The Sea Star Rebound
For the past two years, west coast sea kayak populations have been decimated by a phenomenon called “Sea Star Wasting Syndrome.” The culprit was a mystery for a long time. Then researchers identified a densovirus that had existed for at least 70 years but had never had such a massive outbreak. Because seemed to be most prevalent in warmer water, things seemed ominous with global climate change gathering steam. And while the virus has been identified, the mechanism of this particular outbreak is unknown. as it whether or not it will occur again.
Here’s the Good News
This spring the West Coast is awash in baby sea stars! After an 80% decline at some sites by the end of 2014, the young sea stars surged, and at some sites, baby sea star numbers are triple that of last year. Researchers at Oregon state University west coast universities have complied data that show an unprecedented number of baby sea stars on the west coast that survived the tail end of the viral outbreak in 2015. “The numbers were astonishing,” said biologist Benjamin Miner, from Western Washington University in Bellingham. “I’ve been walking around at low tides looking at sea stars for 20 years, and rarely do you find lots of juveniles.”
The Potentially Sad News
It’s unclear exactly what led to the massive rebound and whether or not it will last. One possibility is that the die-off of 2014-15 opened up a vast amount of intertidal real estate, and the youngsters moved in. Sea stars produce thousands of young each year, and the larvae are tiny, free-floating critters that slosh around in the sea for six weeks to two months. During that time they can travel quite a distance, so it’s easy for sites to be repopulated from far away.
Another possibility is that the ocean conditions have shifted, and that whatever set of conditions led to the virus outbreak has abated. There’s no telling whether this is a strong positive trend, or if we’re riding a longer roller coaster of sea star population ups and downs as conditions cycle. Some biologists suspect another outbreak may be in the offing as these youngsters become adults.
What This Means Now
Sea stars are keystone species: one of a small number of critters that create large ripple effects that define how an ecosystem function (other examples are beavers, sea otters, and ghost shrimp). Sea stars are a voracious predator on mussels and gooseneck barnacles, which means that these bivalves don’t exist low in the intertidal zone, where the hydraulically powered sea stars can get to them. This gives a whole zonation pattern to tidepools that even the most casual beachgoer quickly notices. If sea star populations decline and mussels and gooseneck barnacles extend lower into the intertidal, the whole structure of tidepools may shift.
So there are lots of unknowns. We may not know how good a sign, but clearly the rebound of sea star kiddos is a good sign. At the very least, 2016 should be a good year for tidepooling.