288
J.C. Oliveira and G. Cabe<;adas
(Table 11.1) as well as rates of photosynthetic efficiency (21.6 mg C mg- I
chI a-I h-t, mean value between July and September) indicate that the
lagoon system presents good environmental conditions.
11.3 Symptoms of Eutrophication
and Effects on Benthic Vegetation
The most extensive study on the taxonomy and ecology of the
Portuguese marine algae is still that of Ardre (1969, 1971), referring to
more than 460 species, their distribution and abundance. Succeeding
studies have concentrated mainly on the biomass, distribution and
growth of Gelidium sesquipedale, the major exploited agarophytes
(Palminha et al. 1982; Oliveira 1986, 1989; Santos 1993).
Due to geographic and oceanographic conditions, several species have
their northern or southern limits of distribution in the Portuguese west
coast.
Observed temporal changes in the density of algal communities of
brown algae, mainly Laminariales and Fucales, are probably due to natural
causes such as variation in solar irradiance levels (Ardre 1971). More
recent surveys confirmed these cyclic oscillations, and were also
observed in Porphyra and Gelidium populations, the harvest of which was
affected by these temporal variations. On the other hand, the exposure of
the open west coast to strong wave action and tidal currents rapidly
disperses polluted waters discharged from rivers or coastal towns. Changes
in the natural flora on account of pollution have therefore not been noticed, except occasionally near harbours or sewage discharges.
Because of lack of long-term studies on coastal algal vegetation in
Portugal, no reliable information on significant changes or modifications
is available. Nevertheless, in spring and summer, in some eastern
beaches of the south coast, occasional green tides of Ulva rigida, U.
lactuca and Enteromorpha spp. (free floating species) have occured. The
Table 11.1. Nutrient levels
Zones
N0 3 -N
P0 4 -P
Si0 2
chi a
(f.lM)
(J.lM)
(f.lM)
(mg/m3)
Faro-Olhao
0.3-4.1
0.05-4.4
0.8-7.2
1.2
Tavira
0.3-10.7
0.05-3.9
0.5-26.1
2.4
J.C. Oliveira and G. Cabe<;adas
(Table 11.1) as well as rates of photosynthetic efficiency (21.6 mg C mg- I
chI a-I h-t, mean value between July and September) indicate that the
lagoon system presents good environmental conditions.
11.3 Symptoms of Eutrophication
and Effects on Benthic Vegetation
The most extensive study on the taxonomy and ecology of the
Portuguese marine algae is still that of Ardre (1969, 1971), referring to
more than 460 species, their distribution and abundance. Succeeding
studies have concentrated mainly on the biomass, distribution and
growth of Gelidium sesquipedale, the major exploited agarophytes
(Palminha et al. 1982; Oliveira 1986, 1989; Santos 1993).
Due to geographic and oceanographic conditions, several species have
their northern or southern limits of distribution in the Portuguese west
coast.
Observed temporal changes in the density of algal communities of
brown algae, mainly Laminariales and Fucales, are probably due to natural
causes such as variation in solar irradiance levels (Ardre 1971). More
recent surveys confirmed these cyclic oscillations, and were also
observed in Porphyra and Gelidium populations, the harvest of which was
affected by these temporal variations. On the other hand, the exposure of
the open west coast to strong wave action and tidal currents rapidly
disperses polluted waters discharged from rivers or coastal towns. Changes
in the natural flora on account of pollution have therefore not been noticed, except occasionally near harbours or sewage discharges.
Because of lack of long-term studies on coastal algal vegetation in
Portugal, no reliable information on significant changes or modifications
is available. Nevertheless, in spring and summer, in some eastern
beaches of the south coast, occasional green tides of Ulva rigida, U.
lactuca and Enteromorpha spp. (free floating species) have occured. The
Table 11.1. Nutrient levels
Zones
N0 3 -N
P0 4 -P
Si0 2
chi a
(f.lM)
(J.lM)
(f.lM)
(mg/m3)
Faro-Olhao
0.3-4.1
0.05-4.4
0.8-7.2
1.2
Tavira
0.3-10.7
0.05-3.9
0.5-26.1
2.4