Many of the coastal dune
systems along western Mediterranean shores are in an advanced state of
fragmentation and show distinct signs of erosion, largely because of blowout development
along the dune front. The Es Comú de Muro beach-dune system on the island of
Mallorca (Spain) is a good example of this. In order to better understand and
quantify the current situation, fifty-eight blowouts along an about 1.5-km-long
dune front were investigated. In each case, a number of morphometric and ecological
variables were analyzed as a basis for comparison and classification, in
particular blowout dimensions and orientation, inner morphometry and
topography, morphological types, the role of vegetation in defining the state
of the foremost dune line, and the link between vegetation and blowout typology.
In comparison with a recent preliminary investigation, the results of the
present study provide a more comprehensive picture of the advanced state of
fragmentation along the dune front. The blowouts are not evenly distributed,
highest densities occurring along the southernmost part of the beach, lowest
densities along the northern part. The blowouts were divided into two
categories on the basis of their shape and general structure, trough blowouts
being the most prevalent, followed by mixed trough-saucer shapes. Distinctly
saucer-shaped blowouts could not be distinguished. In addition to this
subdivision, the blowouts were divided into two morphological categories, i.e.
simple and branched blowouts. It was also possible to link the morphological
state of the dune front to particular ecological parameters, in particular
vegetation which, in the present case, comprised herbaceous and woody plants. Cluster
analyses of species associations
(Bray-Curtis similarity indices) were carried out on the basis of the
presence/absence of each species. It is shown that, on account of presence counts
and the degree of similarity of species associations, some species play a more
important role in stabilizing the mobile dune sands than others, a foremost
candidate being Ammophila arenaria. It is concluded that active support for
such plants should form part of any management strategy aiming to reduce and
reverse coastal dune fragmentation processes.
Mir-Gual, M., Pons, G.X., Martín-Prieto, J.A., Roig-Munar, F.X., Rodríguez-Perea, A. (2012). "Geomorphological and ecological features of blowouts in a western Mediterranean coastal dune complex: a case study of the Es Comú de Muro beach-dune system on the island of Mallorca, Spain". Geo-Marine Letters (on-line)
Miquel Mir Gual
