Introduced species in the Great Barrier Reef

Most marine invasive species have been introduced to Australian waters unintentionally through shipping activities and mariculture.

Australia’s large volume of shipping trade with South-east Asia and the similarity of marine environments increases the risk of introducing marine species. Yachts and smaller vessels can also unintentionally provide a mechanism for transporting marine invaders either as fouling or in ballast water.

Heavily fouled vessels can carry up to 5kg of fouling material per square metre of exposed surface. In the right conditions, the exotic species carried as fouling can be released or spawn and establish in new locations.

It is estimated that about 7000 different marine species, including viruses, bacteria and small marine invertebrates are transported around the world in ballast water every day. More than 150 million tonnes of ballast water is discharged into Australia’s major ports each year. Toxic dinoflagellate algae for example can survive in ballast water for weeks. Dinoflagellates can accumulate in mussels, osters and scallops and when eaten cause paralytic shellfish poisoning in humans.

Despite port surveys to define the state of introductions and occurrences of non indigenous species, knowledge about the occurrence and abundance of toxic microalgae in the Great Barrier Reef World Heritage Area remains scarce and incomplete, especially in regard to introductions and invasiveness.

Exotic marine species can also be introduced unintentionally when released from aquariums or deliberately introduced for aquaculture.

In 2001, the Asian green mussel (Perna viridis) was found on a vessel’s hull in Cairns harbour. This mussel is considered a potential threat and is included on the Next Pest List (potential pests which have not yet established).

The discovery caused concern because in other parts of the world populations of the Asian green mussel can grow quickly and cover underwater walls, boat hulls and intake pipes and compete with native fauna.

The Caribbean tubeworm (Hydroides sanctaecrucis) has also been introduced into Cairns harbour and other Australian ports and marinas. It is a native of the Caribbean which inhabits muddy coastal lagoons. It is a nuisance for vessel owners because it builds calcareous tubes on hard surfaces such as boat hulls which can reduce the boat’s performance and speed, and increase costs of maintenance.