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: On Antarctic shelves, glass sponges (Porifera, Hexactinellida) dominate the megabenthic epifauna. But in spite of intensive research on epifauna community structure, process studies on the ecophysiology of key species are so far lacking, due to the difficulty of accessing glass sponges in their habitat and keeping them alive for experimental work. Here, we present preliminary results of an in situ study carried out in the Weddell Sea using a remotely operated vehicle (ROV) to measure feeding, respiration, ammonium excretion and silicate uptake in the common glass sponges Rossella nuda / Anoxycalyx joubini, R. racovitzae and R. villosa. A custom-developed ROV-mounted water sampler was successfully deployed. A total of 22 samples from sponge oscula and 21 samples from ambient waters were analyzed for picoplankton, ammonium and dissolved silicate concentrations. Optode measurements in the ambient water and inside the sponge oscula revealed a measurable difference of ~0.5 µM oxygen between ambient and exhalant waters. Together with estimates of the exhalant volume flow from concomitant fluorescein dye experiments, the oxygen and silicon uptake as well as the ammonium excretion of individual sponges can be estimated. Our findings will help elucidate the role of hexactinellid sponges in carbon and silicon cycling and contribute to understanding future effects of sea-ice and productivity changes on Antarctic ecosystem structure, functioning and services.

Description: Declines in the abundance of long-lived and habitat-forming species on continental shelves have attracted particular attention given their importance to ecosystem structure and function of marine habitats. The study of undisturbed habitats defined as “pristine areas” is essential in creating a frame of reference for natural habitats free of human interference. Gorgonian species are one of the key structure-forming taxa in benthic communities on the Antarctic continental shelf. Current knowledge of the diversity, distribution and demography of this group is relatively limited in Antarctica. To overcome this lack of information we present original data on pristine and remote populations of gorgonians from the Weddell Sea, some of which display the largest colony sizes ever recorded in Antarctica. We assessed the distribution patterns of seven gorgonian species, a morphogroup and a family in front of the Filchner Ronne Ice Shelf (Weddell Sea) by means of quantitative analysis of video transects. Analysis of these videos showed a total of 3140 colonies of gorgonians with the highest abundance in the southern section and a significantly clumped distribution. This study contributes to the general knowledge of pristine areas of the continental shelf and identifies the eastern Weddell Sea as a hotspot for habitat-forming species.

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: Glass sponges (Porifera, Hexactinellida) are an important part of epibenthic communities in the shelf areas of Antarctica. They can grow to considerable sizes of up to 2 m height and form vast sponge beds which provide habitat for various other animals. Despite continuous research on Antarctic benthic community structure and distribution and the obvious dominance of glass sponges in some shelf communities, very little is known about their physiology and their role in biogeochemical cycles. While past studies hypothesized that they have a significant impact on carbon and silicon cycling, this had so far not been investigated in Antarctic glass sponges in situ. During a recent expedition with RV Polarstern to the south-eastern Weddell Sea in 2015/16, we conducted a first in-situ study of pump rates and metabolism in Antarctic hexactinellids. Using a remotely operated vehicle (ROV), we investigated 27 sponges of various sizes (15-65 cm height) belonging to several common species (Rossella sp. and Anoxycalyx joubini) at four stations between 210 m and 420 m water depth. We applied a fluorescent dye at the outside wall of the sponges to measure their pump rates. 63% of the sponges were found to be actively pumping. Furthermore, we sampled the exhalant current and the corresponding ambient water of 22 individuals with a new custom-made water sampling system. The samples were analysed for dissolved silicon, ammonium and picoplankton and the differences between ambient water and exhalant current were calculated for each sponge. In addition to that, we measured oxygen consumption in 10 sponges using an oxygen optode. Here, we relate the measured pump rates to sponge size, and present biomass-specific fluxes of carbon, nitrogen, and silicon, as well as clearance and respiration rates for these important foundation species. Extrapolation of our findings to larger spatial scales will help to better estimate the role of Antarctic glass sponges on carbon and silicon cycling.

Description: Glass sponges (Porifera, Hexactinellida) are an important part of epibenthic communities in the shelf areas of Antarctica. They can grow to considerable sizes of up to 2m height and form vast sponge beds which provide habitat for various other animals. Despite continuous research on Antarctic benthic community structure and distribution and the obvious dominance of glass sponges in some shelf communities, very little is known about the physiology of these sessile filter feeders and their role in biogeochemical cycles. While past studies hypothesized that they have a significant impact on carbon and silicon cycling, this had so far not been investigated in situ. During a recent expedition with RV Polarstern to the south-eastern Weddell Sea in 2015/16, we conducted a first in-situ study of pump rates and metabolism in Antarctic glass sponges. Using a remotely operated vehicle (ROV), we investigated 27 sponges of various sizes (15-65cm height) belonging to several common species (Rossella sp. and Anoxycalyx joubini) at four stations between 210m and 420m water depth. We applied a fluorescent dye at the outside wall of the sponges to measure their pump rates and found 63% of them to be actively pumping. Furthermore, we sampled the exhalant current and the corresponding ambient water of 22 individuals with a new custom-made water sampling system. The samples were analysed for dissolved silicon, ammonium and picoplankton and the differences between ambient water and exhalant current were calculated for each sponge. In addition to that, we measured oxygen consumption in 10 sponges using an oxygen optode. Here, we relate the measured pump rates to sponge size, and present biomass-specific fluxes of carbon, nitrogen, and silicon, as well as clearance and respiration rates for these important foundation species. Extrapolation of our findings to larger spatial scales will help to better estimate the role of Antarctic glass sponges on carbon and silicon cycling.