Pacific starfish see mass die-off

Starfish wasting disease sends populations crashing.

They are the many-legged, quasi-brained, voracious apex predators of marine benthic invertebrate ecosystems, and they are under attack. Starfish populations on both coasts of the United States and Canada have been seeing mass die-offs since July of last year, and the cause remains unknown. Marine biologists and conservationists have been floundering to understand the phenomena, which may have huge implications to the starfishes’ populations and their effect on native ecosystems.

The affliction is known as starfish wasting disease, and has been described by some marine biologists as a ‘starfish plague’. The number of starfish killed in these events is highly speculative, with estimates ranging from hundreds of thousands to several million. One survey of a northern California tide pool system saw ninety-five per cent of the starfish population killed.

The disease begins symptomatically as small white lesions on the starfishes’ arms, which spread to the central body and begin softening tissue. The disease then attacks the invertebrate’s hydrostatic skeleton, analogous to our endoskeleton, made rigid by water pressure, and the animal begins to ‘deflate’. All the while the starfish’s arms, semi-autonomous with their own nervous system, violently twist, tearing their tissues and eventually breaking off. A study by the Pacific Rocky Intertidal Monitoring Program found that mortality in most starfish takes less than a week, with some starfish succumbing within several days.

Despite its frequency, scientists are uncertain of what causes starfish wasting disease. The possibilities fall into two broad categories: pathogens or environmental effects. The pathogenic model is supported by what resembles contagious behaviour observed in a Brown University study last year, but causative bacteria, virus, or fungus has yet to be found. Many marine biologists suspect that rising sea temperatures and ocean acidification are responsible for the disease, which affects the starfishes’ feeding habits and life processes. While environmental factors alone are likely not cause enough for starfish wasting disease, they may inhibit starfishes’ immunity enough for a pathogen to infect, meaning the phenomena could still be linked to climate change.

Surprisingly, this is not the first instance of starfish wasting disease that has been observed. In 1972 and 1978, large starfish die-offs were recorded on the East Coast of the United States and in the Gulf of California, respectively. These events, however, pale in comparison to the recent surge of disease witnessed, both in terms of geography and species affected. Starfish wasting disease was first observed in this case in a single species on the West Coast of the United States: the sunflower starfish. It then jumped to the intertidal ochre star, and now infects about a dozen species on North America’s Pacific coast, from Alaska to Mexico. In both past starfish wasting disease events, only one species had been affected, and over a much smaller spatial scale.

In its early stages, media hype attributed starfish wasting disease to the 2011 Fukushima Daiichi nuclear power plant meltdown in Japan, asserting that irradiated Pacific seawater was to blame. There is a dearth of scientific evidence showing that radiation is not to blame for the disease: namely that it was observed well before the meltdown occurred and that it is simultaneously happening in other oceans.

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