"Heterotrophic dinoflagellates with symbiotic cyanobacteria and nitrogen limitation in the Gulf of Aqaba"
ABSTRACT: Many symbiotic associations characteristic of tropical and subtropical oceanic waters
were observed near shore during a long-term study of the microbiota in the northern part of the Gulf of
Aqaba, Red Sea. Among such associations were the heterotrophlc dinophysoid genera Omithocercus,
Histioneis and Citharistes with cyanobacterial symbionts. The detection of these heterotroph-autotroph
consortia repeatedly coincided with extended nitrogen limitation in the fall season. Populations of
free-living cyanobacteria, with known N fixation capability, such as the unicellular Synechococcus/
Synechocystis spp. and colonial forms, e.g. Trichodesmiurn spp., also peaked at the same time. We
propose that heterotrophic dinoflagellate hosts may provide the cyanobacterial symbionts with the
anaerobic microenvironment necessary for efficient N fixation. Thus, these self-supporting consortia
increase in numbers during the long period of stratification and nitrogen limitation in the oligotrophic
subtropical waters of the Gulf of Aqaba.
And another - lakes - but the same principle.
THE IMPACT OF NITROGEN AND
PHOSPHORUS CONCENTRATION AND
N/P RATIO ON CYANOBACTERIAL
DOMINANCE AND N2 FIXATION
IN SOME ESTONIAN LAKES
ILMAR TÕNNO
"Cyanobacteria appear responsible for most of planktonic N2fix in
aquatic ecosystems, this ability gives a significant competitive advantage to
these organisms during the periods of nitrogen limitation (Tilman et al., 1982;
Howarth et al., 1988a; Leppänen et al., 1988)."
many hypotheses have been presented to explain cyanobacterial dominance and blooms in lakes. One of the
most common is resource ratio competition theory, predicting that cyano-
bacteria tend to dominate in lakes where the ratio of nitrogen and phosphorus
(P) is low, mainly because of the ability of some of these species to use
molecular nitrogen (Elser 1999). This theory has been proved both empirically
and experimentally. Cyanobacteria, both fixing and not fixing N2, tend to
dominate if the ratio of total nitrogen (TN) and total phosphorus (TP) in the
water column is below ca. 5–10 by mass (Schindler 1977, Seip 1994, Michard
et al., 1996, Bulgakov & Levich 1999),
