12
R. L. Fletcher
Lithothamnion (Ffrench-Constant 1981), in restricting the distribution of
Laminaria spp. (Burrows and Pybus 1970; Ebling et al. 1960) and in the
general absence! impoverishment of algae, leaving only a few selected species!
life-forms, in the vicinity of sewage outfalls (North 1963; Clendenning and
North 1964; Borowitzka 1972; Kindig and Littler 1980).
The high organic loading of many effluent-derived sediments, particularly those originating from sewage treatment works, also exerts a number
of secondary influences on marine benthic communities. Probably the
most notable of these is the role played by organic matter as an additional
food source to benthic animal communities, especially filter feeders (Bellamy
et al. 1972). For example, a number of authors have noted an increase in the
predominance and biomass of mussels in polluted waters, especially in the
vicinity of sewage outfalls. Bellan and Bellan-Santini (1972), Bellan-Santini
(1969) and BeHan (1967a; 1970) reported an increase in Mytilus galloprovincialis in the vicinity of a sewage outfall near Marseilles, whilst there
have been numerous similar reports for the species My til us edulis, especiallyin the Baltic (Bleguad 1932; Ehrhardt 1968; Johnston 1971!72; Riggio et al.
1990; Vogt and Schramm 1991; Kautskyet al. 1992). In situations of pollution
abatement, for example, as a result of redirecting sewage effluent into deeper
water or by improving treatment practices, a concomitant reduction in
organic loading has been matched by a decline in Mytilus edulis populations
(Bokn et al. 1992). This competitive advantage given to mussels in the
vicinity of sewage outfalls has significant ecological connotations, especially
for marine benthic algae. For example, reports suggest that mussels are
unsuitable substrata for many algae (Klavestad 1967); they compete for
available space (Johnston 1971172), have been reported to cover surfaces of
algae (Kautsky et al. 1992) and act as very efficient filters of potentially
settling spores. Not surprisingly, therefore, several authors have linked
increased mussel populations with declines in algal settlement and establishment, leading to their impoverishment and elimination (Johnston 1971172;
Riggio et al. 1990; May 1985; Vogt and Schramm 1991; Kautsky et al. 1992).
Note, however, Letts and Richards (1911) reported that mussels provided
firm anchorage to Ulva plants in Belfast Lough, Ireland with their attaching
byssal threads holding onto the fronds.
There have also been many reports of increased grazing activity in the
vicinity of many sewage outfalls, with sea urchins, in particular, deriving
nourishment from the organic component of the sewage (North 1963, 1979,
1983; Devinny and Volse 1978; Dean et al. 1984; James et al. 1990). The
increased number of grazers has been reported to cause a decline in
Macrocystis kelp beds in California (Clendenning and North 1959; North
1963; Devinny and V olse 1978) by subjecting old kelp plants to high grazing
pressure, attacking holdfasts and chewing the stipe leading to the loss of the
R. L. Fletcher
Lithothamnion (Ffrench-Constant 1981), in restricting the distribution of
Laminaria spp. (Burrows and Pybus 1970; Ebling et al. 1960) and in the
general absence! impoverishment of algae, leaving only a few selected species!
life-forms, in the vicinity of sewage outfalls (North 1963; Clendenning and
North 1964; Borowitzka 1972; Kindig and Littler 1980).
The high organic loading of many effluent-derived sediments, particularly those originating from sewage treatment works, also exerts a number
of secondary influences on marine benthic communities. Probably the
most notable of these is the role played by organic matter as an additional
food source to benthic animal communities, especially filter feeders (Bellamy
et al. 1972). For example, a number of authors have noted an increase in the
predominance and biomass of mussels in polluted waters, especially in the
vicinity of sewage outfalls. Bellan and Bellan-Santini (1972), Bellan-Santini
(1969) and BeHan (1967a; 1970) reported an increase in Mytilus galloprovincialis in the vicinity of a sewage outfall near Marseilles, whilst there
have been numerous similar reports for the species My til us edulis, especiallyin the Baltic (Bleguad 1932; Ehrhardt 1968; Johnston 1971!72; Riggio et al.
1990; Vogt and Schramm 1991; Kautskyet al. 1992). In situations of pollution
abatement, for example, as a result of redirecting sewage effluent into deeper
water or by improving treatment practices, a concomitant reduction in
organic loading has been matched by a decline in Mytilus edulis populations
(Bokn et al. 1992). This competitive advantage given to mussels in the
vicinity of sewage outfalls has significant ecological connotations, especially
for marine benthic algae. For example, reports suggest that mussels are
unsuitable substrata for many algae (Klavestad 1967); they compete for
available space (Johnston 1971172), have been reported to cover surfaces of
algae (Kautsky et al. 1992) and act as very efficient filters of potentially
settling spores. Not surprisingly, therefore, several authors have linked
increased mussel populations with declines in algal settlement and establishment, leading to their impoverishment and elimination (Johnston 1971172;
Riggio et al. 1990; May 1985; Vogt and Schramm 1991; Kautsky et al. 1992).
Note, however, Letts and Richards (1911) reported that mussels provided
firm anchorage to Ulva plants in Belfast Lough, Ireland with their attaching
byssal threads holding onto the fronds.
There have also been many reports of increased grazing activity in the
vicinity of many sewage outfalls, with sea urchins, in particular, deriving
nourishment from the organic component of the sewage (North 1963, 1979,
1983; Devinny and Volse 1978; Dean et al. 1984; James et al. 1990). The
increased number of grazers has been reported to cause a decline in
Macrocystis kelp beds in California (Clendenning and North 1959; North
1963; Devinny and V olse 1978) by subjecting old kelp plants to high grazing
pressure, attacking holdfasts and chewing the stipe leading to the loss of the