Flipping for Food: The Use of a Methane Seep by Tanner Crabs (Chionoecetes tanneri)

Abstract

Methane seep habitats are widespread chemosynthesis-based ecosystems that span continental margins and interact with surrounding marine systems. With many of these habitats occurring below 200 m, seeps can serve as an important source of nutrients in otherwise food limited deep-sea environments. However, the potential for marauding megafauna to assimilate seep derived nutrition has been difficult to quantify. Here, we provide the first evidence of a commercially harvested species, Chionoecetes tanneri (tanner crab), assimilating chemosynthetic production. Although bulk isotope analysis of C. tanneri tissue indicated no quantifiable incorporation of seep-derived carbon or sulfur (mean δ 13 C, −18.5‰; mean δ 34 S, 19.5‰), depletions in 13 C (δ 13 C as light as −38.8‰) were noted in fatty acid (FA) compounds. In addition, diagnostic biomarkers for seep bacteria, including 16:1ω6 and 18:1ω8c FA's, were found to have been assimilated by C. tanneri. Futher supporting a trophic link between the seep and the C. tanneri, seep associated bacteria and archaea were, in certain cases, the dominant taxa in the gut contents of the crabs. This work provides the first insights into a link between seep production and deep-sea ecosystem services, specifically fisheries production. In addition, it reveals a methodological bias that could exist in some trophic studies where bulk isotopes under-represent the role of seep nutrition in the diet of marauding animals.

Methane Seeps on the US Atlantic Margin and Their Potential Importance to Populations of the Commercially Valuable Deep-Sea Red Crab, Chaceon quinquedens

“…In addition, US Atlantic margin seeps can provide trophic support to commercially important red crab populations and some seeps may act as a reproductive hotspot for red crabs. Numerous studies have found commercially important species to be present at seep ecosystems but few studies discuss trophic (Seabrook et al, 2019; this study) or reproductive (this study) connections between seeps and commercial species, suggesting that this is a fruitful area for future research. Given the hundreds of unexplored methane seeps on the US Atlantic margin, continued exploration will build a more complete picture of the ecosystem services provided by methane seeps.…”

“…Recently, a comparison of stable isotope methodologies has suggested bulk stable isotope analysis (as used here) may underestimate the role of chemosynthetically-derived nutrition in seep-associated fauna (Seabrook et al, 2019). At methane seeps off British Columbia (Canada), seep-associated bacteria were identified as dietary sources for tanner crabs (Chionoecetes tanneri) based on fatty acid analysis and molecular analysis of stomach contents, while carbon isotope values of the leg muscle suggested the species relied solely on photosyntheticallyderived carbon (Seabrook et al, 2019). Differing results between compound specific fatty acid analysis and bulk stable isotope analysis may be explained by the amount of time needed for muscle tissue to reflect the isotopic composition of the food ingested (Seabrook et al, 2019).…”

“…At methane seeps off British Columbia (Canada), seep-associated bacteria were identified as dietary sources for tanner crabs (Chionoecetes tanneri) based on fatty acid analysis and molecular analysis of stomach contents, while carbon isotope values of the leg muscle suggested the species relied solely on photosyntheticallyderived carbon (Seabrook et al, 2019). Differing results between compound specific fatty acid analysis and bulk stable isotope analysis may be explained by the amount of time needed for muscle tissue to reflect the isotopic composition of the food ingested (Seabrook et al, 2019). Fatty acids have a turnover time of a few days to a few weeks (Ruess and Chamberlain, 2010), while muscle tissue provides an integrated signal of the individual's diet over a period of months (Lorrain et al, 2002;Freire et al, 2009).…”

“…At a seep off Svalbard, a single snow crab (Chionoecetes opilio) was observed grazing within a bacterial mat (Sen et al, 2018). At seeps off the coast of British Columbia (Canada), tanner crabs (Chionoecetes tanneri) have been observed sifting through areas of active methane bubbling and feeding on bacterial mats, with chemosynthetically-derived carbon providing some trophic support (Seabrook et al, 2019). Within the broader literature, commercially important species are known to occur in high abundance at seeps around the world.…”

“…For example, intense levels of primary and secondary productivity present at seeps have long been hypothesized to contribute to fishery productivity on the continental margins of Europe (Hovland et al, 1985;Judd and Hovland, 1989;Berndt, 2005) and Canada (Levy and Lee, 1988). Recently, molecular gut content analysis and compound specific stable isotope analysis has shown that seeps off the west coast of Canada provide some nutritional support to the commercially important tanner crab (Chionoecetes tanneri), which formed dense aggregations around the Barkley Canyon seep in 2014 (Seabrook et al, 2019). Seeps are also recognized as reproductive hotspots for octopus (Graneledone sp.…”