Asteroids, ophiuroids and holothurians from the South-Eastern Weddell Sea (Southern Ocean)

Keywords: Asterozoa, Occurrence, EARTH SCIENCE, ECHINODERMS, ANIMALS/INVERTEBRATES, Holothuroidea, SEA STARS, Southern and South-Eastern Weddell Sea, Ophiuroidea, Asteroidea, BIOLOGICAL CLASSIFICATION, abundances, whole-assemblage approach
Temporal coverage: 1983/1985

The South-Eastern Weddell Sea in the Atlantic Sector of the Southern Ocean is a typical high-latitude Antarctic region. It is located in the circumpolar permanent pack-ice zone (Hempel 1985a), characterized by summary polynyas (areas of open water surrounded by sea ice). Due to its remoteness and persistent sea-ice cover, it was not accessible for extensive scientific surveys before the availability and support of modern research platforms that are capable to operate independently in sea-ice covered waters. 
     First multidisciplinary marine research was carried out in this area in the 1980s during the first Antarctic cruises of the German icebreaking research and supply vessel "Polarstern”. Embedded in a broad ecological research programme, addressing a range of evolutionary, systematic, zoogeographical and ecological issues, first comprehensive faunistic inventories of the asteroid (starfish), ophiuroid (brittle star) and holothurian (sea cucumber) bottom fauna were conducted, based on field sampling efforts during “Polarstern” cruises ANT-I/2 (PS01), ANT-II/04 (PS04), and ANT-III/3 (PS06) (for cruise reports see Hempel 1983, Drescher et al. 1983, Kohnen 1984, and Hempel 1985b, respectively). 
     The major objective of this collection work was to provide material for subsequent zoogeographical and ecological studies on the asterozoan (asteroid and ophiuroids together; Voß 1988, Piepenburg et al. 1997) and holothurian fauna (Gutt 1988, Gutt 1991), as well as for analyses of entire macrozoobenthos communities (Gutt 2000; for a compilation: Gutt et al. 2013). Here, we publish the complete original dataset of asteroid, ophiuroid and holothurian abundances (and absences) that formed the basis of the scientific findings published in the research papers mentioned above, to allow for the general accessibility to such data associated with starfishes, brittle stars and sea cucumbers from the South-Eastern Weddell Sea.

Asteroid, ophiuroid, and holothurian specimens were sampled at a total of 59 sites distributed across the South-Eastern Weddell Sea at water depths between 160 and 1,180 m (for more detailed information see section on “Geographic coverage” below). In general, this region characterized by a relatively homogenous physical environment, especially in terms of water masses, poorly sorted sediments, persistent sea-ice cover and hardly predictable occurrence of coastal polynyas. As such, it is representative for the entire high-latitude Antarctic habitat. Some drivers of faunistic heterogeneity, in addition to biological interactions and unknown unpredictable factors, are briefly summarized in the section on “Project Data - Study area description” below.
   The field samples were mainly taken by means of an Agassiz trawl, but also with a commercial bottom trawl and, in one case, a smaller dredge. During the cruises, GPS positions were available approximately each six hours. Between the GPS fixes, the ship's positions were death reckoned. Swept areas were estimated for each haul as described in Voß (1988) and Gutt (1988). Water depths were measured by a DWD echo sounder. For more detailed information see section on “Sampling methods - Sampling description” below. 
     Specimens were collected from either total catches or, in some cases subsamples, counted and preserved on board. Using the swept-area estimates, individual counts were standardized to abundance values (ind m^-2). After the cruises, the preserved specimens were identified to species in the lab. Some holothurian species, which were assumed to be new to science, were formally described (Gutt 1990a, b). Some of these new descriptions were later revised. The specimens were not integrated into a museum's collection, and original data were never published at that time when electronic data bases did not yet exist.
     The quality of the data and metadata published here was enhanced prior to publication following the best practices suggested in the literature during the digitalization and geo-referencing processes. Moreover, the current accurate spelling of scientific names - except for the ophiuroid Theodoria conveniens ("nomen dubium") - was reviewed based on the World Register of Marine Species (www.marinespecies.org/). For more information see “Sampling methods - Quality control” below.

The dataset comprises a total of 4,509 records of absences and abundances of 35 asteroid species (with a total of 2,089 specimens) and 38 opiuroid species (with a total of 18,484 specimens) from 34 stations, as well as of 66 holothurian species (with a total of 20,918 specimens) from 59 stations. 
     Asteroid, ophiuroid and holothurian species were present at all sites investigated in the study area but composition and abundance of the asterozoan and holothurian assemblages varied considerably.     In the case of asterozoan patterns (Voß 1988, Piepenburg et al. 1997), water depth and latitude seemed to be the most important drivers of assemblage distribution and composition. At shallow shelf sites rare asteroid and ophiuroid predators, such as, e.g., Acodontaster conspicuus and Odontaster validus, respectively, as well as epibiotic ophiuroids, e.g., Astrotoma agassizii, occurred in addition to the common and widely distributed opportunistic feeders. In the case of holothurians (Gutt 1988, Gutt 1991), one assemblage co-occurred with the rich macrozoobenthic community dominated by dense epifauna consisting of, e.g., sponges and gorgonians, which are often used as substratum by epibiotic filter feeders. Others live mainly as vagrant deposit feeders on the predominantly non-colonised substratum, such as typical deep-sea species, e.g. Elpidia glacialis and Protelpidia murrayi (Gutt and Piepenburg 1991). In addition, a mixed holothurian assemblage was identified. 

Virtually nothing was known about echinoderms in the south-eastern Weddell Sea before the field sampling work, in the course of which the data published here have been gained. Also from other Antarctic regions only sporadic information on the three echinoderm classes, especially holothurians, was available at that time, mainly found published in the taxonomic literature. However, the application of a whole-assemblage approach was novel, and comparable surveys are even nowadays rare.
     The unique dataset encompasses some of the first observations of asteroids, ophiuroids and holothurians in this area and represents a significant contribution of primary data about Antarctic benthos assemblages. Moreover, it provides unique baseline data for future faunistic, ecological and conservation studies to evaluate the effects of climate change and possible future fishing activities in this area. At present and in the future these faunistic data can gain further importance in the context of a number of further applications:
(1) More comprehensive circumpolar analyses and comparative studies with other large taxa become possible if these data are merged with similar datasets from other regions, see e.g., http://ipt.biodiversity.aq/resource.do?r=asteroidea_zoogeography and http://ipt.biodiversity.aq/resource.do?r=biopearl_asteroida. Data on these three echinoderm classes can also be compared within the same region with other taxa or environmental parameters, as compiled, e.g., by De Broyer et al. (in press). 
(2) At the time of sampling in the 1980s, the study area was almost pristine and hardly affected by any anthropogenic activities. In the meantime, exploratory fishing started on the deeper shelf, and the knowledge on the fauna before the onset of these activities can serve as a valuable baseline for an assessment of the impact of further fishing. 
(3) The same holds true for the study of the effects of climate change. The area is so far climatologically relatively stable but an increase of bottom-water temperatures is expected during the 21st century (Hellmer et al. 2012). 
(4) The data can also be used for nature conservation initiatives (Teschke et al. 2013). They are especially suited for such applied ecological comparative studies, since all specimens - with few well-defined exceptions - were sorted from the catches, meaning that not only the presence of the species were registered but also very valuable absence data and the even more informative abundances. In general, the latter data are known to be more sensitive indicators of environmental change than binary presence-absence data.