Habitat loss
Habitat conversion and degradation are generally thought to be the most significant threats to terrestrial life. Within marine ecosystems, they rank along with overexploitation and pollution as major causes of biodiversity loss [5].
Coastal development contributes to habitat loss in a number of ways. These include conversion of mangroves and other wetlands as a result of urbanization and agricultural expansion, the building of shoreline stabilization structures such as breakwaters, mining, oil drilling, and dredging and filling. These result both in the destruction of wetlands and other habitats and in the degradation of nearby areas (through siltation and changes in water temperature and flow, salinity, and other physical factors).
Damming of rivers and water diversion projects lead to changes in downstream estuarine and marine communities, because interruption of freshwater flow changes the physical environment of such areas and the amount of nutrients that they receive. Completion of the Aswan Dam on the Nile River in 1965 led to the erosion of delta habitats and is considered an actor in the subsequent collapse of eastern Mediterranean fisheries [6]. In addition, dams can cut off species access to spawning areas--this includes not only species that live in saltwater and reproduce in rivers (such as salmon) but also freshwater species that breed at sea (such as freshwater eels).
Intense exploitation of marine resources can indirectly lead to habitat loss. For example, trawling disturbs bottom-dwelling communities--both adjacent to shorelines and in deeper coastal waters--as nets scour seabeds and smother burrowing creatures and other species with sediments. Fishing with dynamite and harvesting of corals are major threats to coral reef areas.
