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Scenario simulations of the changing Black Sea ecosystem

Periodic Reporting for period 1 - SIMSEA (Scenario simulations of the changing Black Sea ecosystem)

Reporting period: 2015-06-16 to 2017-06-15

Marine modelling provides a tool to examine the present and future state of the marine ecosystem and can support a variety of EU policies.
The Black Sea has suffered from severe ecological changes since the 1970s due to concurrent effects of
intense eutrophication, overfishing, outburst of gelatinous carnivores and natural climatic variations.
For understanding these processes an advanced ecosystem model for the complex Black Sea ecosystem has been implemented and validated.
Using the JRC hydrodynamic model several future scenario simulations considering different policy options and climate change scenarios were generated.
The data generated from these scenario simulations were thoroughly analysed using state of the art statistical methods like singular spectrum analysis and breakpoint detection methods.
The results of this work have been broadly disseminated not only to the scientific community but also various groups, public bodies and agencies
(e.g. the Commission on the Protection of the Black Sea Against Pollution, etc.), outside of academia can utilise the knowledge produced.
This work helps member states to achieve a Good Environmental Status in the Black Sea as required by the Marine Strategy Framework Directive.
Work Performed

1.1 Model development
The regional Black Sea ecosystem model (BSEM) has been applied for the first time for biogeochemical simula¬tions of the Black Sea ecosystem.
One of the key modification of the existing models is the introduction of two new components - the carnivore predators Mnemiopsis and Noctiluca shunt.
The model is coupled to the General Estuarine Transport Model (GETM). It is forced with fluxes, obtained from realistic meteorological conditions and tuned for the Black Sea ecosystem in particular.
Main results of the hydrodynamic model development are published.

1.2 Testing and model validation
– Coupled BSEM and JRC hydrodynamic model has been rigorously and precisely verified and validated against measured data and independent calculations
– The quality of the forcing data affecting our simulations has been analysed and reported

1.3 Assessing and developing the scenarios
It has been concluded that the model has the potential to simulate realistically evolution in the Black Sea ecosystem at seasonal and inter-annual scales:
the growth in the phytoplankton/zooplankton biomass and changes in seasonal cycles of the main ecosystem components
Scenarios with nutrient load and without nutrient load from the rivers have been performed.

Final Results and Impact

The coupled model is able to capture basic physical and biological processes affecting phytoplankton variability and presents a good agreement with available data and model studies. Areas near the Danube plume and along the western Black sea coast and shelf are characterised by relatively high production throughout the year due to the continuous supply of nutrients by river discharge (primarily by Danube and also by Dniepr and Dniestr) and additionally due to the increased stratification caused by the low salinity zone. The Danube influenced area is clearly identified in the satellite chlorophyll im-ages and the simulated phytoplankton especially during summer when nutrient supply from the deep waters is limited and Danube provides the main nutrient supply. In the absence of any physical mechanism to efficiently supply these inorganic nutrients into the euphotic zone, eutrophication could not play effective role in bıological production throughout the entire basin, except coastal regions.
Despite that the North-Western Shelf area is rich in nutrients, this contribution is not the main source of nutrients in the deep sea area. Nitrate load from rivers is mainly spreading and circulating along the Rim current. The dynamical processes necessary to supply nutrients into the surface layer are generated by the strong wind stress forcing and intense cooling in the region, which subsequently lead to strong convective mixing in the water column to bring the nutrients from its subsurface pool. Therefore, the changing climatic forcing introduced an efficient mechanism, which intensified the anthropogenically-driven biogeochemical processes during the 80s. It is found that the vertical flux of nutrients from the pycnocline in winter is a key factor for phytoplankton growth in the sea interior and supports new production. Conversely, without appreciable subsurface nutrient accumulation in the absence of the eutrophication, strong vertical advective and convective processes in the water column might not be so effective for generating strong biological production in the basin. Consequently, the ecosystem conditions observed in the Black Sea in the recent 3-4 decades could be interpreted as the result of the joint process of anthropogenic and natural climatic forcing.
The Black Sea has suffered from severe ecological changes since the 1970s due to intense eutrophication (associated with excessive anthropogenic nutrient load and pollutants), trophic cascades (as a result of overfishing and invasive non-indigenous gelatinous carnivores) and natural climatic variations.
The Marine Strategy Framework Directive (MSFD) obliges all EU Member States to take the necessary measures to maintain or progressively achieve Good Environmental Status (GES) in the marine environment by the year 2020. It recognises that invasive species and eutrophication pose significant pressures on the marine environment that need to be addressed. These pressures are among the eleven descriptors defined by the MSFD to measure the GES of the marine environment, which specifically requires that eutrophication/invasive species do not cause harm to coastal and marine environments.
Invasions of non-indigenous species are among the greatest drivers of biodiversity loss, and pose a threat to the integrity and functioning of ecosystems.
The SIMSEA project resulted in the successful implementation of an advanced model of the complex Black Sea ecosystem (including selected alien species), which can be used to generate baseline and first scenario simulations, considering different policy options and climate change scenarios.
The gelatinous carnivore Mnemiopsis leidyi (most likely imported via ballast water in ships from its origin on the east coast of America), which almost led to the complete collapse of anchovy fisheries in the Black Sea in the 1980s-90s, is specifically considered in the model.
The project further implements a target setting process that integrates scientific knowledge on thresholds of environmental sustainability with the evaluation of externalities associated with the affected socioeconomic activities. It will confront the complex behaviour of marine ecosystems against the complexity in valuation of the human activities affecting environmental quality.
The first scenario simulations using the new Black Sea model suggest that only a very significant reduction in nutrient inputs from large rivers could help to mitigate coastal eutrophication within about a decade.
The project can support the implementation process of the Marine Strategy Framework Directive (MSFD) in the Black Sea by developing a database of policy relevant scenario simulations, including a statistical analysis and graphical presentation of these data.