44.69% of feeding in the SSL by weight. Using these feeding estimates, and assuming a micronekton sampling efficiency of 33.33% for the MOCNESS-10, the active flux due to decapod migrations was calculated to be 382.7 - 625.0 µgC/m²/day. Compared to the local passive flux, this active flux was equal to 4.8 - 7.8% of passive flux at the mean night time residence depth (710.7 m), 2.1 - 3.4% of passive flux at the mean daytime residence depth (261.8 m), and 1.5 - 2.4% of passive flux at the base of the euphotic zone (173 m).
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