Description: Time-series studies of arctic marine ecosystems are rare. This is not surprising since polar regions are largely only accessible by means of expensive modern infrastructure and instrumentation. In 1999, the Alfred Wegener Institute, Helmholtz-Centre for Polar and Marine Research (AWI) established the LTER (Long-Term Ecological Research) observatory HAUSGARTEN crossing the Fram Strait at about 79° N. Multidisciplinary investigations covering all parts of the open-ocean ecosystem are carried out at a total of 21 permanent sampling sites in water depths ranging between 250 and 5500 m. From the outset, repeated sampling in the water column and at the deep seafloor during regular expeditions in summer months was complemented by continuous year-round sampling and sensing using autonomous instruments in anchored devices (i.e., moorings and free-falling systems). The central HAUSGARTEN station at 2500 m water depth in the eastern Fram Strait serves as an experimental area for unique biological in situ experiments at the seafloor, simulating various scenarios in changing environmental settings. Long-term ecological research at the HAUSGARTEN observatory revealed a number of interesting temporal trends in numerous biological variables from the pelagic system to the deep seafloor. Contrary to common intuition, the entire ecosystem responded exceptionally fast to environmental changes in the upper water column. Major variations were associated with a Warm-Water-Anomaly evident in surface waters in eastern parts of the Fram Strait between 2005 and 2008. However, even after 15 years of intense time-series work at HAUSGARTEN, we cannot yet predict with complete certainty whether these trends indicate lasting alterations due to anthropologically-induced global environmental changes of the system, or whether they reflect natural variability on multiyear time-scales, for example, in relation to decadal oscillatory atmospheric processes.

Description: Seagrass meadows are among the most diverse and productive coastal ecosystems in the world. Currently, the accelerating loss of these habitats is recognized worldwide. In the southern Baltic Sea, a natural recovery of Zostera marina meadows has occurred after a dramatic reduction within the last century. The aim of this study is to understand if and how the recovering eelgrass meadows affect the functioning of benthic ecosystems. The trophic links within the benthic food webs in the seagrass meadows and bare sandy bottoms were depicted and compared. The trophic connections were examined by combining stable isotope (SI) composition (δ13C, δ15N) and fatty acid (FA) profiles of meio- and macrofauna consumers and of potential food sources (particulate organic matter, surface sediment organic matter, epiphytes, microphytobenthos/bacteria and macrophytes) in a Bayesian mixing model framework (MixSIAR). Significantly higher amounts of the FA bacterial marker (C18:1ɷ7) were observed in meiofauna (approximately 40%) than in the macrofauna (1% on average), suggesting that bacteria are an important part of the meiofauna diet. The mixing model results indicated that the benthic consumers in the vegetated habitat utilized more food sources (e.g., epiphytes in the diets of meiofauna and macrofaunal grazers) and thus had a more diverse diet. Macrofaunal omnivores relied to a larger degree on animal-derived organic matter in vegetated habitat, which could be linked to higher invertebrate prey availability. The results highlight the importance of recovering seagrass meadows in driving the mechanisms responsible for food web organization. Any type of change to the state of seagrass meadows is crucial to the functioning and stability of marine ecosystems.

Description: We present bathymetric patterns in benthic community structure and functioning at the LTER (Long-term Ecological Research) observatory HAUSGARTEN in the Fram Strait. Meiofauna, macrofauna and sediments were sampled at 15 stations along a bathymetric gradient from Spitsbergen coastal waters (100-300m) across the Vestnesa Ridge (1000m) to a Molloy Hole (5561m). Benthic organisms were identified, enumerated and photographed to obtain individual dimensions, biovolume and biomass. Secondary production, respiration and carbon demand were estimated based on individual biomass data. Benthic size spectra were constructed by plotting the biomass against the log2-transformed size classes. Benthic standing stocks, production and carbon demand declined with depth alongside with the decline in food quantity and quality (as indicated by POC and chlorophyll a content in sediments). Compared to those for the meiofauna, bathymetric clines were stronger for macrofauna and a transition towards a system dominated by smaller organisms in deeper ocean zones could be documented. Meiofauna:macrofauna biomass and production ratios increased from 0.1 and 0.6, respectively, in coastal waters to 0.3 and 1.9 on the rise (4042-5102m). The benthic biomass size spectra was bimodal in shape, the width of size spectra declined with increasing depth (from 32 to 23 classes). A reduction of the number of size classes was stronger in macrofaunal part of the spectra. The largest and the smallest size classes as well as the peak in biomass for macrofauna were shifted towards smaller sizes in deeper zones. Fragmented size spectra observed at the two stations (including the Molloy Hole) could be interpreted as effects of physical sediment disturbance (by currents or bioturbation) and resulted in dramatic increase in meiofauna:macrofauna ratio in biomass (0.8) and production (6.5) in the Molloy Hole. The presented patterns are likely to be modified by on-going regional changes in ice coverage and productivity, and the food supply to the deep sea in the course of the climate warming.

