Northern Pacific seastar

Asterias amurensis

Overview

Photo credit: Marine Pest Photo album, TMAG

Asterias amurensis - Northern Pacific seastar

Description:

5 arms, all ending in small, upward-turned tips and a small central disc
A wide variety of colour morphs, orange to yellow with purple markings and tips on their dorsal side
Underside is completely yellow
Arms are covered in small, jagged-edged spines, which line the groove where the tube feet lie, and join-up at the mouth in a fan-like shape
A straight row of spines along the centre of the dorsal surface of each arm in an irregular, ‘zig-zagging’ pattern
Capable of growing to a diameter of 50cm

Habitat:

Lives in estuarine, intertidal, and coastal zones, with a depth range up to 220m
Found near protected coast areas, avoiding areas with high wave action
Has adapted to warmer waters and therefore able to survive in a temperature range of 0-25ºC
Due to habit of residing in estuarine habitats, they can also tolerate a large salinity range from 18.7-41.0 ppt

Origin and Distribution:

Native to parts of the Pacific Ocean near Japan, Northern China, Korea and Russia
Introduced to oceanic habitats near Europe, Southern Australian Coast and Alaska

Impacts:

A voracious predator known for population outbreaks which heavily impact local bivalve populations, shellfish harvesting practises and associated mussel and oyster beds
Competes with native species that utilise the same prey resources
Negatively impacts populations of habitat forming polychaetes and erect macrofauna
Knock-on effect on sediment processes and nutrient cycling

Is it found in Northern Ireland?

It is not currently present in Northern Ireland

How could it get here?

The primary pathway is via accidental shipping of larvae in ballast water
Fouled fishing gear which hasn’t been appropriately cleaned and dried before use in another water body/area can introduce non-native and invasive species or diseases to the area
Can spread through hull fouling on ships and recreational vessels
Can be transferred along with shellfish and live fish
While unlikely to cause global spread alone, currents carrying larvae contribute to the wide dispersal of this species

Prevent Spread

Prevention via enforcing the IAS (Enforcement and Permitting) Order (Northern Ireland) ensuring that Asterias amurensis is not introduced to Northern Ireland
Reporting any sightings so that Rapid Response can be instigated
If you think you have incidentally caught a Northern Pacific seastar, do not return it to the water
Ensure that boats and equipment are checked, cleaned and dried before putting into another body of water. See Check Clean Dry for further information
Aquaculture managers and owners should avoid getting spat material from areas that are known to have Northern Pacific seastars present or nearby
You can help by reporting any sightings:@ the Centre for Environmental Data & Recording (CEDaR) - Or via the iRecord App.

Current legislative position (Entered into Force on 7^th August 2025): This species must not intentionally be brought into the Union; kept; bred; transported to, from or within the United Kingdom, unless for the transportation to facilities in the context of eradication; placed on the market; used or exchanged; permitted to reproduce, grown or cultivated; or released into the environment.

For further queries, you can contact the Invasive Non Native Species (INNS) Team in the Northern Ireland Environment Agency on 028 9056 9558 or Email: invasivespecies@daera-ni.gov.uk

Northern Pacific seastar

Asterias amurensis

Overview

Invasive Species Northern Ireland