September 2003

The Oyster’s Odyssey

Article By Larry Bozka
Photos by Jim Olive

Texas oysters are an incredibly precious but with a little help readily renewable coastal resource.

The lukewarm flats north of Rockport are massaged by a pulsing southeast breeze and bathed by a summer moon. Soft shards of light reflect off the waves, making even the finger mullet and glass minnows riding the ripples easy to see. But there is another animal world in the water that can’t be seen except with a microscope. This world consists of larval forms of oysters, and billions upon billions of them, clouds of living, waterborne dust, are washed with the current over hard-packed sand bars, around shoreline points and inside a small cove that thousands of tides have carved into the banks of San Antonio Bay.

A field mouse in a rattlesnake den stands a better chance of survival than one of these tiny oysters. It may not, and probably won’t, make it through the night. It faces too many predators and too much chance of hostile conditions to reach maturity.

The oyster’s odyssey is a perilous but fascinating journey. When a hungry Texan pulls up a bar stool at an oyster bar or, trout rod in hand, steps atop a shallow reef while wade fishing and hears the sharp crunch of shell, he’s not likely to consider that the creature before him is one that conquered immeasurable odds.

Sex Shifts and Giga-spawn

Throughout the upper coast, oysters usually begin spawning in the spring, when water temperatures reach approximately 77 degrees, and continue until early fall.

Upon discharge into the water by females, oyster eggs are fertilized by the resident males of the reef. Which oysters are male and which are female depends on conditions. Bizarre as it may seem, young oysters can and do change sex in accordance with their environment.

Oysters are a “protandric” species. When individuals first mature, they generally function as males. For many, however, that gender changes with time. In their first year, larger oysters are more likely to become females than their smaller counterparts. The degree to which oysters change from male to female largely depends on the availability of food.

“There is some evidence to indicate that food limitations will lead to a greater preponderance of male oysters in a population,” says Lance Robinson, regional director of the Texas Parks and Wildlife Department’s Coastal Fisheries Division. “Females need a good food supply in order to produce viable eggs.”

Regardless of sex, only a tiny fraction of the eggs is ultimately fertilized. According to Robinson, studies have shown that a single female oyster can produce anywhere from 10 million to 20 million eggs at one spawning, with occasional spawnings of as many as 100 million. A single female, he notes, can produce as many as 500 million eggs during the spawning season. Even with a minuscule rate of fertilization, enough embryonic shellfish are created to perpetuate the resource year after year.

The Vulnerable Veliger

Within a couple of days after fertilization, the eggs develop into free-swimming, shell-bearing larvae called veliger, which means velum-bearing. The velum is a ciliated organ that the larvae use to propel themselves through the water as well as to gather in the single-celled algae on which they feed. Hungry predators devour a great many veliger.

Tidal currents transport the microscopic organisms into uncertain environments, some more suitable than others. The range of lethal environs varies from outright fresh water at the mouths of rivers to the salty waters of the open Gulf. Either too much or too little salt will kill the vulnerable veliger.

Only a few veliger will complete their journey as part of the substrate reef structure that is the literal foundation of the species’ survival. Says Robinson: “The larvae orient to chemical cues on the water that some researchers hypothesize is generated by a bacterial film that develops on hard substrates. Since oysters need a hard substrate to attach to, these cues are the trigger ‘telling’ the larvae that suitable substrate is nearby.”

Upon receiving this cue, the veliger begin to metamorphose into thinly shelled, non-swimming “spat.” This unusual name is derived from the fact that their amber, nearly invisible shells resemble tiny specks of freshly chewed tobacco. “Once in contact with the hard surface,” Robinson says, “the spat cements itself into place and begins growing into the oyster with which we are all so familiar.”

As hard surfaces go, oyster spat prefer oyster shell. An empty oyster shell, placed back in the water, becomes a place for new oysters to live. Unfortunately, oyster shell remains a precious commodity.

“Oyster shell is still sold for road-bed material,” Robinson notes, “although the price has fallen to the point that it is not as economical as it was in the past. It is also still sold to poultry feed processors, where it is ground to a fine powder and added to feeds as a supplement to strengthen egg shells. Some shell is returned to private oyster leases [see sidebar], but there is currently no program to get this shell back to the natural beds in the bay.”

