ALBERT

Description: In a bid to further understand processes that influence deep-sea epibenthic megafauna, which fulfil critical roles in the global carbon cycle, we present data from the Arctic Long-Term Ecological Research observatory HAUSGARTEN, in the Fram Strait, showing significant temporal changes in total biomass of 3 key organisms (Kolga hyalina, Elpidia heckeri and Mohnia spp.) at stations N3, HG-IV and S3 during repeated deployments over a time series spanning 2004−2015. Overall, all species investigated displayed a similar reproduction/recruitment cycle, with increasing mean mass per individual leading to decreases in abundance, and vice versa. However, there were 3 ‘events’ that deviated from this pattern. The first was a mass reproduction event of E. heckeri at HG-IV from 2012 onwards, likely due to an increased carrying capacity. The second event involved migration of K. hyalina from HG-IV between 2004−2007, with a return in 2011. This coincided with a shift in the composition of the particle flux at the station. The final event was a mass migration of K. hyalina to N3 between 2004 (0 ind. m−2) and 2007 (4.765 ± 0.084 ind. m−2). This event coincided with a 4-fold increase in phytodetrital food availability at the seafloor at N3. Our results highlight the importance of time-series studies to ascertain the key factors that influence epibenthic megafaunal communities. It also highlights the fact that more needs to be done in understanding the life history of these organisms, as this understanding is, so far, widely lacking.

Description: Established in the Fram Strait in 1999, the LTER (Long-Term Ecological Research) observatory HAUSGARTEN enables us to study changes on the deep Arctic seafloor. Repeated deployments of a towed camera system (Ocean Floor Observation System) along the same tracks allowed us to build a time series longer than a decade (2004 - 2015). Here, we present the first time-series results from a northern and the southernmost station of the observatory (N3 and S3, ~2650m and 2350m depth respectively) obtained via the analysis of still imagery. We assess temporal variability in community structure, megafaunal densities and diversity, and use a range of biotic and abiotic factors to explain the patterns observed. There were significant temporal differences in megafaunal abundances, diversity and abiotic factors at both stations. A particularly high increase in megafaunal abundance was recorded at N3 from 12.08 (±0.39; 2004) individuals m-2 to 35.21 (±0.97; 2007) ind. m-2 alongside a ten-fold increase in (drop-)stones. At S3, megafaunal densities peaked in 2015 (22.74 ±0.61 ind. m-2) after an increasing trend since 2004 (12.44 ±0.32 ind. m-2). Holothurians showed particularly striking temporal differences: densities of the small sea cucumber Elpidia heckeri densities rose ten-fold from 0.31 ind. m-2 (±0.04; 2004) to 3.74 ind. m-2 (±0.14; 2015) at S3, coinciding with a sustained increase in phytodetritial matter (chloroplastic pigment equivalents) at the seafloor. Initially entirely absent from N3, densities of the larger holothurian Kolga hyalina peaked in 2007 (5.87 ±0.22 ind. m-2) and declined continuously since then. Overall diversity (γ) increased at both stations over the course of the study, however, with varying contributions of α and β diversities. Our results highlight the importance of time-series studies as megafaunal community composition is characterised by continuous changes. This indicates that epibenthic communities from the deep seafloor are reactive and dynamic, with no “null” community state. To continue to monitor them is therefore crucial in understanding natural and anthropogenic impacts in an area exposed to the effects of climate change.

