In situ observations show vertical community structure of pelagic fauna in the eastern tropical North Atlantic off Cape Verde.

Distribution patterns of fragile gelatinous fauna in the open ocean remain scarcely documented. Using epi-and mesopelagic video transects in the eastern tropical North Atlantic, which features a mild but intensifying midwater oxygen minimum zone (OMZ), we established one of the first regional observations of diversity and abundance of large gelatinous zooplankton. We quantified the day and night vertical distribution of 46 taxa in relation to environmental conditions. While distribution may be driven by multiple factors, abundance peaks of individual taxa were observed in the OMZ core, both above and below the OMZ, only above, or only below the OMZ whereas some taxa did not have an obvious distribution pattern. In the eastern eropical North Atlantic, OMZ expansion in the course of global climate change may detrimentally impact taxa that avoid low oxygen concentrations (Beroe, doliolids), but favour taxa that occur in the OMZ (Lilyopsis, phaeodarians, Cydippida, Colobonema, Haliscera conica and Halitrephes) as their habitat volume might increase. While future efforts need to focus on physiology and taxonomy of pelagic fauna in the study region, our study presents biodiversity and distribution data for the regional epi- and mesopelagic zones of Cape Verde providing a regional baseline to monitor how climate change may impact the largest habitat on the planet, the deep pelagic realm.

Bathyal feasting: post-spawning squid as a source of carbon for deep-sea benthic communities.

In many oceanic carbon budgets there is a discrepancy between the energetic requirements of deep-sea benthic communities and the supply of organic matter. This suggests that there are unidentified and unmeasured food sources reaching the seafloor. During 11 deep-sea remotely operated vehicle (ROV) surveys in the Gulf of California, the remains (squid carcasses and hatched-out egg sheets) of 64 post-brooding squid were encountered. As many as 36 remains were encountered during a single dive. To our knowledge this is one of the largest numbers of natural food falls of medium-size deep-sea nekton described to date. Various deep-sea scavengers (Ophiuroidea, Holothuroidea, Decapoda, Asteroidea, Enteropneusta) were associated with the remains. Although many of the 80 examined ROV dives did not encounter dead squids or egg sheets (n = 69), and the phenomenon may be geographically and temporally restricted, our results show that dead, sinking squid transport carbon from the water column to the seafloor in the Gulf of California. Based on food fall observations from individual dives, we estimate that annual squid carcass depositions may regionally contribute from 0.05 to 12.07 mg C m-2 d-1 to the seafloor in the areas where we observed the remains. The sinking of squid carcasses may constitute a significant but underestimated carbon vector between the water column and the seafloor worldwide, because squid populations are enormous and are regionally expanding as a result of climate change and pressure on fish stocks. In the future, standardized methods and surveys in geographical regions that have large squid populations will be important for investigating the overall contribution of squid falls to regional carbon budgets.

Morphology, ecology, and molecular biology of a new species of giant larvacean in the eastern North Pacific: Bathochordaeus mcnutti sp. nov.

Bathochordaeus mcnutti sp. nov. is described from the mesopelagic northeast Pacific Ocean (Monterey Bay, California, USA). Larvaceans in the genus Bathochordaeus are large, often abundant zooplankters found throughout much of the world ocean, but until recently it was unclear whether more than a single species of Bathochordaeus existed. Using remotely operated vehicles, we have made hundreds of in situ observations, compiled two decades of time-series data, and carefully collected enough specimens to determine that three species of Bathochordaeus occur in Monterey Bay: B. charon (Chun), B. stygius (Garstang), and B. mcnutti sp. nov. Bathochordaeus mcnutti is readily distinguished from its two congeners by the distinct blue outline visible around the periphery of its tail, and by other aspects of its morphology, ecology, and genetics. The abundance of larvaceans means they are ecologically important as particle processors. Species within the genus, Bathochordaeus, comprise the largest of described larvaceans.

Can coelenterates make coelenterazine? Dietary requirement for luciferin in cnidarian bioluminescence.

In the calcium-activated photoprotein aequorin, light is produced by the oxidation of coelenterazine, the luciferin used by at least seven marine phyla. However, despite extensive research on photoproteins, there has been no evidence to indicate the origin of coelenterazine within the phylum Cnidaria. Here we report that the hydromedusa Aequorea victoria is unable to produce its own coelenterazine and is dependent on a dietary supply of this luciferin for bioluminescence. Although they contain functional apophotoproteins, medusae reared on a luciferin-free diet are unable to produce light unless provided with coelenterazine from an external source. This evidence regarding the origins of luciferin in Cnidaria has implications for the evolution of bioluminescence and for the extensive use of coelenterazine among marine organisms.