Description: Polar marine regions are facing rapid changes induced by climate change, with consequences for local faunal populations, but also for overall ecosystem functioning, goods and services. Yet given the complexity of polar marine ecosystems, predicting the mode, direction and extent of these consequences remains challenging. Trait-based approaches are increasingly adopted as a tool by which to explore changes in functioning, but trait information is largely absent for the high latitudes. Some understanding of trait–function relationships can be gathered from studies at lower latitudes, but given the uniqueness of polar ecosystems it is questionable whether these relationships can be directly transferred. Here we discuss the challenges of using trait-based approaches in polar regions and present a roadmap of how to overcome them by following six interlinked steps: (1) forming an active, international research network, (2) standardizing terminology and methodology, (3) building and crosslinking trait databases, (4) conducting coordinated trait-function experiments, (5) implementing traits into models, and finally, (6) providing advice to management and stakeholders. The application of trait-based approaches in addition to traditional species-based methods will enable us to assess the effects of rapid ongoing changes on the functioning of marine polar ecosystems. Implementing our roadmap will make these approaches more easily accessible to a broad community of users and consequently aid understanding of the future polar oceans.

Description: Time-series studies of arctic marine ecosystems are rare. This is not surprising since polar regions arelargely only accessible by means of expensive modern infrastructure and instrumentation. In 1999, theAlfred Wegener Institute, Helmholtz-Centre for Polar and Marine Research (AWI) established the LTER(Long-Term Ecological Research) observatory HAUSGARTEN crossing the Fram Strait at about 79◦N.Multidisciplinary investigations covering all parts of the open-ocean ecosystem are carried out at a totalof 21 permanent sampling sites in water depths ranging between 250 and 5500 m. From the outset,repeated sampling in the water column and at the deep seafloor during regular expeditions in summermonths was complemented by continuous year-round sampling and sensing using autonomous instru-ments in anchored devices (i.e., moorings and free-falling systems). The central HAUSGARTEN stationat 2500 m water depth in the eastern Fram Strait serves as an experimental area for unique biologicalin situ experiments at the seafloor, simulating various scenarios in changing environmental settings.Long-term ecological research at the HAUSGARTEN observatory revealed a number of interesting tem-poral trends in numerous biological variables from the pelagic system to the deep seafloor. Contrary tocommon intuition, the entire ecosystem responded exceptionally fast to environmental changes in theupper water column. Major variations were associated with a Warm-Water-Anomaly evident in sur-face waters in eastern parts of the Fram Strait between 2005 and 2008. However, even after 15 years ofintense time-series work at HAUSGARTEN, we cannot yet predict with complete certainty whether thesetrends indicate lasting alterations due to anthropologically-induced global environmental changes of thesystem, or whether they reflect natural variability on multiyear time-scales, for example, in relation todecadal oscillatory atmospheric processes.

Description: Time-series studies of arctic marine ecosystems are rare. This is not surprising since polar regions are largely only accessible by means of expensive modern infrastructure and instrumentation. In 1999, the Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) established the LTER (Long-Term Ecological Research) observatory HAUSGARTEN crossing the Fram Strait at about 79°N. Multidisciplinary investigations covering all parts of the open-ocean ecosystem are carried out at a total of 21 permanent sampling sites in water depths ranging between 250 and 5,500 m. From the outset, repeated sampling in the water column and at the deep seafloor during regular expeditions in summer months was complemented by continuous year-round sampling and sensing using autonomous instruments in anchored devices (i.e., moorings and free-falling systems). The central HAUSGARTEN station at 2,500 m water depth in the eastern Fram Strait serves as an experimental area for unique biological in situ experiments at the seafloor, simulating various scenarios in changing environmental settings. Long-term ecological research at the HAUSGARTEN observatory revealed a number of interesting temporal trends in numerous biological variables from the pelagic system to the deep seafloor. Contrary to common intuition, the entire ecosystem responded exceptionally fast to environmental changes in the upper water column. Major variations were associated with a warm water anomaly evident in surface waters in eastern parts of the Fram Strait between 2005 and 2008. However, even after 15 years of intense time-series work at HAUSGARTEN, we cannot yet predict with complete certainty whether these trends indicate lasting alterations due to anthropologically-induced global environmental changes of the system, or whether they reflect natural variability on multiyear time-scales, for example, in relation to decadal oscillatory atmospheric processes.