Algal Studies Aimed at Avoiding Harmful Blooms
A carpet of algae filled Onslow Bay in October 1987, sickening fishermen and people on central North Carolina beaches and rendering oysters and other shellfish caught in area waters inedible for months. Such harmful algal blooms, often referred to as "red tide" because of the color of the algae, have become more widespread in recent years, according to the National Oceanic and Atmospheric Administration. They cost the U.S. an estimated $82 million a year in lost income from fishing and tourism, treatment of illnesses, and monitoring efforts. NC State researchers are studying different organisms responsible for harmful blooms along the Eastern Seaboard and Gulf Coast to better understand their biology and how to forecast when they grow to unhealthy levels.
The organism that wreaked havoc in Onslow Bay, Karenia brevis, has caused problems in the Gulf of Mexico for centuries, says Dr. Dan Kamykowski, an expert on plankton and a professor in the Department of Marine, Earth and Atmospheric Sciences (MEAS). K. brevis is a dinoflagellate—algae that use whip-like appendages to move through the water—that secretes toxins that can become airborne and cause respiratory distress in humans. The toxins also are absorbed by shellfish, which can make people who eat them sick, and have been known to kill birds, fish, and other aquatic animals that feed in the waters near a bloom.
To determine how K. brevis blooms are formed, Kamykowski sailed the waters near the Florida panhandle, using an array of monitoring devices to measure factors like algae concentrations, nutrient levels, and water temperature throughout the water column. His studies have shown that, unlike other dinoflagellates that go dormant for a period, K. brevis remains active under the surface, moving up to get enough sunlight for photosynthesis and back down to the sediment to find necessary nutrients to survive. A shift in current can then suddenly bring them close to shore and expose them to the surface, Kamykowski says. "They can form a bloom without much growth," he says. Still, nutrient-laden runoff from farm fields, urban stormwater, and septic-enriched groundwater, as well as rising sea temperatures, could be creating larger, more frequent K. brevis blooms. "We've shown that red tide is a natural phenomenon," he says, "but man-made troubles might be aggravating the problem."
"Pollution from continued development is overwhelming the natural balance of the estuarine food web."
Dr. JoAnn Burkholder's research has linked production hog farms in eastern North Carolina to growing blooms of Heterosigma akashiwo in the Neuse River Estuary. The alga can produce toxins that lead to fish kills. Ammonium levels in the estuary have soared by 450 percent since 1993, according to Burkholder, a professor in the Department of Plant Biology and director of NC State's Center for Applied Aquatic Ecology. "Ammonium is a nutrient that many phytoplankton prefer to consume," she says. Her research team has tracked changes in land use in the Neuse River basin over time, and the growth of swine operations in the southeastern part of the state—and the wastes they produce—correlates directly with the increased ammonium levels. "Other factors likely contribute to a degree," she says, "but industrialized swine operations have been the major change in the watershed in that time." NC State has wired the Neuse River from headwaters to coastal estuary for real-time monitoring of water quality, and Burkholder's data show that the amount of plankton in the estuary has increased by 50 percent in 15 years. The hydrology of the system lends itself to problems—winds routinely roil nutrients up from the sediment in the shallow estuary, and algae aren't easily flushed out because the estuary drains into Pamlico Sound instead of the ocean—but Burkholder says human activities in the river basin have helped a number of algae species thrive in the estuary. "Even with clean-up efforts, we're running to stand still," she says. "Pollution from continued development is overwhelming the natural balance of the estuarine food web."
Accepting red tide as part of the natural balance in the Gulf of Maine, Dr. Ruoying He has developed a forecast model to help public health officials and fishermen in the Northeast work around spikes in algae levels. A physical oceanographer by training, the MEAS associate professor began studying Alexandrium fundyense during his previous position at Woods Hole Oceanographic Institute in Massachusetts. The dinoflagellate produces a toxin that is potentially fatal to people who eat shellfish from areas near a recent algal bloom. "I'm used to the physical science of the ocean currents," He says, "but I find the biological interaction in studying algal blooms fascinating."
Biologists at Woods Hole take sediment samples from the ocean every winter to determine the distribution of dormant A. fundyense cysts across the region, and they also provide He with algal growth and mortality rates. He combines that information with data on ocean currents, water temperatures, sea levels, and river flows to produce his predictive model. Various scenarios are run through the model to develop a range of possibilities for each season. "We're trying to create an envelope, similar to hurricane forecasting," He says. Water samples are then routinely collected throughout the spring and summer to help validate the model and provide data for shorter-term forecasts, which help determine when to close beaches and shellfish beds and to monitor oysters, clams, and mussels for toxicity. "Red tide is very problematic," he says. "We need a better understanding of algae to combat harmful blooms and avoid the dangers they pose to public health."
Agencies providing funding for research cited in this story include:
- National Science Foundation
- Ecology and Oceanography of Harmful Algal Blooms Research Program (ECOHAB)