238
R.L. Fletcher
1979; (Fig. 8.2), the Wash (Anonymous 1976b), Dublin Bay (Jeffrey et al.
1992; Fig. 8.3) and the Firth of Clyde (Perkins and Abbott 1972). Owens
et al. (1979) reported that a similar summer bloom of green algae occurs in freshwater lochs in Scotland; see also Ho (1979). Usually, Enteromorpha begins development in April/May, reaches maximum development in July/August, begins to decline in September and is usually
absent in November (Cotton 1911; Anonymous 1976a, b; Nicholls et al.
1981; Owens and Stewart 1983). There are also some indications of a
sequential change occurring in the floristic component of the algal mats
in some regions, for example, the occurrence of an annual spring growth
of Ulothrix flacca preceding the Enteromorpha in the Wash,
England (Anonymous 1976b) and a seasonal shift from Enteromorpha to
Ulva in Dublin Bay, Ireland (Walsh 1988; Jeffrey et al. 1992). Ulva also
appears to be less tolerant than Enteromorpha to aerial exposure
on the mudflats and will only extend above high tide level in pools,
streams and shallow water (Cotton 1911). Jeffrey et al. (1992)
also reported Ulva to occur in greatest quantites in the permanent chan120
:E
'"
"~
80
i!'
1:1
'" "E 40
'"
o
150
125
E
CI 100
"i
~
75
"C
'":
E
50
CI
25
0
J
M A M J J
1978
f f f f ~
J A SON
19S!il
Enteromorpha
site 7
A S O N D J F M
1979
f I
t
~
o J F M A M J J A S
1990
Fig. 8.2. Seasonal variation
in Enteromorpha spp. in
the Eden Estuary, Scotland
measured during 1978. (After Owens and Stewart
1983)
Fig. 8.3. Seasonal variation
in green algal biomass
during 198911990 in the
South Lagoon of Dublin
Bay, Ireland. (After Jeffrey
et al. 1992)