Aliens in Our Waters: Marine Invasive Alien Species

Alien is a term everyone is familiar with – creatures with long limbs and large eyes come to mind, like E.T. the Extra-Terrestrial from the popular 80s movie. While the existence of extra terrestrial life has been long debated, Sri Lanka is vulnerable to a very real threat from alien species of a different nature. These organisms travel a considerably smaller distance on earth (compared to E.T. from outer space) to colonise Sri Lankan soil and waters. Simply put, an Invasive Alien Species (IAS) is anything that exists and thrives where it doesn’t belong.

In recent years, movement of species from one end of the globe to the other has been accelerated, and is no longer moderated by winds, currents, and other environmental factors. These species are able to colonise their new environment and grow exponentially due to the lack of natural predators, parasites, or diseases to control their population in those areas, and often wipe out native ecosystems.

Most marine IAS catch a free round-the-word trip in ship ballasts. Large ships have tanks in their hulls that are filled with sea water to counterbalance the weight of the cargo and provide stability. These ships will take on water at one port and discharge it at another. It is estimate that 7,000 species are carried around the world in ballast water every day, and 10 billion tonnes of ballast water are transferred globally each year. Sri Lanka’s ports, being located in the middle of the east- west trans oceanic route, are world famous stopover points for ships marine alien species alike, and so is at high risk.

Marine species can also invade new ecosystems by hitching rides in scuba gear, packaging, on the hulls of ships, or in consignments of live organisms traded to provide live bait or gourmet food. Additionally if pets acquired through the aquarium trade are released into the wild, they may become invasive.

Climate change is also playing a part in the spread of marine IAS. Sea temperature rise is allowing alien species to populate habitats that were once too cold. Around the world, fish, crab, mussels, clams, jellyfish, corals, sea squirts, sea weeds, sea grasses, as well as microscopic disease causing pathogens are just some of the life forms that have wreaked havoc after they were introduced.

The marine IAS ‘Zebra Mussel,’ for example, was introduced by cargo ship ballast water to North America from the Black Sea in 1988. It multiplied uncontrollably, starving out the native mussel populations and interfering with human structures like factory pipes and ship rudders. The mussel quickly spread from Canada to Mexico and between 1989 – 2000 is it estimated that US$ 750 million – 1 billion were spent on controlling this maritime invader.

This non-beneficial exchange of species was mutual, as in another case, the accidental introduction of a jellyfish to the Black Sea lead to a collapse of fish stocks in the area. The jellyfish larvae hitched a ride in the ballast tank of a ship from North America and rapidly took hold in these food rich and predator free waters. The jellyfish population numbers grew exponentially and preyed on fish eggs and larvae and in less than 14 years, the area’s anchovy fishery had almost disappeared.

Equally formidable is the red sea jellyfish. It entered the Mediterranean in 1869 through the then newly built Suez Canal. Now, each summer, huge swarms appear along the coast, sometimes with 25 jellyfish per square meter, forming a ‘jellyfish belt.’ This has had a devastating impact on fisheries, tourism and coastal infrastructure across Israel, Egypt, Lebanon, Turkey and Cypress.

It can be difficult to predict which introduced species will become invasive, and when. For example, the Chinese mitten crab was found in coastal areas in the UK for around 60 years after introduction, causing minimal ecological disturbance. However, a series of very dry summers in the 1990s reduced the flow of rivers in the south allowing crabs to settle, reproduce and boom in number. These crabs then traveled long distances upstream, feeding on native species, and burrowing into stream and river banks and leading to bank collapse.

In Sri Lankan waters, research on marine IAS is sparse, with one study on the introduction of alien plankton through ballast water, finding the effects of plankton to be negligible. However, out of the 57 different taxa of plankton found in the ballast water, 30 taxa – i.e. 53% of the plankton – were not recorded from the local sites and hence were likely alien species from other parts of the world. In addition, a global study reported 8 marine IAS in Sri Lankan waters.

The effects from such species can be catastrophic in a nation like Sri Lanka which relies so heavily on resources from its marine ecosystems. The fisheries sector, which accounts for 1.8% of the GDP and 2.4% total export earnings, would be the worst hit from marine IAS. The tourism sector would not be far behind if Sri Lanka’s scenic beaches and coral reefs were to be compromised.

Sri Lanka has legal framework to combat terrestrial and freshwater invasive species with the Flora and Fauna Protection Ordinance (No. 02 of 1937, as amended), Fisheries and Aquatic Resources Act (No. 02 of 1996 as amended) and the Plant Protection Act (No. 35 of 1999).  There are currently no regulations regarding ballast water. However, the provisions of the Marine Pollution Prevention Act (No. 35 of 2008) can be used to bring in necessary regulations to control and regulate the release of ballast waters in the seas of Sri Lanka.

Worldwide, governments are focusing on ways of handling ship ballast, and surveillance and monitoring of marine ecosystems. Some countries have laws requiring that ships release ballast while out at sea or treat/kill stowaway species before releasing the water into the coastal waters. Eradication of Marine IAS poses a much bigger threat compared to their land based counterparts. Marine areas cannot to quarantined, cordoned off, or otherwise separated from the rest of the environment. Where eradication of marine IAS is not possible, some form of control might be feasible, but it is always better – and cheaper! – to prevent introduction.




 – Dhiya S Sathananthan

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