A Surprising Effect of Texas Drought: Changes to the Marine Food Web

When Texas' worst drought on record hit the state between 2011 and 2015, it did more than dry up rivers and lakes. It changed the chemical composition of fish eggs, which revealed bigger changes to the marine life in Aransas Bay.

According to a new paper from marine biologist Lee Fuiman at the University of Texas Marine Science Institute, published in the journal Ecological Monographs, extreme weather events, like severe drought, can have big—and unexpected—impacts on marine food webs. And, these changes can be detected in the smallest and unlikeliest of places…fish eggs.

Fish eggs are an important part of the ocean's food web. They are abundant, they're easy for organisms of almost any size to eat and they carry a high concentration of key nutrients, like essential fatty acids. Fuiman studied red drum, a popular game fish on the Texas coast. Red drum gather for large mating events where eggs are released and fertilized. The vast majority of the eggs will not become adult fish and instead end up as an important food source for other animals, or what's known as an egg boon.

Fuiman studied egg boons for an eight-year period from 2009 to 2017. He found that during the drought, the eggs became more nutritious, with higher concentrations of omega-3 and omega-6 fatty acids. Before the drought, the eggs contained 19 percent essential fatty acids. During the drought, the percentage of essential fatty acids climbed to 24 percent. After the drought, the concentration went back down to 17 percent.

"It was assumed for a long time that the composition of the eggs wouldn't change because the embryo needs a particular balance of nutrients to develop properly," Fuiman said. "When we discovered that the eggs were changing dramatically from year to year, that was a surprise. When we noticed that the change correlated with the drought index, that was an even bigger surprise."

As it turns out, the drought increased the salinity in Aransas Bay, which in turn affected the species the red drum were preying on. Red drum normally go after blue crabs, but increased salinity meant a decrease in blue crabs. The red drum turned to shrimp to fill out the menu and this altered the composition of their eggs.

Understanding how nutrients move through the marine food web and how climate change affects that movement is critical for understanding the health of marine ecosystems for years to come. Fuiman believes the unexpected findings in this research demonstrate that fish eggs are a new tool that scientists can use to gauge the consequences of extreme weather for marine life. Understanding those consequences can help state and federal agencies manage fish populations so that heavy fishing does not deal species that are affected by a drought or other climate events a second blow before they recover.

"One of the consequences of climate change is that we're expecting droughts to be more frequent and more severe," Fuiman said.

Fuiman plans to continue his work with red drum to see what effects Hurricane Harvey had on the food web and hopes to expand his studies to other species.