166
1. Wallentinus
3. The often mosaic pattern of different macro algal species
in areas with only a small degree of anthropogenic impact, which
creates several niches for the fauna, will change into a more homogeneous structure and since many species show a trend towards
moving upwards, the deeper areas become poor in or devoid of
macroalgae.
4. The great diversity of macroscopic organisms is lost which may
also have an impact on the biodiversity of the system at the genetic
level since the gene pools might differ between the populations on
the various Atlantic shores due to isolation and/or sterility.
5. Eutrophication might also enhance the establishment of introduced
foreign species, because other competitive species may already have
been lost as a result of the anthropogenic impact. This may have
favoured for example the establishment of the Japanese brown alga
Sargassum muticum in some areas. In other cases, the introduced
species might itself be favoured by nutrient enrichment as observed
for example in Fucus evanescens in several areas (e.g. the Oslo fjord,
the Swedish west coast, Denmark).
Most of these functional and structural changes caused by eutrophication are in principle the same worldwide, although the dominant species
may differ. The phenomenon of large amounts of drifting algae, mainly
filamentous or sheet-like species, which can be a hindrance to both
fishery and recreation, is another feature recognized in most eutrophicated areas. Nutrient enrichment favouring the opportunistic macroalgae may also affect other subsystems. Seagrasses may be affected by
increased amounts of epiphytes on the plants or by sedimenting material
covering the leaves. The microphytobenthic communities in shallow
sediments may become covered by accumulation of drifting macro algae
(e.g. Sundback et al. 1990) with resultant damage to their structure and
function or sediment areas may be converted to communities dominated
by macro algae (e.g. Nilsson et al. 1991).
The life span of macroalgae makes them suitable for detecting integrated effects caused by eutrophication, and like all sessile organisms they
reflect changes in the area from which they are sampled. Such responses
are either due to direct effects, such as increase or decrease in abundance
of species by increased nutrient loads and increased incorporation of
nutrients in the algal tissues, or to indirect effects, such as decreased
depth distribution of the algae. These changes in depth may be caused by
the greater turbidity in eutrophicated waters, but also by increased
epiphytism as well as changed substrate conditions as sedimenting material accumulates on rocky bottoms.
1. Wallentinus
3. The often mosaic pattern of different macro algal species
in areas with only a small degree of anthropogenic impact, which
creates several niches for the fauna, will change into a more homogeneous structure and since many species show a trend towards
moving upwards, the deeper areas become poor in or devoid of
macroalgae.
4. The great diversity of macroscopic organisms is lost which may
also have an impact on the biodiversity of the system at the genetic
level since the gene pools might differ between the populations on
the various Atlantic shores due to isolation and/or sterility.
5. Eutrophication might also enhance the establishment of introduced
foreign species, because other competitive species may already have
been lost as a result of the anthropogenic impact. This may have
favoured for example the establishment of the Japanese brown alga
Sargassum muticum in some areas. In other cases, the introduced
species might itself be favoured by nutrient enrichment as observed
for example in Fucus evanescens in several areas (e.g. the Oslo fjord,
the Swedish west coast, Denmark).
Most of these functional and structural changes caused by eutrophication are in principle the same worldwide, although the dominant species
may differ. The phenomenon of large amounts of drifting algae, mainly
filamentous or sheet-like species, which can be a hindrance to both
fishery and recreation, is another feature recognized in most eutrophicated areas. Nutrient enrichment favouring the opportunistic macroalgae may also affect other subsystems. Seagrasses may be affected by
increased amounts of epiphytes on the plants or by sedimenting material
covering the leaves. The microphytobenthic communities in shallow
sediments may become covered by accumulation of drifting macro algae
(e.g. Sundback et al. 1990) with resultant damage to their structure and
function or sediment areas may be converted to communities dominated
by macro algae (e.g. Nilsson et al. 1991).
The life span of macroalgae makes them suitable for detecting integrated effects caused by eutrophication, and like all sessile organisms they
reflect changes in the area from which they are sampled. Such responses
are either due to direct effects, such as increase or decrease in abundance
of species by increased nutrient loads and increased incorporation of
nutrients in the algal tissues, or to indirect effects, such as decreased
depth distribution of the algae. These changes in depth may be caused by
the greater turbidity in eutrophicated waters, but also by increased
epiphytism as well as changed substrate conditions as sedimenting material accumulates on rocky bottoms.