472
N. A. H. El Semary
N 2 O hence increasing atmospheric greenhouse gas levels rather than decreasing them
[36].
Degradation of iron-enhanced biomass may cause decrease oxygen concentrations in the subsurface waters [35]. Dimethylsulfide (DMS) the possible precursor
of sulfate aerosols that cause cloud formation and climate cooling was estimated
during the experiments [30]. [23] reviewed the results of the different experiments
and concluded that significant increases in DMS production were found in some
experiments but not in all. Also, iron fertilization experiments resulted in stimulated
growth and even dominance in phytoplankton community of the neurotoxic domoic
acid producer the diatom ‘Pseudo-nitzschia’ in some experiments [32].
5 Toxic Algae
Microalgae are microscopic forms of algae which play an important role in primary production in vast areas of fresh and marine water bodies [37]. However,
some microalgae are toxic such as cyanobacteria and dinoflagellates. Cyanobacteria
are prokaryotic oxygenic phototrophs, whereas dinoflagellates are eukaryotic algae
that are major toxin producers in marine environments [38]. The latter group of
flagellated phytoplankton largely proliferate during summer time as well as other
microalgal groups such as diatoms, coccolithophorids and cyanobacteria [38] in
marine water bodies. Those microalgae owe their success in dominating their niches
to their remarkable metabolic ability that enabled them to efficiently utilize all available resources such as nutrients and light. However, more information is needed to
investigate and clarify the factors that increase their proliferative capacity especially
for dinoflagellates, which causes red tide phenomenon during summer. The interest
in these algae stems from the fact that 75% of them are toxin-producers and can
profoundly increase fish mortalities and poison the people who eat them as well as
decreasing water quality thereby causing tremendous economic loss and imposing
health threats. For example, cyanobacteria and dinoflagellates sometimes bloom during summer in concentrations of more than a million cells/ml. Some species produce
toxins, which in such quantities kill fish. Moreover, their toxins can accumulate in
aquatic animals which in turn may pass them on to people who eat them (http://www.
issha.org/Welcome-to-ISSHA/Harmful-algae).
5.1 Cyanobacterial Toxins
According to [39], cyanobacteria are prokaryotic oxygenic phototrophs that are of
wide occurrence worldwide. They are unicellular, colonial or filamentous. The latter
can be heterocystous or non-heterocystous. Heterocystous cyanobacteria are capable
of nitrogen fixation under conditions of limited available combined nitrogen. Several
cyanobacterial strains produce toxins of variable toxigenic activities. Some strains are
N. A. H. El Semary
N 2 O hence increasing atmospheric greenhouse gas levels rather than decreasing them
[36].
Degradation of iron-enhanced biomass may cause decrease oxygen concentrations in the subsurface waters [35]. Dimethylsulfide (DMS) the possible precursor
of sulfate aerosols that cause cloud formation and climate cooling was estimated
during the experiments [30]. [23] reviewed the results of the different experiments
and concluded that significant increases in DMS production were found in some
experiments but not in all. Also, iron fertilization experiments resulted in stimulated
growth and even dominance in phytoplankton community of the neurotoxic domoic
acid producer the diatom ‘Pseudo-nitzschia’ in some experiments [32].
5 Toxic Algae
Microalgae are microscopic forms of algae which play an important role in primary production in vast areas of fresh and marine water bodies [37]. However,
some microalgae are toxic such as cyanobacteria and dinoflagellates. Cyanobacteria
are prokaryotic oxygenic phototrophs, whereas dinoflagellates are eukaryotic algae
that are major toxin producers in marine environments [38]. The latter group of
flagellated phytoplankton largely proliferate during summer time as well as other
microalgal groups such as diatoms, coccolithophorids and cyanobacteria [38] in
marine water bodies. Those microalgae owe their success in dominating their niches
to their remarkable metabolic ability that enabled them to efficiently utilize all available resources such as nutrients and light. However, more information is needed to
investigate and clarify the factors that increase their proliferative capacity especially
for dinoflagellates, which causes red tide phenomenon during summer. The interest
in these algae stems from the fact that 75% of them are toxin-producers and can
profoundly increase fish mortalities and poison the people who eat them as well as
decreasing water quality thereby causing tremendous economic loss and imposing
health threats. For example, cyanobacteria and dinoflagellates sometimes bloom during summer in concentrations of more than a million cells/ml. Some species produce
toxins, which in such quantities kill fish. Moreover, their toxins can accumulate in
aquatic animals which in turn may pass them on to people who eat them (http://www.
issha.org/Welcome-to-ISSHA/Harmful-algae).
5.1 Cyanobacterial Toxins
According to [39], cyanobacteria are prokaryotic oxygenic phototrophs that are of
wide occurrence worldwide. They are unicellular, colonial or filamentous. The latter
can be heterocystous or non-heterocystous. Heterocystous cyanobacteria are capable
of nitrogen fixation under conditions of limited available combined nitrogen. Several
cyanobacterial strains produce toxins of variable toxigenic activities. Some strains are