It?s estimated that the red tide algae, Karenia brevis, costs approximately
$20 million per bloom in economic damage off the coast of Florida alone.
Scientists at the Georgia Institute of Technology have found that a diatom
can reduce the levels of the red tide?s toxicity to animals and that the
same diatom can reduce its toxicity to other algae as well. If scientists
can learn to use this process to reduce the toxicity of red tide, they could
reduce the vast amount of economic damage done to the seafood and tourism
industries. The research appears as articles in press for the Web sites of
the journals Harmful Algae and the Proceedings of the Royal Society of
London B.

?We found that red tide toxins can be metabolized by other species of
phytoplankton. That holds true for both the brevetoxins that damage members
of the animal kingdom and the as yet unknown allelopathic toxins that kill
other competing species of algae,? said Julia Kubanek, an associate
professor with a joint appointment in Georgia Tech?s School of Biology and
School of Chemistry and Biochemistry.

Red tide is a dramatic case of an ecosystem that?s out of control. In normal
seawater, K. brevis makes up about 1 percent or less of the species, but
during a red tide, that share increases to more than 90 percent. Filter
feeders such as oysters, mussels and clams ingest the dinoflagellate and
become unsafe to eat. Fish killed by the red tide wash on the shore, which
can be contaminated and essentially unusable to tourists for months at a
time.

Kubanek and her researchers found in previous work that the growth of the
diatom Skeletonema costatum was only moderately suppressed by the
brevetoxins released by the red tide. So, they figured that the diatom might
have a way to deal with the toxins. According to their study, they were
right.

In one experiment, detailed in the journal Harmful Algae, Kubanek?s students
grew the red tide algae along with the S. costatum diatom to test her group?s
hypothesis and found that the samples with both organisms had a smaller
concentration of brevetoxin B than samples without the diatom. They also
tested the algae with four different S. costatum diatom strains from around
the world and came up with largely the same results. That suggests that
evolutionary experience with the red tide algae was not necessary for the
diatom to resist the toxins.

In another experiment, covered in Proceedings of the Royal Society B, they
found that the red tide algae was able to reduce the growth of the S.
costatum diatom, but that exposure of the red tide organism to S. costatum
makes the red tide less toxic to microscopic algae. That suggests that the
diatom is somehow able to reduce the potency of red tide?s toxins.

?It could be that Skeletonema is degrading Karenia?s allelopathic chemicals
just like it degrades brevetoxins. Or, it could be that Skeletonema is
stressing Karenia out, making it harder to produce allelopathic chemicals,?
said Kubanek.

What they do know is that the brevetoxins that harm oysters and other
members of the animal kingdom aren?t the whole story.

?We found that when we took seawater and added purified brevetoxins to it,
the live algae didn?t suffer much, so there must be other chemicals released
by the red tide that are toxic to these algae,? said Kubanek.

How that?s done, isn?t clear yet, but Kubanek and her group are currently
working on finding the answer to that question.

?What we do know is that this diatom, S. costatum, is able to undermine
these toxins produced by the red tide, as well as the brevetoxins that are
known to kill vertebrate animals like fish and dolphins,? said Kubanek.

If scientists such as Kubanek and her team can learn more about the
strategies that microscopic algae use to reduce the toxicity of red tide,
they might be able to use that knowledge to help reduce the poisonous
effects the tide has on the animal kingdom, not to mention the damage it
does to the seafood and tourism industries.

Kubanek?s research team for these studies consisted of Tracey Myers and
Emily Prince from Georgia Tech and Jerome Naar of the Center for Marine
Science at the University of North Carolina at Wilming
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