Seagrass-Watch Magazine Issue 47 - March 2013 | Page 30

threats:
Posidonia oceanica is threatened at depth by mechanical damage from trawling, boat anchoring, and turbidity. Coastal development including shoreline hardening, urban and harbour
infrastructure, and sand mining affect the upper limit of Posidonia meadows. Eutrophication (fertiliser from agriculture and urban waste) and pollution, especially in coastal regions that are
heavily populated, is a problem. Fish farm activities and aquaculture affect surrounding Posidonia meadows. Invasive species also compete for habitat (e.g., seaweeds species such as
Caulerpa taxifolia and Caulerpa cylindracea). Climate change will be an additional threat through warming of waters (in excess of 28°C) and erosion from sea level rise.
Posidonia oceanica is protected by EU legislation (Habitat directive), the Bern and Barcelona Conventions and national legislation (10 Mediterranean countries such as France, Spain, Italy,
etc.). Fishing regulations limit trawling activities near the shore (either above 50 m or a certain distance from the coast), which constitute an indirect protection measure for the species (EC
Council Regulation N° 1967/2006 and national regulations).
Source: Pergent, G., Semroud, R., Djellouli, A., Langar, H. & Duarte, C. 2010. Posidonia oceanica. In: IUCN 2012. IUCN Red List of Threatened Species. V
ersion 2012.2. www.iucnredlist.org.

Trawling has caused marked reductions
of some P. oceanica meadows: 12% of the
surface area in northeastern Corsica,
France; almost 50% in the region of
Alicante, Spain; at least 80% in the Gulf of
Gabès, Tunisia; and trawling is the main
cause of deep meadow losses along the
Latium coast, Italy(3).
Recovery of seagrass meadows may
occur after trawling is banned, but the very
low growth rate of P. oceanica rhizomes (a
few centimetres per year) results in a
recuperation time in the order of at least
one century(7).

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To ensure seagrasses continue to thrive in
the Mediterranean coastal waters, they
must be protected from bottom trawling
and fishing pressure reduced as much as
possible; current regulations banning
trawling on Posidonia meadows in most
Mediterranean coastal areas need to be
enforced and greater areas of seagrasses
included in marine protected areas totally
closed to fishing. Campaigns to raise
awareness together with effective
monitoring and surveillance may be an
effective way forward(8).

References
1. Short FT & Wyllie-Echeverria S. (2000). Global seagrass declines and effect
of climate change. In: CRC. Sheppard (Ed.), “Seas at the millennium: an
environmental evaluation”, Pergamon, Elsevier, Amsterdam, 3: 1011.
2. Pergent et al. (2012). Mediterranean seagrass meadows: Resilience and
contribution to climate change mitigation. Gland, Switzerland and Málaga,
Spain: IUCN. 40 pages
3. Boudouresque et al. (2009). Botanica Marina, 52: 395-418.
4. Martin et al. (1997). Publ. Espec. Inst. Esp. Oceanogr. 23: 243253.
5. Sanchez-Jerez & Ramos-Espla (1996) Journal of Aquatic Ecosystem Health
5: 239-253
6. Sánchez Lizaso et al (1990) Rapp Comm Int Mer Médit 32: 7
7. Gonzalez-Correa et al. (2005). J. Exp. Mar. Biol. Ecol. 320: 6576.
8 Tudela (2004) Ecosystem effects of fishing in the Mediterranean. General
Fisheries Commission for the Mediterranean. Studies & Reviews no. 74