Description: The LTER (Long-Term Ecological Research) observatory HAUSGARTEN, in the eastern Fram Strait, provides us the unique ability to study the composition of benthic megafaunal communities through the analysis of seafloor photographs. This, in combination with extensive annual sampling campaigns, which have yielded a unique data set on faunal, bacterial, biogeochemical and geological properties, as well as on hydrography and sedimentation patterns, allows us to address the question of why variations in megafaunal community structure and species distribution exist within regional (60-110 km) and local (〈4 km) scales. Here, we present first results from the latitudinal HAUSGARTEN transect, consisting of three different stations (N3, HG-IV, S3) between 78°30’N and 79°45’N (2500m depth), obtained via the analysis of images acquired by a towed camera (Ocean Floor Observation System) in 2011. We assess variability in megafaunal densities, species composition and diversity as well as biotic and abiotic factors, which may cause the patterns observed. While there were significant differences in megafaunal composition and densities between all stations (N3 = 26.74 ±0.63; HG-IV = 11.21 ±0.25; S3 = 18.34 ±0.39 individuals/m2), significant local differences were only found at HG-IV. We discuss our results in the context of sea ice coverage in the area and biogeochemical sediment parameters indicating food availability on the deep seafloor. These parameters were measured in parallel to the photographic transects, to develop the understanding of external factors that affect species distribution patterns amongst arctic benthic megafauna. Finally, we focus on specific individual species, such as the sea cucumber Kolga hyalina and the amphipod Neohela lamia, that display particularly significant and varied distribution patterns across the latitudinal transect, as well as within each transect, in 2011 and other years. The results will be discussed in the context of diminishing sea ice coverage with projections of completely ice free areas within 30 years.

Description: Benthic fauna constantly modifies their physical, chemical and biological environment. The permanent biological reworking of surface sediments mediates biogeochemical processes at the seafloor and is, therefore, of global importance. There are numerous studies measuring the rate and extent of bioturbation worldwide, however, information on mixing rates in the deep ocean and especially in the Polar Regions are extremely scarce; to our knowledge there is, by now, only a single study providing bioturbation rates from the deep Arctic Ocean. The present study presents mixing rates and mixed layer depths for the deep seafloor at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in Fram Strait, Arctic Ocean. Two stations at similar water depths (2400 m and 2500 m water depth, respectively) but approx. 55 km apart from each other were chosen to carry out long-term (2 and 4 years, respectively) in situ bioturbation experiments using luminophores as a tracer. Biodiffusion-like mixing rates Db at the experimental sites were rather similar (0.26 cm2 a-1 at HG-IV; 0.28 cm2 a-1 at S3); slightly (non-significantly) higher Db values at the southern HAUSGARTEN site S3 could be explained by more favorable environmental conditions and related differences in the faunal composition. Indications for a non-local transport of sediment particles from the surface to deeper parts of the sediment, resulting in higher values for the Non-Local Index (NLI), could only be found for the central HAUSGARTEN site HG-IV. Elevated densities of burrowing megafauna at HG-IV, compared to S3, might be responsible for the subsurface maxima in luminophore distribution and comparably higher NLI values at the central HAUSGARTEN site (5.37 at HG-IV; 3.26 at S3). Mixed layer depths L at the two sites were almost identical; considerable mixing of surface sediments occurred down to max. 6-7 cm sediment depth.

Description: Ecosystems deeper than 2,000 m cover ~60% of the Earth's surface and represent the world's most vast biome. Although megafaunal organisms play an important role in deep benthic ecosystems and contribute significantly to benthic biomass little is known about their temporal dynamics. Established in the Fram Strait in 1999, the LTER (Long-Term Ecological Research) observatory HAUSGARTEN enables us to study the composition of Arctic epibenthic megafaunal communities through the analysis of seafloor photographs from repeated camera transects. This, in combination with annual sampling campaigns, which have yielded data on faunal, bacterial, and biogeochemical properties at the seafloor, as well as on the local hydrography and the vertical export of organic matter, allows us to identify drivers of temporal variations in megafaunal abundances, diversity and community structure. Here, we present the first time-series results from a northern and the southernmost stations of the observatory (N3 and S3, ~2500 m depth) from 2004 to 2015, obtained via the analysis of images acquired by a towed camera system (Ocean Floor Observation System). We assess variability in megafaunal densities, species composition and diversity as well as biotic and abiotic factors, which may cause the trends observed. There were significant differences in megafaunal abundance, diversity and abiotic factors between years at both stations with N3 in particular seeing a significant increase in megafaunal abundance from 12.1 ind. m-2 in 2004 to 35.2 ind. m-2 in 2007. At S3, megafaunal densities increased over time from 12.4 ind. m-2 in 2004 to a peak in 2015 (22.7 ind. m-2). Megafaunal community structure underwent significant changes over the study period, which is reflected in a significant overall increase in (γ) diversity at both stations, however, with varying contributions of α and β diversities. While the small-sized sea cucumber Elpidia heckeri increased significantly over time, the larger-sized Kolga hyalina decreased continuously. The trends will be discussed in the context of changes recorded in water temperatures, related changes in surface production and varying food availability on the deep seafloor. The results indicate that epibenthic communities from the deep seafloor are reactive and dynamic, with no “null” community state. Our study highlights the importance of long-term ecological research (LTER), as the megabenthic community composition appears to be characterised by continuous changes.

