How The Abundance of Anchovies Can Make Better Fish Habitat

Small things can make a big difference. That is the premise of the well-known butterfly effect. But could it apply to anchovies? Say, the anchovy effect? And could that effect, in turn, impact the abundance of the kinds of fish anglers would like to see on the ends of their lines? In a study measuring the role that spawning anchovies play in coastal ecosystems, published recently in the journal Nature Geoscience, researchers at the University of Southampton seemed to conclude it could.

To test for the diminutive fish’s outsized role, lead research fellow Dr. Bieito Fernández Castro and his team set sail to Ría de Pontevedra, a bay on the northwest coast of the Iberian Peninsula. There, they used an instrument known as a microstructure profiler to measure turbulence, or ocean mixing, the phenomenon by which heat, oxygen, and micronutrients move between layers of coastal ocean waters. Turbulence plays a key role in the nutrition of phytoplankton, which photosynthesize near the ocean’s surface. 

Because the microscopic, single-celled phytoplankton are the ocean’s top producer, generating 45 billion tons of biomatter each year, virtually all other ocean creatures in the food chain depend on them. Including marlin, sailfish, salmon, tarpon, shark, and any other fish an angler might care to land.

But, how do key micronutrients that float near the bottom of the ocean make their way to the surface where phytoplankton can utilize them to kickstart the entire oceanic food chain? While putting his microstructure profiler to work off the Iberian Peninsula, Fernández Castro found that, despite calm surface waters, turbulence beneath the surface ramped up significantly each night. Using sieve nets, the team checked the water to see what might be causing the extreme turbulence. And they found anchovy eggs. Lots of them.

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After more observations, they concluded that large aggregations of spawning anchovies created tiny currents that influenced larger currents to usher micronutrients to the surface. Fernández Castro told Science Daily, “Previous studies have suggested that biological turbulence causes minimal mixing because the circular motions of water that the fish generate while swimming are too small. This is certainly true in the open ocean, where temperature changes occur over tens of meters. However, we have shown that closer to land, where the layers change over a much shorter distance, the anchovies are able to mix them together.”

So, anchovies, the study concludes, besides being good on pizza, and also serving as a food source for many fish, play a key role in supporting the survival of phytoplankton, which in turn feed the entire coastal ecosystem. So, next time you land a tarpon, raise a glass to the little guys and the role they played in your catch. To the phytoplankton. And to the anchovy effect.