What does it look like?
Dead man's fingers is a large, branching, dark-green seaweed. It can reach lengths of 1 metre and can weigh up to 3.5kg. It can look like a fuzzy patch of tubular fingers that hang down from rocks during low tide, hence its common name. The "fingers" are branches up to 1cm wide and sometimes over 30cm long. There are several native Codium species (including another subspecies –the perennial C. fragile novaezealandiae) that are difficult to differentiate from Green Sea Fingers.
Green Sea Fingers prefers the intertidal and subtidal zone in sheltered estuarine and marine habitats such as harbours and bays. It can survive and grow in tide pools on wave-swept shores, on natural hard surfaces such as rocks, boulders, pebbles, and on both living and dead shellfish. It can also be found on artificial structures such as wharves, jetties, ropes and mussel lines or oyster racks. It can tolerate large variations in salinity and temperature but optimal growth conditions seem to be around 24ºC .
Why is it a problem?
Dead man's fingers is native to Japan but has established itself worldwide, and is found along the coasts of Europe, New Zealand, Australia, Chile, the Mediterranean and the East Coast of North America. It has the capacity to spread rapidly and can tolerate wide ranges of temperature and salinity. It has negative impacts on benthic communities and can dominate the habitats it invades and alter community composition and function.
With separate sexes, Dead man's fingers reproduces sexually releasing eggs and sperm into the water and asexually both by producing free-swimming ‘swarmers’ and also from fragments that break off and grow into separate individuals. Spores and fragments are dispersed by water currents and the action of wind and waves and may be spread in ballast water. Plants that attach to the hulls of boats or marine equipment may be transported in this way. When growing on small objects such as shells, the buoyancy of Dead man's fingers may result in it being displaced and moved by currents and wave action.