35
3 Effects of Eutrophication
cies of annual algae or filter feeders, and community diversity declined consistently by 24–46 % in the Northwest Atlantic and eutrophied sites in the Baltic Sea (Worm 2006).
Under hypoxic conditions owing to decomposing algal
mat on shallow sandy bottoms in the northern Baltic Sea,
the bivalve Macoma balthica emerged at the sediment surface, and exposed to epibenthic predators, such as the isopod
Saduria entomon, the brown-shrimp Crangon crungon and
the flounder Platichthysflesus (Norkko and Bonsdorff 2008).
However, the intensive growth of periphytic algae caused an
increase in the number of egg-carrying females of gammaridean Gammarus locusta as their egg reared on periphyton
(Kraufvelin et al. 2006). On the other hand, eutrophication
causes shifts in plant communities by qualitative changes in
the dominance of perennial macroalgae and seagrasses toward the dominance of ephemeral macroalgae and pelagic
microalgae (Borum 1996), which may lead to pronounced
changes in habitat quality for animals such as the disappearance of the scallops when seagrasses were replaced by macroalgae (Kennish et al. 2007).
3.4.2 Effect on Trophic Linkage
Eutrophication plays a significant role in trophic linkage
between pelagic and benthic communities in the coastal
waters. In Lake Tahoe, zoobenthos obtained 27 % of their
energy from phytoplankton sources before eutrophication,
while after 43 years of eutrophication, they obtained 62 %
from pelagic sources.
1. This led to a change in the feeding habit of higher consumers, such as the benthic fish (Catostomus tahoensis)
which now derives ∼ 21 % of its energy from pelagic primary production source (Chandra et al. 2005).
2. Intermediate link between the water column and demersal
fishes could also be affected by eutrophication and will
impact (as prey) on the demersal fish production.
In the Neuse River Estuary, North Carolina, the low oxygen
level in bottom-water caused dramatic decrease (over 90 %)
in abundance of the clam Macoma balthica, a key prey item
for fishes and crabs, which resulted in a shift in croaker diet
away from clams to less nutritional items such as plant and
detrital material (Powers et al. 2005).
Eutrophication can indirectly affect the trophic linkage in
the marine environment. Increasing turbidity with eutrophication in a Baltic inlet, led to a shift from a perch dominated community to a cyprinid dominated one, because perch
growth was reduced in eutrophic areas, especially in the
size range owing to change from foraging on zooplankton to
benthic organisms (Sandstrom and Karas 2002). The growth
rates of yellow perch in Lake Erie’s declined sharply at the
hypereutrophy conditions owing to food limitation related to
a reduced size of their benthic prey (Hayward and Margraf
1987). In the Kattegat, the diets of five dominant bottomfeeding fish species, Atlantic cod (Gadus morhua), whiting
(Merlangius merlangus), plaice (Pleuronectes platessa), dab
(Limanda limanda), and American plaice (Hippoglossoides
platessoides) showed a general long-term change owing
to changes in species composition of benthic macrofauna,
whereas several infaunal species increased in dietary importance during recent hypoxia, and reduction of epibenthic
crustaceans was observed in the fish diet (Pihl 2011).
In shallow coastal areas along the Swedish west coast, a
general proliferation of filamentous algae caused less successful foraging areas for cod and consequently led to considerable alterations in trophic relationships (Isaksson et al.
1994). The frequent mass mortality of the benthos under anoxia conditions in the Bay of Somme, France led to the disappearance of benthic bivalve Cerastoderma edule and the
proliferation of the polychaete Pygospio elegans and consequently to apparent higher-up in the food chain through
changes in the diet of the two main predators of the bivalve,
the oystercatcher Haematopus ostralegus and the common
gull Larus canus (Desprez et al. 1992).
3.4.3 Effect on Seagrasses
Eutrophication is one of the factors contributing to the decline of seagrass ecosystems worldwide (Richardson 2006).
Severe shading and light attenuation caused by blooms of
both macroalgae and phytoplankton hinder photosynthetic
processes in benthic plants and sea grass habitats (Walker
et al. 1999), that reached at some coastal areas > 70 % of the
seagrass habitats (Lamote and Dunton 2006). Water turbidity
also negatively effects the depth distribution of macroalgae
(Fucus vesiculosus), while dense accumulations of macroalgae form thick canopies on seagrass beds and smother
shellfish and other invertebrate fauna inhabiting the beds
(McGlathery et al. 2007). Significant losses of seagrass beds
associated with the algal bloom of the persistent brown tides
have been reported in Laguna Madre (Cloern 2001), and an
increase of epiphyte loads in some mid-Atlantic areas (Silberstein et al. 1986), which represents the major mechanism
of seagrass die-off worldwide (Bricker et al. 1999).
High nutrients levels may lead to a disturbance in nitrogen and phosphorus metabolism in seagrass (Touchette and
Burkholder 2000), and consequently cause a change in plant
communities relative to their responses to the different nutrients, such as the toxicity of ammonium to the eelgrass
Zostera marina (Van Katwijk et al. 1997). Strong inverse
relationship was reported between eelgrass habitat and nitrogen concentration in the overlying water in Danish estuaries (Risk et al. 1995), and between the global declines of
seagrasses and depletion of dissolved silicon (Herman et al.
1996).
