228
R.L. Fletcher
associated sewage, was also held responsible for both qualitative and
quantitative changes observed in the flora and fauna of the inner parts of
the Firth of Forth Estuary (Johnston 1971/92) and the Firth of Clyde
Estuary (Clokie and Boney 1979); all these authors reported a reduced
flora compared with that recorded in the 19th century. Fletcher (1974)
also suggested that perhaps the increased incidences of algal deposits on
beaches in Thanet (SE England) were the result of increased sewage
discharges in local bays. In one locality (Langstone Harbour, south coast
of England), increased nutrient inputs (12 to 36 ml/day over a lO-year
period in the 1960s to 1970s) from a newly built sewage works, were held
responsible for increased growths of green algae on the surface of the
mudflats (Dunn 1972; Anonymous 1976a; Montgomery and Soulsby
1980; Tubbs 1980a). There was, for example, little evidence of green algal
growths on the mud flats in 1961 but they were fairly widespread in 1966
and 1967 (Dunn 1972; Anonymous 1976a). Dunn (1972) also noted that
Perraton (1953) did not mention any obvious colonization of the
Langstone Harbour mudflats by green algae except for some plants
associated with Spartina root hummocks. Later, Soulsby et al. (1978) also
concluded that sewage input was mainly responsible for the large algal
mats in Langstone Harbour. No notable increase, however, has been
reported in algal cover of the mud flats in recent years (Montgomery and
SouIsby 1980; Soulsby et al. 1985). SouIsby et al. (1985), for example,
recorded no trends in algal cover from 1974 to 1983 in Portsmouth
Harbour and from 1973 to 1983 in Langstone Harbour, although it is
likely that nutrient input had increased.
Although high levels of nutrients are generally recognised as the prima
facie reason for many of the observed changes in benthic algal populations, other environmental factors can also playa major role. There are,
for example, many regions in the British Isles, such as the Thames
Estuary, which have very high nutrient concentrations but are not associated with reports of excessive blooms of algae (Southgate 1972). Probably one of the most important environmental factors that determine
the response of algal communities to excess nutrient loading is the degree of "exposure" at the locality. A characteristic of many of the affected
areas, for example, is their relatively enclosed and sheltered aspect. These
include, for example, sheltered loughs such as Belfast Lough in Ireland,
sheltered estuaries like the Rogerstown in Ireland (Fahy et al. 1975), the
quiet Backwater of Weymouth Harbour, the very enclosed, shallow harbour systems of Poole, Langstone and Portsmouth on the south coast of
England and large, but enclosed bays, such as Dublin Bay. Even within
the large harbours and bays, the algal growth is often restricted to the
quieter, inner regions. In some situations, these quiet regions are natural
R.L. Fletcher
associated sewage, was also held responsible for both qualitative and
quantitative changes observed in the flora and fauna of the inner parts of
the Firth of Forth Estuary (Johnston 1971/92) and the Firth of Clyde
Estuary (Clokie and Boney 1979); all these authors reported a reduced
flora compared with that recorded in the 19th century. Fletcher (1974)
also suggested that perhaps the increased incidences of algal deposits on
beaches in Thanet (SE England) were the result of increased sewage
discharges in local bays. In one locality (Langstone Harbour, south coast
of England), increased nutrient inputs (12 to 36 ml/day over a lO-year
period in the 1960s to 1970s) from a newly built sewage works, were held
responsible for increased growths of green algae on the surface of the
mudflats (Dunn 1972; Anonymous 1976a; Montgomery and Soulsby
1980; Tubbs 1980a). There was, for example, little evidence of green algal
growths on the mud flats in 1961 but they were fairly widespread in 1966
and 1967 (Dunn 1972; Anonymous 1976a). Dunn (1972) also noted that
Perraton (1953) did not mention any obvious colonization of the
Langstone Harbour mudflats by green algae except for some plants
associated with Spartina root hummocks. Later, Soulsby et al. (1978) also
concluded that sewage input was mainly responsible for the large algal
mats in Langstone Harbour. No notable increase, however, has been
reported in algal cover of the mud flats in recent years (Montgomery and
SouIsby 1980; Soulsby et al. 1985). SouIsby et al. (1985), for example,
recorded no trends in algal cover from 1974 to 1983 in Portsmouth
Harbour and from 1973 to 1983 in Langstone Harbour, although it is
likely that nutrient input had increased.
Although high levels of nutrients are generally recognised as the prima
facie reason for many of the observed changes in benthic algal populations, other environmental factors can also playa major role. There are,
for example, many regions in the British Isles, such as the Thames
Estuary, which have very high nutrient concentrations but are not associated with reports of excessive blooms of algae (Southgate 1972). Probably one of the most important environmental factors that determine
the response of algal communities to excess nutrient loading is the degree of "exposure" at the locality. A characteristic of many of the affected
areas, for example, is their relatively enclosed and sheltered aspect. These
include, for example, sheltered loughs such as Belfast Lough in Ireland,
sheltered estuaries like the Rogerstown in Ireland (Fahy et al. 1975), the
quiet Backwater of Weymouth Harbour, the very enclosed, shallow harbour systems of Poole, Langstone and Portsmouth on the south coast of
England and large, but enclosed bays, such as Dublin Bay. Even within
the large harbours and bays, the algal growth is often restricted to the
quieter, inner regions. In some situations, these quiet regions are natural