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Revision as of 12:19, 3 February 2009
Habitat destruction and fragmentation is a process that describes the emergences of discontinuities (fragmentation) or the loss (destruction) of the environment inhabited by an organism. Marine ecosystems are experiencing high rates of habitat loss and degradation, and these processes are considered as one of the major threats to marine biodiversity. It is estimated that every day between 1960 and 1995, a kilometer of coastline was developed, causing permanent losses of valuable habitats, such as coastal wetlands, seagrasses meadows and rocky shores [1]
Habitat can be defined as predominant features that create structural complexity in the environment, such as plants (e.g., seagrass meadows, kelp forests), or animals (e.g. Sabellaria reefs, burrowing fauna in sandflats).
Relationships between habitat loss and species diversity Researchers have identified three major components of habitat loss [2]:
1) The loss of resident species
There is a unique plant and animal diversity living in close association with specifics habitats or habitat forming species. For example, invertebrate assemblages associated with mussel beds, epiphytic and epibenthic assemblages communities living in kelp forests or fish communities associated with coral reefs. The risk of diversity loss associated with the destruction of these habitats has been estimated using several ecological models, e.g. species-area curves. However, in general it is predicted that the effect of habitat loss is likely to be synergistic, rather than the sum of the loss of individual species, because of the interaction between species leading to a chain of impacts.
2) The loss of food resources Most biogenic habitats such as kelp forests, seagrass meadows, and other vegetated habitats and their associated organisms are known to be highly productive compared to structurally simpler habitats such as sandy habitats. They export a large amount of nutrients and particulate matter to coastal food webs either through direct transfer of animal biomass (i.e. predation, movements of individuals) or indirectly through dissolved and particulate organic. The loss of these food resources can negatively affect the productivity of individual species or communities, with more profound effects that are likely to propagate along food chains.
3) The loss of ecosystem functions provided by the habitat
Structurally complex habitats provide a wide range of ecosystem functions to the environment including food and refuge provision for other species, trapping sediment, modifying light and hydrodynamic conditions, providing resilience to the system. When the habitats are lost this functions are lost with them. For example, the replacement of macroalgal canopies by turfs affects sediment dynamics on rocky coasts, where fronds prevents accumulation of sediments while turfs tend to trap sediments even on exposed coasts.
Effects of habitat loss on biodiversity
Habitat loss has been generally associated to drastic declines in overall abundance and diversity of marine organisms. For example, in the Wadden Sea, the destruction of biogenic habitats has caused the regional extinction of at least 26 species during the past 2000 years [3]. Similarly, the loss of seagrass meadows results in a reduction in the number of species and abundance of fishes.
Human activities
Some anthropogenic activities responsible for habitat destruction include the construction of coastal protection, land reclamation, aggregate (sand and gravel) extraction, recreation and developments including ports, harbours and industries. Additionally, the growing number of tourists presents a significant threat to many coastal habitats in Europe, which can disturb by trampling or direct harvesting. In offshore waters, exploration and development of oil and gas activities threaten marine habitats, mainly with discharges of oil and other pollutants. Physical damage to marine habitats can result from fishing activities such as bottom trawling. Deep-water trawlers use heavy rock-hopping equipment, which has been reported to cause long-term to seabed habitats such as cold-water coral reefs in Norwegian, Scottish and Irish waters.
References
- ↑ Airoldi, L., Beck, W.M. 2007. Loss, status and trends for coastal marine habitats of Europe. Oceanogr. Marine Biology Annual Review 45, 345–405.
- ↑ Airoldi, L., Balata, D., Beck, M.W. 2008. The Gray Zone: Relationships between habitat loss and marine diversity and their applications in conservation. Journal of Experimental Marine Biology and Ecology 366, 8-15.
- ↑ Wolff, W.J. 2000. Causes of extirpations in the Wadden Sea, an estuarine area in the Netherlands. Conservation Biology. 14, 876–885.
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