"We were pretty shocked," said marine biologist
Correa and colleagues sampled sponges at the sanctuary in 2016, 2017 and 2018. They showed samples collected after extreme storm flooding in 2016 and 2017 contained E. coli and other human fecal bacteria. They also used a catalog of E. coli genetic markers contributed by Rice environmental engineer and co-author
"This shows perhaps they aren't protected from severe events," said Shore, an assistant professor of biology at
Correa said, "That's the other piece of this. There actually was a massive flooding event in 2015 with the
Shore and co-authors
She said previous studies have shown sponges have a microbiome, a population of bacteria that normally live in and on these animals. In this study, Shore characterized the microbiomes on two species: giant barrel sponges, or Xestospongia muta, and orange elephant ear sponges, or Agelas clathrodes. It was the first time the species' microbiomes had been assayed at Flower Garden Banks, and Correa said that was one reason it took so long to understand what happened in the flood years.
Correa said, "In 2016, we saw differences between sponge bacteria at a location that showed signs of death and a location that didn't show signs of death, but we couldn't get at the cause of the differences because we had no baseline data. We thought we'd be able to get the baseline data -- the normal year -- the next year in 2017. But then there was another disaster. We couldn't get a normal sample in a no-flood year until 2018."
Shore joined Correa's lab in 2018, helped collect samples that year and analyzed the microbiomes from each year.
Correa said, "There was a big change in community composition, a shift of the team players, on the sponges that were most affected in 2016. Then, following
"Because we got lucky with ocean currents," Shore said. "Instead of going straight out from
Correa said the story in 2016 was more complicated.
"There was an upwelling event that brought nutrients and cooler waters up from the deep to the top part of the Flower Garden Banks," she said. "Fresh water is less dense than salt water, and we think the floodwaters came at the surface and sort of sat there like a lens on top of the salt water and kept oxygen from mixing in from the top. The combination of this surface event and the nutrients coming up from the bottom contributed to a bacterial bloom that drew down so much oxygen that things just asphyxiated."
The big question is whether pollution from extreme storms poses a long-term threat to the Flower Garden Banks. Correa said the answer could come from an investment in research that follows the health and microbiomes of individual sponges and corals on the reef over time. She said her group at Rice and her collaborators are committed to learning as much as they can about the reefs, and they are determined to support efforts to conserve and protect them.
Study co-authors also include
The research was funded by the