Seabed Habitats

In order to maximise the potential offered by the European marine basins in terms of growth and employment, and to protect the marine environment, we need to know more about the seafloor. European Directives, such as the Marine Strategy Framework Directive (MSFD), call for a full-coverage seabed habitat map of all European seas. In general, habitat maps are very costly and time consuming to produce from survey. The creation of a detailed habitat map involves surveying the seafloor with sonar equipment and collecting samples or photos of the seabed, before analysing and integrating these data types to generate a map. It can take several years from planning a survey to completing a detailed map. By contrast, broad-scale mapping of seabed substrate at a low resolution combined with using modelling techniques to classify habitats in terms of physical parameters is an efficient way to meet the need for a full coverage habitat map at a reasonable cost and a shorter time frame.

EUSeaMap products have been used for assessing and reporting the status of European seas, designing ecologically coherent Marine Protected Area networks, establishing monitoring programmes for seabed habitats and informing marine planning. For more information and some examples of how EUSeaMap products have been applied, see Use Cases.

It is possible to produce a ‘predictive map’ of expected seabed habitat types by combining a series of proxy measurements, such as water depth and light levels amongst others, using statistical analysis and Geographical Information System modelling.

Principal drivers for seabed habitat distributions include the type of seabed substrate (rock, mud, mixed sediment, etc.), depth, light availability and the energy of water movements. To describe the variation in environmental conditions with depth, EUNIS divides subtidal habitats into zones: Infralittoral, Shallow Circalittoral (or Circalittoral), Deep Circalittoral and Deep Sea. In this project we further subdivide the Deep-Sea zone into bathyal and abyssal zones, following scientific literature and recognising the diversity of these huge areas.

The division of marine sublittoral habitats into biological zones (©MESH Atlantic Blue Box, 2013).

Another factor that can be fundamental in driving habitat types is the degree of exposure to wave and water current energy. For some more enclosed basins other parameters, such as salinity, oxygen levels and temperature of water at the seabed are also considered to be fundamental for habitat mapping.

During the first phase of EMODnet Seabed Habitats (2009-2012), a consistent method was developed to take into account the diverse range of seabed habitats found in different regions.

The first step is to acquire the best-available spatial data for several environmental variables. This includes data provided by EMODnet Geology and EMODnet Bathymetry. The data are organised and harmonised into pixelated images divided into classes. These data can be combined by ‘layering’ the data in GIS to create a combined output describing the habitat.

Illustration of how a predictive habitat map can be created by ‘layering’ data in GIS

The principal input layers are the type of seabed substrate and the biological zones. Depending on the basin, layers of hydrodynamic energy levels, salinity and/or oxygen are also produced. For example, the hydrodynamic energy layer is divided into ‘Low’, ‘Medium’ and ‘High’ classes.

Example of an input layer: biological zones. Input layers are also useful per se and are available online through the Map Viewer.

The EUSeaMap model was developed in ESRI^TM ArcGIS ModelBuilder and can be saved and executed multiple times, which ensures that the systems are repeatable and easily updated when new layers or methods are available.

In order to create EUSeaMap, it is necessary to define meaningful threshold values for classifying the environmental (input) layers into ecologically-relevant classes for the determination of habitat types. A threshold value indicates where the change in the physical conditions reaches a critical point that defines an expected change in habitat type (at the map-scale adopted in EUSeaMap, 100mx100m blocks). For example, the infralittoral zone is the area of the seabed where photosynthetic algae is able to grow. This is mapped by finding a threshold value of light at the seabed that best fits observations of this limit in the field. More information on EUSeaMap methodology is available in the documents section, including the EUSeaMap 2023 Technical Report, EUSeaMap 2021 Technical Report , EUSeaMap 2019 Technical Report , and EUSeaMap 2016 Technical Report 

There have been six iterations of broad-scale seabed habitat maps in Europe in the past decade. The current release of the EMODnet broad-scale seabed habitat map for Europe (EUSeaMap 2023) is the recommended product to use as it supersedes all previous maps (such as EUSeaMap, 2021, EUSeaMap 2019, EUSeaMap 2016, EUSeaMap 2012, BALANCE, MESH broad-scale map, MESH Atlantic).

The latest products are available to view and download for free from the Map Viewer.