1.32 Many habitats are important, in terms of
heritage, by virtue of their representativity in the Mediterranean
context and the direct and indirect threats they face.
1.33 For 15,000 years man has been exerting his
influence as an integral part of the ecological system of the Strait
of Bonifacio. Man-induced factors (sample-captures, alteration or
destruction of habitat, disturbances, introduction of species...),
whether old or more recent, direct or indirect, are exerting an increasing
impact as methods of navigation and sampling techniques evolve. Those
factors are responsible for the disappearance of the monk seal (Monachus
monachus) and the reduced populations of the limpet Patella
ferruginea, a process which has been affecting that mollusc
since prehistoric times, and the grouper Epinephelus marginatus for
30 years.
1.34 It is also quite clear that climate change,
especially the increases in air and sea temperatures, as well as fishing
activities across the Mediterranean, is exerting an ever increasing
influence on the overall functioning of the Strait of Bonifacio.
1.35 Increase in seawater temperature triggers
significant changes in the ways that pelagic communities (tropicalization
of plankton production) or benthic communities function in the north-west
Mediterranean. It benefits tropical species, such as the yellowmouth
barracuda Sphyraena viridensis, to the detriment of certain
Mediterranean species that cannot support the rise in temperature.
In this regard, the spectacular rise in mortality rates since 1998
among gorgonias is cause for concern.
1.36 Man-induced activities also generate cascade
effects. Such occurrences may be confined to the territory of a protected
marine area or affect its periphery. Thus, the destabilization of Posidonia
oceanica owing to increased numbers of unregulated anchorages
or sediment erosion is leading to a reduction in the populations of
species associated with this habitat, in particular the pen shell Pinna
nobilis. Failure to manage household waste and the existence
of open-air public landfill sites for over 30 years have brought about
an increase in the population of yellow-legged gulls (Larus
cachinnans) and a serious deterioration in the micro-insular
systems of southern Corsica (destabilization of vegetation by the
action of nitro-phosphates on floristic corteges, and inter-species
competition between the very rare Audouin's gull (Larus audouinii)
and the yellow-legged gull, to the latter's advantage).
1.37 Waste from purification plants undergoing
repair is also likely to affect the existing habitats. Large-scale
recreational use of the location also produces effluent and larger
waste products, particularly plastic bags, which become mixed in with
schools of jellyfish and are then consumed by loggerhead turtles and
bottlenose dolphins, causing obstruction of their digestive systems.
1.38 The habitat known as "silty sands in sheltered
areas (Mediterranean) biocoenosis" in the large creeks and shallow
bays of Lavezzi, Cavallu, Ventilegne, Santa Manza, Porto Novo and
Rondinara remain under the influence of the nutrients and pollutants
which arrive from the drainage basins, bringing the risk of hypoxia
or anoxia owing to the low water renewal rate. This habitat can also
prove to be a good indicator of anthropization level in the drainage
basins themselves.
1.39 The habitats of submerged or semi-submerged
sea caves are extremely sensitive to the impact of man. The Sdragonato
cave and undersea caves used in diving are areas of particular sensitivity.
1.40 In France, the belts of Lithophyllum
lichenoides have receded in polluted areas. The situation of
the algal limestone belts, like that of L. Lichenoides at the mediolittoral
level, and their porous structure, makes these formations highly vulnerable
to surface pollution by effluents, oily film on the water and other
agents. The loss of even a little salinity in the water prevents them
from forming. There could also be a threat from phosphate ions and
detergents (LABOREL, unpublished, in Boudouresque et al., 1990). A
belt appears to take an exceptionally long time to build up (several
centuries) and it is imperative to protect the existing ones (Boudouresque
et al., 1990).