22
R. L. Fletcher
1.5 Characteristics of Green Tide Forming Algae
Not surprisingly, particular interest has been directed towards obtaining a
better understanding of the biology of the relatively small number of genera
(and species) which contribute to the formation of these "green tides". In
general, they can be termed opportunistic and are frequently reported as
early colonizers or pioneering organisms on newly immersed, denuded or
disturbed substrata (Murray and Littler 1976; Wennberg 1992). For this
reason, they often occur as important marine fouling organisms and as
early colonizers of substrata denuded by natural disturbances e.g. sand
scouring, storm damage, or by man's activities, e.g. oil pollution treatment
(Nelson-Smith 1972; Fletcher 1988). This pioneering role appears to be
aided by a wide geographical distribution, a common local abundance and
wide seasonal occurrence, a copious production of reproductive spore
bodies (Littler and Murray 1974), a short, simple life history (Littler and
Murray 1974; Murray and Littler 1974) and an inherent rapid rate of
colonization and growth (Vogt and Schramm 1991; Park 1992). All these
biological features ensure a rapid and successful colonization of a wide
range of habitats and environments and provide a competitive edge over
many other algae.
The floristic components of these "green tides" can also be described as
stress-tolerant and physiologically hardy (Kindig and Littler 1980). Genera
such as Ulva and Enteromorpha, in particular, exhibit a wide tolerance to
adverse environmental conditions of temperature, light intensity and
salinity (Gordon et al. 1980; Chan et al. 1982; Vermaat and Sand-Jensen
1987). Ulva, for example, has been reported to show high adaptability to
different irradiances, being especially tolerant of low light conditions
(Ramus 1983; Vermaat and Sand-Jensen 1987; Sand-Jensen 1988; Henley
and Ramus 1989; Martinez-Arroyo and Romero 1990); it is also markedly
tolerant of anoxic conditions, presence of sulphide etc. (Vermaat and
Sand-Jensen 1987; Sand -Jensen 1988) and to extended periods of desication
(Beer and Eshel 1983). The ability of Ulva to adapt to low irradiance
levels, with its low compensation light intensity, will optimize production
rates in tidal waters (Henley and Ramus 1989), including those with high
sediment loading, and should prove particularly beneficial for plants
forming dense growths similar to those contributing to the "green tides"
(Lavery and McComb 1991). Ulva rotundata is also known to photoaclimate (Henley and Ramus 1989), whilst the red alga Gracilaria confervoides
is known to be markedlyresistantto hydrogen sulphide (Stokke 1956). Both
the ability to photoaclimatize and tolerate H2 S would be particularly
beneficial to plants existing in large, dense mats. Additional adaptive
R. L. Fletcher
1.5 Characteristics of Green Tide Forming Algae
Not surprisingly, particular interest has been directed towards obtaining a
better understanding of the biology of the relatively small number of genera
(and species) which contribute to the formation of these "green tides". In
general, they can be termed opportunistic and are frequently reported as
early colonizers or pioneering organisms on newly immersed, denuded or
disturbed substrata (Murray and Littler 1976; Wennberg 1992). For this
reason, they often occur as important marine fouling organisms and as
early colonizers of substrata denuded by natural disturbances e.g. sand
scouring, storm damage, or by man's activities, e.g. oil pollution treatment
(Nelson-Smith 1972; Fletcher 1988). This pioneering role appears to be
aided by a wide geographical distribution, a common local abundance and
wide seasonal occurrence, a copious production of reproductive spore
bodies (Littler and Murray 1974), a short, simple life history (Littler and
Murray 1974; Murray and Littler 1974) and an inherent rapid rate of
colonization and growth (Vogt and Schramm 1991; Park 1992). All these
biological features ensure a rapid and successful colonization of a wide
range of habitats and environments and provide a competitive edge over
many other algae.
The floristic components of these "green tides" can also be described as
stress-tolerant and physiologically hardy (Kindig and Littler 1980). Genera
such as Ulva and Enteromorpha, in particular, exhibit a wide tolerance to
adverse environmental conditions of temperature, light intensity and
salinity (Gordon et al. 1980; Chan et al. 1982; Vermaat and Sand-Jensen
1987). Ulva, for example, has been reported to show high adaptability to
different irradiances, being especially tolerant of low light conditions
(Ramus 1983; Vermaat and Sand-Jensen 1987; Sand-Jensen 1988; Henley
and Ramus 1989; Martinez-Arroyo and Romero 1990); it is also markedly
tolerant of anoxic conditions, presence of sulphide etc. (Vermaat and
Sand-Jensen 1987; Sand -Jensen 1988) and to extended periods of desication
(Beer and Eshel 1983). The ability of Ulva to adapt to low irradiance
levels, with its low compensation light intensity, will optimize production
rates in tidal waters (Henley and Ramus 1989), including those with high
sediment loading, and should prove particularly beneficial for plants
forming dense growths similar to those contributing to the "green tides"
(Lavery and McComb 1991). Ulva rotundata is also known to photoaclimate (Henley and Ramus 1989), whilst the red alga Gracilaria confervoides
is known to be markedlyresistantto hydrogen sulphide (Stokke 1956). Both
the ability to photoaclimatize and tolerate H2 S would be particularly
beneficial to plants existing in large, dense mats. Additional adaptive