STRIVE - Environmental Protection Agency

Molecular Diversity and Dynamics of Toxigenic Blue-green Algae in Irish Lakes
in those areas; the latter domain is much larger and
deeper and more susceptible to wind exposure and
associated water column mixing. On the other hand,
the lower end of the Upper Corrib is a very shallow
and narrow strait. Hence, this body of water can warm
up more quickly and is often protected from winddriven
turbulence, two aspects that can contribute to
phytoplankton biomass development when sustained
by the necessary nutrient inputs. A comprehensive
study of Ballyquirke Lough, where cyanobacterial
proliferations have occurred in the past, was previously
carried out with respect to water quality determination
and analysis of a number of physical, chemical and
biological variables (Irvine et al. 1998). Interestingly,
the phosphate and chlorophyll-a concentrations
obtained in 1997 were largely comparable to those
determined in the present study, suggesting that the
lake status has probably remained stable in the past
15 years. A major difference between Lough Corrib
and Ballyquirke Lough during summer 2010 was the
observation in the latter of an anoxic layer in the deepest
part of the lake (station D) on several occasions. Even
though thermal stratification was also observed in
Lough Corrib (station 4), the dissolved oxygen levels
measured were always greater than 7.0 mg.l-1 . The
likely difference in microbiological activity in the anoxic
and oxic compartments of Ballyquirke Lough needs
however to be considered in relation with the rapid
flushing rate of the lake and the frequency of winddriven
water column homogenisation, as near-uniform
distribution of the physical and chemical variables
across the water column was also observed on
occasions.
Even though the morphological and hydrological
features of Lough Corrib and Ballyquirke Lough
differ markedly, a shift in spherical cyanobacteria
community occurred in July in both lakes. Temporal
changes in microbial community may occur in
freshwater over a short period of time (Jaspers et
al. 2001, Van der Gucht et al. 2001). It is likely that
the changes in community structure could be related
to changes in water column structure. Unfortunately,
vertical profiling was not carried out during July due to
instrument malfunction. Together with the interactions
with phytoplankton, bacteria, viruses, protozoa and
zooplankton, nutrient availability, temperature and
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meteorological conditions influence the composition
and dynamics of cyanobacterial communities in
aquatic environments (van Hannen et al. 1999,
Riemann et al. 2000, Pernthaler et al. 2001, Muylaert
et al. 2002). It has been demonstrated that abundance
variations caused by competition for a few limiting
abiotic resources can account for the coexistence
of multiple species (Armstrong & McGehee 1980,
Hastings 1980, Huisman & Weissing 1999). Wind resuspension
and rainfall cause pulsed availability of
phosphorus and nitrogen forms; different strategies in
response to nutrient limitation, such as storage or high
affinity uptake, may hence support the coexistence of
multiple species and affect the outcome of competitive
interactions (Gons et al. 1991).
4.7 Monitoring Cyanobacteria:
Molecular Biology, Toxins and
Autonomous Sampling
Microcystins are the most common cyanotoxins and
the only type for which the World Health Organisation
has issued recommended levels (Sivonen and Jones
1999). In 2009, the presence of the mcy-A gene was
detected in 18 nucleic acid extracts obtained from
surface water samples of western and north-western
Irish lakes. Subsequent RFLP analysis showed the
clustering of the lakes into three assemblages. After
examining microscopy-derived abundances, lakes
in cluster B had significantly less amounts of the
filamentous cyanobacterial genera Anabaena and
Oscillatoria, suggesting the existence of polymorphism
in mcy-A gene sequences between the two filamentous
taxa and spherical cyanobacteria such as Microcystis
and Gomphosphaeria, which were more abundant
in cluster B. Nevertheless, interpretation about
cyanobacterial toxicity based solely on mcy-A gene
analysis warrants caution given that the many existing
variants of microcystins display a wide range of
toxicities and that toxin profiles can be complex and vary
in time according to the physiological state of the cells
(Kardinaal & Visser, 2005). It has been hypothesised
that there might be a succession of genotypes of
varying toxicity according to light competition during
cyanobacterial bloom development. In particular,
the competitive replacement of toxic genotypes by
nontoxic strains offers a plausible explanation for the