Oyster shell is far too valuable a resource to waste on the streets of housing subdivisions and driveways. Still, although state law clearly establishes oyster shell as the property of the state, prohibitively high enforcement costs prevent the implementation of an effective reclamation program.

Fortunately, spat will attach to a variety of materials such as bricks and cinder blocks, broken concrete and culvert pipe, bottles, tires and even cans. The latter were a favorite of the late Rudy Grigar, a legendary Texas-born flats fisherman and professional fishing guide who, late in his career, strung beer cans by the hundreds near Curlew Island on Louisiana’s Chandeleur Island chain. Rudy died several years ago, but his flourishing reefs will thrive for ages to come.

Backbone of a Fishery

From deep-water shell pads supporting mid-bay production platforms, to jagged reefs that protrude out of the water during low tide, oysters are the keystones of inshore marine life. Displayed on the tables of restaurants nationwide, laid out on the half shell and supplemented with cocktail sauce, horseradish and saltine crackers, oysters are the backbone of a long and historic commercial fishery.

The American commercial or “eastern” oyster, Crassostrea virginica, is found in Texas coastal waters all the way from Beaumont to Brownsville. Also present, but not nearly so commercially viable, is the Gulf oyster, Ostrea equestris.

Though oysters are abundant from Rockport on north, they are nearly nonexistent in the hypersaline waters of the Laguna Madre. Farther south, at Port Isabel’s South Bay, a remote and much smaller oyster fishery exists. Still, no area of the coast compares with the Galveston Bay system in terms of sheer abundance and sustained annual yield.

Gulf oysters have a decided preference for high-salinity waters although they are rarely found, as the name implies, in the Gulf of Mexico. Instead, they favor parts of bay systems with higher salinities and tend to concentrate near bay-to-Gulf passes.

Eastern oysters, conversely, thrive in the brackish waters of enclosed bay systems. During the low-tide phases of wintertime, Karankawa Indians and later, settlers to the Texas Coast, relied on eastern oysters as an important food source from fall through early spring. Harvesting oysters was a far less strenuous undertaking, after all, than stalkingwhite-tailed deer and other game animals. What was important to these hardy coastal residents was that the food source was there, year after year. No one knew, or really cared, how the nutritious shellfish reproduced.

That mentality changed with the advent of the oyster-harvesting industry. Before 1870, oysters were not commercially harvested because there was essentially no way to transport them inland for sale. By 1890, however, with the growth of processing and railroads along the coast, Texas oystermen were harvesting more than 2 million pounds of oyster meat from the state’s bays and estuaries. A decade later, that figure had climbed to 3.5 million pounds.

Today, depending on seasonal and environmental trends, the average annual harvest is even higher. Total commercial oyster landings for 2001 amounted to 4.8 million pounds of meat. More than 94 percent of these landings came from Galveston Bay. The total annual economic benefit to the State of Texas generated from the commercial oyster fishery is approximately $34 million. As an oyster-producing state, Texas ranks second only to Louisiana.

Oystermen intimately understand the need to maintain existing reefs and create new ones in favorable areas. Compared to commercial finfish, the perpetuation of oysters as a renewable resource is a process that is both refined and, environmental variables aside, quite controllable.

From the recreational angler’s standpoint, oysters are invaluable. Bay fishers regularly wade and drift fish for speckled trout and redfish over submerged oyster reefs. Old salts like Grigar understand better than anyone that where there are oysters there are usually sport fish as well. Reefs comprise the base of a massive food chain, one that is absolutely essential to the health of coastal bays and estuaries. The sharp crunch of shellbeneath wade fishing boots is a promising harbinger of bent rods and steady action.

As for Grigar’s unique methodology, please don’t consider this an endorsement for sinking chains of beer and soda cans in coastal waters. Rudy was an extremely colorful fellow who did things his own way. Even he, were he alive today, would agree that your well-intentioned effort would likely be construed as littering. It would be much better if we would all endorse the continual restocking of oyster shell into existing oyster habitats.

Indicators of Water Quality

Mature oysters are extremely adaptable creatures. Veliger and spat are considerably more delicate than their full-grown, hard-shelled counterparts. Nonetheless, mature oysters face their share of natural hazards.

A major influx of red tide algal bloom and related health concerns prompted the closure of Texas bays by the Texas Department of Health to all oyster harvesting in the fall of 2000. Around 300 miles of Texas coastline were affected by the red tide, so called because of its propensity to turn seawater reddish-brown. The microscopic algae not only saturated oyster beds but also paralyzed some fish species.

