Abstract. 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 watercolumn 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.

In this paper we synthesize the new knowledge on oxygen and oxygen-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 land-locked 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 analysed in field studies in various aquatic environments, including the Baltic Sea, the Black Sea, Scottish and Scandinavian fjords, Ionian Sea lagoons and embayments, and in 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 submicromolar oxygen distributions were resolved. Existing multi-decadal 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 not 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 natural and anthropogenic hypoxia overlap. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on 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. Therefore, technical issues are addressed, including the availability of suitable sensor technology to resolve gradual changes in bottom-water oxygen that can be expected as a result of climate change in deep-sea waters. 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 may contribute to global earth observation attempts

The Zernov's Phyllophora Field (ZPF) is a water area in the northwestern Black Sea (NWBS) that occupied about 11 000 km 2 in the early 20 th century. Since 2008, a water area of 4025 km 2 has been given the status of a botanical sanctuary of national importance «Zernov's Phyllophora Field». The goal of the present study is to assess the species richness and quantitative development of macrozoobenthos of the ZPF and their long-term variations under the current conditions of de-eutrophication of the Black Sea basin. The work is based on the material of 43 benthos stations performed in 2010-2013 within an area of 8400 km 2 in the ZPF. In 2010-2013, a total of 162 macrozoobenthos species were identified: Polychaeta (49 species), Mollusca (39), Crustacea (43), Ascidiacea (6); the other taxa comprised 25 species. The current level of species richness of macrozoobenthos is the highest for the entire historical period of the ZPF studies. The mean abundance and wet biomass of macrozoobenthos were estimated at 2417 ± 175 individuals/m² and 283 ± 32 g/m² (without mantle cavity fluid of bivalves). Values for Polychaeta amounted to 1017 individuals/m² and 6 g/m², Mollusca -887 individuals/m² and 256 g/m², Crustacea -165 individuals/m² and 1.3 g/m², Ascidiacea -42 individuals/m² and 17 g/m². The biomass of the dominant species, the filter-feeders Mytilus galloprovincialis, reaches 73% of the total macrozoobrnthos biomass. Our research of the long-term alterations in benthic macrofauna covers the period 1957 to 2013, including the pre-crisis time of the Black Sea ecosystem (1957)(1958)(1959)(1960), its crises of the second half of the 20 th century (1979, 1984, 1991) and the modern (post-crisis) stage (2010)(2011)(2012)(2013). Based on the maps of biomass spatial distribution for all periods mentioned above, the mean values and the total stocks of macrozoobenthos within the area 8400 km 2 of the ZPF were evaluated. The long-term changes of the macrozoobenthos biomass were analysed in relation to the main factors adversely affected the bottom biocoenoses in NWBS -i.e. anthropogenic eutrophication, oxygen depletion and near-bottom hypoxia in summer, as well as the secondary siltation of the seabed due to intensive near-bottom trawling. The most critical period for the ZPF ecosystem state occurred in the late 1970s, when the mean biomass and the total stock of macrozoobenthos decreased by 7 times in comparison with the pre-crisis period. The data collected in the first decades of the 21 st century indicate the actual recovery of the mean macrozoobenthos biomass and of its total stock in the ZPF area to the level of 1957-1960, which is related to the improving of the general ecological situation in the region.Ключевые слова: Phyllophora, биомасса, запасы макрозообентоса, макрофауна бентоса, многолетняя динамика, морская особо охраняемая природная территория, численность Nature Conservation Research. Заповедная наука 2018. 3(4): 32-43

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