3 Effects of Eutrophication
cies of annual algae or filter feeders, and community diversity declined consistently by 24–46 % in the Northwest Atlantic and eutrophied sites in the Baltic Sea (Worm 2006).
Under hypoxic conditions owing to decomposing algal
mat on shallow sandy bottoms in the northern Baltic Sea,
the bivalve Macoma balthica emerged at the sediment surface, and exposed to epibenthic predators, such as the isopod
Saduria entomon, the brown-shrimp Crangon crungon and
the flounder Platichthysflesus (Norkko and Bonsdorff 2008).
However, the intensive growth of periphytic algae caused an
increase in the number of egg-carrying females of gammaridean Gammarus locusta as their egg reared on periphyton
(Kraufvelin et al. 2006). On the other hand, eutrophication
causes shifts in plant communities by qualitative changes in
the dominance of perennial macroalgae and seagrasses toward the dominance of ephemeral macroalgae and pelagic
microalgae (Borum 1996), which may lead to pronounced
changes in habitat quality for animals such as the disappearance of the scallops when seagrasses were replaced by macroalgae (Kennish et al. 2007).
3.4.2 Effect on Trophic Linkage
Eutrophication plays a significant role in trophic linkage
between pelagic and benthic communities in the coastal
waters. In Lake Tahoe, zoobenthos obtained 27 % of their
energy from phytoplankton sources before eutrophication,
while after 43 years of eutrophication, they obtained 62 %
from pelagic sources.
1. This led to a change in the feeding habit of higher consumers, such as the benthic fish (Catostomus tahoensis)
which now derives ∼ 21 % of its energy from pelagic primary production source (Chandra et al. 2005).
2. Intermediate link between the water column and demersal
fishes could also be affected by eutrophication and will
impact (as prey) on the demersal fish production.
In the Neuse River Estuary, North Carolina, the low oxygen
level in bottom-water caused dramatic decrease (over 90 %)
in abundance of the clam Macoma balthica, a key prey item
for fishes and crabs, which resulted in a shift in croaker diet
away from clams to less nutritional items such as plant and
detrital material (Powers et al. 2005).
Eutrophication can indirectly affect the trophic linkage in
the marine environment. Increasing turbidity with eutrophication in a Baltic inlet, led to a shift from a perch dominated community to a cyprinid dominated one, because perch
growth was reduced in eutrophic areas, especially in the
size range owing to change from foraging on zooplankton to
benthic organisms (Sandstrom and Karas 2002). The growth
rates of yellow perch in Lake Erie’s declined sharply at the
hypereutrophy conditions owing to food limitation related to
a reduced size of their benthic prey (Hayward and Margraf
1987). In the Kattegat, the diets of five dominant bottomfeeding fish species, Atlantic cod (Gadus morhua), whiting
(Merlangius merlangus), plaice (Pleuronectes platessa), dab
(Limanda limanda), and American plaice (Hippoglossoides
platessoides) showed a general long-term change owing
to changes in species composition of benthic macrofauna,
whereas several infaunal species increased in dietary importance during recent hypoxia, and reduction of epibenthic
crustaceans was observed in the fish diet (Pihl 2011).
In shallow coastal areas along the Swedish west coast, a
general proliferation of filamentous algae caused less successful foraging areas for cod and consequently led to considerable alterations in trophic relationships (Isaksson et al.
1994). The frequent mass mortality of the benthos under anoxia conditions in the Bay of Somme, France led to the disappearance of benthic bivalve Cerastoderma edule and the
proliferation of the polychaete Pygospio elegans and consequently to apparent higher-up in the food chain through
changes in the diet of the two main predators of the bivalve,
the oystercatcher Haematopus ostralegus and the common
gull Larus canus (Desprez et al. 1992).
3.4.3 Effect on Seagrasses
Eutrophication is one of the factors contributing to the decline of seagrass ecosystems worldwide (Richardson 2006).
Severe shading and light attenuation caused by blooms of
both macroalgae and phytoplankton hinder photosynthetic
processes in benthic plants and sea grass habitats (Walker
et al. 1999), that reached at some coastal areas > 70 % of the
seagrass habitats (Lamote and Dunton 2006). Water turbidity
also negatively effects the depth distribution of macroalgae
(Fucus vesiculosus), while dense accumulations of macroalgae form thick canopies on seagrass beds and smother
shellfish and other invertebrate fauna inhabiting the beds
(McGlathery et al. 2007). Significant losses of seagrass beds
associated with the algal bloom of the persistent brown tides
have been reported in Laguna Madre (Cloern 2001), and an
increase of epiphyte loads in some mid-Atlantic areas (Silberstein et al. 1986), which represents the major mechanism
of seagrass die-off worldwide (Bricker et al. 1999).
High nutrients levels may lead to a disturbance in nitrogen and phosphorus metabolism in seagrass (Touchette and
Burkholder 2000), and consequently cause a change in plant
communities relative to their responses to the different nutrients, such as the toxicity of ammonium to the eelgrass
Zostera marina (Van Katwijk et al. 1997). Strong inverse
relationship was reported between eelgrass habitat and nitrogen concentration in the overlying water in Danish estuaries (Risk et al. 1995), and between the global declines of
seagrasses and depletion of dissolved silicon (Herman et al.
1996).