Description: Trophic structure is among the most fundamental characteristics of an ecosystem since it is a useful way to determine the main energy flow at the ecosystem level. In the Magellan Strait, the local spatial heterogeneity at the shallow-waters ecosystems may have a great variety of potential food sources; however, knowledge about their biological communities and their structure is still unclear. We examined the trophic structure of shallow-water-mixed bottom communities at two sites in the sub-Antarctic Magellan Strait based on carbon (d13 C) and nitrogen (d15 N) stable isotope ratios. The benthic communities were composed of 46 species from 20 major taxa at Bahı´a Laredo (BL) and 55 species from 18 major taxa at Punta Santa Ana (PSA). Benthic macroalgae and organic matter associated with sediment are the major primary food sources at both sites. Although both sites are quite similar in their food sources and in their vertical trophic structure (C three trophic levels), the food web structure varied distinctly. Functionally, predators and grazers dominated both communities, but top predators were shorebirds, carnivore anemones and predatory nemerteans at BL, and sea stars, shorebirds, crabs and fishes at PSA. The distinct differences in the trophic structure at BL and PSA highlight the important variability of d15 N at the base of the benthic food web, the role of local environmental conditions and community dynamics in structuring shallow-water communities.

Description: Complex marine-terrestrial interactions characterize Chilean fjords, where benthic communities influence the distribution of organic matter (OM). We examined spatial and seasonal changes in the hydrography, sediment conditions and soft-bottom macrobenthic, meiobenthic, and total microbial biomass in a glacial Patagonian fjord (Martinez Channel, Chile). The transport of a high load of glacial mineral and particulate OM to the fjord in the austral summer coincided with low total live benthic biomass. Multivariate analysis evidenced temporal-related macrofaunal groups influenced by the different environments produced by the advection of sediment transport and terrestrial OM from the Baker River, Chile. The relationships between density/biomass and respiration versus body size varied considerably with distance from major riverine inputs, but the slopes of density size spectra and normalized biomass size spectra were less negative in summer than in winter. Occasional large-scale advective processes in the water column affected sediment conditions and removed surface macrofauna, influencing the slope and intercept of the regression models. In the outer fjord, lateral advection and subsequent sedimentation of terrestrial OM contributed a significant fraction to total OM sediments (〈14.76%). Stable carbon isotopes measured in benthic organisms suggest that benthic communities in the inner fjord may assimilate a significant fraction of terrestrial OM via heterotrophic bacteria in contrast to the minor input of terrestrial OM in the outer fjord.

Description: The Filchner-Rønne Outflow System (FROS) in the southernmost Weddell Sea is unique, as sea ice persists longer there than in any other region in the Southern Ocean (SO), strongly determining the ecological processes in the water column and on the seabed. It consists of the deep Filchner Trough (〉 1000 m in depth), which conducts water into and from the Filchner-Rønne Ice Shelf and separates two high-Antarctic shelf regions east and west of it. As the system is situated in a remote high-latitude area rather difficult to access, which greatly hampers scientific studies in the region, the knowledge about ecological processes in the FROS was scarce. However, during two cruises of R/V Polarstern in 2013/14 and 2015/16 field campaigns were performed, which united a multidisciplinary community of scientists intensely collaborating with a common overarching approach to study the FROS. Novel data was gathered by means of corers (multi-corer and multi-grab) and seabed imagery to investigate both infaunal and epifaunal seabed assemblages. First analyses indicated that the macro- and megabenthos on the shelf west of the Filchner Trough was clearly poorer in both abundance and diversity than that at eastern stations. Based on this evidence, we hypothesize that the western and eastern Filchner shelf regions are contrasting ecological systems, characterized by pronouncedly different environmental conditions and distinct benthic communities. We hypothesize further that this difference is primarily due to the contrasting sea-ice regimes, with almost permanent ice cover in the western region vs. the formation of a recurrent summer polynya in the east. As a result, the western system lacks the typical high-Antarctic summer conditions, such as occurrence of wide open-water areas, enhanced light regime, upper water-column stratification triggering phytoplankton blooms, high primary production and particle fluxes, and, hence, strong pelagic-benthic coupling and enhanced food supply to the benthos. In addition, this east-west contrast in the general environmental setting is sustained by the isolating effect of the regional oceanographic current pattern, impeding advective exchange processes (organic matter, larvae, propagules) between the two shelf regions across the trough. As there was evidence from bathymetric as well as seabed imaging data that iceberg scouring likewise impacts both the eastern and western shelf, we further hypothesize that this process, which is generally of high ecological significance for SO shelf benthic systems, does not explain the striking difference in epibenthic community structures. However, as the available evidence is based on admittedly rather few point-type and snapshot-like data, further samples are required to rigorously test those hypotheses.

Description: Glass sponges (Porifera, Hexactinellida) are important structuring components of the benthos in Antarctic shelf regions. These sessile filter feeders can grow up to 2 m in height and form extensive sponge beds in some areas, dominating the benthic biomass and providing habitat for a variety of other animals. However, much of their ecology is still unknown to date, including the factors determining their distribution and abundance. In the current study, we investigate glass sponge distribution and abundance in the south-eastern Weddell Sea in relation to environmental factors (water mass characteristics, currents, ice cover), as well as food availability and abundance of predators. During two recent expeditions with RV Polarstern, we collected photos and videos of the ocean floor by using different gear equipped with HD cameras: a multi grab (MG), an Ocean Floor Observation System (OFOS) and a Remotely Operated Vehicle (ROV). For each of 28 stations, 30 images are selected and analyzed for abundance and species composition of glass sponges and their predators, as well as substrate characteristics. In addition to that, we measured temperature, salinity, dissolved silicate, particulate silicate and bacterial cell numbers. Furthermore, model and/or satellite data on current strength and mean annual ice cover will be included in the study. Glass sponge abundance will be analyzed in relation to the environmental data and predator abundance in order to identify the factors determining the abundance and distribution of glass sponges in the south-eastern Weddell Sea. Our findings will provide an important baseline to assess how glass sponge communities might change in a changing Antarctic environment.

