230
R.L. Fletcher
main constituent. Fletcher suggested the deposits might be related to
increased sewage discharges in the vicinity of the bays. Although the
bays are relatively exposed to the English Channel, the situation might be
similar to that described for several bays on the Brittany coast. In the
gently sloping Bay of Brieuc, for example, large deposits of green algae
(Ulva sp.), stimulated by anthopogenic sources of nutrients, become
trapped in small residual bodies of water between the tides and are
periodically swept up onto the shores as large beach deposits (Piriou
et al. 1991; Piriou and Menesguen 1992).
Given the right hydrological conditions for the formation of excessive
growths of algae, other influential factors include the availability of
suitable substrata and the salinity of the water. Cotton (1910, 1911), for
example, suggested that mussels played an important role in the development of algal populations in Southampton Water, Weymouth Harbour
and Belfast Lough; they provided a firm anchorage for the plants, retaining vegetative fragments by their byssus threads, thereby, allowing the
algae to overwinter until new growth was initiated in spring. Jeffreyet al.
(1992) suggested that the tubeworm Lanice played an important role in
the build-up of Ectocarpus populations in Dublin Bay by providing a
solid substratum and liberating nitrogen and phosphorus as excretory
products. Lowthion et al. (1985) reported that the increased development
of green algal mats in Langstone Harbour coincided with a decline in
Spartina beds (Haynes and Coulson 1982) which increased the amount
of available mud flat for the algae to colonize. Finally, the ability of Ulva
lactuca (identified as var. latissima) to thrive in brackish water was
considered to be an important factor in its successful colonization of
localities such as Belfast Lough, Southampton Water and Weymouth
Harbour (Cotton 1911).
Whilst many of the above described floristic changes have been attributed to excess nutrient loadings from sewage, some have been attributed to secondary pollutants, notably the high volume of suspended
matter discharged with the effluents. Johnston (1971/72), for example,
concluded that the depauperate flora observed on the sewage-contaminated shores at Joppa in the Firth of Forth, Scotland, was probably
largely the result of the high levels of suspended matter in the water
column which reduced light penetration and interfered with the settlement and growth of germlings. It also increased the quantity of mussels
which competed for space with the benthic algae. Other reported detrimental effects of suspended matter on plant and animal communities
around the British Isles include a reduction in net annual production and
depth range of the kelp Laminaria hyperborea in heavily polluted sites on
the northeast coast of England compared to non-polluted localities in
R.L. Fletcher
main constituent. Fletcher suggested the deposits might be related to
increased sewage discharges in the vicinity of the bays. Although the
bays are relatively exposed to the English Channel, the situation might be
similar to that described for several bays on the Brittany coast. In the
gently sloping Bay of Brieuc, for example, large deposits of green algae
(Ulva sp.), stimulated by anthopogenic sources of nutrients, become
trapped in small residual bodies of water between the tides and are
periodically swept up onto the shores as large beach deposits (Piriou
et al. 1991; Piriou and Menesguen 1992).
Given the right hydrological conditions for the formation of excessive
growths of algae, other influential factors include the availability of
suitable substrata and the salinity of the water. Cotton (1910, 1911), for
example, suggested that mussels played an important role in the development of algal populations in Southampton Water, Weymouth Harbour
and Belfast Lough; they provided a firm anchorage for the plants, retaining vegetative fragments by their byssus threads, thereby, allowing the
algae to overwinter until new growth was initiated in spring. Jeffreyet al.
(1992) suggested that the tubeworm Lanice played an important role in
the build-up of Ectocarpus populations in Dublin Bay by providing a
solid substratum and liberating nitrogen and phosphorus as excretory
products. Lowthion et al. (1985) reported that the increased development
of green algal mats in Langstone Harbour coincided with a decline in
Spartina beds (Haynes and Coulson 1982) which increased the amount
of available mud flat for the algae to colonize. Finally, the ability of Ulva
lactuca (identified as var. latissima) to thrive in brackish water was
considered to be an important factor in its successful colonization of
localities such as Belfast Lough, Southampton Water and Weymouth
Harbour (Cotton 1911).
Whilst many of the above described floristic changes have been attributed to excess nutrient loadings from sewage, some have been attributed to secondary pollutants, notably the high volume of suspended
matter discharged with the effluents. Johnston (1971/72), for example,
concluded that the depauperate flora observed on the sewage-contaminated shores at Joppa in the Firth of Forth, Scotland, was probably
largely the result of the high levels of suspended matter in the water
column which reduced light penetration and interfered with the settlement and growth of germlings. It also increased the quantity of mussels
which competed for space with the benthic algae. Other reported detrimental effects of suspended matter on plant and animal communities
around the British Isles include a reduction in net annual production and
depth range of the kelp Laminaria hyperborea in heavily polluted sites on
the northeast coast of England compared to non-polluted localities in