In many coastal zones, population increase and changes
in economic activities are leading to alterations of
coral reefs, the seafloor, beachfronts and shores. Urban
expansion can result in destruction of important coastal
habitats, particularly wetlands. As individual species
respond to new conditions, the composition and geographic
distribution of ecosystems will change and biological
diversity may be threatened as species become locally
The loss of biological diversity may take many forms
but the most dramatic aspect is the extinction of species.
The extinction rate depends mainly on environmental
changes and the possibility of species to adapt to these
changes. In the recent years, species extinction caused
directly or indirectly by humans occurs at much higher
rate than the natural extinction.
Four factors in the coastal zone are of special interest
considering the loss of biodiversity:
of species, objects of fishery
of alien species
Example Posidonia oceanica
The beds of Posidonia oceanica, an endemic species
of the Mediterranean Sea, occur in linear fringes in
most of the infralittoral, between 0.2 and 40 m depth.
It is a priority habitat in the EU Habitats Directive.
Posidonia beds are one of the most important ecosystem
of the Mediterranean Sea for a number of reasons:
- they are the nurseries of the sea (high primary
productivity and supply of oxygen)
- support 25% of the region's flora and fauna and
provide essential feeding grounds for sea turtles,
waterfowl, cephalopodes, crustaceans, shellfish and
- they are of great economic importance for fisheries
- they protect against coastal erosion; a loss of
1 m of Posidonia bed may cause a shoreline regression
of nearly 20 m.
Posidonia beds are not rare (France alone has 115 000
hectares), but they have suffered a progressive and
irreversible regression throughout the Mediterranean
- Sand extraction and development of infrastructure,
harbours and artificial beaches, enhancing turbidity
and covering the beds with sand;
- Damming of rivers. Changes in sedimentation in the
littoral zone have led to either exposing or burying
- Trawling and anchoring are especiallly destructive
to exposed rhizomes;
- Eutrophication, augmenting algal blooming. Sewage
and industrial waste discharge cause a complete loss
of the habitat locally.
- Caulerpa taxifolia (a tropical alga introduced in
the French Mediterranean in 1984) that is progressively
overwhelming Posidonia beds.
The situation in the Western Mediterranean is most
serious. Shoot density is rapidly decreasing, up to
50% over a few decades. Besides, increased turbidity
and pollution have resulted into a squeeze of the beds;
in various places living beds have withdrawn between
10 and 20 m depth. Dead beds occur abundantly, even
in waters which have already been protected for 35 years.
For the French mainland coast habitat loss is estimated
10-15%; but taking into account the decrease of shoot
density the overall decline of the resource will be
between 30 and 40%. This is probably a good estimate
for most Western Mediterranean coastlines, although
the situation around the islands and in the Eastern
Mediterranean is better.
Fish from the Dinosaur age are struggling to survive in Black Sea!
Many species of fish species in the world are posing extension because of human generated reasons like water pollution, destruction of their habitat and reproduction environment, overfishing and illegal fishing. Sturgeon, caviar of which, in other words processed eggs, are called “black gold”, is top in the list of the fish which faces extinction. These fish living almost in every sea, river and lakes of the northern hemisphere for about 200 million years are called living fossils.
Example eutrophication; Black Sea coast, Russia
High content of organic and blooming of unicellular
algae based on the rich content of biogenic matters
increase the water turbidity. This means that
the photic layer becomes more shallow. The macroalgae
follow the lower border of the photic zone, along the
slope, because they need sunlight for photosynthesis.
The following data are known from the Russian coast
of the Black Sea. During the last two decades, the belt
of macro-algae in the area of Novorossisik (Gelengik)
moved up on about 20 meters due to high turbidity of
water (and in some area, for example sub tidal slope
near Odessa Cystoseira disappeared completely, Zaitsev,
1991). Mussel beds, that in previous time were hidden
by the brushwood of Cystoseira, became available for
carnivorous gastropod Rapana and practically disappeared
(were eaten). See Vinogradov et al, 1991. (www.ocean.ru)