Magic in the Mud
From the common stingray to the bizarre sea robin, bottom dwellers are a vital part of our marine ecosystems.
By G. Elaine Acker and Michael Guerra
In the early morning light, a small, flat-bottomed boat makes its way across Espiritu Santo Bay. The water is scarcely two-feet deep in many places, and fishermen have already waded far from their boats, casting for redfish and trout. Optimistic brown pelicans fly low across the water, and great blue herons linger in the shallows.
TPWD Fisheries Technician Jeremy Helms guides the boat through a mangrove slough to a gravel shore near Pass Cavallo and anchors the boat. He and TPWD biologist Teresa Krenek step into the water and pull a bag seine along the shore, stretching a long white net perpendicular to the shoreline.
While Krenek pivots on one end, Helms drags the other in a half-moon pattern, seining for a sample of the sea grasses and wriggling saltwater creatures that inhabit the soft, muddy floor of the bay. “When we’re conducting monitoring studies, we count, measure and identify every creature and species of grass,” says Krenek. “We measure the depth, temperature and turbidity of the water. “Our studies give us long-term comparative data that is the basis for determining the health of the bays. Without the baseline studies we can’t predict how to best protect game fish or threatened marine life in the estuary ecosystem.”
The survey reveals myriad species of grasses, pinfish, grass shrimp, blue crabs, hermit crabs and jellyfish that attract little attention from most Texans, but others find them positively fascinating. “Whether they’re wade-fishing in the bays or combing the beach for seashells, people rarely stop to consider the world of crawly things beneath their feet,” says Paul Montagna, professor at The University of Texas Marine Science Institute in Port Aransas. “The formal term is ‘infauna,’ but I like to call them the ‘invisible fauna.’ Texas has 2,300 different species of infauna, from razor clams to polychaete worms, and they create an intricate, three-dimensional world of interconnecting tunnels. There are literally hundreds of these invisible fauna under every footstep.”
Collectively, the soft sediment and aquatic plants and animals at the bottom of the bay are known as the “benthic” community. It teems with life and is an essential food supply for Texas’ “poster” species, including shorebirds and sportfish. “It’s an amazing thing,” says Montagna. “The biomass produced by infauna is the major energy source that fuels fish in coastal seas. Texas’ prized fish, red drum, black drum, trout, flounder, are all being supported by this invisible fauna. Almost all of the bottom-feeding fish spend their time laying on top of the mud, hunkered down, sucking up these organisms.” Montagna’s invisible fauna also feed Texas’ shorebirds, including terns, herons and pelicans. “Oyster catchers are flying around oyster reefs. Whooping cranes are poking at the bottom and feeding primarily on crabs and other benthic creatures. Spoonbills take their beak and wash it back and forth along these surface sediments and literally strain out all the invisible fauna.”
Snuggled into the mud are other lesser-known species, including sand eels and sea robins. Sand eels are not actually related to eels, but rather are long, slender fish that bear a faint resemblance to a centipede. They have a long dorsal fin and sharp, pointed noses, which they use to burrow deep into the silt, where they become a taste treat for fish and shorebirds. And there are 16 species of sea robins that can be found “walking” along the bottom of Texas’ bays. “They’re neat animals,” says Mark Fisher, TPWD’s Coastal Fisheries Division Science Director based in Rockport. “They’re kind of ugly but I like them. They go walking along the bottom on feeler-like fins looking for anything small enough to fit in their mouth. You don’t see them caught much most are too small to take a baited hook into their mouth but when fishermen do see them, their first instinct is to drop the rod and run. They make a chirpy chatter sound like a bird, and that may be where they get their name.” The sea robins’ bony heads and sharp spines are sufficient to deter most predators, including humans.
“Wetland loss in Texas is primarily due to urbanization,” says Montagna. “We see very few barriers to municipal development.” For a long time, towns like Port O’Connor, Rockport and Port Aransas were sleepy fishing villages. But in the last 12 months, real estate prices have skyrocketed.
Other species, such as stingrays are more memorable, especially by those unfortunate people who chance to step on one and find themselves on the stinging end.
The rays most often found in Texas waters are the common Atlantic ray and the cow-nosed ray. The mud is their home and provides protection from predators such as their relatives: sharks.
Fisher recently eavesdropped on this dynamic benthic community using a hydrophone. “When the sun goes down, it gets really noisy,” Fisher says. “Shrimp click constantly. When a stone crab or blue crab cracks an oyster, there’s a pop like a gunshot.” In addition to what it revealed about the aquatic culture, using the hydrophone helped Fisher identify spawning areas for spotted sea trout. “There is a particular drumming that we can identify with the equipment. If we can locate and better understand the spawning needs and habitat associated with sea trout, we’ll be better able to manage this and other sport fish species.”
