290
J.e. Oliveira and G. Cabe<;adas
tides has increasingly been observed in Portuguese coastal waters, mainly
in five restricted areas (Sampayo 1987; Fig. 11.1).
It is generally assumed that development of red tide blooms is associated with adequate amounts of nutrients and specific physical conditions. As the referred coastal zones are influenced by upwelling (Fiuza
1982) and are often located in the vicinity of lagoons or estuaries
subjected to river discharges and! or large urban and industrial effluents, it cannot be excluded that eutrophication processes are involved
in this phenomenon.
Most red tides which have been detected along the Portuguese coast
had no deleterious effects (Sampayo and Cabec;adas 1981; Sampayo and
Moita 1984; Brogueira and Sampayo 1983; Cabec;adas et al. 1983). However, the red waters observed in the polluted Obidos lagoon caused PSP,
DSP and fish kills (Moita et al. 1984), and the phytoplankton bloom on
the north-west coast in 1986, involving the presence of the dinoflagellate
Gymnodinium catenatum, was responsible for an outbreak of PSP intoxication in bivalves (Sampayo 1987).
11.4 Conclusions
The morphology of the main Portuguese lagoons and estuaries, together
with their tidal regimes, favours interchange with the sea and limits
eutrophication to localised interior areas, confirmed by several environmental studies.
Quantitative and qualitative changes in benthic vegetation (algae and
marine phanerogams) of some lagoonal and estuarine areas as a result of
human activities have been observed and studied. Most conspicuous are
local proliferations of Ulva and Enteromorpha spp. in areas disturbed by
waste discharges or other sources of nutrients. On the open coast, where
strong wave action and tidal currents rapidly disperse urban and industrial effluents, no algal proliferation or significant floristic changes have
been observed, except occasionally near coastal towns. However, recent
settlements of the invasive Sargassum muticum, which forms dense communities in the north, green tides of Ulva in the south, as well as red tide
blooms in several coastal areas, generally unrelated to eutrophication,
have occurred. Long-term changes in the density of observed algal communities of brown and red algae (Laminaria, Fucus, Porphyra, Gelidium)
are probably due to natural causes such as the pluriannual variation
J.e. Oliveira and G. Cabe<;adas
tides has increasingly been observed in Portuguese coastal waters, mainly
in five restricted areas (Sampayo 1987; Fig. 11.1).
It is generally assumed that development of red tide blooms is associated with adequate amounts of nutrients and specific physical conditions. As the referred coastal zones are influenced by upwelling (Fiuza
1982) and are often located in the vicinity of lagoons or estuaries
subjected to river discharges and! or large urban and industrial effluents, it cannot be excluded that eutrophication processes are involved
in this phenomenon.
Most red tides which have been detected along the Portuguese coast
had no deleterious effects (Sampayo and Cabec;adas 1981; Sampayo and
Moita 1984; Brogueira and Sampayo 1983; Cabec;adas et al. 1983). However, the red waters observed in the polluted Obidos lagoon caused PSP,
DSP and fish kills (Moita et al. 1984), and the phytoplankton bloom on
the north-west coast in 1986, involving the presence of the dinoflagellate
Gymnodinium catenatum, was responsible for an outbreak of PSP intoxication in bivalves (Sampayo 1987).
11.4 Conclusions
The morphology of the main Portuguese lagoons and estuaries, together
with their tidal regimes, favours interchange with the sea and limits
eutrophication to localised interior areas, confirmed by several environmental studies.
Quantitative and qualitative changes in benthic vegetation (algae and
marine phanerogams) of some lagoonal and estuarine areas as a result of
human activities have been observed and studied. Most conspicuous are
local proliferations of Ulva and Enteromorpha spp. in areas disturbed by
waste discharges or other sources of nutrients. On the open coast, where
strong wave action and tidal currents rapidly disperse urban and industrial effluents, no algal proliferation or significant floristic changes have
been observed, except occasionally near coastal towns. However, recent
settlements of the invasive Sargassum muticum, which forms dense communities in the north, green tides of Ulva in the south, as well as red tide
blooms in several coastal areas, generally unrelated to eutrophication,
have occurred. Long-term changes in the density of observed algal communities of brown and red algae (Laminaria, Fucus, Porphyra, Gelidium)
are probably due to natural causes such as the pluriannual variation