Anchovy sex is a force of nature| Trending Viral hub

This article originally appeared on the same magazine, an online publication on science and society in coastal ecosystems. Read more stories like this at

Bieito Fernández Castro did not expect to find a turbulent hotbed of sex with anchovies.

Tasked by the Spanish government with investigating the conditions behind algae blooms, which kill mussels, Castro and his team were studying a quiet spot in a bay in northwestern Spain. In the absence of strong winds or waves, toxic algae blooms occur more frequently here compared to surrounding areas, to the detriment of resident mussels and mussel farmers. But after two weeks of monitoring the seemingly calm water with sensors that measure small changes in temperature and speed, Castro and his colleagues discovered that the calm surface of the bay contradicted what was happening below.

“Every night and for no apparent reason, we were seeing very, very high levels of turbulence,” says Castro, a physical oceanographer at the University of Southampton in England. Castro and his colleagues eventually tracked down the source of all this concoction: the effervescence of an anchovy orgy.

Most animals mate, but few do so as frequently and with as many bodies as close together as anchovies. As Castro and his colleagues’ data show, these fornicating fish stir up the water as much as a big storm.

Anchovies are among the ocean’s most loving residents. Fish move in large groups of millions or more, and a female anchovy may release between 20,000 and 30,000 eggs each year, which the males quickly fertilize like aquatic fumigators.

All this “frantic activity,” as Castro calls it, causes quite a stir. And it’s something other ocean dwellers could benefit from.

Turbulence is crucial for mixing heat and nutrients throughout the ocean. Previous research largely shows that the turbulence that animals cause as they live their lives is not enough to substantially mix the layers of the ocean’s water column. But Castro study—which was published in 2022 and won a Ig Nobel Prize 2023 by entertaining and thought-provoking scientific achievements, shows that within the layers of the ocean, anchovy spawning causes significant, if subtle, temperature changes. This finding suggests that in shallower waters, the commotion produced by numerous pool participants all breeding at once could be more powerful and important for ocean mixing than previously thought.

Watch this short video about ocean stratification to find out why mixing in the ocean is so important. Hakai Institute Video

In general, winds, tides, and strong currents are the main elements that stir and mix the ocean. Kirstin Schulz, a physical oceanographer at the University of Texas at Austin who studies small-scale mixing and was not involved in Castro’s research, says scientists typically don’t consider animal movement as a major cause of mixing in the ocean. as a whole. However, Ella Schulz says researchers have a lot to learn about how small turbulent motions mix ocean layers of different densities, salinities and chemical compositions in shallow bays and other bodies of water. “This study shows that this definitely happens and may be important in a more local setting,” she says.

It’s even possible, Castro says, that his study doesn’t actually represent the effects of anchovy sex. Local fishermen told him that the aggregation of anchovies he studied was much smaller than similar swarms seen further offshore. In places like La Jolla, California, researchers have observed anchovy aggregations between 10 million and billion fish: shoals so vast and dense They look like an oil spill running through clear water.. Other schooled species, such as sardines and herring, they swim in groups of similar sizes. But scientists have very little data on whether these species produce similarly exciting turbulence.

Curtis Deutsch, an oceanographer at Princeton University in New Jersey who studies oxygen and nutrient cycling and who was not involved in the study, says that to get a full idea of ​​the extent to which fish and other marine life could be mixing in the sea, scientists will need to study its effects in the depths of the ocean and in surface waters. The water in the depths of the ocean is generally calmer than that on the surface, as it is not disturbed by wind or waves. Down there, Deutsch says, biological activity would be disproportionately important to the mixing of the oceans. Unfortunately, he adds, that’s where “a lot of school behavior goes unnoticed.”

While much more research is needed to fully understand ocean mixing and the role marine animals could play in the process, Castro’s accidental discovery of the anchovy shows there’s more to the muggy lives of sea creatures. than we surface dwellers might think.

This article first appeared in the same magazine and is republished here with permission.

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