Antonina Rogacheva

Export of algal biomass from the melting Arctic Sea ice

Diatom Fall 2012 saw the greatest Arctic ice minimum ever recorded. This allowed unprecedented access for research vessels deep into the Arctic Ocean to make high-latitude observations of ice melt and associated phenomena. From the RV Polarstern between 84° to 89° North, Boetius et al. (p. 1430, published online 14 February; see the cover) observed large-scale algal aggregates of the diatom Melosira arctica hanging beneath multiyear and seasonal ice across a wide range of latitudes. The strands of algae were readily dislodged and formed aggregates on the seabed up to 4400 meters below, where the algae are consumed by large mobile invertebrates, such as sea cucumbers and brittle stars. Although Nansen observed sub-ice algae in the Arctic 100 years ago, the extent of this bloom phenomenon was unknown. The dynamics of such blooms must impinge on global carbon budgets, but how the dynamics will change as ice melt becomes more extensive remains unclear. As polar ice retreated in 2012, it left evidence of large algal deposits in its wake. In the Arctic, under-ice primary production is limited to summer months and is restricted not only by ice thickness and snow cover but also by the stratification of the water column, which constrains nutrient supply for algal growth. Research Vessel Polarstern visited the ice-covered eastern-central basins between 82° to 89°N and 30° to 130°E in summer 2012, when Arctic sea ice declined to a record minimum. During this cruise, we observed a widespread deposition of ice algal biomass of on average 9 grams of carbon per square meter to the deep-sea floor of the central Arctic basins. Data from this cruise will contribute to assessing the effect of current climate change on Arctic productivity, biodiversity, and ecological function.

Does Presence of a Mid-Ocean Ridge Enhance Biomass and Biodiversity?

In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR) using sonar, corers, trawls, traps, and a remotely operated vehicle to survey habitat, biomass, and biodiversity. Satellite remote sensing provided information on flow patterns, thermal fronts, and primary production, while sediment traps measured export flux during 2007–2010. The MAR, 3,704,404 km2 in area, accounts for 44.7% lower bathyal habitat (800–3500 m depth) in the North Atlantic and is dominated by fine soft sediment substrate (95% of area) on a series of flat terraces with intervening slopes either side of the ridge axis contributing to habitat heterogeneity. The MAR fauna comprises mainly species known from continental margins with no evidence of greater biodiversity. Primary production and export flux over the MAR were not enhanced compared with a nearby reference station over the Porcupine Abyssal Plain. Biomasses of benthic macrofauna and megafauna were similar to global averages at the same depths totalling an estimated 258.9 kt C over the entire lower bathyal north MAR. A hypothetical flat plain at 3500 m depth in place of the MAR would contain 85.6 kt C, implying an increase of 173.3 kt C attributable to the presence of the Ridge. This is approximately equal to 167 kt C of estimated pelagic biomass displaced by the volume of the MAR. There is no enhancement of biological productivity over the MAR; oceanic bathypelagic species are replaced by benthic fauna otherwise unable to survive in the mid ocean. We propose that globally sea floor elevation has no effect on deep sea biomass; pelagic plus benthic biomass is constant within a given surface productivity regime.

Revision of the Arctic group of species of the family Elpidiidae (Elasipodida, Holothuroidea)

Abstract Species of the family Elpidiidae are the only representatives of elasipodid holothurians in the Arctic. To date, four species have been recognized in the Arctic basin: Elpidia glacialis Théel, 1876, Elpidia heckeri Baranova, 1989, Irpa abyssicola Danielssen & Koren, 1878 and Kolga hyalina Danielssen & Koren, 1879. The taxonomy of these species is not well known: Elpidia glacialis and Kolga hyalina are regarded tentatively as a combined species and Elpidia heckeri and Irpa abyssicola were known only from single localities. Three known species are recognized in the examined material: Elpidia glacialis, Elpidia heckeri and Kolga hyalina. One species appears to be new to science: Elpidia belyaevi sp. nov. Irpa abyssicola was not found. A lectotype has been designated for Kolga hyalina. Diagnoses of all examined species have been revised. Elpidiids from the deeper parts of the Arctic Ocean, determined previously as Elpidia glacialis, are identified as Elpidia heckeri or Elpidia belyaevi sp. nov. All Arctic specimens of Kolga are referred to Kolga hyalina. Distribution patterns and vertical ranges of all examined species have been clarified. Zoogeographical aspects are discussed.

