Amino Acid-Compound Specific Stable Isotope Analysis of Micronekton around Hawaii Reveals Suspended Particles are an Important Nutritional Source in the Meso/Bathypelagic

Gloeckler, Kristen
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[Honolulu] : [University of Hawaii at Manoa], [December 2016]
The mesopelagic food web is poorly understood due to its remoteness and difficulty in sampling. Several studies have found that the demand for carbon by the mesopelagic community exceeds the sinking flux of particulate carbon by up to two to three orders of magnitude. This suggests that additional overlooked sources of carbon exist in the mesopelagic. Suspended particles have been suggested as one of these sources but little has been done to estimate their relative contribution to the mesopelagic food web. In this study, we investigate whether suspended particles are an important nutritional source in the mesopelagic using amino acid compound specific nitrogen isotope analysis. Suspended particles have distinct nitrogen isotope values in their source amino acids which can be traced through the food web. The objective of this study was to determine if mesopelagic micronekton around Station ALOHA feed from a suspended particle based food web. Our results suggest that micronekton feed from food webs based on a variety of nutritional sources including surface dwelling phytoplankton and bacteria, sinking particles and suspended particles with micronekton generally becoming more reliant on suspended particles with depth. Several species were identified as feeding from a suspended particle based food web including Cyema atrum, Cyclothone pallida, Japatella diaphana, Melanocetus johnsonii and Serrivomer sector which were the deepest living micronekton from this study suggesting that in the lower mesopelagic/upper bathypelagic micronekton rely on a nutritional source separate from the fresh surface derived material utilized by epipelagic and upper mesopelagic micronekton. Additionally, we investigated whether species which feed from a suspended particle food web can be identified using bulk tissue nitrogen isotope analysis, a less expensive and less time-consuming method, hypothesizing that these species will have high 15N values driven by the high 15N values at the base of the food web. We found that not all species that feed from a suspended particle based food web have high 15N values and therefore bulk tissue nitrogen isotope analysis is not a suitable technique for this type of study. Our results indicate that suspended particles are an important nutritional source in the lower mesopelagic and upper bathypelagic and should be taken into account when estimating food and carbon supplies for these communities.
M.S. University of Hawaii at Manoa 2016.
Includes bibliographical references.
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