As ISMAR-CNR will be present at Seafuture 2009, we'd like to introduce one of the most pressing issues regarding the use of technology in the reserch and fighting of solid pollution.
Here's a brief interview with Dr. Stefano Aliani.
- How do the Mediterranean gyres turn?
The Mediterranean circulation model is very complex and a lot of variability has been recently reported. Please take a look to the MFStep project website for a daily forecast ( http://www.bo.ingv.it/mfstep/ ).
- What would be the route of a plastic bag if it were dropped at Barcelona coast, for example?
There are different possible scenarios:- Released during storms, often in a river plume. The debris will be trapped in the plume of the river and very likely stranded on local beaches due to SW or SE storm winds. This plastics are often broken by waves.- Released in good weather conditions. Floating objects are mainly subject to surface breeze and general circulation. If they leave the local/coastal eddies (with their own local pattern, which can be predicted only with targeted local studies), they enter the general circulation and are expected to move westward. A sketch of the circulation in the area can be found at http://www.noveltis.net/mfstep-wp9/interface/english/bulletin/bul.php?b=1&z=0&c=1 - They sink. A lot of debris is not transported by surface currents but just sinks locally due to vertical currents or changes in floation due to fouling. Large debris is usually found in the nets by fishermen and also visible on the sea floor in ROV images.- They are reduced to small size by the mechanical interaction with waves and are transformed in small stripes or pellets falling on the seabed. Here they can be ingested by detrivorous animals and further reduced in size to became a component of modern marine sediments.- They are actively removed by cleaning programs (volunteers or paid staffs) or by animals (birds, mammals) that will die elsewhere.
- You probably know about the Pacific Garbage Patch, is the Mediterranean in a similar situation?
No situation comparable to the Pacific Patch has been reported for the Mediterranean Sea. In the Mediterranean there are some accumulation points in the middle of some large permanent gyres where the currents force is low. However the size of the Mediterranean basin is smaller than the area affected by recurrent meteorological perturbations and severe storms can drive the debris from the low energy center of the gyre to the high energy border preventing accumulation as in the Pacific. The Pacific Garbage Patch is in an area of Equatorial calm with special current pattern that does not take place in the Mediterranean.
- What’s your experience with the Mediterranean debris? Do you usually find floating objects on the sea?
There is a lot of rubbish all over the world oceans. You know the Pacific plastic monster, but plastic has been found even in remote areas like the Antarctic waters. We evaluated the quantity of debris in the Western Mediterranean and we found about 15‚25 objects per km2 during good weather and about 3 objects per km2 after storms in open water far from the coastal areas. In coastal areas the values can be higher. The amount reported in this paper from the Ligurian Sea is not so different from what you can usually find in the Mediterranean Sea.
- Which is the strangest object you’ve found?
You can find every human product: beds, doors, refrigerators, containers lost from ships, everything.
- Is the problem worst at sea floors or at the surface?
The problem is global: you cannot say if it's worse here or there. Surface debris is visible, so it may directly affect tourism and nautical activities, entangle animals (turtles, mammals, birds) and you can perceive it immediately. Sunken debris is more subtle. Fishermen are well aware of it; it destroys nets and is a common by-catch of trawling. But, we don't know the fate of all this chemicals we released at sea as small pellets in the sediments. They are eaten by animals and accumulate at higher trophic levels entering the food web. There are very few scientific data on the effect of this return molecule in the environment. We put garbage under the carpet. Nobody see it, but surely it is not so healthy to leave it there in our living room!
- How is “hitch-hiking” debris affecting the Mediterranean sea? Could you give us some examples?
In the Mediterranean Sea there is large migration trend of marine species after the opening of the Suez Channel. The original path of the Suez Channel was across the Bitter Lakes that are very salty and were an ecological/physical barrier for migration of marine species. Recently, the Suez channel has been deepened and a new path exists across the Channel. This new path doesn't pass through the Bitter lakes and the barrier to migration is lost. A number of alien species is entering the Mediterranean Sea, also finding a suitable habitat in the warmer-than-before Mediterranean waters http://www.ciesm.org/online/atlas/index.htm ). Floating debris is a way for alien species to migrate over long distances, as debris travels faster than larvae and is less predated than free swimming larvae.
Dr. Stefano Aliani is a researcher at the Institute of Marine Science of the National Research Council, Italy. His research interest is on the interplay of physical and biological forcing and on the control they exert in the functioning of the ecosystems, especially under extreme conditions. Among other, he recently studied floating marine debris as an important mean of transport for alien species, coupling biodiversity studies with lagrangian modelling.
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