The lively community living in the state’s bays is one of the reasons the Texas coast is still considered a gem. And it can stay that way if Texans plan ahead and understand the threats to this “invisible” ecosystem that has such a tremendous impact on the state’s quality of life. According to TPWD, Texas has already lost approximately 50 percent of its wetlands a figure that mirrors the national average. While industrial and agricultural developments that cost wetlands in the past are now limited, population growth is the tidal surge that could threaten the future of vital marshes and estuaries.
“Wetland loss in Texas is primarily due to urbanization,” says Montagna. “We see very few barriers to municipal development.” For a long time, towns like Port O’Connor, Rockport and Port Aransas were sleepy fishing villages. But in the last 12 months, real estate prices have skyrocketed. “People are attracted to the Texas Coast because it’s still very pristine,” says Montagna. “There’s little pollution. We have abundant fisheries. It’s not overbuilt like Florida.”
By some estimates, the Gulf Coast could become one unending metropolitan area stretching from Key West to Cancun by the year 2100. A baby girl born today (with excellent genes) might live to see the day that this coastal population explosion becomes a reality.
The population growth along the coast is highlighted in sales of fishing licenses. At a time when most of the country is holding steady or declining, Texas has seen continued increases in license sales. And although the influx of people can be a bad thing if it means development over wetlands, Larry McKinney, director of Coastal Fisheries for TPWD, is quick to note that anglers also help the coastal conservation efforts. “If people enjoy fishing and start supporting conservation organizations, they become the political voice for protecting bays,” says McKinney. “And they pay the bills. Their money helps restore wetlands, manage fisheries and support hatcheries.”
In addition to overpopulation, pollution is a factor that cannot be ignored. Contaminants are a growing concern. “We’re seeing more fish-consumption advisories for things like mercury in the bays and offshore,” says McKinney. “Once contaminants like mercury are in the sediment, they are difficult to remove, and some of the first organisms affected are bottom dwellers. Then, whatever is found in the bay bottom can also be found in sport fish.”
Whatever finds its way into Texas rivers, including municipal wastewater, can also be found downstream in one of the state’s seven major bays. “About a third of our coastal waters are closed for shellfish harvest because of pollution,” says McKinney. “We depend upon these waters to treat our waste and assimilate our pollution, and so far, these systems can do that and the benthic community is an important reason why. In our cities, we have never contemplated treating wastewater to a level where it’s drinkable. Our wastewater treatment is at the secondary level. The water ends up in the bays, and the sand eels and oysters are out there working to ensure we have a healthy and productive system. If the system is not healthy — if we lose our wetlands and benthic communities — the whole bay will turn into a giant sewage treatment pond.”
Abundant sea grass meadows also play a significant role in maintaining healthy wetlands by acting as a water filter, by helping stabilize the sediment and by serving as a major nursery area for numerous species. However, with larger numbers of boaters in the bay, biologists are finding that props tear through sea grass and can do lasting damage to the habitat. “Prop scarring happens when the boats go through the sea grasses and cut down into sediment,” explains McKinney. “It’s the difference between mowing grass or plowing through it. The more delicate grasses can take seven or eight years to restore, and others never come back. Some scars act like erosional gullies on land, and never recover. Some areas are as much as 80-90 percent scarred. The seagrass covers a diverse benthic community and the scarring affects that habitat. All the bottom dwellers — including rays, crabs and redfish — depend on animals in sea grass for food.”
TPWD’s coastal fisheries team, including Mark Fisher, has now begun studying the effects of prop scarring on sea grasses in Redfish Bay. They have laid out 30 transects (grids), each measuring 100 meters, and are snorkeling the entire area, marking prop scars with a GPS unit. Their studies will make it possible to determine if changes in boating regulations are having a positive effect and further to determine where damage is most severe so that proper measures can be taken for protection.
McKinney describes the estuaries as amazingly resilient. “They can take a lot,” he says. “And it makes people complacent. But we’ve learned from other systems around that world that they do have breaking points. The world abounds with broken systems: the Aral Sea, the Colorado River (the western one emptying into the Gulf of California), the Mississippi River, the Nile, the Everglades, and on and on. The reasons they are in trouble, in hindsight, are obvious: poor planning, greed, ignorance and just plain bad luck.” To date, Florida has committed $1.3 billion to the Everglades restoration effort alone, and other projects worldwide are similarly costly. Texas has an opportunity to learn from, and avoid, others’ mistakes.
“All the sediments are the memory of the ecosystem,” says Paul Montagna. “Whether it’s an oil spill, pollution, things washing into bay, a rainy year when you’re looking at the sediment, you’re literally looking at what’s happened over time.” The extraordinary life at the bottom of the bay, and under every footstep you take while walking on the beach is, as Montagna refers to it, “magic in the mud.” Catch a glimpse of a vibrant roseate spoonbill wading in the marsh, poking at tiny shrimp, or wade into the bay and cast a line for a fat redfish it all is magic that is tied to the mud and the invisible fauna that live there. In this brief window in time, Texans have an extraordinary opportunity to create and maintain a coastal habitat for both people and wildlife that is unrivaled anywhere else in the world.