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physical instabilities such as tidal mixing and upwelling; for large-scale dinoflagellate blooms,
relatively shallow pycnocline/nutricline, controlled by tidal mixing, upwelling or geostrophic
effects. He also points out that exceptional blooms often involve phytoplankton species
avoided by grazers (e.g. Phaeocystis, Gyrodinium aureolum) or develop in areas where
grazing pressure is low. As a result, the biomass of phytoplankton becomes dominated by
ungrazed large cells, even in the face of a significant contribution to primary production by
small cells. In a review of nuisance phytoplankton blooms, Paerl (1988) came to similar
conclusions as to the factors most likely leading to bloom-sensitive waters. In general, the
combination of high nutrients with strong vertical stability is only found in transient situations
or in areas subjected to continental inputs (Margalef, 1978). Legendre (1990) has briefly
reviewed the reasons for the increasing occurrence of exceptional blooms, which often consist
of noxious species. The reasons invoked are still conjectural, but it has been suggested that
the general eutrophication of the coastal zone by human activity (inorganic and organic
effluents, etc.) is a contributing factor; fish farming may also be involved in some blooms,
but the question is still under debate.
Boalch (1984) has reviewed the effects of exceptional blooms on commercially exploited
species in the English Channel and elsewhere. These effects include, in the case of toxic
species, poisoning and kills of vertebrates (fish, birds and humans) and, more generally, such
consequences as mortality resulting from oxygen depletion and mechanical damage to animals
(e.g. clogging of fish gills). He concluded that no case is recorded of an exceptional bloom
that was of advantage to fishing. Concerning the export of carbon to depth, exceptional
blooms can result in significant sedimentation (e.g. Lancelot et al., 1987). According to
Peinert et al. (1989), rapid sedimentation has been reported for blooms of most of the large
cells, which include diatoms, coccolithophores and such flagellates as Phaeocystis. The ageing
standing stock at the final phase of a bloom due to species unpalatable to herbivores is likely
to be recycled by decomposers. These will be grazed upon by microheterotrophs which, in
tum, may fall prey to microphagous metazoans (including carbonate-rich pteropods) under
certain conditions (see above). Actual sequestration of carbon would largely depend on the
depth of the waters into which the particles will eventually sink.
physical instabilities such as tidal mixing and upwelling; for large-scale dinoflagellate blooms,
relatively shallow pycnocline/nutricline, controlled by tidal mixing, upwelling or geostrophic
effects. He also points out that exceptional blooms often involve phytoplankton species
avoided by grazers (e.g. Phaeocystis, Gyrodinium aureolum) or develop in areas where
grazing pressure is low. As a result, the biomass of phytoplankton becomes dominated by
ungrazed large cells, even in the face of a significant contribution to primary production by
small cells. In a review of nuisance phytoplankton blooms, Paerl (1988) came to similar
conclusions as to the factors most likely leading to bloom-sensitive waters. In general, the
combination of high nutrients with strong vertical stability is only found in transient situations
or in areas subjected to continental inputs (Margalef, 1978). Legendre (1990) has briefly
reviewed the reasons for the increasing occurrence of exceptional blooms, which often consist
of noxious species. The reasons invoked are still conjectural, but it has been suggested that
the general eutrophication of the coastal zone by human activity (inorganic and organic
effluents, etc.) is a contributing factor; fish farming may also be involved in some blooms,
but the question is still under debate.
Boalch (1984) has reviewed the effects of exceptional blooms on commercially exploited
species in the English Channel and elsewhere. These effects include, in the case of toxic
species, poisoning and kills of vertebrates (fish, birds and humans) and, more generally, such
consequences as mortality resulting from oxygen depletion and mechanical damage to animals
(e.g. clogging of fish gills). He concluded that no case is recorded of an exceptional bloom
that was of advantage to fishing. Concerning the export of carbon to depth, exceptional
blooms can result in significant sedimentation (e.g. Lancelot et al., 1987). According to
Peinert et al. (1989), rapid sedimentation has been reported for blooms of most of the large
cells, which include diatoms, coccolithophores and such flagellates as Phaeocystis. The ageing
standing stock at the final phase of a bloom due to species unpalatable to herbivores is likely
to be recycled by decomposers. These will be grazed upon by microheterotrophs which, in
tum, may fall prey to microphagous metazoans (including carbonate-rich pteropods) under
certain conditions (see above). Actual sequestration of carbon would largely depend on the
depth of the waters into which the particles will eventually sink.