The seas surrounding Japan seem to stay in the headlines lately. Between territorial conflicts, animal die-offs, and the Fukushima disaster, Japanese waters just can’t get out a break. Now, one of the Earth’s oldest surviving species appears to be faring poorly in Japanese seas, and scientists aren’t sure why.
According to Japanese news outlet Asahi Shimbun, close to 500 dead horseshoe crabs have washed ashore along the beaches of Kitakyushu in southwest Japan. While a few dozen horseshoe crabs normally wash ashore during the mating season, this year’s crab corpse count was the largest in twenty years. The crabs began washing ashore in early June and continued into August, and estimates made from observations of crab mating groups indicate that as much as 20% of the crab population might have died off.
Hiroko Koike, biologist at the nearby Kyushu University Museum, told Asahi Shimbun he believes the mysterious crab deaths are the result of environmental stresses, but the cause still remains unknown:
Rises in the sea level caused by global warming, shortages of places to lay eggs and a lack of nutrition could have resulted in their deaths. We have to be careful to identify the cause.
The Sonehigata tidal flat where the crabs were found is one of the most populated horseshoe crab habitats in the world. Other known horseshoe crab mating grounds have also been experiencing unexplained die-offs in recent months, stoking fears of a marine mass extinction.
The horseshoe crab’s name is a bit of a misnomer; the crabs are actually arthropods, making them more closely related to spiders or scorpions than to crustaceans. In the 450 million years that horseshoe crabs have been on the Earth, their species has survived several mass extinctions. Thus, this recent unexplained die-off has marine biologists concerned. What’s more, Horseshoe crab’s blue blood is used in pharmaceutical manufacturing and laboratory equipment testing, making this die-off doubly troubling for scientists.