The British Isles
229
and involve tidal movements which swing currents, carrying the nutrients or sewage, onto shores (Smyth 1968). In other situations, they are
produced artificially. For example, the Backwater represents a section of
Weymouth Harbour impounded by a dam (Cotton 1910). The situation
was then worsened when the construction of a railway bridge reduced
the middle current and formed an additional backwater where green
algae could flourish. Johnston (1971172) also reported that coastal developments which increased shelter may have contributed to the floristic
changes observed in the Firth of Forth whilst Fahy et al. (1975) reported
that the construction of a causeway in Rogerstown, Ireland reduced the
current flow and led to the development of mudflats containing dense
algal mats. In all these examples, restricted tidal flow and water exchange
occurs, the absence of strong currents and breakers allowing nutrients to
accumulate in the water column. This was clearly shown by Parsons and
Fisher (1977) using radioactive tracer surveys in Langstone Harbour;
they reported that the hydrography of the Harbour permitted a very slow
turnover and that most of the water re-enters the Harbour on the flood
tide permitting a build-up in effluent concentration at the north end. In
addition, low current activity will allow the build-up of floating and/or
loose-lying mats of algae in the sheltered regions of many of the affected
sites. Such a build-up is reported to be a particular problem in Dublin
Bay, Langstone Harbour and Belfast Lough. Montgomery and Soulsby
(1980), for example, reported that the initial build-up of green algal mats
in Langstone Harbour during the 1960s occurred largely in the sheltered
mudflat areas. In general, it is likely that in situations where good water
circulation occurs, pollution will have only a minimal effect on marine
plant and animal communities around the British Isles (Edwards 1975).
In contrast to the above findings, however, have been reports of excessive algal deposits occurring on more open coasts in the south of
England. For example, very large annual deposits of macro algae (ca.
50 000 to 60 000 tonnes in recent years) have occurred on relatively
exposed beaches in the Worthing area as far back as 1850 and have
produced nauseating smells, encouraged large numbers of seaweed flies
(Coelopa frigida and Coelopa pilipes) and necessitated expensive clearance operations (Anonymous 1987). In a study by Binnie and Partners
(Anonymous 1987, 1988), however, it was concluded that the problem
was unlikely to relate to the release of nutrients in wastewaters and that
the major cast weed deposits, largely comprising the kelp Laminaria
saccharina, originated from offshore beds and were caused by particular
combinations of wind, wave and tides.
A different beach cast flora was, however, identified by Fletcher
(1974) in sheltered bays on the Thanet Coast, with Ulva lactuca being a
229
and involve tidal movements which swing currents, carrying the nutrients or sewage, onto shores (Smyth 1968). In other situations, they are
produced artificially. For example, the Backwater represents a section of
Weymouth Harbour impounded by a dam (Cotton 1910). The situation
was then worsened when the construction of a railway bridge reduced
the middle current and formed an additional backwater where green
algae could flourish. Johnston (1971172) also reported that coastal developments which increased shelter may have contributed to the floristic
changes observed in the Firth of Forth whilst Fahy et al. (1975) reported
that the construction of a causeway in Rogerstown, Ireland reduced the
current flow and led to the development of mudflats containing dense
algal mats. In all these examples, restricted tidal flow and water exchange
occurs, the absence of strong currents and breakers allowing nutrients to
accumulate in the water column. This was clearly shown by Parsons and
Fisher (1977) using radioactive tracer surveys in Langstone Harbour;
they reported that the hydrography of the Harbour permitted a very slow
turnover and that most of the water re-enters the Harbour on the flood
tide permitting a build-up in effluent concentration at the north end. In
addition, low current activity will allow the build-up of floating and/or
loose-lying mats of algae in the sheltered regions of many of the affected
sites. Such a build-up is reported to be a particular problem in Dublin
Bay, Langstone Harbour and Belfast Lough. Montgomery and Soulsby
(1980), for example, reported that the initial build-up of green algal mats
in Langstone Harbour during the 1960s occurred largely in the sheltered
mudflat areas. In general, it is likely that in situations where good water
circulation occurs, pollution will have only a minimal effect on marine
plant and animal communities around the British Isles (Edwards 1975).
In contrast to the above findings, however, have been reports of excessive algal deposits occurring on more open coasts in the south of
England. For example, very large annual deposits of macro algae (ca.
50 000 to 60 000 tonnes in recent years) have occurred on relatively
exposed beaches in the Worthing area as far back as 1850 and have
produced nauseating smells, encouraged large numbers of seaweed flies
(Coelopa frigida and Coelopa pilipes) and necessitated expensive clearance operations (Anonymous 1987). In a study by Binnie and Partners
(Anonymous 1987, 1988), however, it was concluded that the problem
was unlikely to relate to the release of nutrients in wastewaters and that
the major cast weed deposits, largely comprising the kelp Laminaria
saccharina, originated from offshore beds and were caused by particular
combinations of wind, wave and tides.
A different beach cast flora was, however, identified by Fletcher
(1974) in sheltered bays on the Thanet Coast, with Ulva lactuca being a