Algue de mer

The reduction of water clarity, both by increased nutrient loading and increased turbidity, can reduce light penetration, causing the loss and declining growth of Zostera marina populations. Direct impacts from human activities, such as fishing and aquaculture, boating and anchoring, and habitat alteration (dredging, land and coastal construction) threaten the habitat where the species flourish and directly removes it.

Deterioration of water quality, eutrophication and sediment deterioration by coastal developments, construction and maintenance of ports, marinas, aquaculture farms or coastal industry can remove decrease surface. Nutrient loading from runoff has also resulted in some local declines.

Large-scale coastal engineering, beach erosion and land reclamation often alters circulation and salinity distributions, leading to seagrass loss, even beds located kilometres away. The primary effect of increased turbidity on seagrasses is a reduction in the amount of light available for photosynthesis. For Zostera marina, the minimum light requirement (expressed as % of surface irradiance) varies between 11 to 37 % of SI (Erftemeijer and Lewis 2006).

In the 1930s, Zostera marina wasting disease produced by a marine fungus of the genus Labyrinthula, led to a catastrophic die-back of these beds on both sides of the Atlantic. Fortunately, these types of outbreaks haven’t been recorded in the Mediterranean (Den Hartog 1987,1996; Ralph and Short 2002).

Regression has also been observed in areas where human pressures are reduced, leading to questions about the role of other external factors such as climate warming as an important factor in the dynamics and distribution of this species (Pergent-Martini 2000).

Cumulative effects and extreme events caused by storms, unusual river discharges and wind-induced wave actions can further exacerbated the anthropogenic perturbations and the natural variability and resilient of this species.

Legislation protects Zostera marina at the national, European and Mediterranean levels.

At the Mediterranean level, Zostera marina is included in the Barcelona Convention of 1976, amended in 1995, Annex II, List of endangered or threatened species.

At the European level, Zostera marina is included in Annex I of the Bern Convention as strictly protected flora species in the Mediterranean. EU regulation also prohibits towed trawling on all the seagrass meadows (no.1626/94 EC Regulation Council).

In Spain, Zostera marina is included in the National Red List of Endangered Species (Royal Decree 139/2011 of 4 February, for the development of the List of Wildlife Special Protection Regime and the Spanish Catalogue of Threatened Species BOE no. 46, 23/2/2011). In the Red List of Vascular Spanish Flora 2008, it is considered a vulnerable species (Moreno 2011). Furthermore, the governments of some Spanish autonomous regions, like Catalonia, Valencia and the Balearic Islands, have established regulations to protect this and other seagrass species. In Catalonia’s case, an Order dated 31 July 1991 (DOGC no. 1479 12/08 / 91) includes the protection of Zostera marina prohibiting the destruction, sale, purchase or use of this species. In the Region of Valencia, there are considered areas of fishing importance and banned its destruction (DOGV no. 1724, of 14/02/92). The government of the Balearic Islands, through an Order dated 21 September 2991, regulates any fishing, shellfishing and aquaculture activities to be conducted in or above seagrass beds.   

 In France, this species has legal protection in several regions. The species is protected in the PACA region (Provence-Alpes-Côte d'Azur, in south-eastern France) (Boudouresque et al. 2006).

 In Italy, seagrass species like Zostera marina, are nationally protected by the law no. 175, dated 27 May 1999 (Pergent-Martini et al. 2006).

 In Montenegro, Zostera beds are protected by the national legislation and considered as a rare or endangered species. The species is also included in the slovenian catalogue as rare species with National Threatened status and its conservation needs to be achieved through habitat protection or management. (Directorate of Culture and Cultural and Natural Heritage 2004).

 In Albania, Zostera marina is protected under the national legislation by a Decision of the Council of Ministers on protected species (2003). Equally, the species is protected in Croatia by an ordinance on “Proclamation of Wild Taxa as Protected or Strictly Protected” (Official Gazette no. 7/2006).