Trophic structure and energy flow in a shallow-water hydrothermal vent: Insights from a stable isotope approach

Abstract

© 2018 Chang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Shallow-water hydrothermal vent ecosystems are distinct from the deep-sea counterparts, because they are in receipt of sustenance from both chemosynthetic and photosynthetic production and have a lack of symbiosis. The trophic linkage and energy flow in these ecosystems, however remain elusive, which allows us poor understanding of the whole spectrum of biological components distributed across such environmental gradients. In this study, a thorough isotopic survey was conducted on various biological specimens and suspended particulates collected along four transects across the venting features of a shallow-water hydrothermal field off Kueishan Island, Taiwan. The isotope data combined with a Bayesian-based mixing model indicate that the vent-associated particulate organic matter (vent POM), as primary contribution of chemoautotrophic populations, has a high δ 13 C value (−18.2 ± 1.1) and a low δ 15 N value (−1.7 ± 0.4). Zooplankton and epibenthic crustaceans, as the fundamental consumers, exhibit δ 13 C and δ 15 N values ranging from −21.3 to −19.8 and +5.1 to +7.5, respectively, and can utilize the vent POM for 38-53% of their diets. The vent-obligate crab Xenograpsus testudinatus shows a large variation in δ 13 C (from −18.8 to −13.9) and δ 15 N values (from 1.1 to 9.8), although an omnivorous trophic level (2.5) is identified for it using δ 15 N values of amino acids, and it can utilize the vent POM for 6-87% of its diet. The consistently low (< 10.0) and overlapping δ 15 N values for most of the analyzed macroinvertebrates suggest extensive ingestion of chemosynthetic production complementing the photosynthetic production, a weak prey-predator relationship and low trophic complexity possibly imposed by the extreme environmental contexts of shallow-water hydrothermal ecosystems.