Have you seen a sick starfish?

A New Zealand reef starfish, thought to be suffering from sea-star wasting disease. Photo / Richard Taylor / IMS

Beachgoers are being asked to keep an eye out for sick-looking starfish, amid concerns a disease ravaging the marine animals overseas could also be lurking here.

Millions of starfish on the west coast of North America have been suffering from what's called sea-star wasting disease, or SSWD, which begins with curled limbs and lesions, and ends with the loss of arms, deflation and death.

It's affected more than 20 starfish species and has been found from Alaska to Baja California - making it the largest-ever observed incidence of marine disease.

Here, the University of Auckland's Professor Mary Sewell and Associate Professor Ian Hewson, a SSWD expert from New York's Cornell University, have been checking for it in three main New Zealand starfish - the reef starfish, at Piha, and the eleven-armed star and common cushion star, near Leigh.

Hewson said that although SSWD had also been found in China and Australia's Port Phillip Bay, its cause was not yet fully understood.

"However, we believe it may be related to infection by a virus, abrupt swings in water temperature or precipitation, or a combination of these variables, Hewson said.

"Since waters of the Tasman Sea and surrounds have been anomalously warm over the last few months, it is possible that wasting may occur in New Zealand - so having eyes out there to report the disease is crucial for our understanding of causality."

Sewell said there had so far been one suspected New Zealand case of it, in a specimen reported by another Auckland University marine biologist.

Outbreaks in North America had followed periods of unusual temperatures and large rainfall events.

"Conditions in northern New Zealand this summer – with unusually warm seawater temperatures and the rainfall associated with several tropical storms – make it possible that we may see SSWD in New Zealand in the next few months."

People who spotted any suspected cases were asked to send pictures and details directly to the researchers, at m.sewell@auckland.ac.nz or hewson@cornell.edu, or to the SSWD - New Zealand Facebook Page.