Description: The LTER (Long-Term Ecological Research) observatory HAUSGARTEN, in the eastern Fram Strait, provides us the unique ability to study the composition of benthic megafaunal communities through the analysis of seafloor photographs. This, in combination with extensive sampling campaigns, which have yielded a unique data set on faunal, bacterial, biogeochemical and geological properties, as well as on hydrography and sedimentation patterns, allows us to address the question of why variations in megafaunal community structure and species distribution exist within regional (60-110 km) and local (〈4 km) scales. Here, we present first results from the latitudinal HAUSGARTEN transect, consisting of three different stations (N3, HG-IV, S3) between 78°30’N and 79°45’N (2500 m depth), obtained via the analysis of images acquired by a towed camera (Ocean Floor Observation System) in 2011. We assess variability in megafaunal densities, species composition and diversity as well as biotic and biogenic habitat features, which may cause the patterns observed. While there were significant regional differences in megafaunal composition and densities between the stations (N3 = 26.74 ±0.63; HG-IV = 11.21 ±0.25; S3 = 18.34 ±0.39 individuals m-2), significant local differences were only found at HG-IV. Regional-scale variations may be due to the significant differences in ice coverage at each station as well as the different quantities of protein available, whereas local-scale differences at HG-IV may be a result of variation in bottom topography.

Description: The Long-Term Ecological Research (LTER) observatory HAUSGARTEN was established in the eastern Fram Strait in 1999 and since then has yielded a large data set on faunal, bacterial, biogeochemical, hydrological and geological properties. Within this thesis I explore spatial and temporal variations of the epibenthic megafaunal communities at three stations (N3, HG-IV and S3), as well as drivers for such variation, using primarily the image analysis of photographic images from 2004 – 2015. Following a brief introduction, Chapter II investigates potential variation within regional- (between different stations 60-110 km apart) and local- (within stations along photographic transects of 〈 4 km length) scales. Presented is data from N3, HG-IV and S3 from 2011 regarding variations in epibenthic megafaunal densities, community structure, diversity indices and biogenic habitat features. While there were significant regional-scale variations between the stations in these categories, there was only local-scale variability observed at HG-IV, likely corresponding to relevant slope effects. Each station, despite large taxonomic overlap, harboured completely separate communities. In Chapter III I assess temporal variability at stations N3 and S3 between 2004 – 2011. Once again, each station showed significant variations in community structure, megafaunal densities, and diversity over time. The largest increase in density was recorded at N3 from 12.08 (±0.39; 2004) individuals m-2 to 35.21 (±0.97; 2007) ind. m-2. This result coincides with a four-fold increase in sediment bound chloroplastic pigment equivalent (CPE). Three taxa that had a large effect on the temporal variations in the community structure were Kolga hyalina, Mohnia spp. (N3 & S3), and Elpidia heckeri (S3). Chapter IV focuses on temporal population dynamics of these three taxa. Length-weight conversion factors derived from physical specimens were used to convert lengths measured via image analysis to biomass, which were then compared with abundance data. On the whole the trend of increased mean mass per individual resulting in lower abundances was observed and vice versa. There were three exceptions to this trend including the first recorded mass migration for K. hyalina, perhaps deep-sea epibenthic holothurians in general, potentially in response to the CPE increase first mentioned in Chapter III. Finally to complete the thesis, Chapter V presents the general conclusions for the research presented in the previous chapters.