A crustacean branded a 'skeletal alien invader' could be threatening New Zealand's marine biodiversity, marine scientists say.
The National Institute of Water and Atmospheric Research (NIWA) has issued a warning about the spread of skeleton shrimps called Caprella mutica in New Zealand waters.
In a statement it said the crustaceans were migrating around the country by attaching themselves to boat hulls or drifting algae.
They had recently spread to southern waters including around Dunedin, Bluff and Lyttelton Harbour and could pose a risk to other marine life.
NIWA biosecurity scientist Dr Chris Woods said the shrimps, known as the "praying mantis of the sea", would colonise artificial structures - sometimes appearing in huge densities on anchored buoys, fish cages, wharves and vessel hulls.