We have developed a global biogeographic classification of the mesopelagic zone to reflect the regional scales over which the ocean interior varies in terms of biodiversity and function. An integrated approach was necessary, as global gaps in information and variable sampling methods preclude strictly statistical approaches. A panel combining expertise in oceanography, geospatial mapping, and deep-sea biology convened to collate expert opinion on the distributional patterns of pelagic fauna relative to environmental proxies (temperature, salinity, and dissolved oxygen at mesopelagic depths). An iterative Delphi Method integrating additional biological and physical data was used to classify biogeographic ecoregions and to identify the location of ecoregion boundaries or inter-regions gradients. We define 33 global mesopelagic ecoregions. Of these, 20 are oceanic while 13 are ‘distant neritic.’ While each is driven by a complex of controlling factors, the putative primary driver of each ecoregion was identified. While work remains to be done to produce a comprehensive and robust mesopelagic biogeography (i.e., reflecting temporal variation), we believe that the classification set forth in this study will prove to be a useful and timely input to policy planning and management for conservation of deep-pelagic marine resources. In particular, it gives an indication of the spatial scale at which faunal communities are expected to be broadly similar in composition, and hence can inform application of ecosystem-based management approaches, marine spatial planning and the distribution and spacing of networks of representative protected areas

Tracing the origin of nutrients is a fundamental goal of food web research but methodological issues associated with current research techniques such as using stable isotope ratios of bulk tissue can lead to confounding results. We investigated whether naturally occurring δ¹³C patterns among amino acids (δ¹³C_AA) could distinguish between multiple aquatic and terrestrial primary production sources. We found that δ¹³C_AA patterns in contrast to bulk δ¹³C values distinguished between carbon derived from algae, seagrass, terrestrial plants, bacteria and fungi. Furthermore, we showed for two aquatic producers that their δ¹³C_AA patterns were largely unaffected by different environmental conditions despite substantial shifts in bulk δ¹³C values. The potential of assessing the major carbon sources at the base of the food web was demonstrated for freshwater, pelagic, and estuarine consumers; consumer δ¹³C patterns of essential amino acids largely matched those of the dominant primary producers in each system. Since amino acids make up about half of organismal carbon, source diagnostic isotope fingerprints can be used as a new complementary approach to overcome some of the limitations of variable source bulk isotope values commonly encountered in estuarine areas and other complex environments with mixed aquatic and terrestrial inputs.

The dissolution of anthropogenically emitted excess carbon dioxide lowers the pH of the world's ocean water. The larvae of mass spawning marine fishes may be particularly vulnerable to such ocean acidification (OA), yet the generality of earlier results is unclear. Here we show the detrimental effects of OA on the development of a commercially important fish species, the Atlantic herring (Clupea harengus). Larvae were reared at three levels of CO₂: today (0.0385 kPa), end of next century (0.183 kPa), and a coastal upwelling scenario (0.426 kPa), under near‐natural conditions in large outdoor tanks. Exposure to elevated CO₂ levels resulted in stunted growth and development, decreased condition, and severe tissue damage in many organs, with the degree of damage increasing with CO₂ concentration. This complements earlier studies of OA on Atlantic cod larvae that revealed similar organ damage but at increased growth rates and no effect on condition.