This article was originally featured on Hakai Magazine, an online publication about science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com.
Bieito Fernández Castro wasn’t expecting to find a turbulent hotbed of anchovy sex.
Commissioned by the Spanish government to investigate the conditions behind algae blooms, which kill mussels, Castro and his team were studying a peaceful spot in a bay in northwestern Spain. In the absence of strong winds or waves, toxic algae blooms occur more frequently here compared with surrounding areas, to the detriment of the resident mussels—and mussel farmers. But after two weeks of monitoring the apparently tranquil water with sensors that measure small shifts in temperature and velocity, Castro and his colleagues found that the bay’s calm surface belied what was happening below.
“Every night and without any apparent reason, we were seeing very, very high levels of turbulence,” says Castro, a physical oceanographer at England’s University of Southampton. Castro and his colleagues eventually traced the source of all this mixing: the frothing free-for-all of an anchovy orgy.
Most animals mate, but few do so with such frequency, and with so many bodies packed so closely together, as anchovies. As Castro and his colleagues’ data shows, these fornicating fish churn the water as much as a major storm.
Anchovies are among the ocean’s more amorous residents. The fish move in large aggregations of millions or more, and a female anchovy can release between 20,000 and 30,000 eggs each year, which males promptly fertilize like aquatic crop dusters.
All that “frantic activity,” as Castro calls it, causes quite a stir. And it’s something other sea dwellers might actually benefit from.
Turbulence is crucial for mixing heat and nutrients throughout the ocean. Previous research largely shows that the turbulence animals cause living their lives isn’t…
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