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Ship Holds Probed for Invaders

 

By Mary Kelley Hoppe

Sampling of ballast water from more than 60 foreign vessels entering Tampa Bay has uncovered numerous live algae but no new harmful invaders, according to researchers with the Florida Fish & Wildlife Research Institute.  The snapshot study, the first of its kind in the state, provided a preliminary risk assessment of the transport of harmful algae in ship holds.

Ballast water from cargo ships contains numerous aquatic organisms from foreign waters. Those that survive the journey can spread and become invasive, like the Asian green mussel that has become established in Tampa Bay and Charlotte Harbor.

“Blooms of toxic algae are occurring worldwide in areas they have never been documented before,” says FWRI marine researcher Bill Richardson.  While harmful algal blooms are a natural phenomena that have occurred throughout recorded history, they have increased in frequency, intensity and geographic distribution over the last two decades.

Until 1970, blooms of Alexandrium tamarense, which can cause paralytic shellfish poisoning, occurred only in the temperate waters of North America, Europe and Japan.  But by 1990, they had been well documented throughout the Southern Hemisphere, in South Africa, Australia, India and Thailand.

Many of these organisms are marine hitchhikers in ballast water carried by cargo ships to maintain stability at sea.  When cargo is offloaded, a ship compensates for the decreased weight by pumping seawater into its ballast tanks.  When cargo is loaded, ballast water is discharged to offset the increased weight. 

Ballast water may contain viruses, bacteria, algae, fish, crabs and mollusks.  Those that survive the arduous journey are released into non-native waters where they can spread and become invasive. 

Tampa Bay’s best known marauder is the Asian green mussel, which was first reported in 2000 when the mollusk began clogging the pipes of local power plants, and quickly spread on pilings and other manmade structures throughout the bay.  Anecdotal reports suggest that last year’s red tide killed off some of the population but the nettlesome invader is still widespread.

Tampa Bay at High Risk

One toxin-releasing microalgae, Gymnodinium catenatum, is considered to be at high risk for introduction here, since many ships calling on Tampa Bay come from foreign ports where the species is common and water temperatures are similar.  Blooms of G. catenatum forced the closure of shellfish harvesting beds in the Australian port of Hobart for up to six months.  Scientists suspect it entered the country in ballast from Asia.

To collect water samples, researchers insert tubing into a sounding pipe lowered to the bottom of the ballast tank.

Slightly more than half of the known species of harmful algae -- including Karena brevis, responsible for Florida’s red tides – already occur in Florida, whose balmy climate allows numerous organisms to thrive.  Florida has one of the highest numbers of non-native land and marine species of any state in the U.S.

For the Tampa Bay study, researchers accompanied Coast Guard officials inspecting vessels at the Port of Tampa and Port Manatee.  Samples of ballast water were collected, along with sludge vacuumed from the bottom of tanks.

“To date, we’ve gotten a number of toxic species in the ballast water but so far all of them have been previously recorded in Tampa Bay,” says Richardson.

Some microalgae can survive long periods in the dark by forming a resting or “cyst” stage that may remain dormant for years. Because cysts maintain a very low metabolic rate, they can tolerate highly unfavorable conditions.  They often become lodged at the bottom of a ship’s hold where it’s easy to avoid being sucked up in ballast exchange. Dormant cysts are harder to identify, requiring incubation and grow-out in a laboratory. 

Samples are returned to the FWRI lab in St. Pete, where they are examined under a light microscope. Algal cells may be alive or in a resting or dormant “cyst” stage.

Of more than 60 ships sampled, about 38% contained live algae and roughly 45% had cysts in ballast tanks, of which some 16% were made viable in the lab.  Only two new algal species were recorded and neither is toxic.  However, it’s not known how many of the previously recorded toxic algal species were originally introduced in ballast water from foreign ports.

“One limitation is that we have not been able to be as selective as we might like in targeting ships,” Richardson adds.  Lacking jurisdiction, the agency had to rely on cooperation with the Coast Guard to board private ships. 

To reduce the spread of invasive species, the shipping industry encourages open water ballast exchange to rid vessels of unwanted species at sea where they are less likely to survive.  “But in our study it hasn’t necessarily killed cysts or other organisms transported,” Richardson said.

The Pinellas County Environmental Fund and Florida Department of Environmental Protection provided funding for the three-year study, which wraps up this summer.  While no additional monitoring is planned, researchers hope to continue periodic sampling.  

As a result of the investigation, which provided a chance for testing ship-sampling methods and improving skills for identifying algal strains, researchers say they’re better prepared to deal with introductions in the future. 

“Based on what I’ve seen it just seems to be a matter of time,” says Richardson.

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