Northern Pacific seastar

Asterias amurensis

The northern Pacific seastar is an eating machine. They prefer to eat mussels, clams, scallops, and other shellfish. But they will eat anything they can find, like dead fish and even each other.

About the northern Pacific seastar

The northern Pacific seastar comes from the north-western Pacific, near Russia and Japan. It has spread to parts of Australia.

They could live nearly anywhere on New Zealand's coast. They live happily at a range of water temperatures.

Why this is a problem for New Zealand

This seastar could decimate our native biodiversity. Their voracious appetites could damage the entire food chain. They could cause serious declines in our native bivalves (shellfish with 2 shells).

They can settle on mussel lines and salmon cages, becoming a nuisance for our aquaculture industry.

How could it get here?

The seastar could hitchhike on boat hulls coming to New Zealand. While they are small larvae they can swim. During this stage, they could be drawn in to a vessel's ballast water and be brought to New Zealand.

Even if you don't travel overseas, keeping your boat hull clean can stop pests and diseases spreading.

How to identify the northern Pacific seastar

If present in New Zealand, this seastar could be anywhere on the coast.

It has:

  • 5 arms
  • pointed, often upturned tips
  • yellow to orange colour, often with purple markings on top and yellow underneath
  • arms covered with many small, irregularly-arranged, chisel-like spines.

It grows up to 24cm across but can reach 50cm. It often groups together in large numbers.

4 yellow Northern Pacific seastars with purple markings on top
Northern Pacific seastar. Image: CSIRO

You can find more pictures in MPI's pest guides.

If you find the northern Pacific seastar

  • take a photo
  • collect a sample
  • record the location and landmarks
  • call MPI on 0800 80 99 66

Note: This information is a summary of this pest's potential impacts on New Zealand.

Last reviewed: