28
R. L. Fletcher
for Mya arenaria and Cardium edule under Cladophora deposits in Sweden
(Fahyet al. 1975; Rosenberg and Edler 1981; Rosenberg 1985; Rosenberg
and Loo 1988; Baden et al. 1990; Rosenberg et al. 1990) and for the soft shell
clam Mya arenaria and Mercenaria mercenaria under Ulva lactuca by
White and Highlands (1968) in the USA. In general, a number of authors
have reported a reduction in the numbers and diversity of mud infauna
(Ryther 1954; Baalsrud 1967; Perkins and Abbott 1972; Wharfe 1977; Dauer
and Connor 1980; Nicholls et al. 1981; Soulsby et al. 1982; Price and
Hylleberg 1982; Reise 1983; Rosenberg 1985; Thrush 1986; Olafson 1988;
Park 1992), with severe implications to the local fishing industries and bird
populations (Perkins and Abbott 1972; Fahy et al. 1975; Tubbs 1977;
Montgomery and SouIsby 1980; Tubbs and Tubbs 1980; Nicholls et al. 1981).
Usually there is a replacement of the fauna by a small number of
pollution-tolerant species. For example, Wharfe (1977), Montgomery and
Soulsby (1980) and Nicholls et al. (1981) reported a reduced biomass of
infauna under Enteromorpha mats on mud flats on the south coast of
England with high numbers of more pollution-tolerant species such as the
polychaetes Capitella capitata and Scolelepis fuliginosa and the oligochaete
Peloscolex benedenii. The worm Peloscolex was also shown to be encouraged by algal mats on Bull Island, Ireland, to the exclusion of other
forms of interstitial life (see Fahy et al. 1975). Perkins and Abbott (1972)
noted that the lugworm Arenicola marina was able to tolerate anaerobic
conditions and the presence of sulphide under Ulva and Enteromorpha on
mud flats in the Firth of Clyde, Scotland. The decomposing weed has also
been implicated in the release of toxic products (Magre 1974; Johnson and
Welsh 1985).
Additional effects of this anaerobic decomposition process include the
reported high sulphide content of surface waters giving them an opaque
and creamy coloured appearance, referred to as "milky water" (Hanks
1966), the release of noxious smells of hydrogen sulphide (Letts and
Richards 1911; Sawyer 1965; Hanks 1966), the blackening oflead pigment
paints on local buildings (Wilkinson 1963; Sawyer 1965; Hanks 1966) and
the rapid proliferation of chironomid flies, whose larval stages can survive
the anoxic conditions because they have an anaerobic metabolism. The
latter was a particular problem in the Venice Lagoon during 1988 when the
mosquito Chironomus salinarius Kieff invaded the city and islands in
swarms, hindering the railway and airport facilities; a similar problem, with
swarms of the flying midge Dicrotendipes conjunctus has been reported for
the Orielton Lagoon, Tasmania (Buttermore 1977).
An important secondary effect of the decomposition process is the
release of nutrients back into the ecosystem. Drift algal mats do act as a
temporary reservoir of nutrients which are quickly released to the overlying
R. L. Fletcher
for Mya arenaria and Cardium edule under Cladophora deposits in Sweden
(Fahyet al. 1975; Rosenberg and Edler 1981; Rosenberg 1985; Rosenberg
and Loo 1988; Baden et al. 1990; Rosenberg et al. 1990) and for the soft shell
clam Mya arenaria and Mercenaria mercenaria under Ulva lactuca by
White and Highlands (1968) in the USA. In general, a number of authors
have reported a reduction in the numbers and diversity of mud infauna
(Ryther 1954; Baalsrud 1967; Perkins and Abbott 1972; Wharfe 1977; Dauer
and Connor 1980; Nicholls et al. 1981; Soulsby et al. 1982; Price and
Hylleberg 1982; Reise 1983; Rosenberg 1985; Thrush 1986; Olafson 1988;
Park 1992), with severe implications to the local fishing industries and bird
populations (Perkins and Abbott 1972; Fahy et al. 1975; Tubbs 1977;
Montgomery and SouIsby 1980; Tubbs and Tubbs 1980; Nicholls et al. 1981).
Usually there is a replacement of the fauna by a small number of
pollution-tolerant species. For example, Wharfe (1977), Montgomery and
Soulsby (1980) and Nicholls et al. (1981) reported a reduced biomass of
infauna under Enteromorpha mats on mud flats on the south coast of
England with high numbers of more pollution-tolerant species such as the
polychaetes Capitella capitata and Scolelepis fuliginosa and the oligochaete
Peloscolex benedenii. The worm Peloscolex was also shown to be encouraged by algal mats on Bull Island, Ireland, to the exclusion of other
forms of interstitial life (see Fahy et al. 1975). Perkins and Abbott (1972)
noted that the lugworm Arenicola marina was able to tolerate anaerobic
conditions and the presence of sulphide under Ulva and Enteromorpha on
mud flats in the Firth of Clyde, Scotland. The decomposing weed has also
been implicated in the release of toxic products (Magre 1974; Johnson and
Welsh 1985).
Additional effects of this anaerobic decomposition process include the
reported high sulphide content of surface waters giving them an opaque
and creamy coloured appearance, referred to as "milky water" (Hanks
1966), the release of noxious smells of hydrogen sulphide (Letts and
Richards 1911; Sawyer 1965; Hanks 1966), the blackening oflead pigment
paints on local buildings (Wilkinson 1963; Sawyer 1965; Hanks 1966) and
the rapid proliferation of chironomid flies, whose larval stages can survive
the anoxic conditions because they have an anaerobic metabolism. The
latter was a particular problem in the Venice Lagoon during 1988 when the
mosquito Chironomus salinarius Kieff invaded the city and islands in
swarms, hindering the railway and airport facilities; a similar problem, with
swarms of the flying midge Dicrotendipes conjunctus has been reported for
the Orielton Lagoon, Tasmania (Buttermore 1977).
An important secondary effect of the decomposition process is the
release of nutrients back into the ecosystem. Drift algal mats do act as a
temporary reservoir of nutrients which are quickly released to the overlying