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While ocean acidification is a global issue, the severity of ecosystem effects is likely to vary considerably at regional scales. The lack of understanding of how biogeographically separated populations will respond to acidification hampers our ability to predict the future of vital ecosystems. Cold-water corals are important drivers of biodiversity in ocean basins across the world and are considered one of the most vulnerable ecosystems to ocean acidification. We tested the short-term physiological response of the cold-water coral Lophelia pertusa to three pH treatments (pH = 7.9, 7.75 and 7.6) for Gulf of Mexico (USA) and Tisler Reef (Norway) populations, and found that reductions in seawater pH elicited contrasting responses. Gulf of Mexico corals exhibited reductions in net calcification, respiration and prey capture rates with decreasing pH. In contrast, Tisler Reef corals showed only slight reductions in net calcification rates under decreased pH conditions while significantly elevating respiration and capture rates. These differences are likely the result of environmental differences (depth, pH, food supply) between the two regions, invoking the potential for local adaptation or acclimatization to alter their response to global change. However, it is also possible that variations in the methodology used in the experiments contributed to the observed differences. Regardless, these results provide insights into the resilience of L. pertusa to ocean acidification as well as the potential influence of regional differences on the viability of species in future oceans. [ABSTRACT FROM AUTHOR]

Cold seeps are among the most heterogeneous of all continental margin habitats. Abiotic sources of heterogeneity in these systems include local variability in fluid flow, geochemistry, and substrate type, which give rise to different sets of microbial communities, microbial symbiont-bearing foundation species, and associated heterotrophic species. Biogenic habitats created by microbial mats and the symbiotic species including vesicomyid clams, bathymodiolin mussels, and siboglinid tubeworms add an additional layer of complexity to seep habitats. These forms of habitat heterogeneity result in a variety of macrofaunal and meiofaunal communities that respond to changes in structural complexity, habitat geochemistry, nutrient sources, and interspecific interactions in different ways and at different scales. These responses are predicted by a set of theoretical metacommunity models, the most appropriate of which for seep systems appears to be the ‘species sorting’ concept, an extension of niche theory. This concept is demonstrated through predictable patterns of community assembly, succession, and beta-level diversity. These processes are described using a newly developed analytical technique examining the change in the slope of the species accumulation curve with the number of habitats examined. The diversity response to heterogeneity has a consistent form, but quantitatively changes at different seep sites around the world as the types of habitats present and the size-classes of fauna analyzed change. The increase in beta diversity across seep habitat types demonstrates that cold seeps and associated biogenic habitats are significant sources of heterogeneity on continental margins globally. [ABSTRACT FROM AUTHOR]

The upper continental slope in the northeastern Pacific Ocean is intercepted by a deep oxygen minimum zone (OMZ; 650–1100 m) and punctuated by conduits of methane seepage. We examined the effects of these two dominant sources of heterogeneity on the density, composition and diversity of heterotrophic macrofauna off Hydrate Ridge, Oregon (OR; 800 m water depth), where the seeps co-occur within an OMZ, and off the Eel River, Northern California (CA; 500 m), where seeps are overlain by better oxygenated waters. We hypothesized that seeps (containing clam beds and microbial mats) should contribute a suite of distinct species to the regional margin species pool but that OMZ-associated hypoxia would dampen seep-related heterogeneity. Macrofaunal densities were highest (23,000–33,510 ind·m−2) in the CA seep sediments and in the OR near-seep samples, intermediate in the OR seep, CA near seep and CA and OR 500-m margin sediments (10,054–19,777 ind·m−2), and lowest in the CA and OR OMZ habitats at 800 m (4269–7847 ind·m−2). Annelids constituted over 50% of the taxa in all but the CA clam bed and OR microbial mat sediments, where mollusks were abundant. Approximately 50% of seep species appeared to be habitat endemic; species present in microbial mats largely formed a subset of those present in the clam beds. Dorvilleid and ampharetid polychaetes were dominant in the seep sediments; non-seep margin sediments at 500 and 800 m were populated heavily by branchiate polychaetes including cossurids and paraonids. Alpha diversity (Es[20] calculated per core) was lowest and rank 1 dominance was highest in the CA and OR microbial mat habitats. Pooled analyses of Es[100] revealed highest species richness in the CA clam bed and near-seep habitats (30.3 and 29.6, respectively), and lowest species richness in the OR microbial mat and near-seep habitats (16.5 and 17.9, respectively). Non-seep sediments (500 and 800 m) off both CA and OR were more homogeneous (55–57% within-habitat similarity) than clam bed and microbial mat sediments (only 32–37% within-habitat similarity). CA sediment macrofauna generally exhibit higher alpha diversity, and as habitats are combined, a higher rate of increase in the slope of the species accumulation curves than do OR margin macrofauna. Methane seeps in the NE Pacific introduce significant heterogeneity that increases margin biodiversity at multiple spatial scales. However, our hypothesis that the OMZ would lessen the seep contributions to diversity was not supported. The better oxygenated CA seeps at 500 m shared more of the background margin fauna (at 500 m) than did the OR seeps at 800 m (with OMZ fauna at 800 m). Geographical differences in the fluxes of methane-rich fluids and the increased reliance on chemosynthetic food sources with increased depth could explain these results. [ABSTRACT FROM AUTHOR]