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Seagrass loss leads to changes in fish populations

New research led by the California Polytechnic State University (Cal Poly) has found that the loss of seagrass caused a dramatic shift in fish species in Morro Bay, California. The period following the decline of seagrass habitats was characterized by increases in flatfish and staghorn sculpin, and decreases in previous populations of bay pipefish and shiner perch.

Seagrass meadows were very common throughout the Morro Bay estuary and represented one of the most biologically productive biomes on Earth, providing shelter, food, and nurseries to a large variety of fish and invertebrate organisms. Following their significant decay in recent decades, they have been largely replaced currently with a less dynamic, muddy seafloor habitat.

“Seagrass, like the eelgrass in Morro Bay, is important because it supports a range of marine life,” said study lead author Jennifer O’Leary, who is now the Western Indian Ocean coordinator for the Wildlife Conservation Society. “It’s like the trees in a forest – these underwater plants provide food, structure, and shelter to many of the marine animals that live in the bay.”

Morro Bay, one of the 28 estuaries that the U.S. Environment Protection Agency deemed critical for the environmental and economic health of the country, has witnessed a dramatic transformation.  Seagrass declined by more than 95 percent, dropping from covering 344 acres in 2007 to only 15 acres in 2017.

Instead of resulting in fewer fish, seagrass loss has led to changes in the fish species that are present. The once common pipefish, a species perfectly adapted to hide among seagrass, has been replaced by flatfishes such as the speckled sanddab (Citharichthys stigmaeus) and the staghorn sculpin (Leptocottus armatus), which are more adapted to live among muddy seafloors.

“The relatively sudden and near complete collapse of eelgrass in Morro Bay has not only changed fish populations, but it has also resulted in substantial changes to estuary physics and geomorphology,” added study co-author Ryan Walter, a professor of Physics at Cal Poly. The loss of seagrass in Morro Bay has led to widespread erosion, or loss of sediment, throughout the estuary.

According to the scientists, a multifaceted approach to protect the remaining seagrass is essential, including local planting initiatives and transplantation efforts.

The study is published in the journal Estuaries and Coasts.

By Andrei Ionescu, Staff Writer

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