Action A1. Cartography of the Posidonia fields.
Partner: Direcció general de Biodiversitat
The action’s aim was to draw up detailed maps of the Posidonia fields found in SCI areas round the Balearic Islands.

To hire, through the drawing up of service contracts, companies reputed for their expertise in mapping benthic habitats in the Mediterranean, most specially in mapping Posidonia oceanica fields.

Methods and Techniques:
The technique to be used was that of the side-scan sonar for depths of between 5 and 35 metres, plus the interpretation of recently taken ortophotos of shallow waters situated at a depth of between 0 and 5 metres.


  • “Side-scan sonar” for depths of between 5 and 40 metres.
  • Video system for the simultaneous capture of images of the sea floor.
  • Full coverage of the sea floor.
  • For depths of between 0 and 5 metres, the mapping was to be carried out by photographing from the air, generating ortophotos through the usual systems.

Interpretations derived from both the ortophotos and the side-scan sonar were rigorously contrasted by verifications carried out at the locations themselves.


  • The X-Y positioning was done using differential GPS.
  • The positions were established by means of an echo-sound.

Information Processing
The results of data registered by the sonar were saved in digital form.
At a minimum, the following units, sub-units or groups of species were distinctively established:

  1. Several types of fields of Posidonia oceanica, (as , for example, fields with pockets of clearings, continuous and dense fields, continuous fields which do not grow densely, splotchy fields, small groupings with channels between bushes, etc.)
  2. Dead bushes of Posidonia oceanica.
  3. Other plant fields, in particular those of Cymodocea nodosa.
  4. Areas where the sea floor sediment is not covered by plants, defining, as far as possible, the areas holding large units of sediment.
  5. Rocky growth areas.
  6. Maërl areas.
  7. Other points of interest: artificial reefs; signs of marks left by trawler ships; signs of marks left from the extraction of arid ground, canals and pipes; wrecks; structures for anchoring boats; ripple marks; etc.

Verification and assessment of methods.
The interpretation of the sound graphs and ortophotos was double-checked by both the viewing of the films and immersions carried out at the locations to directly verify the data.

In two phases which overlapped in time: In the first phase areas declared SCI round Majorca and part of Minorca were mapped, and in the second phase the remaining SCI areas of Minorca as well as those of Ibiza and Formentera were also mapped.

Once this action had been completed, full mapping of SCI areas included in the project was made available at a scale of 1:1.000.

All the information has been included in a system of geographic information, GIS Posidionia which allows users to both view the information and request bionomic and bathymetric details on the various areas studied.
Furthermore, because of the importance of the information gathered, a full-scale revision and checking of the parameters was undertaken and with this aim a second round of immersions was carried out which produced an improvement of the information and perfected the results.

The mapping was developed with side-scan sonar techniques for general depths of between 3 and 35 metres plus the interpretation of recently taken ortophotos of shallow waters at a depth between 0 and 3 metres. The resulting map scale was of 1:1000 and is of sufficient detail to provide accurate information on the favourable conservation of the fields as stipulated in the Habitats Directive regulating special areas of conservation.

Maps of a higher quality than initially planned have been drawn up, and these constitute an invaluable aid for the optimum management of the SCI sites included in the project.
Therefore, the original objective of this project is considered to have been fulfilled. The results of this project and actions taken thereof are a step in the right direction towards the aim of improving and expanding knowledge on the habitat as well as towards establishing conservation categories.

See results obtained