December 18, 2013

Mysterious Disease Affecting Sea Stars along the Pacific Coast of North America

A leather star (Dermasterias imbricata) just beginning to show signs of the disease, seen on San Juan Island in October 2013; Photo: Keith Rootsaert

By Megan Wehrenberg, Reef Check California’s Central/North Coast Regional Manager

The past few months have not been kind to sea stars along the Pacific coast of the US and Canada. A mysterious withering or wasting syndrome is sweeping down the coastline infecting sea stars seen in both the intertidal zone and in the shallow subtidal (60ft deep and less). The first sign a star is infected is the development of small lesions on their outer bodies and an overall deflated look. The lesions grow and their tissue continues to deteriorate, causing arms to fall off. In the end the stars more or less disintegrate, often within just a few days. Several species are being affected including ochre stars (Pisaster ochraceus), giant-spined stars (Pisaster giganteus), sunflower stars (Pycnopodia helianthoides), sun stars (Solaster stimpsoni), among others.

This is not the first time coastal California has seen a decimation of sea star populations. Major die-offs of ochre stars in southern California occurred during 1983-1984 and again in 1997-1998. The cause of the infection has been unclear. Past pathological studies have indicated a bacterium (Vibrio) as well as a virus might be the cause of the disease, and the two episodes in southern California were both associated with warm water events. Even though this year’s outbreak did occur during the warmer time of the year, this has not been a particularly warm year for Pacific coast waters.

While notable sea star die-offs have occurred in the last few decades, this year’s outbreak is of concern for several reasons: 1) previously a single species has been affected as opposed to seven now affected; 2) past occurrences have been geographically localized while this year, the Pacific coast from Alaska to San Diego has been affected; and 3) this is the first time sea stars have been affected in cooler waters off Washington and Alaska. Interestingly, a smaller outbreak has also been reported in the Atlantic off the coast of Rhode Island and Maine, however, it is unknown whether it is linked to the west coast outbreak in any way.

A diseased sun star (Solaster stimpsoni) seen on San Juan Island in October 2013; Photo: Keith Rootsaert

Since earlier this summer a research monitoring group called PISCO (Partnership for the Interdisciplinary Study of the Coastal Oceans) has been tracking the spread of the disease at their study sites and by collecting reports from the general public. Turning to citizens has been a successful way to obtain information over a much broader geographic area, from both on land and underwater.

Reef Check California has added the task of noting the presence/absence of diseased sea stars to our reef monitoring surveys. Since finding out about the disease, volunteers observed 25 sites from Sonoma County to San Diego and the Channel Islands. Reef Check volunteers have also been observing reefs during their own recreational dives and sending in any sightings. It is a situation in which the more eyes that are on the water the better we will understand what is happening.

Sea stars play an important ecological role in the marine environment, particularly in the intertidal where they have been identified as “keystone” predators, a predator that has an exceptionally large influence on the distributions of their prey. Because of this, ecological changes are likely to occur due to the die-off, though the extent is difficult to predict. Monitoring programs such as PISCO and Reef Check track ecological changes over time, providing important data, not only on sea star populations, but also of their habitats, predators, and prey. Time will tell what changes may occur and Reef Check volunteers will be in the water to track them.

To report sightings of diseased or healthy sea stars: