BEACH CITY, Texas (AP) - From the boat slips of this Chambers County hamlet, Galveston Bay looks just as beautiful as ever, with the sun rising from the flat-line horizon to cast a greenish-blue tint on the calm waters.
But the view masks a troubling reality: The bay isn’t as alive as it once was.
Scientists are finding fewer rangia clams in a northeast inlet of the bay, suggesting that not enough fresh water is flowing from the Trinity River to protect the ecological health of a drought-plagued state’s most bountiful estuary.
For ages, the inflows mixed with the Gulf of Mexico’s salty backwash to produce ideal conditions for crabs, shrimp, oysters and a wide variety of fish. Rangia, an important but often overlooked resident of the bay, served as a first link in its food chain.
Now, a team of scientists raking the muck where the quarter-size bivalves once were found is coming up with only empty shells. The reasons are unclear, but rangia clams cannot reproduce or mature if the bay is too salty.
“The first step is to know where they are and where they aren’t,” said Norman Johns, an Austin-based scientist for the National Wildlife Federation, which is conducting the two-year study of clams in Galveston Bay. “Already, we are surprised by the contraction,” he told the Houston Chronicle (https://bit.ly/1wKEGRt).
The abundance of clams matters because they are found near sources of fresh water and cannot leave for better conditions when the estuary becomes too salty. For those reasons, a panel of scientists advising state regulators on the required amount of inflows is looking at the mollusk as a species whose well-being is indicative of the ecosystem.
The study comes amid some abnormally dry years in Texas. While drought always has been part of the state’s ecology, environmentalists and some researchers fear that less water will reach the bays and estuaries as its population surges.
The Trinity River, in particular, is carrying a heavy burden, supplying water to the state’s two largest metropolitan areas, Houston and Dallas-Fort Worth. And Texas law requires at least some of a river’s unallocated flow be set aside for the benefit of the environment.
But the Trinity, like many other Texas rivers, is tapped, with virtually every drop appropriated by farmers, industry and growing cities. And the question of just how much water is needed for healthy bays and estuaries is difficult to answer.
Understanding why clams are disappearing could help.
The small creatures tend to form beds near where the rain-fed Trinity empties into the bay. That’s where salinity levels usually are the lowest.
But the waters became as salty as the Gulf during 2011, the state’s worst one-year dry spell on record. Without the usual rainfall, every drop in the Trinity below Dallas and Fort Worth was treated wastewater.
The bay’s saltier waters emboldened parasites to feast on prized oysters. And wild celery, a native grass with little capacity to survive high salinity, all but disappeared, robbing young fish and shrimp of shelter.
The drought’s impact on clams is less understood because the species is not commercially harvested in the bay. The Texas Parks and Wildlife Department’s historical data on clams’ location and abundance was based at times on what it found while conducting surveys for oysters.
“All the commercial pressures are on oysters, so they get the attention,” said Bob Stokes, president of the Galveston Bay Foundation, an environmental advocacy group.
On a recent morning, all eyes were on clams. A captain and his deckhand took turns pulling an iron frame wrapped with a half-inch mesh from the bay’s muddy bottom. Each time they found empty shells.
In a place where the research team previously had uncovered live clams, its measurements showed salinity levels as high as 17 parts per thousand. Studies of clams along the Atlantic Coast indicate that levels higher than 10 parts per thousand can limit the ability to reproduce, said Johns, the scientist with the National Wildlife Federation.
Despite the absence of live samples, Johns said the shells’ varying sizes suggests that clams had reproduced at different times. “But we don’t really know the reasons behind the deaths of adults,” he said.
The team is sending any living specimens to the University of Texas Marine Science Institute in Port Aransas, where researchers are using techniques developed by tree-ring scientists to see if there is a link between the bivalves’ annual growth increments and drought conditions.
Trees grow more when they are wet, so scientists use ring size as an indicator of water abundance. In a similar way, a clam’s life history is in its shell.
“By working from the edge of the shell at the known year of death, I can assign the correct calendar year of formation to each increment back to the origin,” said Bryan Black, who is conducting the analysis.
Once the increments have been measured and effects of age removed - rangia grow quickly when young - Black said he can correlate the bivalves’ growth rates with records of inflows, salinity and drought.
The work isn’t without limitations. While trees can live for hundreds of years, rangias typically don’t live more than 15 years. Also, the clams’ range covers about 60 square miles, meaning each individual’s experience could influence its growth rates.
Other researchers said the decline of clams could be attributed to a variety of factors, from drought to parasites to more particles in the bay because of dredging and increased traffic in the Houston Ship Channel.
Antonietta Quigg, a marine biologist at Texas A&M University at Galveston, said the clams’ decades-long slide - based on Texas Parks and Wildlife data - started before the state’s lingering drought and the widening of the ship channel.
Without knowing the reasons, it’s too early to conclude what the drop in clams says about the bay’s well-being, said Jim Lester, a biologist and president of the Houston Advanced Research Center. He also serves as chair of the state’s research and monitoring committee for the estuary.
Galveston Bay, he said, is “surprisingly resilient,” considering its proximity to a large city, its collection of heavy industries and busy ship channel. While inflows matter, pollution is his primary concern.
Texas law requires enough inflows into the bay “to maintain a healthy ecosystem,” he said. “If you raise the salinity in Galveston Bay, it can still be healthy. But it will be different.”
The National Wildlife Federation, which commissioned the study with funding from the Houston Endowment, is hopeful that a deeper look at the clams’ decline will bring greater attention to inflows and help inform water policy.
Myron Hess, an Austin-based attorney and policy expert for the advocacy group, said drought-like conditions can be made more severe by water-management decisions. If the bay needs more fresh water, he said, one idea would be to use money awarded the state from the 2010 oil spill in the Gulf to purchase water rights in the Trinity basin.
“It’s easy to see the drought’s effects on rivers and streams,” Hess said. “But it’s less obvious in the bay.”
Information from: Houston Chronicle, https://www.houstonchronicle.com
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