Texas bays struggle to adjust in Harvey’s aftermath
On a typical September day, the water lapping against Galveston Bay’s western shoreline adjacent to the village of Bacliff is a slightly murky green, about the color of original Gatorade but without that sports drink’s almost neon tint and considerably more salty.
Based on long-term sampling and monitoring of such things, the average salinity level of Galveston Bay water along the Bacliff shoreline in early September is 10.5 parts per thousand. That’s salty but not especially so - about a third of the 35 ppt salinity level in the open Gulf of Mexico and half the average September salinity in lower reaches of the sprawling bay.
But that 10.5 ppt salinity level is just fine for speckled trout and redfish, black drum, bay anchovies and most of the rest of the assemblage of marine life that must have a saline environment to survive.
Last week, however, water in Galveston Bay off Bacliff registered a salinity level of 0.6 ppt. Some Texas rivers are saltier than that in late summer. Instead of Gatorade green, the Galveston Bay water had the color and nearly the syrupy consistency of cafe au lait.
Galveston Bay, like bay systems from Sabine Lake on the Texas/Louisiana border to Nueces Bay near Corpus Christi, was awash in silt-laden freshwater as the trillions of gallons of rain generated during Hurricane/Tropical Storm Harvey’s prolonged, deadly, devastating, record-setting careen around Texas slowly drain.
That runoff, as well as the storm’s other side effects, will have significant impacts on the coastal marine environment, the creatures that live there, the anglers who pursue the bay’s sport fish and even the landscape along the coast.
Some of the effects will be short term. Others will last longer. And some are simply unknown.
“This is all new ground,” Lance Robinson, deputy director of coastal fisheries for Texas Parks and Wildlife Department and a veteran marine scientist with decades of experience on Texas bays, said of gauging Harvey’s effects on coastal ecosystems. “This is an unprecedented event.
“No one has ever seen something on this scale, so no one can say they know what all the impacts will be.”
TPWD will be making a huge effort to learn as much as possible about the storm’s effects, he said. But some short-term effects easily can be seen or guessed, and longer-term effects inferred based on past experiences.
One of the most obvious is the overwhelming of bays with freshwater runoff that promises to swamp huge expanses of upper and mid-coast bays for weeks if not months.
This is highly unusual for a hurricane. Tropical cyclones typically increase salinity levels in bays, with their storm surges pushing massive slugs of high-salinity water from the Gulf into the bays and beyond.
Harvey did a bit of that along the mid-coast when it came ashore, devastating Rockport, Port Aransas and Aransas Pass as its storm surge shoved into and over Redfish, Aransas, Nueces and Corpus Christi bays and combined with the high winds to wreck the region.
That wind, storm surge and its powerful currents also changed the face of some of the coast. Most dramatically, it “blew open” Pass Cavallo near Port O’Connor.
Cavallo, one of the major, natural bay/Gulf exchanges on the Texas coast and a crucial avenue for marine life whose life cycles depend on access/egress to both Gulf and bays, had been slowly sanding shut - a result of man-made changes in coastal hydrology. The storm’s powerful surge scoured Pass Cavallo’s channel, widening and deepening it.
It also tore a new adjacent channel when it breached the tip of Matagorda Island, cutting through a spot called Sunday Beach and mating the new channel with Pass Cavallo.
In one of those inexplicable twists all too common with hurricanes, the storm did not do the expected and scour open Cedar Bayou/Vinson Slough just 20 miles or so down Matagorda Island from Pass Cavallo. That natural connection between the Gulf and Mesquite Bay, separating Matagorda Island and San Jose Island, had been reopened in 2014 after a multimillion-dollar public/private effort to restore the long-closed pass.
Cedar Bayou/Vinson Slough channel had again sanded closed earlier this summer.
Most assumed - or hoped - Harvey’s powerful storm surge would reopen the pass. It did not.
But Harvey’s rains, and not its storm surge or winds, are having the most profound and immediate impacts on coastal fisheries.
Search for saltier water
Short-term effects of the inundation of coastal bays with silty, muddy, freshwater runoff include forcing major movement of marine fish in affected systems. Fish and other marine life that can’t survive long-term exposure to fresh water move away from the swamped portions of the bay, searching for saltier water.
This leaves huge swaths of bays most affected by Harvey’s runoff - Sabine, Galveston and Matagorda - devoid of the fish coastal anglers most often target, especially speckled trout.
“They will move out of those areas and find areas where salinities are more suitable,” Robinson said of marine fish hit by freshwater flooding.
In the Galveston Bay system, West Galveston Bay currently is holding the saltiest water. Late last week, salinity levels along the south shoreline of West Galveston Bay ranged from 8 ppt to as much as 15 ppt in some pockets. Typically in September, those areas hold salinities above 20 ppt.
Similar situations exist in the Matagorda Bay system, where some areas in both East and West Matagorda bays hold salinities below 1 ppt while others - portions of East Matagorda Bay and areas along the south shore of West Matagorda away from where the flooding Colorado River is pouring billions of gallons of freshwater into the bay and Gulf - are holding 10 ppt to 15 ppt salinities. Fish are concentrated in those saltier areas.
The farther down the coast you go, the less freshwater flooding is seen, and the bays and the fishing prospects are significantly better.
While fish can get out of the way of the freshwater inundation in Texas bays, oysters can’t. And these marine mollusks, crucial pieces of the bays’ ecosystem, stand to see the greatest short-term and perhaps long-term effect from the flooding.
Oysters can’t survive much more than a few days in freshwater, and flooding for a week or two will result in almost complete die-offs of all oysters in affected areas. That almost certainly is going to occur in bays along the upper coast.
But the situation isn’t necessarily grim for oysters, Robinson said.
“Oysters are extremely resilient animals,” he said. They’ve been around for millennia and have faced every kind of environmental challenge. They have found ways to persist.”
While reefs in areas that see weeks of freshwater swamping may die, their shells will remain, serving as habit for a plethora of marine life as well as providing the hard surface to which larval oysters attach when conditions moderate.
And the flooding-caused changes in salinity gradient in the bay can benefit oysters by opening up new areas to colonization. That is what happened in the wake of a somewhat similar flooding event in 1979 when Tropical Storm Claudette dumped biblical amounts of rain that sweetened high-salinity West Galveston Bay enough that oysters could thrive but their major parasites and predators - oyster drills and dermo, which require high-salinity levels to survive - could not.
All is not lost
The result was an explosion of oysters in West Galveston Bay in the wake of that epic flooding.
“Events like this have devastating and heartbreaking effects on us. This is an unimaginable tragedy on an unprecedented scale,” Robinson said. “For the bays, there are positive and negative effects. It can be like a forest fire, destroying things but also pumping nutrients into the bays. Almost invariably, productivity goes up in the years after something like this.”
That’s at least something positive to hold onto.