Benthic megafauna in the Arctic Ocean - Dynamics in temporal community composition

Benthic megafauna in the Arctic Ocean plays a pivotal role in the functioning of deep-sea ecosystems and influences the global carbon cycle. The structure of benthic communities in the Arctic Ocean is primarily determined by food availability and therefore by phytodetrital flux from surface layers. Hence, highly productive marginal sea-ice zones provide high food supply for benthic communities. With the advance in climate change, marginal sea-ice zones are shifting and organisms are faced with changing phytodetrital fluxes. This study was designed to increase the understanding of benthic megafauna community dynamics in the Arctic Ocean and infer predictions about the future. Therefore, the benthic megafauna was quantified at three stations, with contrasting extent of sea-ice coverage, located in the north (N3), centre (HG-IV) and in the south (S3) of the HAUSGARTEN observatory in the Fram Strait. Image data from different years between 2016 and 2021 were annotated and analysed in context with sea- ice coverage measurements. The benthic megafauna communities showed a shift in dominant functional traits, from sessile suspension feeders, to mobile deposit feeders at all stations. The dominance of mobile deposit feeders was attributed to one species, the sea cucumber, Elpidia heckeri. Additionally, a positive relation between benthic megafaunal density and the extent of sea-ice coverage at N3 and HG-IV was indicated. Variations in phytodetrital quality and quantity are most likely the reasons for these strong density increases of the opportunistic sea cucumber. For the future, similarly strong variations in deposit feeding holothurian densities are expected, given their ability to quickly respond to changing phytodetrital fluxes. The results also indicate that benthic megafauna community composition as a whole is likely to exhibit strong variations in density and diversity. This research shows how valuable image data from time-series studies are in order to detect long-term trends in the future Arctic Ocean

Benthic megafauna in the Arctic Ocean - Future dominion by sea cucumbers?

Benthic megafauna in the Arctic Ocean are important for the functioning of deep-sea ecosystems and influence the global carbon cycle. Food availability, as represented primarily by the phytodetrital flux from surface layers, influences the structure of benthic communities in the Arctic Ocean. Along the highly productive marginal sea-ice zones, benthic communities benefit from enhanced food supply. With the advance in climate change, marginal sea-ice zones are shifting and organisms at the seafloor are faced with changing environmental fluxes. This study was designed in order to deepen our understanding of benthic megafauna community dynamics in the Arctic Ocean, from which to infer predictions about the future. Benthic megafauna was quantified by annotating image data from 2016 to 2021. Image data was derived from three different stations, located in the north (N3), centre (HG-IV) and south (S3) of the HAUSGARTEN observatory in the Fram Strait, and was analysed in context with sea-ice coverage measurements. The benthic megafauna communities showed a shift in dominant functional traits, from sessile suspension feeders, to mobile deposit feeders at all stations over the study period. The dominance of mobile deposit feeders was attributed to one species, the sea cucumber Elpidia heckeri. This species showed increases in density of more than 20% across all three stations during the study period. Variations in phytodetrital quality and quantity are most likely the reasons for these strong density increases of the opportunistic sea cucumber. Additionally, a positive relationship between benthic megafaunal density and the extent of sea-ice coverage at N3 and HG-IV was indicated. From these data, into the future, similar strong variations in deposit feeding holothurian densities are expected, given their ability to quickly respond to changing phytodetrital fluxes. This research shows how valuable long-term image-based data studies are in order to detect trends in the future Arctic Ocean

Arctic Seafloor Integrity Cruise No. MSM95 – (GPF 19-2_05)

The main aim of the MSM95 research expedition was to investigate and map physical impacts on the arctic seafloor in two distinct and contrasting Arctic areas (The Svalbard shelf edge and the HAUSGARTEN time series stations in the FRAM strait) with a range of research equipment. A ‘nested’ data approach was conducted in each research area, with broad seafloor mapping conducted initially with the R/V MARIA S. MERIAN onboard acoustic systems (The EM122 and EM712 bathymetric systems), followed by focused subsequent mapping conducted by PAUL 3000 automated underwater vehicle (AUV) sidescan and camera deployments, Ocean Floor Observation and Bathymetry System (OFOBS) towed sidescan and camera trawls and finally with very high resolution investigations conducted with a new mini-ROV launched directly from the OFOBS for close seafloor visual analysis. These data will be used to produce spatial distribution maps of iceberg and fishery impacts on the seafloor at three locations to the north, south and west of the Svalbard Archipelago, as well as maps of drop stone and topography variations across several of the HAUSGARTEN stations

