Methane seepage often generates precipitation of carbonate rocks, which host microbes and a diverse fauna. These rocks may also promote an interaction between seep and background communities that may last for centuries, providing hard substrate even after seepage ceases. I analyzed composition, density, and trophic structure of macrofaunal invertebrates on carbonate rocks at and surrounding Mound 12, a methane seep site off the coast of Costa Rica, to examine how species and trophic diversities respond to changes in seepage activity at different spatial and temporal scales. By sampling in situ carbonate rocks at active and transition sites, I observed declining density and a community shift from a gastropod dominance to more annelids and peracarid crustaceans under less seepage, while carbonates promoted an interaction between such communities functioning as hard substrate for attachment. Defaunated carbonates deployed for 7 years at active and transition sites indicated that grazers are amongst the most successful colonizers, although the community and its trophic structure were not able to fully recover. However, both seep and transition communities showed rapid response, persistence and recovery when carbonates were transplanted to sites with lesser/more seepage activity for 17 months. Finally, wood and bone deployed for 7 years at active and transition sites showed shared species indicating potential interaction between whale, wood, and seep ecosystems when in close proximity. This multi-experimental study offers insight on the resilience of macrofaunal communities and helps us predict community responses to disturbances in seepage activity that may result from growing anthropogenic interference on margins.

Hard substrates in the deep sea create habitat heterogeneity for diverse invertebrate communities through the provision of substrate and cues for attachment, food, and refuge. However, the same environmental conditions that allow for the formation of these substrates are influencing the biological communities. By analyzing community and trophic dynamics of invertebrates associated with carbonate rocks at methane seeps on the Costa Rica Pacific margin and on mineral-rich hardgrounds off Southern California, I observed that low dissolved oxygen concentration and depth play a role in structuring these communities, as well as seepage activity at seeps and substrate type on mineral hardgrounds. Low oxygen decreases community abundance and community and trophic diversity at both ecosystems and creates complex trophic interactions for fauna on mineral-rich substrates at intermediate depths within the oxygen minimum zone. At seeps, low oxygen seems to override the effects of seepage activity, and the dependence of macrofauna on chemosynthetic production increases with depth. Manipulative experiments with carbonate rocks at seeps demonstrated how the environment influences recovery and resilience of macrofauna. Low oxygen limits colonization and resilience, but seepage activity favors bacterial-grazing seep fauna and food supply. Some macrofaunal species are associated with specific microbial operational taxonomic units (OTUs) for provision of food and habitat, and the responses of these OTUs to changes in seepage activity are correlated to macrofaunal assemblages. Thus, microbial activity seems to play a role in the resilience of macrofaunal at seeps. These findings highlight how the environment and animal-microbe interactions influence macrofaunal communities and their responses to physical and environmental disturbances. They can provide insights for future management and conservation efforts as seeps and mineral-rich hardgrounds provide many ecosystems services but are threatened by human activities and climate change. A first economic valuation analysis of methane seeps reveals that Costa Ricans are willing to pay for protection of seeps and, most importantly, seem to have an affection and care about deep-sea ecosystems (especially endemic species) that become stronger when there is more knowledge of these ecosystems. This finding highlights the importance of biodiversity research, engaging with the public and communicating our findings to facilitate management of deep-sea ecosystems.