Posidonia

Posidonia is vital to the health of our seas.

12-09-2019ARCHIVO

The seagrass Posidonia oceanica is an endemic marine plant from the Mediterranean Sea that provides multiple ecosystem services such as increasing biodiversity, transparent waters, white sand beaches, oxygen, helps to palliate global warming acting as an important carbon sink, among others.

But posidonia meadows are vulnerable and fragile habitats that are declining in the Mediterranean Sea. The main causes for its regression are:

- Physical impacts. Including:

  • Anchoring
  • Coastal works
  • Dredging
  • Erosion
  • Bottom trawling

- Eutrophication due to excess of nitrogen and phosphorus inputs. Including:

  • Urban sewage
  • Aquaculture
  • Agriculture
  • Sewage from boats
  • Climate change
  • Invasive species

Protecting Posidonia meadows requires a systemic approach at various levels. We need the right legal frameworks and the action on the ground. Legal frameworks are already there both at EU level and at regional level with the Posidonia decree; which in spite of its rocky start, it is pioneering and has tremendous potential. Now the challenge is to translate this into effective conservation. Now the challenge lies in having an effective implementation of these laws and bringing all sectors of the Balearic society along with it.

This means the boating sector in particular but also fishermen and the tourism sector.

Marilles advocates for an integrated approach to protect Posidonia meadows. These are 5 key areas which require intervention.

1. Prevent anchoring of recreational boats over posidonia meadows. To achieve this goal we propose:
-Installation of ecological anchoring buoys. This requires a marine spatial plan and in order to develop this plan we need better knowledge on number of boats and carrying capacity of our coast.
-Increase the number of surveillance vessels to ensure compliance with regulations and that these are adequately enforced.
- Provide more and better information to prevent anchoring in Posidonia meadows. Boat users are the best “eyes on the sea” many of them already understand the benefits of conserving seagrass meadows and are best placed to get this message across.
- Develop user-friendly and accessible tools such as Posidonia Maps. An app which tells you if the boat is in an area where you can anchor or not. And related to this, amend nautical charts accordingly. To date, in nautical charts the areas where posidonia meadows are present are marked with a symbol indicating that are appropriate areas for anchoring. This needs to change as it has already happened in Formentera.

2. Fight against excess of nutrients like nitrogen and phosphorus, which can lead to algal blooms that can impair Posidonia survival and make our seabed less pleasant to swim in. To achieve this goal the main sources of organic matter and nutrient should be reduced:
- Urban sewage should never leak into the sea without any treatment. To achieve this goal, rain and urban wastewaters have to be collected separately.
- Pipelines of wastewater treatment plant effluents leaking into the sea should be extended further into the sea to avoid dumping the treated water into posidonia meadows.
-Wastewater treatment plants need to improve its treatments to avoid increase nutrient and organic matter inputs into the sea.
-Wastewater from recreational boats should never be dumped into the sea.
-The excessive use of inorganic fertilizers in agriculture should be reduced.

3. Fight against climate change. This is probably the largest threat to our marine environment and we all need to play our part in reducing C emissions.

4. Avoid the coastal developments and building works, which put at risk Posidonia meadows such as the enlargement of marinas.

5. Avoid dredging, near Posidonia meadows as this increases water turbidity and decreases survival of seagrasses.

Making this possible requires action at all levels. We all have a role to play.

Marilles works to make the Balearic Islands a world-leading example of marine conservation and having healthy seagrass meadows an essential part of that.

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