Atlantic Coastal Biome
223
of maximal probability that its most suitable larval food will be available in satisfactory
abundance.
A very recent demonstration of the same issue in the Bay of Biscay may be noted;
here, the anchovy (Engraulis anchoa) population comprises only three year-classes, and
population size is strongly variable between years. However, there is no significant relationship between adult spawning stock size and subsequent recruitment success: this is
now known to be forced by the effects of strong or weak seasonal coastal upwelling on the
success of each year class (De Oliveira et al., 2005). This finding requires that “classical”
techniques for setting catch quotas that incorporate some level of assumption of the
elusive “stock-recruitment” relationship be replaced with novel techniques for prediction
of future stock sizes. Of course, this generality is not yet accepted by the fishery science
community.
Regional Benthic and Demersal Ecology
Here in NECS, exploration of benthic ecology has had a long history—and has perhaps
been carried further—than in most other coastal provinces. I shall concern myself mostly
with the macrobenthos, though recognizing the significance everywhere of the benthic
meio- and microfauna that utilize the particulate organic material—small crustaceans,
annelids, and nematodes, together with protists and bacteria. It is, of course, these
organisms that are responsible for much of the benthic nutrient regeneration that occurs
in shallow seas.
Many studies in recent decades have extended our knowledge of the distribution of the
benthic communities, both offshore in the North Sea and in coastal regions, especially
off England, where detailed ecological studies of Amphiura, Venus, Abra, Macoma, and
Modiolus reef communities were undertaken in relation to tidal stress and other factors
(e.g., Warwick and Uncles, 1980). These studies emphasized the trophic links between
macro- and meiofauna and the relative importance of deposit and suspension feeding in
relation to bottom type.
The Peterson-Thorson system for the description of benthic species groupings, though
often challenged (see Chapter 3), remains a useful basis for thinking about how these
organisms are arranged on continental shelves. It is subjectively simple to reach concordance between this and the more holistic system of benthic “étages” of J.-M. Pérès (see
Glémarec, 1973). Just as for the pelagic ecosystem, we find that the regional ecological
response of the benthos is a function of the regional oceanographic regime, in this case
mediated through surficial geology. It is the grain size and organic content of a sediment
that principally determine what benthic organisms will occur within it, and this sedimentary regime itself is a function of physical mixing and resuspension by wind and tides, as
I have discussed in previous sections.
It is relatively simple to integrate the results of modern studies, such as the ICES
North Sea benthos survey (1986), with earlier summations by Thorson, Glémarec, and
others (e.g., Duineveld et al., 1991) into an informal recognition of this relationship,
grosso modo, for the NECS Province. Wherever sandy ground occurs, the benthic fauna
will be some version of a Venus association, or, if the median size of fine particles is
<200 m it will be a Tellina association. The transition from coarse sand to gravel will be
accompanied by progressive changes in component species; where median size of small
particles is around 1 mm, then we may expect Amphioxus to abound with Venus fasciata.
The biomass of sandy-ground benthos is dominated by suspension-feeding organisms—
Venus gallina, Mactra corallina, Tellina fabula, and Pharus legumen in shallow water. The
deeper sands below the mud line are usually not so clean as in shoaler water, and here
we should expect organisms such as Venus casina, Astarte sulcata, Spatangus purpurea,
Dentalium entalis, and, specifically, Hyalonoecia tubicola. The annual production/biomass
ratio for Venus species associations is relatively low, in one case around 0.5.
223
of maximal probability that its most suitable larval food will be available in satisfactory
abundance.
A very recent demonstration of the same issue in the Bay of Biscay may be noted;
here, the anchovy (Engraulis anchoa) population comprises only three year-classes, and
population size is strongly variable between years. However, there is no significant relationship between adult spawning stock size and subsequent recruitment success: this is
now known to be forced by the effects of strong or weak seasonal coastal upwelling on the
success of each year class (De Oliveira et al., 2005). This finding requires that “classical”
techniques for setting catch quotas that incorporate some level of assumption of the
elusive “stock-recruitment” relationship be replaced with novel techniques for prediction
of future stock sizes. Of course, this generality is not yet accepted by the fishery science
community.
Regional Benthic and Demersal Ecology
Here in NECS, exploration of benthic ecology has had a long history—and has perhaps
been carried further—than in most other coastal provinces. I shall concern myself mostly
with the macrobenthos, though recognizing the significance everywhere of the benthic
meio- and microfauna that utilize the particulate organic material—small crustaceans,
annelids, and nematodes, together with protists and bacteria. It is, of course, these
organisms that are responsible for much of the benthic nutrient regeneration that occurs
in shallow seas.
Many studies in recent decades have extended our knowledge of the distribution of the
benthic communities, both offshore in the North Sea and in coastal regions, especially
off England, where detailed ecological studies of Amphiura, Venus, Abra, Macoma, and
Modiolus reef communities were undertaken in relation to tidal stress and other factors
(e.g., Warwick and Uncles, 1980). These studies emphasized the trophic links between
macro- and meiofauna and the relative importance of deposit and suspension feeding in
relation to bottom type.
The Peterson-Thorson system for the description of benthic species groupings, though
often challenged (see Chapter 3), remains a useful basis for thinking about how these
organisms are arranged on continental shelves. It is subjectively simple to reach concordance between this and the more holistic system of benthic “étages” of J.-M. Pérès (see
Glémarec, 1973). Just as for the pelagic ecosystem, we find that the regional ecological
response of the benthos is a function of the regional oceanographic regime, in this case
mediated through surficial geology. It is the grain size and organic content of a sediment
that principally determine what benthic organisms will occur within it, and this sedimentary regime itself is a function of physical mixing and resuspension by wind and tides, as
I have discussed in previous sections.
It is relatively simple to integrate the results of modern studies, such as the ICES
North Sea benthos survey (1986), with earlier summations by Thorson, Glémarec, and
others (e.g., Duineveld et al., 1991) into an informal recognition of this relationship,
grosso modo, for the NECS Province. Wherever sandy ground occurs, the benthic fauna
will be some version of a Venus association, or, if the median size of fine particles is
<200 m it will be a Tellina association. The transition from coarse sand to gravel will be
accompanied by progressive changes in component species; where median size of small
particles is around 1 mm, then we may expect Amphioxus to abound with Venus fasciata.
The biomass of sandy-ground benthos is dominated by suspension-feeding organisms—
Venus gallina, Mactra corallina, Tellina fabula, and Pharus legumen in shallow water. The
deeper sands below the mud line are usually not so clean as in shoaler water, and here
we should expect organisms such as Venus casina, Astarte sulcata, Spatangus purpurea,
Dentalium entalis, and, specifically, Hyalonoecia tubicola. The annual production/biomass
ratio for Venus species associations is relatively low, in one case around 0.5.