Holothuroidea of the Charlie Gibbs Fracture Zone area, northern Mid-Atlantic Ridge

Abstract Holothurians are among the most species-rich taxa in the megabenthos on the northern Mid-Atlantic Ridge at depths of 2200–3700 m. Extensive new collections of 32 holothurian species were made in 2007–2010 in the Charlie Gibbs Fracture Zone area as part of the ECOMAR project. New material includes samples taken using a trawl and the ROV Isis. Samples and in situ observations from the ROV were of particular value because the morphological details of a number of holothurian species could be clarified. Many of these species are gelatinous and fragile and were damaged in trawls. Three species of elasipodid holothurians are described as new to science. An annotated check-list of all species of deep-sea holothurians collected in the Charlie Gibbs Fracture Zone area is provided. The checklist includes synonyms, distribution data and morphological descriptions as well as photographs taken in situ and in vivo. Ecological remarks are given for some species.

Penilidia desbarresi sp. nov. (Echinodermata: Holothuroidea: Elasipodida) from the upper slope of Newfoundland and re-description of P. ludwigi (von Marenzeller, 1893)

Abstract Penilpidia desbarresi sp. nov. was collected in the Desbarres Canyon at a depth of 525 m, off the southeastern coast of insular Newfoundland, eastern Canada. The new species differs from the type species Penilpidia ludwigi (von Marenzeller, 1983) in having larger middle spines on arched rod-type ossicles on the dorsum and by having the lobe around the posterior body end formed by six pairs of very small tube feet. Penilpidia desbarresi sp. nov was photographed in situ and sampled on a single occasion in July 2007. This gonochoric species (~1–2 cm long) was found on a muddy substrate and individuals were aggregated, reaching a density of ~50 ind. m−2 . Preliminary evidence points to brooding, which would be a first for the family Elpidiidae. Penilpidia ludwigi, not recorded for more than 100 years after its first description, is re-described.

An Externally Brooding Acorn Worm (Hemichordata, Enteropneusta, Torquaratoridae) from the Russian Arctic

A single specimen of a previously undescribed acorn worm in the family Torquaratoridae was trawled from a bottom depth of about 350 m in the Kara Sea (Russian Arctic). The new species is the shallowest of the exclusively deep-sea torquaratorids found to date, possibly an example of high-latitude emergence. On the basis of ribosomal DNA sequences and morphology, the worm is described here as the holotype of Coleodesmium karaensis n. gen., n. sp. It is most similar in overall body shape to the previously described enteropneust genus Allapasus, but is uniquely characterized by a tubular component of the proboscis skeleton ensheathing the collar nerve cord. Additionally, within the proboscis, the sparseness of the musculature of C. karaensis clearly distinguishes it from the much more muscular members of Allapasus. The holotype is a female bearing about a dozen embryos on the surface of her pharyngeal region, each recessed within a shallow depression in the dorsal epidermis. The embryos, ranging from late gastrula to an early stage of coelom formation, are a little more than 1 mm in diameter and surrounded by a thin membrane. Each embryo comprises an external ectoderm of monociliated cells (not arranged in obvious ciliated bands) and an internal endo-mesoderm; the blastopore is closed. In the most advanced embryos, the anterior coelom is starting to constrict off from the archenteron. Coleodesmium karaensis is the first enteropneust (and indeed the first hemichordate) found brooding embryos on the surface of the mother’s body.

Review of the genus Zygothuria Perrier, 1898 and the Atlantic group of species of the genus Mesothuria Ludwig, 1894 (Synallactidae: Holothuroidea) with description of the new species Mesothuria milleri sp. nov.

Species of the genus Mesothuria (fam. Synallactidae) occurring in the Atlantic Ocean are revised. The genus includes 25 valid species, nine of them known from the Atlantic. The new species Mesothuria milleri sp. nov. is described from the north-east Atlantic. It is argued that the genus Zygothuria, established by Perrier in 1898 and recognized later only by Deichmann, should be maintained as a separate genus. Mesothuria and Zygothuria differ in body form, arrangement of ambulacral appendages, and structure of segments of calcareous ring and ossicles from the body wall. The six known species of Zygothuria are reviewed. Zygothuria oxysclera, a former variation of Zygothuria lactea, is proposed as a valid species. Identification keys to species of the genus Zygothuria and Atlantic species of the genus Mesothuria are provided. Data on the life history and reproductive biology of Mesothuria milleri and Zygothuria lactea are given. Both species are common in the north-east Atlantic.

Rediscovery of the elpidiid holothurian Peniagone horrifer (Elasipodida, Holothuroidea: Echinodermata) in the southern Indian Ocean

Peniagone horrifer Théel, 1882 was collected at abyssal depths from around the Crozet Islands in the southern Indian Ocean on RRS Discovery Cruise 300 in 2005. Previously known from only one specimen, P. horrifer is re-described based on a large haul of preserved material and an in situ photograph of the species on the seabed.