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Luis Herrera Mesa, Full Professor emeritus of Environmental Biology of the University of Navarra
Invasive species: a major threat to ecological and economic balance
Today, World Oceans DayIn addition, it is worth raising the alarm about the introduction of Invasive Alien Species (IAS) through shipping, endangering the conservation of biodiversity in the oceans. A large issue of marine species, identified as invasive species, are transported every day through the ballast water of ships or the hulls of ships.
In order to prevent the spread of IAS through ballast water the International Maritime Organization agreed in 2004 on the internationalagreement for the control and management of ships' ballast water and sediments, which aims to prevent the spread of harmful aquatic organisms from one sea to another by establishing standards and procedures for the management and control of ballast water. The agreement - to which numerous countries have acceded or ratified - entered into force on September 8, 2017.
The problem of the spread of IAS by ships has intensified in recent decades due to the volume of maritime traffic, which continues to increase. The effects in many areas of the world have been devastating. Quantitative data show that the rate of invasions continues to increase at an alarming rate. The spread of invasive species has been recognized as one of the greatest threats to the ecological balance and economic well-being of the planet.
These species cause, first and foremost, enormous damage to biodiversity and to the valuable natural wealth of the seas and oceans on which we depend. In the Mediterranean, for example, more than half of the marine alien species (54%) are thought to have been introduced via ships' ballast water or to have become embedded in their hulls. As a result, aquatic plants account for 30% in the western Mediterranean and 10% in the eastern Mediterranean.
Some researchers estimate that some 300 species have been introduced through ballast water; about 100 species have been introduced through the Suez Canal; about 50 species of macroalgae have invaded areas that were not their own through oyster farming and about 20 through aquaculture. In addition, some eighteen invasive species may have spread through the aquarium trade.
In this regard, it should be remembered that the direct and indirect effects and the damage caused to the environment by practices such as these are often irreversible. In fact, ballast water carries a multitude of bacteria, small invertebrates, algae, eggs, cysts and larvae of different species that have serious ecological and health effects. Certain cholera epidemics are associated with ships' ballast water, since the bacterium that causes the disease(Vibrio cholerae) is found in marine ecosystems in phytoplankton and zooplankton. When sea temperatures are warm, phytoplankton and bacterial populations tend to increase and this is when cholera outbreaks can occur. In addition, V. cholerae can develop in waters with leave salinity if its temperature is relatively high and it confluences with a high concentration of nutrients.
Last but not least, the effect on biodiversity of invasive species has a very significant economic impact on industries that depend on the marine and coastal environment, such as tourism, aquaculture and fisheries, as well as costly damage to infrastructure. Therefore, we hope that this agreement for the control and management of ballast water and sediments from ships will contribute to mitigate the serious damage that invasive species are already causing.