Anne Murray: Mystery disease killing millions of West Coast starfish
Summertime is beach time but all is not well on the coast.
I recently visited my favourite rocky beach, on the southern coast of a Gulf island, in the midst of the Salish Sea. Turquoise blue water sparkled under a cloudless sky and a warm glow lit the encircling bluffs. An otter pulled up on shore, its glossy pelt glistening with salt and sea foam. It held a large rock crab in its claws and chewed on it with relish. The current swirls around the rocks here, carrying cold, oxygen-rich waters into shore, where clusters of mussels, clams, and starfish await the nutrients it brings.
Yet, on this day, something was wrong. The thick clumps of purple ochre stars that normally crammed into every rock gully along the beach were missing. Not one starfish remained. Only empty black crevices remained, devoid of life.
This scene is repeated up and down the West Coast of North America this year. Starfish of many species have suddenly disappeared, in a vast die-off event that has scientists puzzled.
They have succumbed to starfish wasting disease (also known as starfish wasting syndrome), but whether the cause is a virus, fungus, bacteria, or a combination of factors is not known. The starfish may be picking up the pathogen from mussels or other shellfish they consume.
So far researchers have failed to find any one definitive causal agent, although warm water temperatures appear to be linked to the high mortality events.
The term “wasting disease” is descriptive. The animals suddenly develop an unnatural, twisted appearance, followed by their arms falling off, and their bodies dissolve quickly into a jellied mass. Divers report piles of white goo and pieces of starfish arms on the ocean floor, where thousands used to live.
Starfish wasting syndrome is being tracked by the Pacific Rocky Intertidal Monitoring group at the University of California at Santa Cruz. Their interactive map shows that the syndrome reaches from Baja California to the Alaska panhandle.
According to the Vancouver Aquarium, dead and dying starfish were first observed on the B.C. coast in early September 2013, at locations such as Bamfield and Ucluelet on the west coast of Vancouver Island.
For a few winter months the disease died down, but then the outbreak restarted as the water warmed up. It reached the wildlife-rich waters around the San Juans and the southern Gulf Islands, and progressed northwards up the coast.
At first it was the many-legged sunflower stars and sun stars that were most affected, but now a majority of starfish species have fallen prey to the disease, including the common purple ochre stars that live in rocky beaches all around the Salish Sea.
Even aquaria are not immune, as they use ocean waters in their tanks. Sarah Friesen, working at the Shaw Ocean Discovery Centre in Sidney, told me how they lost most of their starfish within the space of a few weeks, with only a few bat and leather stars surviving so far.
There are hundreds of intertidal species found along local beaches, yet none is more familiar than the colourful starfish, recognized from childhood and epitomizing the ocean shore. For such a common and well-known species to suddenly disappear is more than disconcerting: it is truly shocking. The speed with which it left our shores is mystifying. Yet the great die-off has not attracted that much media coverage, beyond the initial reports.
Starfish wasting disease has occurred at various times in other locations. In 1978, southern California and the Channel Islands had an outbreak, from which it took many years for populations to recover, and some species never did regain their former numbers. Sea urchins and sea cucumbers were also affected in the Channel Islands.
The East Coast of North America experienced an attack of the syndrome in 1972 when large numbers of common starfish died, and the West Coast had further outbreaks in 1982-83 and in 1997-98. These occurrences were associated with warm waters during El Nino years.
The present severe outbreak began in June 2013 and has affected coastal waters much further north than any previous events. Biologists at the Vancouver Aquarium’s Howe Sound Research and Conservation Team and the University of California are currently working to identify the mystery pathogen.
Sea stars are predators that feed on other marine species, and few species, other than the occasional gull, eat these normally tough creatures. The removal of predators that were formerly very abundant is going to have a significant effect on the ecosystem and may allow some creatures that used to be preyed upon to build up their populations.
Biologists at Santa Cruz are turning their attention to monitoring sites which have been depleted of sea stars to see what species replace them, and how long it takes for sea stars to replenish. They are looking for help from the public and have online forms for submitting observations of juvenile stars (identification information is also available).
They report that some sites along the coast have already seen recruitment of new baby sea stars, which is very encouraging after such a major die-off.
Nature often operates on rhythmic cycles that we barely know about or comprehend. Who would guess that there are cicada broods that only emerge every 17 years, or that some aphids do not mate for up to 13 generations? Pacific tent caterpillars build up to peak populations every eight to 11 years, and painted lady butterflies are on a 10-year cycle. Sockeye salmon swimming up the Fraser River this month hatched from eggs in 2010 and are returning en masse to spawn on the completion of their four-year life cycle. Mammals such as voles, lemmings, and snowshoe hares have cyclical two- to four-year cycles that drive the abundance of predators such as hawks, owls, and lynx.
Even the Earth itself moves to rhythms, such as the tens of thousands of years’ long Milankovitch cycles, caused by the Earth’s orbit, the tilt of its axis, and the precession of the equinoxes. There are solar cycles of 80 and 180 years, and an 11-year sunspot cycle, thought to correlate with northern precipitation levels and perhaps with the snowshoe hare and lynx cycle. The phenomena of El Nino and La Nina, warming and cooling events in the Pacific Ocean, are linked with cyclical climate patterns, and underlie the distribution and movements of marine wildlife.
So perhaps the sudden death of millions of sea stars is part of a larger pattern of death and renewal that we know little about. This would be far preferable to alternatives such as drastic anthropogenic damage to the ocean ecosystem, caused by climate change or toxic run-off, or a new and deadly disease.
Most scientific reports suggest that the trigger for this massive starfish die-off lies not only with a pathogen but with the ocean’s changing physical or chemical attributes, such as temperature and acidity. Time will tell. Society must wake up to the many impacts we are causing to our planet’s ecosystems. If it is starfish today, what else might follow tomorrow?
The public and particularly divers can help provide information to researchers on the geographical spread of the syndrome and any sign of young starfish returning. You can find out more about how to help by checking the Vancouver Aquarium and Pacific Rocky Intertidal websites. I will not be alone in watching those Gulf island rocks at every visit for any hint of the sea stars’ return.