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<P sizset="11" sizcache="45"><ABBR class=published
title=2010-01-11T20:00:00Z></ABBR> </P></DIV></DIV></DIV>
<DIV class=formatpublished sizset="21" sizcache="45"><FONT size=3>Nature<!--COinS--></FONT></DIV>
<DIV class=formatpublished sizset="21" sizcache="45"><FONT size=3>Published
online <ABBR class=published title=2010-01-11T20:00:00Z>11 January
2010</ABBR></FONT></DIV>
<DIV class=formatpublished><FONT size=3>doi:10.1038/news.2010.5</FONT> </DIV>
<DIV class=formatpublished> </DIV>
<DIV class=type-of-article><FONT size=4>Harmful algae stun their
prey</FONT></DIV>
<DIV class=intro>Toxic blooms may help single-celled algae to eat their
competitors.</DIV>
<DIV class=byline><SPAN class=vcard><SPAN class="author fn">Brendan Borrell
</SPAN></SPAN></DIV>
<DIV class=byline><SPAN class=vcard><SPAN class="author fn"><A
href="http://www.nature.com/news/2010/100111/full/news.2010.5.html">http://www.nature.com/news/2010/100111/full/news.2010.5.html</A></SPAN></SPAN></DIV>
<DIV class=byline><SPAN class=vcard><SPAN
class="author fn"></SPAN></SPAN> </DIV>
<DIV class="hentry article" sizset="21" sizcache="45"><SPAN class=cleardiv><!-- --></SPAN>
<DIV class=entry-content sizset="21" sizcache="45">
<DIV class="inline-image right" style="WIDTH: 180px">
<DIV><IMG alt="Red tide"
src="http://www.nature.com/news/2010/100111/images/news.2010.5.redtides.jpg"></DIV>
<DIV><SPAN class=imagedescription><FONT size=1>Red tides may help
dinoflagellates to trap prey.<SPAN class=imagecredit>Bill Bachman / Science
Photo Library</SPAN></FONT></SPAN></DIV></DIV>
<P>The toxins produced by some algal blooms may have evolved to give predatory
algae an advantage when it comes to capturing their prey, researchers say.
Knowing how algae use toxins in nature could help scientists who are trying to
predict when and where the devastating blooms, sometimes called 'red tides', are
going to strike.</P>
<P>Single-celled algae called dinoflagellates are one of the organisms
responsible for harmful algal blooms that poison shellfish and leave fish
floating belly-up. Because the toxins are energetically costly to make,
biologists have long wondered whether they are more than just a way to defend
algae from getting eaten or preventing competitors from moving in on their
space. Although many dinoflagellates can survive through photosynthesis alone,
some species are able to grow twice as fast by preying on other algae — and it
is this feeding mechanism that is now thought to be aided by the production of
toxins.</P>
<P>"People suspected that one of the roles of the toxins is to immobilize prey,"
says marine ecologist Diane Stoecker of the University of Maryland's Horn Point
Laboratory in Cambridge, Maryland, who was not involved in the research. "This
is the first paper that really shows that."</P>
<P sizset="21" sizcache="45">Biophysicist Jian Sheng of the University of
Minnesota in Minneapolis and his colleagues studied toxic and non-toxic strains
of a dinoflagellate species, found in Chesapeake Bay on the eastern US coast,
called <SPAN class=i>Karlodinium veneficum</SPAN>. In the lab, the team mixed
each strain of <SPAN class=i>K. veneficum </SPAN>with a species of algae on
which it preys, and recorded the three-dimensional motions of thousands of cells
using a high-speed holographic microscopy technique they described in 2007<SUP
sizset="21" sizcache="45"><A
href="http://www.nature.com/news/2010/100111/full/news.2010.5.html#B1">1</A></SUP>.
The resulting videos contained over 4 terabytes of data, which Sheng and his
colleagues crunched to compare the swimming behaviours of predator and prey
species in the presence of different toxin levels. </P>
<H2 class=inlineheading><FONT size=3>Paralyzing poison</FONT></H2>
<P>Toxic strains of <SPAN class=i>K. veneficum </SPAN>immediately caused the
prey to slow down by more than 50%, and nearly doubled the proportion of
immobile algae in the water relative to non-toxic strains. After 5 hours, more
than 90% of the prey were immobile. According to Sheng's description of the
process, <SPAN class=i>K. veneficum </SPAN>can swoop in, shoot out a 'tow line'
and reel in the immobile prey before swallowing it whole. The prey algae is 2–3
times the size of <SPAN class=i>K. veneficum</SPAN>. Notably, <SPAN class=i>K.
veneficum </SPAN>also slows down in the presence of prey, which may be a means
of staying within the toxic cloud to aid predation.</P>
<P sizset="22" sizcache="45">"The food is not usually considered in models, only
the physical conditions like temperature and nutrient availability," says Sheng.
The study will be published in <SPAN class=i>Proceedings of the National Academy
of Sciences</SPAN><SUP sizset="22" sizcache="45"><A
href="http://www.nature.com/news/2010/100111/full/news.2010.5.html#B2">2</A></SUP>
this week.</P><!-- 300x250 ad -->
<DIV class="ad ad300x250" sizset="23" sizcache="45">
<P>Stoecker says that there has been circumstantial evidence that
dinoflagellates use their toxins to capture prey, but notes that Sheng's work is
"pretty cool" because of the detailed visualizations and quantitative data.
Although some scientists have suggested that the nutrients netted by algae
through fish kills are enough to justify the toxins, Stoecker believes that
phenomenon is just a "side effect" of prey-capture activities.</P></DIV>
<P>Marine ecologist Daniel Kamykowski of North Carolina State University in
Raleigh cautions that the study was conducted in a laboratory and not in the
marine environment, but welcomes the findings nonetheless. "We don't know what
triggers the toxin in some strains and not in others," he says, "Once that's
better known — and if there is anything that can be controlled — then it may be
possible to diminish the frequency of blooms in the future."<SPAN
class=end-of-item> </SPAN></P>
<UL class=xoxo id=article-refrences sizset="24" sizcache="45">
<LI sizset="24" sizcache="45">
<H2 class=heading><FONT size=3>References</FONT></H2>
<OL sizset="24" sizcache="45">
<LI id=B1 sizset="24" sizcache="45"><A name=B1><!-- . --></A>Sheng, J. <I>et
al. </I><SPAN class=journalname>Proc. Natl Acad. Sci. USA</SPAN> <SPAN
class=journalnumber>104,</SPAN> 17512-17517 (<SPAN
class=cite-month-year>2007</SPAN>). | <A class=reftxt title=""
href="http://dx.doi.org/10.1073/pnas.0704658104">Article</A>
<LI id=B2 sizset="26" sizcache="45"><A name=B2><!-- . --></A>Sheng, J.,
Malkiel, E., Katz, J., Adolf, J. E. & Place, A. R. <SPAN
class=journalname>Proc. Natl Acad. Sci. USA</SPAN> advance online
publication doi:10.1073/pnas.0912254107 (<SPAN
class=cite-month-year>2010</SPAN>).
</LI></OL></LI></UL></DIV></DIV></FONT></BODY></HTML>