An environmental baseline for food webs at deep-sea hydrothermal vents in Manus Basin (Papua New Guinea)

Food webs and trophic interactions provide a measure of ecosystem function and have been highlighted as an important element for environmental baselines and environmental impact assessments. Stable isotopes have long been used in the deep sea as a means to explore and summarize food webs, especially in chemosynthetic ecosystems, where there may be multiple sources of primary production with distinctive isotopic compositions. Hydrothermal vents in Manus Basin have been targeted for mining and, if mining proceeds, vent food webs will be altered. Here we describe a pre-mining baseline for the food-web state for 3 active vent fields. Manus vents support at least 9 feeding guilds, and both reverse TriCarboxylic Acid (rTCA) and Calvin-Benson-Bassham (CBB) carbon fixation pathways are inferred for symbionts of holobiont taxa. There are site differences in the C-N-S isotopic trait spaces (convex hulls) of Manus Basin vent food webs that likely reflect environmental variability. Isotopic diversity metrics (divergence, dispersion, evenness) are similar in Solwara 1, South Su, and PACMANUS vent food webs, but South Su has a higher degree of isolation in isotopic space (uniqueness). Because convex hull and isotopic diversity metrics are easy to calculate from multidimensional isotopic data, they may be useful food-web indicators for environmental management.