Download Allelopathic effect of Cochlodinium polykrikoides isolates

5th HAB US Conference Abstract
Allelopathic effect of Cochlodinium polykrikoides isolates from North America on
competing phytoplankton
Ying Zhong Tang and Christopher J. Gobler*
School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 117945000, USA
*Corresponding author. E-mail address: [email protected]. Tel.: +1 631 632
5043, Fax: 631-632-5070
ABSTRACT
The toxic dinoflagellate, Cochlodinium polykrikoides, forms annual harmful algal blooms (HAB)
in estuaries on both coasts of the US, and its acute toxicity to multiple species of finfish, shellfish,
and shellfish larvae has been recently reported by our lab group (Gobler et al 2008, Tang and
Gobler 2009, Tang and Gobler, submitted). The nature of the toxicity of C. polykrikoides led us to
an investigation on its allelopathic effects on other phytoplankton. Our results demonstrated
highly inhibitory and toxic effects exhibited in clonal cultures of C. polykrikoides isolated from
the east and west coasts of North American on a variety of common phytoplankton species,
including Rhodomonas salina, Isochrysis galbana, Aureococcus anophagefferens, Thalassiosira
weissflogii, Chattonella marina, Heterocapsa rotundata, Scrippsiella cf. trochoidea, Akashiwo
sanguinea, Gymnodinium aureolum and Gymnodinium instriatum, with the latter five commonly
co-occurring with C. polykrikoides during bloom seasons. The allelopathic impacts on all species
of microalgae were noticeable in minutes to hours, causing loss of motility, morphological
change, cell lysis, and death. The alleopathic effects depended on both the absolute and relative
cell densities of C. polykrikoides and target species and exposure time (i.e. longer co-culturing
caused higher mortality of cells in the competing species). Treatments of freezing-and-thawing,
heating, sonication, and filtration for the culture of C. polykrikoides led to complete loss of its
allelopathic effect on A. sanguinea, the most sensitive algal species, suggesting that the
responsible allelochemicals are short-lived and associated with live cells. Separation of C.
polykrikoides and other algae by a 5μm-mesh nylon membrane resulted in growth inhibition of
the competitors which was significantly greater than control cultures, but significantly lower than
direct contact indicating that allelopathic agents could be released and dissolved in culture
medium and that direct contact between the C. polykrikoides and target cells maximizes the
allelopathic effect. Additions of the free radical-scavenging enzymes, peroxidase and catalase,
into C. polykrikoides culture eliminated its allelopathic effect, implying a reactive chemical(s) are
responsible for the algae-killing effect of C. polykrikoides. All the above results are consistent
with our results obtained from fish and shellfish larvae bioassays, suggesting that the toxicity of C.
polykrikoides to fish, shellfish, and shellfish larvae and the allelopathic effects on other
phytoplankton were caused by similar mechanisms. The dramatic allelopathic effects exhibited
by C. polykrikoides imply that this process may play an important role in the imitation and
maintenance of mono-specific blooms formed by this species.