Description: Glass sponges (Porifera, Hexactinellida) are important structuring components of the benthos in Antarctic shelf regions. They can grow up to 2 m in height and form extensive sponge beds in some areas, dominating the benthic biomass and providing habitat for a variety of other animals. However, much of their ecology is still unknown to date, including the factors determining their distribution and abundance. In the current study, we investigate glass sponge distribution and abundance in the south-eastern Weddell Sea in relation to environmental factors (water mass characteristics, currents, ice cover), as well as food availability and abundance of predators. During two recent expeditions with RV Polarstern in 2013/14 and 2015/16, we collected photos and videos of the ocean floor by using different gear equipped with HD cameras: an Ocean Floor Observation System (OFOS), a Remotely Operated Vehicle (ROV), and a multi grab (MG). For each of 28 stations, 30 images are selected and analysed for abundance and species composition of glass sponges and their predators, as well as substrate characteristics. In addition to that, we measured temperature, salinity, concentrations of dissolved and particulate silicon, and bacterial cell numbers. Furthermore, model and/or satellite data on current strength, mean annual ice cover and chlorophyll a concentration as a proxy for productivity will be included in the study. Glass sponge abundance will be analysed in relation to the environmental data and predator abundance in order to identify the factors determining the abundance and distribution of glass sponges in the south-eastern Weddell Sea. Our findings will provide an important baseline to assess how glass sponge communities might change in a changing Antarctic environment.

Description: Ice in its different forms affects benthic communities in Polar Regions directly and indirectly. In order to recognize effects of ice on benthic communities we analyzed benthos in four regions of the Weddell Sea: a) the southeastern Weddell Sea shelf (SEWSS); b) the Filchner-Rønne Outflow System (FROS); c) the Larsen A/B embayments; and d) the tip of the Antarctic Peninsula. These regions differ considerably in their ice regimes: The SEWSS is a typical high Antarctic habitat, influenced by seasonal sea ice coverage; the FROS is influenced by seasonal ice on its eastern edge, but under heavy year round ice conditions on its western edge; the Larsen A/B embayments were covered for hundreds of years by thick ice shelves, which recently disintegrated providing large areas for recolonization by benthos; and the shelf around the tip of the Antarctic Peninsula which can be considered as being unaffected by ice. Benthos in these four regions revealed distinct differences in abundance, biomass, and production values. Highest abundance values were found at the tip of the Antarctic Peninsula and along the SEWSS (2,767 and 2,535ind.m-2, respectively), whereas the lowest abundance corresponded to the Larsen A/B region (682ind.m-2). In terms of both, biomass and production, the southeastern Weddell Sea region showed the highest values (3,944.2g wet weight.m-2 and 10.3g C.y-1m-2, respectively), whereas the lowest values were found at Larsen A/B (71.08g.m-2 and 1.62g C.y-1.m-2) and FROS regions (71.08g.m-2 and 1.62 g C.y-1.m-2). A PERMANOVA showed the differences among regions to be significant in all three terms: abundance (Pseudo F=7.10; p=0.001), biomass (Pseudo F=6.01; p=0.001), and production (Pseudo F=6.28; p=0.001). These differences were mainly caused by sponges, ophiuroids and polychaetes. This study also shows pronounced differences in the structure, composition of the benthic communities in the four regions. We hypothesize that these differences are primarily due to the different sea-ice regimes in the regions.

Description: Germany intends to present the Working Group on Ecosystem Monitoring and Management (WG EMM) the background document that provides the scientific basis for the evaluation of a marine protected area (MPA) in the Weddell Sea planning area. The contents and structure of the whole document reflect its main objectives, i.e. to set out the general context of the establishment of MPAs and to provide the background information on the Weddell Sea MPA (WSMPA) planning area (Part A); to inform on the data retrieval process (Part B) and to describe the results of the scientific analyses and the MPA scenario development with the directly science-based aspects of the WSMPA proposal, i.e. the objectives and the boundaries and zones of the MPA (Part C). Here, the authors intend to update WG EMM on the current state of Part A of the document that has been presented at the meeting of the CCAMLR Scientific Committee in 2014. The Scientific Committee had welcomed and endorsed the scientific background document (SC-CAMLR-XXXIII/BG/02) as a foundation reference for the Weddell Sea MPA planning (SC-CAMLR-XXXIII, § 5.21). Part A contains (i) a synopsis in terms of the establishment of MPAs (chapter 1); (ii) a description of the boundaries of the WSMPA planning area (chapter 2); (iii) a comprehensive, yet succinct, general description of the Weddell Sea ecosystem (chapter 3); (iv) and finally a guidance regarding the future work beyond the development of the scientific basis for the evaluation of a WSMPA (chapter 4). Please note that the current state of Part A of the document presents a comprehensive yet incomplete version concerning chapters that have to be (further) developed or revised.