The tide now known as Karenia brevis did not, despite popular notion, kill the oysters, but it did contaminate them. Since oysters are filter feeders, they ingested the algae, releasing brevitoxin into their tissues. This toxin is only minimally impacted during the cooking process, and so the fishery was closed.

According to biologists, the notorious Y2K red tide outbreak was perpetuated in large part by an extensive drought that minimized freshwater inflows into bays. Coupled with extreme summertime heat, the drought made for a red-tide breeding ground.

Oysters are remarkably resilient, and red tide blooms are relatively rare, particularly on the upper Texas Coast where freshwater inflow is generally much higher than in the Laguna Madre. Far more commonly, oysters fall prey to predatory snails appropriately called oyster drills. Virtually anyone who has ever sorted through a stack of oyster shell has seen the telltale holes left behind by the tubular proboscis of these creatures. Several species of crabs also are capable of preying on oysters, cracking their stout shells and devouring the meat. Even fish such as the sheepshead can break and consume a small oyster.

But it’s disease-causing parasites that are the oyster’s public enemy No. 1. The protozoan parasite Perkinsus marinus, or “dermo,” is one of the major threats to oysters. The naturally occurring organism has a higher affinity for saltier waters. During drought periods or times of substantially reduced freshwater inflow, dermo can and does infest and kill entire reefs.

When submerged by tidal waters, oysters feed by filtering phytoplankton from the water column. Oysters are in effect living pumps, capable of filtering up to six gallons of water per hour. They play a significant role in maintaining water quality in bays and estuaries. And, like the proverbial coal-mine canaries, they tend to be indicators of the quality of bay water.

Raw or Cooked?

As someone who became severely ill with hepatitis A in 1990 as a result of eating a bad oyster on the half shell, I have a special appreciation for those who regularly assess the quality of oyster beds. Fortunately, in the past decade-plus the process of monitoring has been refined and more strictly enforced.

Eating raw oysters remains a very risky proposition for people with compromised immune systems. The Texas Department of Health, Centers for Disease Control and Prevention, Food and Drug Administration and even the industry itself stress that such people should never eat raw oysters or, for that matter, any other raw or uncooked seafood. The concern is over Vibrio vulnificus, a naturally occurring bacteria that can be deadly to those in this high-risk category.

Eating raw oysters, especially during the warm-weather months, always entails a bit of risk. That risk is virtually eliminated, though, when oysters are fried or otherwise cooked through-and-through. Despite my single but miserable oyster-related illness, I hold oysters in high esteem.

It is, after all, extremely difficult to dislike anything that sustains so much life and makes it possible for a fanatical bay fisherman such as me to catch so many redfish and speckled trout.

Monitoring Mollusks

For animals that spend most of their lives anchored in one spot, oysters take a lot of looking after. Because of health and economic issues, they may be the most intensively monitored and managed non-endangered species in the state.

TPWD’s Oyster Advisory Committee, appointed by the chairman of the Texas Parks and Wildlife Department Commission, advises the department on issues affecting the oyster fishery. Members of the committee represent holders of private oyster leases, people who take oysters only from public reefs and state agencies with a role in regulating oyster harvest. The latter include the Texas Department of Health, which certifies oysters as safe for harvest; the Texas General Land Office, which controls the bay bottom leased for privately managed oyster beds; and the Texas Commission on Environmental Quality, which works with several agencies to improve water quality in Galveston Bay.

Committee member George Bolin, a former TPWD commissioner, knows first-hand the value of the counsel the committee gives the commission. “When I served on the commission beginning in 1983, we didn’t have many advisory committees,” he says, “and I found it hard to get up to speed on many issues. Texas is a big state, and the commission is charged with overseeing a lot of things. If the committee feels something needs to be changed or addressed, we bring it to the attention of TPWD so commissioners can get a feel for what needs to be done. I think it makes the system work better.” He cites the committee’s work to minimize damage to oyster reefs from spoil produced by dredging of the Houston Ship Channel as an example of how the committee protects the resource.

The committee also works to protect the interests of both those who harvest oysters and those who eat them. “The private lease-holders are the only ones putting something back into the bay system,” Bolin points out. “They are farmers. They are actually growing oysters.” But ultimately, he says, the committee’s job is to protect the public. “We look for the best ways to ensure that good oysters get to the market.”

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