Abstract
AbstractMethane seeps are highly productive deep‐sea ecosystems reliant on chemosynthetic primary production. They are increasingly affected by direct human activities that threaten key ecosystem services. Methane seepage often generates precipitation of authigenic carbonate rocks, which host diverse microbes, and a dynamic invertebrate community. By providing hard substrate, even after seepage ceases, these rocks may promote a long‐lasting ecological interaction between seep and background communities. We analyzed community composition, density, and trophic structure of invertebrates on authigenic carbonates at Mound 12, a seep on the Pacific margin of Costa Rica, using one mensurative and two manipulative experiments. We asked whether carbonate macrofaunal communities are able to survive, adapt, and recover from changes in environmental factors (i.e., seepage activity, chemosynthetic production, and food availability), and we hypothesized a key role for seepage activity in defining these communities and responses. Communities on in situ carbonates under different seepage activities showed declining density with increasing distance from the seep and a shift in composition from gastropod dominance in areas of active seepage to more annelids and peracarid crustaceans that are less dependent on chemosynthetic production under lesser seepage. Response to changing environmental context was evident from altered community composition following (1) a natural decline in seepage over successive years, (2) transplanting of carbonates to different seepage conditions for 17 months, and (3) defaunated carbonate deployments under different seepage regimes over 7.4 yr. Seep faunas on transplants to lesser seepage emerge and recover faster than transition fauna (characterized by native seep and background faunas, respectively) and are able to persist by adapting their diets or by retaining their symbiotic bacteria. The macrofaunal community colonizing defaunated carbonates deployed for 7.4 yr developed communities with a similar successional stage as in situ rocks, although trophic structure was not fully recovered. Thus, macrofaunal successional dynamics are affected by habitat complexity and the availability of microbial chemosynthetic productivity. This multi‐experiment study highlights the interaction between biotic and abiotic factors at methane seeps at different time scales along a spatial gradient connecting seep and surrounding deep‐sea communities and offers insight on the resilience of deep‐sea macrofaunal communities.
Highlights
The deep ocean hosts extreme environments that support unique communities reliant on chemosynthesis rather than photosynthesis (Tunnicliffe et al 2003); they are highly productive due to microbial energy capture from the oxidation of sulfide, methane, and hydrogen (Dubilier et al 2008)
We evaluate whether macrofauna colonizing defaunated carbonates fully recover natural patterns of community composition and trophic structure within 7.4 yr and hypothesize that recolonization varies with seepage activity
The groups contributing to the dissimilarity between the communities at active and transition sites (SIMPER, average dissimilarity = 68.12) were Amphipoda, Tanaidacea, Ophiuroidea, Serpulidae, Chrysopetalidae, and Hydroidolina present mainly at transition sites (Table 1), and gastropods in the families Neolepetopsidae, Provannidae and Cataegidae, and Anomura that were more abundant at active sites (Table 1)
Summary
The deep ocean hosts extreme environments that support unique communities reliant on chemosynthesis rather than photosynthesis (Tunnicliffe et al 2003); they are highly productive due to microbial energy capture from the oxidation of sulfide, methane, and hydrogen (Dubilier et al 2008). Among these systems, methane seeps play key roles in climate regulation and carbon sequestration through aerobic and anaerobic methane oxidation (AOM) and carbonate precipitation (regulating services; Boetius and Wenzhofer 2013, Marlow et al 2014b). Much of the deep ocean is covered by sediments, seeps are frequently associated with extensive cover of authigenic carbonates (Aloisi et al 2000)
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