Seagrass and Bathymetry

Dimitris Poursanidis, FORTH (GR)

It has been recognized that seagrass meadows constitute a significant component of coastal marine ecosystems. They are among the most productive habitats in the coastal zone, providing essential ecosystem functions and deriving essentialecosystem services.

Some of the most critical ecosystem services and functions are water oxygenation and nutrients provision, seafloor and beaches stabilization (as sediment is controlled and trapped within the rhizomes of the meadows), carbon burial, areas for nursery and refuge of several commercial and endemic species.

However, seagrass meadows are presently experiencing a decline globally due to intensive human activities and the climate change. Threats from climate change include increase of sea surface temperature and sea level rise as well as frequent and intensive sea storms. These threats represent a pressing challenge for coastal management and are predicted to have deleterious effects on seagrasses in both deep and swallow limits (upper-lower limits). The Mediterranean Sea contain lush seagrass meadows made by the endemic plant Posidonia oceanica. The meadows are extended from the sea surface down to a maximum depth of 50 m depth in extreme cases and form the basis for a keymarine habitat/ecosystem in the region.

The European Environmental Agency (EEA) has recognizedit as the priority habitat for the European Union (Posidonia oceanica,code: 1120) among the nine marine habitats which have been identified within the Natura 2000 areas. An important issue for the proper management of the seagrass meadows is the knowledge of its spatial distribution. Such datasets are significant to fulfil European Union obligations about the application of maritime spatial planning for a better management of actions like aquaculture, hydrocarbon exploitation, tourism activities, marine protected areas, blue cities. Also, the proper management of seagrasses is vital for achieving the Good Environmental Status which is precisely defined as a target in European Commission’s Marine Strategy Framework Directive as well as the United Nations Sustainable Development Goals  2030 and more specific the goal 14 “Conserve and sustainably use the oceans, seas and marine resources for sustainable development”. 

The knowledge of the spatial distribution of the seagrass meadows is a prerequisite information for the conservation and sustainable use of the marine resources. So far, the spatial distribution of the seagrass meadows has been approached by using acoustic-based remote sensing methods, optical-based remote sensing methods and modelling approach. In the Mediterranean Sea, few studies used satellite-based remote sensing data from a variety of sensors for the identification and the accurate mapping of Posidonia oceanicameadows. Last years, with the development of the Copernicus Sentinel 2 constellation, a new era in the seagrass monitoring and mapping appeared. The availability of high revisit and high radiometric resolution satellite data can overcome the above mentioned limitations and become an essential asset for the conservation activities of the coastal zone habitats. Such data can be used not only for identifying the limits of seagrass meadows but also for other coastal marine habitats like the soft bottoms and the rocky reefs but also the derivation of coastal bathymetry for use in several applications. Within the ECOPOTENTIAL project, FORTH has work using commercial satellites but also Copernicus Sentinel 2 data to map seagrass meadows in the Samaria protected Area but also to calculate bathymetry using cloud computing infrastructures such as the Google Earth Engine.

Some related papers:

Dimitris Poursanidis, Kostas Topouzelis and Nektarios Chrysoulakis. 2018. Mapping coastal marine habitats and delineating the deep limits of the Neptune’s seagrass meadows using VHR earth observation data. International Journal of Remote Sensing. https://doi.org/10.1080/01431161.2018.1490974.

Traganos, D.; Poursanidis, D.; Aggarwal, B.; Chrysoulakis, N.; Reinartz, P. Estimating Satellite-Derived Bathymetry (SDB) with the Google Earth Engine and Sentinel-2. Remote Sens. 2018, 10, 859.

Dimitris Poursanidis, Dimos Traganos, Peter Reinarz and Nektarios Chrysoulakis. 2018. Shallow to deep coastal habitat and bathymetry mapping using super-resolved coastal aerosol band of Sentinel-2. Sentinel-2A Science Special Issue. Remote Sensing of the Environment. UNDER REVIEW.

Traganos, D.; Aggarwal, B.; Poursanidis, D.; K. Topouzelis; Chrysoulakis, N.; Reinartz, P. Towards global-scale seagrass mapping and monitoring using Sentinel-2 on Google Earth Engine: the case study of Aegean and Ionian Seas, Remote Sens. 2018, UNDER REVIEW.

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