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Seagrass habitats are highly productive ecosystems providing a number of critical functions to adjacent ecosystems, coastal zones and their dependent communities. With over 90,000ha being destroyed globally over the past 10 years seagrass and associated habitats are currently experiencing a world-wide decline. An exponentially increasing human population and a continued lack of understanding regarding the ecological and economic significance of seagrass habitats, means that figure is increasing daily.
The following anthropogenic (human) activities have been documented as the primary causes of seagrass degradation throughout the world:
- Overfishing and poor fishing practices
Studies show that seagrass beds serve as essential shelter, spawning and nursery grounds for numerous marine organisms, many of which provide the basis for complex trophic food webs and functional integrity for neighbouring systems such as coral reefs, as well as providing stocks for subsistence and artisanal fisheries relied upon by poor tropical communities. Lack of knowledge regarding the importance of these habitats in terms of the role they play in fisheries results in inappropriate and unsustainable practices such as shellfish harvesting using rakes and blast fishing.
- Dredging and infilling
In many areas of the world, seagrass habitats are being destroyed for development or smothered by increased sediment run-off due to intensive agriculture and deforestation. In Florida, for example, dredging and infilling have destroyed over 9,000ha of seagrass habitat as a result of land reclamation, in order to make way for new housing and tourism developments. As well as direct destruction, the build up of sedimentation increases turbidity blocking out sunlight so vital for photosynthesis.
- Eutrophication from increased input of sewage, fertiliser and effluent
Records show that nutrient loading accounts for around 50% of seagrass habitat degradation throughout the world. Expanding human population and associated waste, poor farming practices, large-scale aquaculture developments all contribute to an increase in nutrients, specifically Nitrogen, which encourage phytoplankton, epiphytes and macroalgae, again leading to increased turbidity.
- Anchor and propeller damage from boat traffic
Damage from anchors and propellers has been shown to be a common cause of degradation in shallow coastal areas resulting in fragmentation, a decrease in productivity and the possibility for further degradation due to the opening up of channels increasing the flow of water.
If the above practices continue unabated many critical ecosystem functions and interactions will be lost. Seagrass habitats stabilise the environment, resulting in important physical and biological support for adjacent ecosystems and the coastal zone as a whole. As well as the continued supply of important commercial species for community fisheries, these habitats also provide vital protection for coastal areas by preventing erosion and attenuating wave energy through the consolidation of sediments. The build-up of sediment can also provide substrate for mangroves which in turn provide numerous services such as nursery grounds, erosion protection and nutrient filtration.
Current losses of seagrass habitats are expected to accelerate as anthropogenic disturbance increases. Although restoration techniques exist they have not been overly successful and to date there have been no long-term assessments of restoration success. There is also little evidence that restored or mitigated habitats function in the same way as their natural counterparts. Therefore it is recommended existing seagrass habitats be conserved rather than attempts made at restoration.
Lack of understanding, particularly in poorer areas, of the values of seagrass beds, both ecologically and economically, is a fundamental cause of degradation and a primary reason why these habitats are treated with disregard. Estimates of the monetary value of goods and services provided by seagrass habitats are substantial. For example, the projected total yield for fisheries supported by seagrass in Australia is more than AUS$60million. However, seagrasses, like coral reefs are highly susceptible to natural and man-made catastrophes and these combined disturbances are resulting in wide-scale loss of this essential resource. |
