Trophic Interactions of Megafauna in the Mariana and Kermadec Trenches Inferred from Stable Isotope Analysis
Date
2020
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Abstract
Hadal trenches house unique ecosystems. Little is known about sources of nutrition to these
deep ecosystems or about their trophic structures. We evaluated megafaunal food web
structure and nutritional sources in the Kermadec and Mariana trenches using carbon and
nitrogen stable isotope analysis (δ15N and δ13C values) of bulk tissues and proteinaceous
individual amino acids (AAs). In the Kermadec Trench, bulk δ15N values ranged from
5.8‰ in trench sediment to 17.5‰ in tissues of the supergiant amphipod, Allicela gigantea.
δ15N values of detritivores exceeded those of sediments by as much as 7.5‰. Bulk δ13C
values ranged from -21.4‰ in sediments to -17.3‰ in the brittle star, Ophiolimna sp., and
did not co-vary with δ15N values. In the Mariana Trench, only bait-attending fauna and
surface sediments were available for analysis. Mariana Trench fishes, amphipods, and
sediments had slightly lower δ15N values than those from the Kermadec Trench, possibly
because the Mariana lies under more oligotrophic surface waters. We found evidence for
multiple food inputs to the system in each trench, as revealed substantially higher δ15N
values in detritivores relative to sediment and high variability in δ13C values. Trophic levels
determined from isotopic analysis of individual AAs in the Kermadec Trench ranged from
level three for detritivores to level five for fishes. Source AA δ15N values were variable
(range of ~7.0‰ in average δ15N source AA values), with much of the variation occurring
in small amphipods. For the other fauna sampled, a significant increase in δ15N source AA
values was observed with increasing collection depth. This increase could reflect larger
quantities of highly microbially reworked organic matter with increasing depth, or sporadic
input from turbidity flows. Although further sampling across a broader faunal diversity will
be required to understand these hadal food webs, our results provide new insights into hadal
trophic interactions and suggest that trench food webs are very dynamic.
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deep sea biology, stable isotope analysis, hadal zone, megafauna
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47 pages
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All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
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Tokuda, Andrew
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