14
R. L. Fletcher
(5-10 ml) will have inhibitory effects (Clendenning and North 1964).
Pertinent to this discussion are reports of the presence of tumours on algae
near sewage outfalls (Katayama and Fujiyama 1957; North et al. 1972; North
1979).
1.4 Eutrophication - Influence on Marine Benthic Algae
Van Bennikom et al. (1975) defined eutrophication as "an acceleration of
chemical inputs that favour photosynthesis and influence algal populations". Probably the most important chemicals required by algae are sources of nitrogen and phosphorus. As nitrogen is very often considered to be
the major limiting nutrient for plant growth in coastal waters, any additional inputs, for example, from sewage effiuent or agricultural runoff, would,
therefore, be expected to exert a major influence on local plant communities.
Probably the most widely noted effect of coastal eutrophication is an
increase in the productivity of a region. Provided other pollutants present
are not limiting and away from the immediate and usually turbid, inhibitory environment of a sewage discharge point (Munda 1974), a number of
authors have reported an increase in primary productivity in the vicinity of
the nutrient source, both with respect to pelagic phytoplankton communities (Revelante and Gilmartin 1976) and macroalgal benthic communities
(Causey et al. 1945; McNulty 1959; Clendenning and North 1964;
Subbaramaiah and Parekh 1966; O'Sullivan 1971; Johannes 1972; Tewari
1972; Anonymous 1973; Saunders and Lindsay 1979; Bell et al. 1989). In
general, the increased phytoplankton activity is considered to be
detrimental to the growth of benthic algae. For example, it was reported to
have increased the number of mussels which compete with the macroalgae
for space, whilst the associated increase in turbidity was reported to have
reduced the lower depth distribution of Fucus in the Baltic (Kautsky et al.
1992). The increased productivity of benthic macro algae, however, has
been manifest in reports of larger plants (Nasr and Aleem 1948; Johannes
1972), an increase in Laminaria hyperborea stipe production (Bellamy and
Whittick 1964), more primary biomass (Jeffrey et al. 1992) and generally
more abundant life (McNulty 1959). This quantitative increase in benthic
algae is, however, tempered by a number of qualitative changes, with many
authors reporting a general impoverishment of the flora and an overall
reduction in species numbers and diversity (Gamulin-Brida et al. 1967;
Smyth 1968; Johnston 1971/72; Borowitzka 1972; Littler and Murray 1974;
Munda 1974, 1993; Enright 1978; Hirose 1978; Ffrench-Constant 1981). It is
these qualitative changes associated with eutrophicated waters which have
R. L. Fletcher
(5-10 ml) will have inhibitory effects (Clendenning and North 1964).
Pertinent to this discussion are reports of the presence of tumours on algae
near sewage outfalls (Katayama and Fujiyama 1957; North et al. 1972; North
1979).
1.4 Eutrophication - Influence on Marine Benthic Algae
Van Bennikom et al. (1975) defined eutrophication as "an acceleration of
chemical inputs that favour photosynthesis and influence algal populations". Probably the most important chemicals required by algae are sources of nitrogen and phosphorus. As nitrogen is very often considered to be
the major limiting nutrient for plant growth in coastal waters, any additional inputs, for example, from sewage effiuent or agricultural runoff, would,
therefore, be expected to exert a major influence on local plant communities.
Probably the most widely noted effect of coastal eutrophication is an
increase in the productivity of a region. Provided other pollutants present
are not limiting and away from the immediate and usually turbid, inhibitory environment of a sewage discharge point (Munda 1974), a number of
authors have reported an increase in primary productivity in the vicinity of
the nutrient source, both with respect to pelagic phytoplankton communities (Revelante and Gilmartin 1976) and macroalgal benthic communities
(Causey et al. 1945; McNulty 1959; Clendenning and North 1964;
Subbaramaiah and Parekh 1966; O'Sullivan 1971; Johannes 1972; Tewari
1972; Anonymous 1973; Saunders and Lindsay 1979; Bell et al. 1989). In
general, the increased phytoplankton activity is considered to be
detrimental to the growth of benthic algae. For example, it was reported to
have increased the number of mussels which compete with the macroalgae
for space, whilst the associated increase in turbidity was reported to have
reduced the lower depth distribution of Fucus in the Baltic (Kautsky et al.
1992). The increased productivity of benthic macro algae, however, has
been manifest in reports of larger plants (Nasr and Aleem 1948; Johannes
1972), an increase in Laminaria hyperborea stipe production (Bellamy and
Whittick 1964), more primary biomass (Jeffrey et al. 1992) and generally
more abundant life (McNulty 1959). This quantitative increase in benthic
algae is, however, tempered by a number of qualitative changes, with many
authors reporting a general impoverishment of the flora and an overall
reduction in species numbers and diversity (Gamulin-Brida et al. 1967;
Smyth 1968; Johnston 1971/72; Borowitzka 1972; Littler and Murray 1974;
Munda 1974, 1993; Enright 1978; Hirose 1978; Ffrench-Constant 1981). It is
these qualitative changes associated with eutrophicated waters which have