The Occurrence of "Green Tides" - a Review
13
upper blade portions etc. (Devinny and V olse 1978; North 1983; Dean et al.
1984; James et al. 1990). Young plants are also extremely vulnerable and
this is borne out by reports of very few young kelps being present near the
outfalls (Clendenning and North 1959). Other changes as a result of
increased pollution-related grazer activity include reports of increased
numbers of detritivorous snails e.g. Hydrobia (Kautsky et al. 1992) and
enhanced grazing pressure by the isopod Idothea baltica on Fucus vesiculosus (Kangas et al. 1982; HaIlfors et al. 1984; Kangas and Niemi 1985;
Wallentinus 1991), both reports being for the Baltic. The latter was
attributed to the increased abundance of the Idothea, possibly due to
nutrient -related changes in the phenolic content of the Fucus plant making
the latter more vulnerable to grazing activity (see Wallentinus 1991 for
discussion).
Apart from the above-described secondary effects of organic enrichment, in cases of severe pollution, with high organic loading, a number of
authors have reported a much reduced and specialized flora. Notably, there
appears to be a predominance of blue-green algae, especially species of the
genera Lyngbya and Phormidium (Nasr and Aleem 1948; Grenager 1957;
Golubic 1970; Munda 1974; Littler and Murray 1974; Murray and Littler
1974, 1976, 1983). This predominance of blue-green algae is probably the
result of the anaerobic conditions and low pH values present (Otte 1979). It
is also noteworthy here that sewage-derived sediments might well have
toxic ingredients (Clendenning and North 1964; Devinny and V olse 1978).
This was revealed for older, deeper sediments in experimental studies using
gametophytes of the kelp Macrocystis (James et al. 1990); re-exposure of
these contaminated sediments by disturbance would, therefore, have undesirable ecological consequences. Similar inhibitory properties of silt on
algae have been recorded by Pybus (1971). Finally, with the possible
presence of conservative materials such as heavy metals, various organic
chemicals, pesticides, surfactants, detergents, chlorine etc., in sewage
effiuent (Bell et al. 1989; O'Sullivan 1971) it is not surprising that the latter
has proved inhibitory to marine organisms. For example, Ogawa (1983)
revealed municipal waste water to be inhibitory to three Sargassum spp, in
culture. Borowitzka (1972) also considered that observed reductions in the
numbers of brown and red algal species near outfalls might be due to the
toxic effects of detergents or surfactants present, whilst Kindig and Littler
(1980) and Edwards (1972), using experimental culture studies, conclude
that toxic chemicals are associated with sewage s>jltfalls. These conclusions
concur with the findings of Burrows (1971ythat detergents affected the
growth of Laminaria saccharina in laboratory culture; detergents have also
been implicated in reducing settlement density in this species (Pybus 1973).
Certainly it is likely that the levels of anionic detergents present in sewage
13
upper blade portions etc. (Devinny and V olse 1978; North 1983; Dean et al.
1984; James et al. 1990). Young plants are also extremely vulnerable and
this is borne out by reports of very few young kelps being present near the
outfalls (Clendenning and North 1959). Other changes as a result of
increased pollution-related grazer activity include reports of increased
numbers of detritivorous snails e.g. Hydrobia (Kautsky et al. 1992) and
enhanced grazing pressure by the isopod Idothea baltica on Fucus vesiculosus (Kangas et al. 1982; HaIlfors et al. 1984; Kangas and Niemi 1985;
Wallentinus 1991), both reports being for the Baltic. The latter was
attributed to the increased abundance of the Idothea, possibly due to
nutrient -related changes in the phenolic content of the Fucus plant making
the latter more vulnerable to grazing activity (see Wallentinus 1991 for
discussion).
Apart from the above-described secondary effects of organic enrichment, in cases of severe pollution, with high organic loading, a number of
authors have reported a much reduced and specialized flora. Notably, there
appears to be a predominance of blue-green algae, especially species of the
genera Lyngbya and Phormidium (Nasr and Aleem 1948; Grenager 1957;
Golubic 1970; Munda 1974; Littler and Murray 1974; Murray and Littler
1974, 1976, 1983). This predominance of blue-green algae is probably the
result of the anaerobic conditions and low pH values present (Otte 1979). It
is also noteworthy here that sewage-derived sediments might well have
toxic ingredients (Clendenning and North 1964; Devinny and V olse 1978).
This was revealed for older, deeper sediments in experimental studies using
gametophytes of the kelp Macrocystis (James et al. 1990); re-exposure of
these contaminated sediments by disturbance would, therefore, have undesirable ecological consequences. Similar inhibitory properties of silt on
algae have been recorded by Pybus (1971). Finally, with the possible
presence of conservative materials such as heavy metals, various organic
chemicals, pesticides, surfactants, detergents, chlorine etc., in sewage
effiuent (Bell et al. 1989; O'Sullivan 1971) it is not surprising that the latter
has proved inhibitory to marine organisms. For example, Ogawa (1983)
revealed municipal waste water to be inhibitory to three Sargassum spp, in
culture. Borowitzka (1972) also considered that observed reductions in the
numbers of brown and red algal species near outfalls might be due to the
toxic effects of detergents or surfactants present, whilst Kindig and Littler
(1980) and Edwards (1972), using experimental culture studies, conclude
that toxic chemicals are associated with sewage s>jltfalls. These conclusions
concur with the findings of Burrows (1971ythat detergents affected the
growth of Laminaria saccharina in laboratory culture; detergents have also
been implicated in reducing settlement density in this species (Pybus 1973).
Certainly it is likely that the levels of anionic detergents present in sewage