The Occurrence of "Green Tides" - a Review
11
Phycodrys rubens and Polysiphonia nigrescens which have apparently
widely replaced Fucus spp. communities in Kiel Bight below 2 m depths
(Vogt and Schramm 1991). Advantage would also be afforded to algae
which can make efficient use of variable irradiances as shown for Ulva
rotundata (Henley and Ramus 1989).
Also reported are changes in algal zonation patterns and depth distributions as a result of increased sediment loading (Gilet 1960; North et al. 1972;
Devinny and Volse 1978; Meistrell and Montagne 1983; Kautsky et al. 1986;
Breuer and Schramm 1988; Rosenberg et al. 1990; Rueness and Fredriksen
1991; Vogt and Schramm 1991; Munda 1993). For example, a reduction in
the kelp depth range has been reported in the vicinity of sewage outfalls
with plants generally restricted to shallow water (Clendenning and North
1959; Bellamyet al. 1972) and very few new kelps present under the old ones
(Clendenning and North 1959). Decreased water transparency has also
been implicated in changes in the depth penetration of eelgrass, from 10-12
to 5-6 m from 1900 to 1989, in the South Kattegat region of the Baltic
(Nielson and Knudsen 1990), in decreased depth penetration of Fucus
vesiculosus in the Baltic, e.g. from a maximum depth of 11 to 2 m between
1944 and 1984 (Vogt and Schramm 1991; Kautskyet al. 1986, 1992) and in
vertical distribution changes of macro algae on the Swedish west coast
(Rosenberg et al. 1990).
Silt deposition will also be increased in the vicinity of sewage outfalls and
this can exert a number of detrimental influences on marine benthic algal
communities. The sediments can cover all available substrata interfering
with the processes of spore (and larval) attachment/recruitment (Devinny
and Volse 1978). They can smother young germlings (Devinny and Volse
1978) and inhibit their growth and development. Combined with water
movement, sediments can also abrasively scour surfaces of settled spores.
As deposits on algal thalli they will also reduce photosynthetic activities, at
the same giving competitive advantages to more adapted speciesllife-forms
of algae. All the above-described detrimental influences of increased
sedimentation on benthic communities have been well-recognized
(Clendenning and North 1964; Rueness 1973) and have been offered as
explanations for the decline of kelp beds off the coast of southern California
(Clendenning and North 1959,1964; North 1963; Devinny and Volse 1978;
Neushal et al. 1976; Meistrell and Montagne 1983; James et al. 1990). They
also find support in the experimental studies of Devinny and Volse (1978)
who revealed that sediments interfere with Macrocystsis gametophyte
development. A similar detrimental effect of silt on zoospore development
was shown for Laminaria saccharina by Burrows (1971). Increased
sedimentation has also been implicated in the decline of Posidonia beds
(Ruiz et al. 1990), in the decline of the red crustose coralline alga
11
Phycodrys rubens and Polysiphonia nigrescens which have apparently
widely replaced Fucus spp. communities in Kiel Bight below 2 m depths
(Vogt and Schramm 1991). Advantage would also be afforded to algae
which can make efficient use of variable irradiances as shown for Ulva
rotundata (Henley and Ramus 1989).
Also reported are changes in algal zonation patterns and depth distributions as a result of increased sediment loading (Gilet 1960; North et al. 1972;
Devinny and Volse 1978; Meistrell and Montagne 1983; Kautsky et al. 1986;
Breuer and Schramm 1988; Rosenberg et al. 1990; Rueness and Fredriksen
1991; Vogt and Schramm 1991; Munda 1993). For example, a reduction in
the kelp depth range has been reported in the vicinity of sewage outfalls
with plants generally restricted to shallow water (Clendenning and North
1959; Bellamyet al. 1972) and very few new kelps present under the old ones
(Clendenning and North 1959). Decreased water transparency has also
been implicated in changes in the depth penetration of eelgrass, from 10-12
to 5-6 m from 1900 to 1989, in the South Kattegat region of the Baltic
(Nielson and Knudsen 1990), in decreased depth penetration of Fucus
vesiculosus in the Baltic, e.g. from a maximum depth of 11 to 2 m between
1944 and 1984 (Vogt and Schramm 1991; Kautskyet al. 1986, 1992) and in
vertical distribution changes of macro algae on the Swedish west coast
(Rosenberg et al. 1990).
Silt deposition will also be increased in the vicinity of sewage outfalls and
this can exert a number of detrimental influences on marine benthic algal
communities. The sediments can cover all available substrata interfering
with the processes of spore (and larval) attachment/recruitment (Devinny
and Volse 1978). They can smother young germlings (Devinny and Volse
1978) and inhibit their growth and development. Combined with water
movement, sediments can also abrasively scour surfaces of settled spores.
As deposits on algal thalli they will also reduce photosynthetic activities, at
the same giving competitive advantages to more adapted speciesllife-forms
of algae. All the above-described detrimental influences of increased
sedimentation on benthic communities have been well-recognized
(Clendenning and North 1964; Rueness 1973) and have been offered as
explanations for the decline of kelp beds off the coast of southern California
(Clendenning and North 1959,1964; North 1963; Devinny and Volse 1978;
Neushal et al. 1976; Meistrell and Montagne 1983; James et al. 1990). They
also find support in the experimental studies of Devinny and Volse (1978)
who revealed that sediments interfere with Macrocystsis gametophyte
development. A similar detrimental effect of silt on zoospore development
was shown for Laminaria saccharina by Burrows (1971). Increased
sedimentation has also been implicated in the decline of Posidonia beds
(Ruiz et al. 1990), in the decline of the red crustose coralline alga