August 25, 2008
Study of Algae’s Appetite May Help Predict Harmful Blooms in the Bay
Like a lot of the best scientific research, the focus of Place’s decade-long work with harmful algae came about by happenstance. In the wake of the 1997 fish kills and public concern surrounding Pfiesteria, the scientist set out to study the algae species blamed for killing fish and sickening humans in the Chesapeake Bay and its rivers.
To aid in the study, Place and his team got hold of another algae, Karlodinium veneficum (at the time called Gyrodinium galatheanum), to serve as a comparison to their species of interest, Pfiesteria. Both Karlodinium and Pfiesteria are dinoflagellates — one-celled algae that propel through water with whip-like flagella. Things took an unexpected turn when they found that Karlodinium’s toxicity to fish appeared even greater than Pfiesteria’s.
Further study has led Place to suspect that Karlodinium was the real culprit in the so-called “ Pfiesteria hysteria” of 1997. He has spent the last ten years researching the microscopic algal cell at UMBI’s Center of Marine Biotechnology (COMB) in Baltimore. Virtually every year since then, blooms of Karlodinium have been implicated in fish kills along the Atlantic coast as well as in Perth, Australia.
But the fish are collateral damage, Place says. They’re not the intended target of the algae’s weapon, karlotoxin.
So what is Karlodinium really after?
Saucer-shaped, one-celled cryptophytes compose a significant portion of the algal biomass in the Chesapeake. While dinoflagellates and their glassy counterparts, diatoms, garner the most attention, cryptophytes account for 25 percent of the total chlorophyll produced in the Bay. They thrive in low-light conditions and can grow in great number when rainstorms wash nutrients downstream, but they are rarely seen as blooms because other species graze on them so voraciously, Place says.
For this reason, Place and his team believe it would be unlikely for Karlodinium to reach densities characteristic of blooms (more than 10,000 cells per milliliter) unless the cells are feeding on something. With funding from Maryland Sea Grant, Place and his colleague Jason Adolf have worked to test their hypothesis that cryptophyte meals help increase Karlodinium’s cell density, and drive the formation of harmful blooms.
Partnering with the Maryland Department of Natural Resources, the pair has monitored the presence of cryptophytes and Karlodinium at study sites on the Corsica and Potomac rivers. The researchers track the two types of algae in different ways. Cryptophytes contain a pigment that most other algae do not. When excited with green light, the pigment will glow orange, a straightforward way to detect cryptophytes. Karlodinium can be detected by a change in chlorophyll-a levels and confirmed by looking at water samples under a microscope.
So far the Corsica and Potomac rivers haven’t experienced any cryptophyte or Karlodinium blooms during the study — the team selected these sites because Karlodinium has bloomed there in the past. Place thinks high temperatures and low salinity levels over the past two years have limited growth.
In June 2006, however, Place and Adolf did observe a Karlodinium bloom in Baltimore’s Inner Harbor, just steps away from their laboratory at COMB. Immediately prior to a bloom of Karlodinium there was a spike in the number of small cryptophytes (less than 10 microns) in the water. This was followed by a bloom of larger cryptophytes (greater than 10 microns) and what Place calls a “massive response” of Karlodinium (concentration approached 66,000 cells per milliliter).
For Place, this illustrates that “not all cryptophytes are created equal for Karlodinium.”
Why not? Place has a few ideas, but so far cryptophytes been very poorly described, he says, something his research is actively trying to address. For now, “we really don’t understand how many different types of cryptophytes there are.”
What they saw cast the interaction between predator and prey in a whole new light. The quick moving Karlodinium cells stop swimming when a cryptophyte is present. They wait for the cryptophytes to come closer and then release karlotoxin, stopping the cells in their tracks before engulfing them whole.
For many harmful algae, the ecological reason for producing a toxin is still unknown. But for Karlodinium, it is clear, Place says.
“ Karlodinium makes toxin for one reason and that’s to capture prey.”
The availability of that prey, like cryptophytes, could determine when the Chesapeake Bay area next experiences Karlodinium’s characteristic coffee-colored bloom. Place hopes to be able to incorporate information on prey availability into models to predict the likelihood of a Karlodinium bloom.
Perhaps in the future, fishermen, swimmers, and boaters will click their computer mouse on harmful algae predictions before heading out on the Bay, just as they check the weather today.
-- Jessica Smits