A vast icefish breeding colony discovered in the Antarctic

A breeding colony of notothenioid icefish (Neopagetopsis ionah, Nybelin 1947) of globally unprecedented extent has been discovered in the southern Weddell Sea, Antarctica. The colony was estimated to cover at least �240 km2 of the eastern flank of the Filchner Trough, comprised of fish nests at a density of 0.26 nests per square meter, representing an estimated total of �60 million active nests and associated fish biomass of >60,000 tonnes. The majority of nests were each occupied by 1 adult fish guarding 1,735 eggs (±433 SD). Bot- tom water temperatures measured across the nesting colony were up to 2�C warmer than the surrounding bottom waters, indicating a spatial correlation between the modified Warm Deep Water (mWDW) upflow onto the Weddell Shelf and the active nesting area. Historical and concurrently collected seal movement data indicate that this concentrated fish biomass may be utilized by predators such as Weddell seals (Lep- tonychotes weddellii, Lesson 1826). Numerous degraded fish carcasses within and near the nesting colony suggest that, in death as well as life, these fish provide input for local food webs and influence local biogeo- chemical processing. To our knowledge, the area surveyed harbors the most spatially expansive continuous fish breeding colony discovered to date globally at any depth, as well as an exceptionally high Antarctic sea- floor biomass. This discovery provides support for the establishment of a regional marine protected area in the Southern Ocean under the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) umbrella

Heavily disturbed seafloor shows recolonization by Paleodictyon nodosum within 26 years

Polymetallic nodules 1) Occur on abyssal plains as lumps of aggregated minerals rendering their collection under commercial consideration 2) Provide hard substrate for sessile fauna and influence distribution of local infauna and bacterial communities

Ocean Floor Observation and Bathymetry System (OFOBS) images of Neopagetopsis ionah ice fish nest arrays in the Filchner Trough, Antarctica collected during the PS124 Polarstern expedition

During the RV POLARSTERN expedition PS124 to the Weddell Sea during Jan - April 2021 the Ocean Floor Observation and Bathymetry System (OFOBS) was used to collect still and video images, as well as sidescan data, from various locations surveyed during the research cruise. During the cruise the first extensive site of Neopagetopsis ionah nesting was discovered. This data set contains images from 4 OFOBS deployments, conducted at 1.5 and 3.5 m flight heights, and 0.5 and 1.5 knots. In the full data set, more than 12000 active fish nests are apparent. The OFOBS system consisted of a towed underwater camera system equipped with both a high-resolution photo-camera (iSiTEC, CANON EOS 5D Mark III) and a high-definition video-camera (iSiTEC, Sony FCB-H11) as well as an integrated sidescan sonar system. The cameras were mounted on a steel frame (140L x 92W x 135H cm), together with two strobe lights (iSiTEC UW-Blitz 250, TTL driven), three laser pointers spaced with a distance of 50 cm used to estimate the size of seafloor structures, four LED lights, and a USBL positioning system (Posidonia) to track the position of the OFOBS during deployments, with additional positioning information provided by the integrated INS and DVL systems. In automatic mode, a seabed photo, depicting an area of approximately 4-10 m**2, with variations depending on the actual height above ground, was taken every ~15 seconds to obtain series of TIMER stills distributed at regular distances along each of the survey profiles. Profile lengths varied in length depending on duration of the cast. At a ship speed of 0.5 kn, the average distance between seabed images was approximately 5 m, with this spacing being 15 m at 1.5 kt speed. Additional HOTKEY photos were taken from interesting objects (organisms, seabed features, etc) when they appeared in the live video feed

Short and decadal impacts of seafloor physical perturbation on the abundances of Lebensspuren ‘traces of life’ in the Peru Basin manganese nodule province

Interest in deep-sea mining for polymetallic nodules as an alternative source to onshore mines for various high-technology metals has risen in recent years, as demands and costs have increased. The need for studies to assess its short- and long-term consequences on polymetallic nodule ecosystems is therefore also increasingly prescient. Recent image-based expedition studies have described the temporal impacts on epi-/megafauna seafloor communities across these ecosystems at particular points in time. However, these studies have failed to capture information on large infauna within the sediments or give information on potential transient and temporally limited users of these areas, such as mobile surface deposit feeders or fauna responding to bloom events or food fall depositions. This study uses data from the Peru Basin polymetallic nodule province, where the seafloor was previously disturbed with a plough harrow in 1989 and with an epibenthic sled (EBS) in 2015, to simulate two contrasting possible impact forms of mining disturbance. To try and address the shortfall on information on transient epifauna and infauna use of these various disturbed and undisturbed areas of nodule-rich seafloor, images collected 6 months after the 2015 disturbance event were inspected and all Lebensspuren, ‘traces of life’, were characterized by type (epi- or infauna tracemakers, as well as forming fauna species where possible), along with whether they occurred on undisturbed seafloor or regions disturbed in 1989 or 2015. The results show that epi- and endobenthic Lebensspuren were at least 50% less abundant across both the ploughed and EBS disturbed seafloors. This indicates that even 26 years after disturbance, sediment use by fauna may remain depressed across these areas