Seagrass-Watch Magazine Issue 47 - March 2013 | Page 28

T

HERE IS GROWING CONCERN
about the worldwide decline of
seagrass meadows. The amplitude
of the decline varies depending on
the species, the area and the human
pressure(1). In the Mediterranean Sea, loss
of seagrass meadows is mainly due to
coastal development, trawling (fishing
with towed gear), pollution, anchoring,
competition with invasive species and sea
level rise(2).
Trawling in the Mediterranean is
probably the most severe and worrying
current cause of loss of the seagrass
Posidonia oceanica(3). In theory, trawling is
prohibited between 0 and 50-100 metres
depth and/or within the ca. 5,600 m
coastal strip in almost all Mediterranean
countries. However, this legislation is
rarely enforced.

slow growing:
Posidonia oceanica is a large, long-living but very slow-growing seagrass. Its shoots, which are able to live for at least 30 years, are produced at a slow rate from rhizomes which grow
horizontally by only 1-6 cm each year. Over centuries the rhizomes form mats which rise up into reefs that help to trap sediment and mediate the motion of waves, thus clarifying the water and
protecting beaches from erosion. Posidonia oceanica is an important habitat forming species and provides habitat for many species, nursery grounds for the juveniles of many commercially
important fishes and invertebrates. Posidonia oceanica is also grazed on by the Green Sea Turtle (Chelonia mydas).
Source: Pergent, G., Semroud, R., Djellouli, A., Langar, H. & Duarte, C. 2010. Posidonia oceanica. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. www.iucnredlist.org.

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