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Little squirts that hang out around the coast

12 February 2013

Little squirts that hang out around the coast

When you are at the beach or harbours this summer, don’t be surprised if you see sea squirts - marine animals we commonly see attached to rocks and wharf piles that have two siphons on the top of their bodies, one to draw in water and the other to expel it. When disturbed, sea squirts contract their siphons, expelling streams of water—hence their name.

NIWA has created a new, colourful and intuitive guide to sea squirts found around New Zealand coasts and ports. Packed with photographs of 28 species, the guide is geared towards easy identification of sea squirts in the field and is a useful tool for keen underwater observers.

The guide includes some of the recently arrived invasive species of sea squirt that have colonised our ports and harbours, as well as many benign native species. It covers species we’re already aware of, so if you spot what you believe is a new one, please let the Ministry for Primary Industries know on their freephone 0800 80 99 66. Checks can be made to make sure it is not likely to be troublesome.

Sea squirts (ascidians) are amongst the most commonly found fouling animals in ports and harbours around the world, including New Zealand’s. They settle and grow in great abundance on submerged structures such as wharf piles, seawalls, ship hulls and aquaculture structures. In some countries, they are eaten by humans.

The guide gives important information about each species: its appearance, whether it is native, its habitat, how common it is, its distribution around New Zealand, and what threats (if any) it poses to New Zealand ecology and aquaculture.

While most native ascidian species are found in low numbers in intertidal and subtidal environments around New Zealand, non-indigenous species can be highly successful, often reaching densities that preclude other species. The potential impact of some of these sea squirt species on the shellfish aquaculture industry in particular, can be serious.

Sea squirts have abundant, highly mobile larvae that settle and grow quickly into adults, competing with other species for food and space. Some species are able to replicate themselves asexually, which causes very rapid growth of the colony. Rapidly growing sea squirt colonies, such as Didemnum vexillum, can overgrow and smother mussels. Pyura praeputialis forms dense mats that alter natural habitats used by other species.

NIWA scientist Mike Page says, “We designed the guide because people want to know what they are, particularly when they are on the hunt for non-indigenous and invasive organisms. Therefore the guide will be useful for the Ministry for Primary Industries, Department of Conservation, regional councils, district councils, schools, universities and port authorities.”

The guide contains easy-to-follow diagrams of sea squirt biology and flowcharts for species identification. It uses clear and user-friendly icons for each species to show key information about its habits and characteristics.

The sea squirt species are illustrated with high-quality images of the animals in their habitat.

“As far as possible, we have used identifying features that can be seen with the unaided eye or a magnifying glass, and language that is non-technical,” says Page.

The guide is dynamic and new species will be added as they are discovered. The guide will be updated on NIWA’s website.

This research was funded by the Ministry of Business, Innovation and Employment.


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