Beschreibung: Total biomass and biomass of large taxonomic groups (polychaetes, molluscs, crustaceans, echinoderms) and species diversity of the macrofauna were determined for almost 200 North Sea stations sampled synoptically by seven vessels during Spring 1986 and for 120 additional stations sampled in earlier years by the Marine Laboratory in Aberdeen. There exists a clear and significant decreasing trend in biomass with latitude, both in total biomass and for the different taxonomic groups. Apart from latitude, sediment composition and chlorophyll a content of the sediment also infuence total biomass and biomass of most groups significantly. Biomass increases consistently in finer sediments and sediments with a higher chlorophyll a content. The same trends are found for the results within laboratories. Some interaction exists, indicating weak laboratory and zonal effects. Diversity, as measured by Hill's diversity index N1 = (exp H′) shows a clear and significant trend with latitude. Towards the north of the North Sea diversity increases considerably. The trend is also found for laboratories separately and is everywhere equally strong. Also longitude and depth show an effect on diversity. Sediment variables have no clear influence on diversity. Other diversity measures show the same trend but are more variable than N1,. Total density tends to increase towards the north, but sediment related variables have a larger influence. Mean individual weight becomes considerably smaller towards the northern part of the North Sea.

Beschreibung: Knowledge on spatial scales of the distribution of deep-sea life is still sparse, but highly relevant to the understanding of dispersal, habitat ranges and ecological processes. We examined regional spatial distribution patterns of the benthic bacterial community and covarying environmental parameters such as water depth, biomass and energy availability at the Arctic Long-Term Ecological Research (LTER) site HAUSGARTEN (Eastern Fram Strait). Samples from 13 stations were retrieved from a bathymetric (1,284-3,535 m water depth, 54 km in length) and a latitudinal transect (∼ 2,500 m water depth; 123 km in length). 454 massively parallel tag sequencing (MPTS) and automated ribosomal intergenic spacer analysis (ARISA) were combined to describe both abundant and rare types shaping the bacterial community. This spatial sampling scheme allowed detection of up to 99% of the estimated richness on phylum and class levels. At the resolution of operational taxonomic units (97% sequence identity; OTU3%) only 36% of the Chao1 estimated richness was recovered, indicating a high diversity, mostly due to rare types (62% of all OTU3%). Accordingly, a high turnover of the bacterial community was also observed between any two sampling stations (average replacement of 79% of OTU3%), yet no direct correlation with spatial distance was observed within the region. Bacterial community composition and structure differed significantly with increasing water depth along the bathymetric transect. The relative sequence abundance of Verrucomicrobia and Planctomycetes decreased significantly with water depth, and that of Deferribacteres increased. Energy availability, estimated from phytodetrital pigment concentrations in the sediments, partly explained the variation in community structure. Overall, this study indicates a high proportion of unique bacterial types on relatively small spatial scales (tens of kilometers), and supports the sampling design of the LTER site HAUSGARTEN to study bacterial community shifts in this rapidly changing area of the world's oceans.

Beschreibung: Epibenthic megafauna play an important role in the deep-sea environment and contribute significantly to benthic biomass, but their population dynamics are still understudied. We used a towed deep-sea camera system to assess the population densities of epibenthic megafauna in 2002, 2007, and 2012 at the shallowest station (HG I, ∼1300 m) of the deep-sea observatory HAUSGARTEN, in the eastern Fram Strait. Our results indicate that the overall density of megafauna was significantly lower in 2007 than in 2002, but was significantly higher in 2012, resulting in overall greater megafaunal density in 2012. Different species showed different patterns in population density, but the relative proportions of predator/scavengers and suspension-feeding individuals were both higher in 2012. Variations in megafaunal densities and proportions are likely due to variation in food input to the sea floor, which decreased slightly in the years preceding 2007 and was greatly elevated in the years preceding 2012. Both average evenness and diversity increased over the time period studied, which indicates that HG I may be food-limited and subject to bottom-up control. The community of HG I may be unique in its response to elevated food input, which resulted in higher evenness and diversity in 2012.

Beschreibung: In this paper we provide an overview of new knowledge on oxygen depletion (hypoxia) and related phenomena in aquatic systems resulting from the EU-FP7 project HYPOX ("In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and landlocked water bodies", www.hypox.net). In view of the anticipated oxygen loss in aquatic systems due to eutrophication and climate change, HYPOX was set up to improve capacities to monitor hypoxia as well as to understand its causes and consequences. Temporal dynamics and spatial patterns of hypoxia were analyzed in field studies in various aquatic environments, including the Baltic Sea, the Black Sea, Scottish and Scandinavian fjords, Ionian Sea lagoons and embayments, and Swiss lakes. Examples of episodic and rapid (hours) occurrences of hypoxia, as well as seasonal changes in bottom-water oxygenation in stratified systems, are discussed. Geologically driven hypoxia caused by gas seepage is demonstrated. Using novel technologies, temporal and spatial patterns of water-column oxygenation, from basin-scale seasonal patterns to meter-scale sub-micromolar oxygen distributions, were resolved. Existing multidecadal monitoring data were used to demonstrate the imprint of climate change and eutrophication on long-term oxygen distributions. Organic and inorganic proxies were used to extend investigations on past oxygen conditions to centennial and even longer timescales that cannot be resolved by monitoring. The effects of hypoxia on faunal communities and biogeochemical processes were also addressed in the project. An investigation of benthic fauna is presented as an example of hypoxia-devastated benthic communities that slowly recover upon a reduction in eutrophication in a system where naturally occurring hypoxia overlaps with anthropogenic hypoxia. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on the microbially mediated redox cycling of elements. Observations and modeling studies of the sediments demonstrate the effect of seasonally changing oxygen conditions on benthic mineralization pathways and fluxes. Data quality and access are crucial in hypoxia research. Technical issues are therefore also addressed, including the availability of suitable sensor technology to resolve the gradual changes in bottom-water oxygen in marine systems that can be expected as a result of climate change. Using cabled observatories as examples, we show how the benefit of continuous oxygen monitoring can be maximized by adopting proper quality control. Finally, we discuss strategies for state-of-the-art data archiving and dissemination in compliance with global standards, and how ocean observations can contribute to global earth observation attempts.

Beschreibung: The influence of sampler type on quantitative estimates of deep-sea meiobenthos is examined by an indirect statistical comparison of box corer and multiple corer samples collected throughout the northeast Atlantic, and by a direct comparison of contemporaneously collected multiple corer and box corer samples from a single abyssal location. The data strongly support the suggestion that the greater down-wash/bow wave associated with box corers results in displacement of surface sediments and any superfic~al detrltus layer together with thelr associated fauna. Total metazoan meiobenthos density estimates from box corer samples are about half those from corresponding multiple corer samples Sampler type may also influence the fauna1 composition of both the metazoan and protozoan components of the meiobenthos.