Marine biosecurity

Status: Progressive containment (with Breaksea Sound and Southern Exemption Areas)

Undaria is an opportunistic invasive seaweed that forms dense stands underwater, giving it the potential to compete for light and space with native species. Due to Undaria's ability to spread rapidly in the marine environment, it is often referred to as the gorse of the sea.

Mature Undaria plants, which can grow 1-2 meters tall, are characterised by a distinct mid-rib. It's a highly invasive seaweed and is now widespread throughout Aotearoa harbours and coastlines, including Bluff Harbour and the northern reaches of Rakiura/Stewart Island.In April 2010, Undaria was found on a mooring line in the remote Sunday Cove in Te Puaitaha/Breaksea Sound. It is now established at locations within the Te Puaitaha/Breaksea Sound – Tamatea/Dusky Sound complex and is the focus of theFiordland Undaria Control Programme. We also manage this species at two sites in the southern reaches of Rakiura/Stewart Island.

Status: Exclusion

Mediterranean fanworm is a segmented worm that lives within a tube attached to hard substrate. This species of fanworm can grow to 40 cm tall and has a singular fan, compared to natives which have two fans. It forms dense colonies and can impact native species by competing for food and space. Recent scientific studies indicate that this fanworm can negatively affect the new generation of some marine species and change nutrient flow.

Mediterranean fanworm is abundant in Auckland’s Waitemata Harbour, Whangarei Harbour, and in Lyttelton Port and has been found in many other harbours including Otago Harbour. Continued efforts focus on restricting the spread of Mediterranean fanworm within New Zealand.

Status: Exclusion

Styela clava is a club-shaped sea squirt with tough leathery skin. It is cylindrical in shape, grows up to 16cm in length, brown in colour, and has a stalk-like holdfast that anchors the animal to structures such as rocks, wharves and boat hulls. Styela clava has two siphons on the top of the organism, which it uses to filter food from its surrounding environment.

Styela clava is known to be present in many Aotearoa harbours, including Otago Harbour. It can potentially compete with native fauna, particularly molluscs, and is of major concern to New Zealand's aquaculture industry. This species can foul aquaculture gear such as mussel lines, smothering and competing for space and food with farmed species.

Status: Exclusion

Asian paddle crabs are relatively large swimming crabs with paddle-like hind legs. The upper shell of adults can reach 12 cm across and is covered in small hairs (which are not always visible). The adults also have six distinct spines or spikes on each side of the shell below the eyes. There are five prominent spines on the upper surface of each claw. The crabs range in colour from pale-green or olive-green to a deep chestnut-brown with purplish markings on the shell.

These crabs are very aggressive and have the potential to compete with native crabs for space and food. They are generalist predators and prey on native species including shellfish, fish, other crustaceans and polychaete worms. They are present in Aotearoa, north of Bay of Plenty.

Status: Exclusion

The Eudistoma sea squirt, also known as the Australian droplet tunicate, forms large colonies that attach to hard surfaces and look like clusters of white or cream-coloured cylindrical tubes. Each colony contains numerous small individuals, and they can appear orange flecked due to the colour of the larvae within them. This species is generally found in soft-bottomed tidal habitats and on hard structures such as wharf piles, aquaculture equipment and mangrove roots. It prefers submerged habitats just below the waterline but can be found out of the water for periods during low tide.

Australian droplet tunicate competes with native species for both space and food. It has a rapid growth rate, can inhabit a wide range of habitats, and can reach high abundances. It is present in the far north of New Zealand, including Auckland

Status: Exclusion

The Pyura sea squirt has a sack-like body with a brown, or reddish-brown, leathery skin. There is sometimes sand and shell material incorporated into the outer skin, and other sea life such as sea lettuce can grow on and around them. Adults grow up to 15 cm or more in height and around 3–5 cm in diameter.

An aggressive competitor for space, the Pyura sea squirt has the potential to significantly alter the structure and composition of intertidal communities. Dense mats have already engulfed and displaced native, green-lipped mussel beds in some areas of the far North. Although not established, it has also been found on vessel hulls as far south as Wellington and Nelson.