New research finds rats are not just a pest terrestrially, but are also a cause of the decline in coral reefs in our oceans. Read on to find out about other invasive species damaging the world’s most fragile ecosystem…
It is no secret that coral reefs are in danger, 90% are expected to be eradicated by 2050 and while the biggest threat to this diverse system is climate change, research has added many other dangers to the list such as overfishing, trawling and invasive species. An invasive species refers to a species that is not native to a given ecosystem. They are introduced either intentionally or unintentionally via escape, dissemination or placement as a result of human activity and lead to both environmental and economic harm. It is thought that invasive species are second-only to habitat alteration in the cause of endangerment and extinction of native species and the process is less reversible than other threats such as climate change.
With this in mind, take a look at the 3 most prevalent invasive species wreaking havoc on our reef ecosystems today and what is being done to prevent this:
The Black Rat
Native range : India and South-East Asia
Non-native range: Europe, Mediterranean and islands of the Indian Ocean.
Description: Commonly known as ship or house rat it is uniform black in colour with a lighter underside and a long tail used for balance. Black rats are omnivores and feed on a wide variety of crops making them a pest of agriculture also.
Cause of Invasion: Human habitation and trade.
Effect on coral reefs: In a recent study conducted at the Chagos Archipelago (500 kilometres south of the Maldives archipelago) by Lancaster University it was found that on islands with rats only 2 birds per hectare occurred whereas their rat-free neighbouring islands hosted over 1,000 seabirds per hectare. The seabirds are responsible for feeding in the oceans and then returning to the islands to deposit nitrogen and phosphorus rich feces. These nutrients are washed into shallow waters and lagoons and feed fish populations. Subsequently these fish grace the corals and provide a healthy balance in seaweed numbers. Therefore on islands with rats, fish populations are smaller due to a lack of nutrients and subsequently less seaweed is removed and corals become smothered and die.
Solution: Eradication is the only method of protecting the ecosystem and has already been completed in 580 islands worldwide. Estimates suggest it would cost two-million dollars to complete all 40 islands of the Chagos Archipelago which while expensive, could save the coral and seabird populations.
Native range: Indo-Pacific, from Australia north to Japan and Micronesia
Non-native range : Caribbean, Bermuda and Florida coastlines
Cause of invasion: Aquarium trade of North America and carried in ships ballast waters.
Description: Lionfish have distinctive maroon and white bands covering their head and body as well as fleshy tentacles above the eyes. Adults can grow as large as 45 cm and they are known to be active predators of 50 different fish species. They ambush their prey using fan like pectoral fins.
Effect on coral reefs: Lionfish are highly reproductive and one female can release two-million eggs per year leading to devastation of up to 80% of coral reefs within five weeks. They have an enormous appetite and stomachs can expand to up to thirty-times their natural size causing them to feed continually on small fish that graze the corals. The biggest concern about Lionfish is that they have no natural predator in the Caribbean waters and as a result their population is continuing to rise at an alarming rate.
Solution: Scientists have readily come to the conclusion that complete eradication will be impossible and instead a focus needs to be made on managing populations in areas where juvenile fish congregate. Florida has recently introduced the ‘Lionfish Challenge’ which offers incentives to divers and fishermen to catch lionfish that are infesting coastal waters and prizes are awarded based on the number of fish collected. While this may only make a small dent in the vast population until other methods are developed, it’s a good start.
Northern Pacific Seastar
Native range: East Asia (Korea, Japan and China).
Non-native range : Great Barrier Reef, Australia.
Cause of invasion: The transport of bivalve shellfish for aquaculture and ship ballasts.
Description: Adult starfish can grow up to 50 cm in diameter and produce free-swimming larvae which disperse before settling on the seafloor and reefs. They are typically yellow in colour with red and purple pigmentation and upturned tips of their tentacles. Wide ranging diet of shellfish, bivalves, molluscs, worms etc.
Effect on coral reefs: Sea Stars have highly regenerative reproductive rates, in fact 12 million were reported in the space of two-years in Australia’s Port Phillip Bay. They damage the reefs by feeding and depleting shellfish populations thus disrupting the natural ecosystem. It is thought 42% of the loss of the Great Barrier Reef is due to starfish species. Like the Lionfish they have no natural predators in Australia and subsequently humans are required to wipe them out.
Solution: Injecting chemicals into ballast water was a primary proposal however this was impractical due to the large volume of water as well as the risk of leakage. Instead the systems within ships are being modified to prevent uptake such as pumping waters through the engine system so the heat kills the sea stars. Aside from this the Australian government has invested fifty-million dollars into research to find a weakness in the lifecycle of a starfish that can be exploited.
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