THE DESTRUCTION OF HABITATS IN THE MARINE ENVIRONMENT BY COASTAL DEVELOPMENT

Damage to the marine environment that is underestimated

Each reclamation from the sea destroys an underwater habitat by building over or enclosing a body of water. A high density of reclamations on small shallow bottom areas represents a major form quantitatively of damage to the underwater environment. The destruction caused is irreversible.

Any assessment of the negative effects on marine ecosystems of reclamations from the sea is often perceived as hostile to development. This means that few studies have dealt with this conflictual and politically sensitive topic, and there has been little investment of funds or human resources devoted to this subject. As a result, taking stock of the full impact of developments on reclaimed land is often neglected.

The coastal environment is by far the richest in terms of biodiversity

The marine environment is divided into two major domains where specific food chains are estabablished. A distinction must therefore be made between the pelagic and the benthic environments.

The pelagic ecosystem is that of the open sea. The food chain is based on vegetal plankton (microscopic vegetal cells used by animal plankton, which is used by pelagic fishes such as anchovies and sardines, which in turn feed the great predators: tuna, dolphin, etc.). These environments extend over the whole of the surface of the seas and oceans, in the well-lit superficial zone (mainly the zone situated between 0 and -100 m).

The benthic ecosystem is that of the sea bottom. This environment includes the species fixed on the sea bottom or buried in the marine substrate and those that need to live near the bottom to develop or to pass part of their life cycle. This life system is much more diversified than the previously cited one. One group of international experts (1) has highlighted this fact with the following axiom:

« Marine biodiversity is greater  in the benthic system than in the pelagic system »

(1) Joint group of Experts on the scientific aspects of marine environmental protection. GESAMP Reports, N°6, 1997; IMO/FAO/UNESCO –IOC/WHO/IAEA/UN/UNEP

The coastal benthic environment is highly diversified in the superficial zone

The well-lit shallow bottoms (mainly between 0 and -20 m) are covered in vegetation consisting of macrophytes (algae and flowering plants such as, in the Mediterranean, Posidonia oceanica). This sub-sea vegetation is a source of food or shelter for a specific fauna (herbivores, detritivores, etc.). In contrast, the bottoms where there is total obscurity (> -100 m) are only colonised by a poorly diversified and sparse fauna (only feeding on organic detritus falling from the surface).

The same group of international experts (1) has thus proposed this second axiom:

« The coastal systems are the richest because of the diversity of coastal habitats. »

The coastal benthic ecosystems only extend over small areas

The richest coastal benthic ecosystems (where the macroscopic algae and the flowering plants can develop) only extend over the superficial area of the continental shelf. In certain regions, such as the rocky coasts of Provence-Côte d’Azur and off the west coast of Corsica, the continental shelf is very narrow. The -20 m isobath is often found less than 500 meters from the shore. The richest zone in terms of biodiversity is in this case reduced to a narrow strip bordering the coastline.
It is upon this strip of ‘oasis’ for marine life that the coastal developments are constructed.

Reclamations from the sea destroy the sub-sea habitats

Reclamations from the sea destroy the richest marine habitats. The marine areas reclaimed and turned into terrestrial areas are totally destroyed and the bodies of water enclose other areas, upsetting environmental conditions. The natural coastal space is thus progressively reduced.

Destruction is cumulative

It is the total of all the areas reclaimed from the sea that should be taken into account to assess the overall impact. This accumulated total corresponds to the destruction of underwater habitats that can be estimated at the scale of geographical or administrative units (state, region, county (département), municipal or rural district (commune) or natural units (cape to cape, rocky coast, alluvial coast, etc.). Each additional construction adds to the total marine surface area destroyed.

The destruction is irreversible

In contrast to the other forms of damage to the marine environment, destruction by reclamations involving building over the sea or enclosing bodies of water is definitive. While local authorities may be able reduce pollution at the source (sewage treatment plants, limitation of toxic discharges, etc.), it would be utopian to envisage the destruction of a harbour in the hope of recreating the destroyed marine habitat. Similarly, the idea that benthic ecosystems might spread offshore from the constructed areas must be ruled out. Those that exist already remain unchanged and the areas beyond do not correspond to the environmental conditions destroyed by the construction (too deep, too little light, etc.,

Construction irreversibly damages the areas reclaimed from the sea.

Impact outside the construction area

Each construction presents specificities with regard to the impact outside the area, such as:

• dilution of polluted waters from the enclosed water within a harbour,
• disturbance of the current regime caused by construction further along the coast,
• the anchoring of boats in the few natural harbour areas, which increases with each new construction of a marina.
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• Positive effects

The submerged blocks (concrete or limestone) used to build the sea walls and breakwaters represent a very narrow strip of rocky substrate (generally less than twenty metres wide). Usually built on soft bottoms, these rocks that enclose bodies of water are colonised or frequented by rocky substrate flora and fauna. While this might be considered as an indirect positive effect of land reclamation, the quantitative amount (surface area) of the solid support thus provided is far from compensating for the areas destroyed by the reclamation. Similarly, the submerged rocks are sometimes implanted on very rich ecosystems (Posidonia seagrass meadows) which do not develop on the submerged rocks of sea walls or groynes. Very often, the withdrawal of the Posidonia meadow relative to the the last of the submerged rocks protecting a redevelopment may be observed.

Non-sustainable development

The development of coastal areas is part and parcel of economic development. The reclamations from the sea occupy the shallow bottoms and artificialise the coastline. The surface areas and coastline available for development are not extensible. On the contrary, they shrink with each new reclamation. Progressively, the natural spaces are irreversibly becoming scarcer and conflict between users is becoming more frequent. The development of human activities on reclaimed areas is not therefore sustainable.