The French Atlantic Coasts
257
Survival and, consequently, mass production of the green tide Ulva,
would not be possible if it could not maintain itself suspended in the
mixed water column and multiply easily by fragmentation. The thinness
(30-40 !lm) and fragility of the thallus are probably conditional to these
capabilities. Generally, the seaweeds involved in eutrophication seem, in
the same way, able to colonize the water column physically.
As far as other species are concerned with regard to eutrophication on
Brittany coasts, it should be mentioned that agglomerations of unattached mixed Porphyra species have been found irregularly in small
quantities since the first reports of the green tide phenomenon. They
have very rarely led to quantitatively significant beachings.
More important is the brown alga Pilayella littoralis (Ectocarpales),
which has been recently noted to produce mass blooms in some localities
of North Brittany. Such blooms occur irregularly from one year to another, sometimes in alternation with Ulva sp. Mass development of
Pilayella littoralis has also been observed along the coasts of other countries, e.g. USA (Massachussetts), and the Baltic Sea (Breuer and Schramm
1988; Pregnall and Miller 1988). In the same way, the filamentous red
alga Falkenbergia rufalonosa (sporophyte of Asparagospsis armata) has
been recently shown to produce mixed mass blooms with the green tides
of the Bay of Douarnenez (South Brittany), indicating trends in diversification or succession for species involved in local coastal eutrophication
(CEVA, unpubl. data).
9.2.2 Fighting Means and Associated Research Programs
What methods could be used for fighting green tides on the coasts of
Brittany? In this context, the relationships between attached and
free-floating populations must be considered. The attached populations
of the Ulva species are scattered and not easily distinguishable from each
other. In practice, it is difficult, even un-feasible to operate selectively on
these populations. Furthermore, this action on the whole would probably
be useless, since sessile populations are not a major cause of the annual
formation of green tides, as was pointed out earlier.
As to the control of floating populations, curative and preventive
means may be distinguished.
Curative means include collecting the seaweeds and removal, or the
direct use of growth inhibitors or toxic compounds. Collecting the
beached biomass is commonly used to clean up recreational areas,
although this method has its limitations and is often expensive (3 million
FF in 1992 for the coasts of Brittany CEVA, unpublished data). Another
257
Survival and, consequently, mass production of the green tide Ulva,
would not be possible if it could not maintain itself suspended in the
mixed water column and multiply easily by fragmentation. The thinness
(30-40 !lm) and fragility of the thallus are probably conditional to these
capabilities. Generally, the seaweeds involved in eutrophication seem, in
the same way, able to colonize the water column physically.
As far as other species are concerned with regard to eutrophication on
Brittany coasts, it should be mentioned that agglomerations of unattached mixed Porphyra species have been found irregularly in small
quantities since the first reports of the green tide phenomenon. They
have very rarely led to quantitatively significant beachings.
More important is the brown alga Pilayella littoralis (Ectocarpales),
which has been recently noted to produce mass blooms in some localities
of North Brittany. Such blooms occur irregularly from one year to another, sometimes in alternation with Ulva sp. Mass development of
Pilayella littoralis has also been observed along the coasts of other countries, e.g. USA (Massachussetts), and the Baltic Sea (Breuer and Schramm
1988; Pregnall and Miller 1988). In the same way, the filamentous red
alga Falkenbergia rufalonosa (sporophyte of Asparagospsis armata) has
been recently shown to produce mixed mass blooms with the green tides
of the Bay of Douarnenez (South Brittany), indicating trends in diversification or succession for species involved in local coastal eutrophication
(CEVA, unpubl. data).
9.2.2 Fighting Means and Associated Research Programs
What methods could be used for fighting green tides on the coasts of
Brittany? In this context, the relationships between attached and
free-floating populations must be considered. The attached populations
of the Ulva species are scattered and not easily distinguishable from each
other. In practice, it is difficult, even un-feasible to operate selectively on
these populations. Furthermore, this action on the whole would probably
be useless, since sessile populations are not a major cause of the annual
formation of green tides, as was pointed out earlier.
As to the control of floating populations, curative and preventive
means may be distinguished.
Curative means include collecting the seaweeds and removal, or the
direct use of growth inhibitors or toxic compounds. Collecting the
beached biomass is commonly used to clean up recreational areas,
although this method has its limitations and is often expensive (3 million
FF in 1992 for the coasts of Brittany CEVA, unpublished data). Another