Harmonizing Marine geological data with the EUNIS habitat classification


"For habitat classification purposes, surficial marine geology is a crucial variable together with e.g., depth, current, salinity and wave exposure. Marine geological mapping involves a range of hydro-acoustic and ground-truthing methods. However, the scope and scale of marine geological surveying is different from biological investigations. To overcome this inconsistency, a framework for reclassification of marine geological information to align with the requirements for habitat mapping has been developmed"

Sea Basin(s): 
Application in MSP: 
Unknown effect
Nature protection
Type of Issue: 
Type of practice: 
Stage of MSP cycle: 
Analyse spatial aspects
Cross-border / trans-national aspect: 
Coherence with other processes: 
Habitats and Birds Directive

Questions this practice may help answer

  • What kind of habitat classification can be used to analyse the human exploitation of natural sea resources?
  • How to harmonize the geological data with the EUNIS habit classifications?

Implementation Context

Habitat classification is an import tool for management of human exploitation of natural resources (fishing, oil, gas, wind power) and nature conservation (monitoring, protection, species distribution and location of marine reserves). A reliable benthic habitat classification requires data concerning hydrography (bathymetry, slope, wind exposure, currents), seabed characteristics (primary sediments, surficial substrates) and species distribution.

Detailed seabed maps are one of the most important variables for describing the marine environment. New techniques has resulted in many descriptions of benthic habitats, but these descriptions can vary from one investigator to another, making it difficult to compare habitats and associated biological communities among geographic regions. However, a large effort to develop a European habitat classification standard has been made through EUNIS (European Nature Information System)

The main structure in a marine habitat is provided by the type of substrate, which is one of the most important factors influencing species composition. Due to a different scope and scale of marine geological survey methodology, the substrate information cannot always be directly obtained from marine geological maps. Therefore a reclassification of surficial layers in the Marine geological map is needed to meet the requirements of habitat mapping. It is also desirable that the reclassification results in a product, which harmonises with common definitions of substrate information and habitat types.

Aspects / Objectives

Establish a classification system, enabling predictions of surficial substrates directly from the Marine geological map – in a mode were geological data and Swedish conditions harmonises with EUNIS habitat classification.


  • Biological analysis of geological field data
  • Compare predictions of surficial material with detailed video- and photo interpretations from Skagerrak, Kattegatt and the Baltic Sea.
  • Tested and modify individual predictions
  • Present ten categories of the seabed sediments in the Marine geological map.

Main Outputs / Results

The report shows the main results of the research, including maps and pictures in the annexes.

The report concludes that the following issues were relevant in the research:

Different scales: In this study focus has been on the substrate forming the habitat, rather than at the occurrence of animals and algae. The use of terms describing observed substrates as “complex” will therefore not be comparable with “habitat complexes” as they are defined in EUNIS (>25 m ), but they will still reflect which surficial substrates we can expect to find on top of the different defined marine sediment classes.

Ambiguos definitions: Apart from definitions of grain size, organic content, sediment mixtures, substrate mobility, exposure and energy levels – are physical characteristics only mentioned briefly in EUNIS. The definitions of these physical factors are however sometimes ambiguously termed, hard to find or just missing.

Different use of substrates and biota in EUNIS hierarichal key: The degree of importance of each habitat-structuring factor varies for different communities, but substratum and the vertical zonation of species appears to play a highly significant role in all communities 

Approximations: Important to remember is that the photo interpretations and SGU:s marine geological maps (based on samples along transects 1-13 km from each other) - are approximations. The main problem in this study has been to bring together data sampled with different techniques at different scales.

  • Previous conclusions have led to the following recommendations:
  • Increased number of samples from each marine geological seabed sediment category
  • Samples should be chosen at random from specific depth interval, since the vertical depth gradient affects the mobility of substrates and the possibility to find certain biological communities (due to light penetration and feeding behaviour). Knowledge of depth is also important since the effect of wind exposure decreases with increasing depth
  • More details should be implemented at level 1-3 in EUNIS habitat classification, dealing with classification of surficial substrates in relation to depth, current, wave exposure and slope
  • Detailed systematic tables with clear definitions (turn to experts from different scientific fields) should be incorporate into EUNIS, in order to investigate detailed aspects of physical characters and define standard terms – which also will simplify interdisciplinary mapping and data exchange
  • To be able to estimate the mobility of substrates using modelling methods and 3D-visualization, it is necessary with detailed data of surficial substrates, depth, slope, wave exposure, current and biological communities
  • In order to to meet the requirements of EU habitats directive (92/43/EEG), the Water framework directive (2000/60/EC) and commercial interest as wind power – scientist are in urgent need of bathymetric data! These data should be used for creating basic maps of seabed topography and substrates before planning any mapping projects
  • Bathymetric data is also needed in order to identify seascapes (underwater landscapes as EUNIS habitat complexes) as estuaries and seamounts, which are defined by their physiographic features (Costello, web reference).
  • Extended use of photo material of the seabed and sampling during acoustic mapping (ground- truthing)


The case study refers to specific sites in the Baltic Sea. However the harmonizing of national Marine geological data with the EUNIS habitat classification is relevant for all European countries. Therefore the findings and recommendations in this practice are relevant for other sea basins too.


Costs / Funding Source

The BALANCE project is part-financed by the EU BSR INTERREG IIIB Neighbourhood Programme and partly by the involved partners.

Responsible Entity

The Swedish Geologocal Survey

Box 670,

SE-751 28


Telephone: +46 18 17 90 00

E-mail: sgu@sgu.se


Greger Lindeberg