The Northern Atlantic Coasts
167
Interpreting the recorded changes in the composition of the seaweed
communities, however, is not always without problems. The nutrients
available are not only a result of direct discharges of sewage, or wastewaters from industries and fish farms, land runoff or atmospheric
deposition. Nutrients can also be brought by deep-water influxes (e.g.
Rydberg et al. 1990). Silt carried by rivers or resuspended through
storms or by dredging also has a similar detrimental effect on the communities by covering the plants or rocks. Furthermore, climatic changes
may have comparable effects, especially if severe winters make the inner
bays freeze and drifting ice in early spring may then erode the rocks.
Combined effects of discharges of nutrients together with detrimental
substances such as TBT and pulp mill effiuents (see e.g. Kautsky et al.
1992 and references therein), or acid metal wastes (see e.g. Bokn 1990)
may also mask the effects of nutrient load, which may not be obvious
until the discharges of the other substances have been stopped. Extremely high loads of ammonium can have negative effects on algal abundance.
For example, in the Baltic Sea the enhancement effect of a nitrogen load
from a factory on the green alga Enteromorpha was not seen until the
amounts of ammonium discharged into the sea had been reduced
(Kautsky 1982). On the other hand, nutrient inputs in areas with low
ionic strength may favour growth of marine species. For example, the
innermost record in the Bothnian Bay (the Baltic Sea) of Fucus vesiculosus is from a location close to a sewage outlet (Pekkari 1973).
Changes in the macro algal communities caused by eutrophication often include disappearance or decrease of fucoids (for references see
below), as well as increasing amounts of the opportunistic filamentous or
sheet-like and tubular species or groups, such as the green algae Blidingia minima, Cladophora spp., Percursaria percursa, Rhizoclonium spp.,
Enteromorpha spp., Ulva spp. and Ulvaria fusca; the brown algae
Ectocarpus spp. and Pilayella litoralis; and the red algae Ceramium spp.,
Polysiphonia spp. and Porphyra purpurea. These algae with high surface
area to volume ratios are characterized by high production and nutrient
uptake rates compared to the much lower rates of the late successional
species such as fucoids (cf. Wallentinus 1984 and references therein).
Structural changes in the macro algal communities are conspicuous
and can easily be observed by the general public. Thus, there will always
be a high demand for information on changes in these communities.
However, in many countries monitoring programmes for the macroalgal
communities are lacking or much reduced in comparison to programmes
on phytoplankton or the macrofauna on the deeper bottoms. Also, when
programmes have been carried out, the results are very often not published in international journals, which hampers comparative analyses.
167
Interpreting the recorded changes in the composition of the seaweed
communities, however, is not always without problems. The nutrients
available are not only a result of direct discharges of sewage, or wastewaters from industries and fish farms, land runoff or atmospheric
deposition. Nutrients can also be brought by deep-water influxes (e.g.
Rydberg et al. 1990). Silt carried by rivers or resuspended through
storms or by dredging also has a similar detrimental effect on the communities by covering the plants or rocks. Furthermore, climatic changes
may have comparable effects, especially if severe winters make the inner
bays freeze and drifting ice in early spring may then erode the rocks.
Combined effects of discharges of nutrients together with detrimental
substances such as TBT and pulp mill effiuents (see e.g. Kautsky et al.
1992 and references therein), or acid metal wastes (see e.g. Bokn 1990)
may also mask the effects of nutrient load, which may not be obvious
until the discharges of the other substances have been stopped. Extremely high loads of ammonium can have negative effects on algal abundance.
For example, in the Baltic Sea the enhancement effect of a nitrogen load
from a factory on the green alga Enteromorpha was not seen until the
amounts of ammonium discharged into the sea had been reduced
(Kautsky 1982). On the other hand, nutrient inputs in areas with low
ionic strength may favour growth of marine species. For example, the
innermost record in the Bothnian Bay (the Baltic Sea) of Fucus vesiculosus is from a location close to a sewage outlet (Pekkari 1973).
Changes in the macro algal communities caused by eutrophication often include disappearance or decrease of fucoids (for references see
below), as well as increasing amounts of the opportunistic filamentous or
sheet-like and tubular species or groups, such as the green algae Blidingia minima, Cladophora spp., Percursaria percursa, Rhizoclonium spp.,
Enteromorpha spp., Ulva spp. and Ulvaria fusca; the brown algae
Ectocarpus spp. and Pilayella litoralis; and the red algae Ceramium spp.,
Polysiphonia spp. and Porphyra purpurea. These algae with high surface
area to volume ratios are characterized by high production and nutrient
uptake rates compared to the much lower rates of the late successional
species such as fucoids (cf. Wallentinus 1984 and references therein).
Structural changes in the macro algal communities are conspicuous
and can easily be observed by the general public. Thus, there will always
be a high demand for information on changes in these communities.
However, in many countries monitoring programmes for the macroalgal
communities are lacking or much reduced in comparison to programmes
on phytoplankton or the macrofauna on the deeper bottoms. Also, when
programmes have been carried out, the results are very often not published in international journals, which hampers comparative analyses.