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Study and monitoring of green tides in Brittany

Presently, the CEVA is a recognized organization it terms of knowledge, long term practice and thorough experience on environmental issues related to “green algae” tidal blooms. The CEVA is also a privileged contact organization for public actors, including coastal departments (SAGE, municipalities, EPCI …), the Brittany Region, the State and Water Agencies to manage this issue.

Historical information in Brittany and current tasks in monitoring green tides by the CEVA

The monitoring of “Green tides” started in Brittany with only periodic assessments of the most affected sectors. It is only in 1997 that almost exhaustive inventories of the regional coasts (by simple counting of sites presenting Ulva stranding) were carried out once a year by the CEVA, and this under the control of the Loire Brittany Water Agency (AELB).
From 1999 to 2001, the most affected sites on the Armor Coast were the subject to reinforced monitoring, including a summary evaluation of the stranding surfaces under the control of the General Council of the Armor Coast. Since 2002 and the beginning of the Regional and Interdepartmental “Prolittoral Program”, the frequency of monitoring remained relatively identical, which now enables to measure the evolution of the phenomenon.


Prolittoral 2002-2007 :

From 2002 to 2007, the CEVA established a monitoring network within the framework of Prolittoral, regional and interdepartmental program in the perspective to combat green tides in Brittany. This network included, on a “regional” scale (from Mont Saint Michel to La Baule) :

  • 4 “exhaustive” annual inventories of sites affected by Ulva strandings (in May, July, August and October),
  • 3 segmented overflights of the largest identified affected area (April, June and September),
  • determining of eutrophication levels at 25 sites (“nitrogen quotas” of Ulvae), and
  • biomass surveys in 8 major sectors (biomass on foreshore + infralittoral).

Since 2008 :

Programs implemented since 2008 are an extension of the initial Prolittoral program. Therefore, at the Brittany regional level, monitoring of green tides carried out by the CEVA is shared between three networks:

  • The Surveillance Control Networks (RCS) and Operational Control Networks (RCO) of the WFD (Water Framework Directive), under the contract of the Loire-Brittany Water Agency.
  • It should be mentioned that since 2008, CEVA has extended its monitoring area to Normandy Region and Gironde area (under the contract of the Seine-Normandy and Adour-Garonne Water Agencies respectively),
  • Additional monitoring is undertaken within the regional program to fight against green tides in Brittany and in relation to CIMAV’s activities (Intervention Cell on Green Tides), financially supported by the Loire- Brittany Water Agency, the Regional Council and 3 County Councils of Brittany.

More information on the CIMAV…

For more than 10 years, the CEVA has been involved in this regional program and in relation to the CIMAV’s activity. Moreover, this work is integrated in the “Acquisition and Sharing of Knowledge – APC” section of the CPER (State-Region Plan Contract) 2015-2020.

The CEVA acts as a contracting authority when interacting with the CIMAV and this on 3 aspects:

  • expertise and advice,
  • improvement of knowledge on the origin, the functioning and the means to deploy when fighting against green tides and the development of a methodology “Studies for mudflats”
  • monitoring of green algae blooms on the Breton coast in addition to the WFD (Water Framework Directive) monitoring control,

A first government plan to fight against green tides (PLAV) was implemented in February 2010, for a duration of 5 years and with the aim of reducing the proliferation of algae in 8 identified coastal bays in Brittany:

  • Fresnaye Bay
  • The Bay of Saint-Brieuc
  • The Beach of Saint-Michel
  • The Cove de Locquirec
  • The Cove of Horn-Guillec
  • The Cove of Guisseny
  • The Bay of Douarnenez
  • The Bay of Concarneau

In view of the conclusions highlighted by the inter-ministerial audit report published in January 2010, the French government adopted an action plan to improve the management of green tides and to prevent its proliferation by reducing the amount of nitrate arriving in the outlet of watersheds.

This action plan includes 3 components:

  • A security component, focused on improving knowledge and managing risks
  • A component involving curative actions: improving the harvesting and development processing capabilities of stranded algae
  • A precautionary component comprising the actions to be implemented to limit the flow of nitrogen to coastal waters.

For more information :  http://draaf.bretagne.agriculture.gouv.fr/IMG/pdf/rapport_inter_AV_2010_cle4cbfec.pdf

2016 was a transitional year, between the prior government plan for 2010-2015 and the future 2017-2021 plan regarding green tides which is intended to extend and intensify. This new cycle for dealing with green tides is called “PLAV 2” and involves watersheds whose nitrate inflows must be reduced by at least 30% (provision 10A-1), this according to the Guidelines for Regional Planning and Water Management (SDAGE) of the Loire-Bretagne Basin 2016-2021, approved on 18/11/2015.