34
M. M. Dorgham
devastating effects on the benthic macrofauna. In several
parts of the Baltic Sea, the benthic fauna was pronouncedly
affected by the anoxia conditions since the 1950s and 1960s
as a result of increased organic enrichment, sometimes below
70 m depth, with a total loss of benthic macrofaunal biomass
of 3 million tonnes (Karin et al. 2002).
Accumulations of attached and/or drift macroalgae in
shallow waters cause changes in bed roughness and trapping
of fine-grained sediments and negatively impact survival
of invertebrate recruits, exclusion of some deposit-feeding
and suspension feeding invertebrates such as amphipods
and spionid polychaetes, and reduced abundance of invertebrate prey for fishes and shorebirds (Raffaelli et al. 1998).
In tropical and subtropical waters, the enhanced macroalgal
production led to the overgrowth and replacement of corals
(Lapointe 1997) and caused a change in the populations of
benthic invertebrates (Diaz and Rosenberg 1995).
The effect of eutrophication on the benthic communities appeared in animal-community responses to change in
organic enrichment (Pearson and Rosenberg 1978), such as
the increased benthic biomass in the Danish estuaries (Josefson and Rasmussen 2000), changes in species composition
of macrozoobenthos in the Dutch Wadden Sea from 1970 to
1990 and in the Oslofjord and Skagerrak (Rosenberg et al.
1987), a sharp decrease in the macrozoobenthic biomass
since the 1980s in the East China Sea (Wang 2006).
The hypoxia condition in bottom waters causes the escape
of sensitive demersal fishes (cod, whiting) and other benthic
fishes (dabs, flounder); mortality of bivalves, echinoderms
and crustaceans; and extreme loss of benthic diversity (Gray
1992) which led to changes in the diet of bottom-feeding
fishes as well as shift in dominance among demersal fish
species in Kattegat (Pihl 1994).
The long-term eutrophication (1980–2000) caused dramatic changes in the Mondego estuary (Portugal), leading
to a decline in seagrass beds and in species richness and
replacement of herbivores by detritivores (Cardoso et al.
2004). Meanwhile, during (1968–1971 and 1993), in shallow coastal areas of the Baltic Sea, eutrophication caused
significant change in the shoot density and biomass of
the sea grass Zostera marina, associated with significant
increase of total abundance and biomass of zoobenthos
(Boström et al. 2002)
In the southern Kattegat, the effects of eutrophication resulted in the change of macrophytes above halocline from
Fucus spp. to filamentous green algae and mortality of benthic macro fauna (mainly bivalves) in most years and seasons. Meanwhile, below the halocline, hypoxic conditions
caused the disappearance of fish, immobilization and/or
death of lobsters, and emergence of benthic infaunal species
from the sediment (Baden et al. 1990).
Increased macroalgal biomass and decreased oxygen concentrations in the bottom waters led to mortalities of benthic
animals and decreased fish catches in the Baltic, Swedish
and Danish coastal areas in the Kattegat and the Belt Sea
as well as in the Danish North Sea coast (Rosenberg 1985).
The hypoxia conditions induced by eutrophication inhibited growth of benthic animals, particularly sediment-dwelling invertebrates, such as the polychaete Nereis (Hediste) diversicolor, the bivalve Abra alba and the brittle star Amphiura filiformis (Hylland et al. 1996). In the lower York River,
Chesapeake Bay, USA, extensive hypoxia caused mass mortalities of benthic organisms on the inner continental shelves
of the New York Bight and the northern Gulf of Mexico off
Louisiana and Texas (Boesch and Rabalais 1991). In addition to mass mortality of the benthos in the Bay of Somme,
English Channel, anoxia conditions led to the disappearance
of the common cockle Cerastoderma edule and proliferation
of the polychaete Pygospio elegans as well as 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).
In Korean coastal waters, low dissolved oxygen and organic enrichment caused defaunation during summer hypoxia, with the persistence of the polychaetes, Sigambra
tentaculata, Mesochaetopterus sp., and Lumbrineris longifolia (Lim et al. 2006), while in the Aland Islands, northern
Baltic Sea, long-term eutrophication caused a drastic change
in abundance and biomass of the benthic communities and
the appearance of a new polychaete species Marenzelleria
viridis over the entire region, which became among the most
dominant benthic assemblages (Perus and Bonsdorff 2004).
Declined macroinvertebrate density and a more variable species composition under eutrophication were also reported in
Peel–Harvey Estuary and the Indian Ocean, associated with
proportionally less abundant crustaceans and high abundant
Polychaetes (Wildsmith et al. 2009).
Excessive nutrient loading has led to the decline and disappearance of rooted vegetation that is critically important to
the survival of animals such as certain zooplankton, finfish,
and/or shellfish which graze on algae (Anderson et al. 2002).
However, increase of algal growth/organic production rates
led to changes in the benthic community structure, such as
replacement of hermatypic corals with coralline algae, filamentous algae, macroalgae, and/or a variety of filter feeders
(Bell et al. 2007), and increase of bioerosion in some forms
(Hutchings et al. 2005).
Under the increase of drifting mats of annual algae in
the Baltic Sea, benthic community reduced significantly in
the species number and the dominance pattern, such as the
significant reduction (> 70 %) of the spat settlement of the
dominating bivalve Macoma balthica, complete disappearance of the dominating polychaetes Pygospio elegans and
Manayunkia aestuarina, and great increase in numbers of
the amphipod Corophium volutator (Bonsdorff 1992). Also,
rocky shore communities became dominated by single spe-
M. M. Dorgham
devastating effects on the benthic macrofauna. In several
parts of the Baltic Sea, the benthic fauna was pronouncedly
affected by the anoxia conditions since the 1950s and 1960s
as a result of increased organic enrichment, sometimes below
70 m depth, with a total loss of benthic macrofaunal biomass
of 3 million tonnes (Karin et al. 2002).
Accumulations of attached and/or drift macroalgae in
shallow waters cause changes in bed roughness and trapping
of fine-grained sediments and negatively impact survival
of invertebrate recruits, exclusion of some deposit-feeding
and suspension feeding invertebrates such as amphipods
and spionid polychaetes, and reduced abundance of invertebrate prey for fishes and shorebirds (Raffaelli et al. 1998).
In tropical and subtropical waters, the enhanced macroalgal
production led to the overgrowth and replacement of corals
(Lapointe 1997) and caused a change in the populations of
benthic invertebrates (Diaz and Rosenberg 1995).
The effect of eutrophication on the benthic communities appeared in animal-community responses to change in
organic enrichment (Pearson and Rosenberg 1978), such as
the increased benthic biomass in the Danish estuaries (Josefson and Rasmussen 2000), changes in species composition
of macrozoobenthos in the Dutch Wadden Sea from 1970 to
1990 and in the Oslofjord and Skagerrak (Rosenberg et al.
1987), a sharp decrease in the macrozoobenthic biomass
since the 1980s in the East China Sea (Wang 2006).
The hypoxia condition in bottom waters causes the escape
of sensitive demersal fishes (cod, whiting) and other benthic
fishes (dabs, flounder); mortality of bivalves, echinoderms
and crustaceans; and extreme loss of benthic diversity (Gray
1992) which led to changes in the diet of bottom-feeding
fishes as well as shift in dominance among demersal fish
species in Kattegat (Pihl 1994).
The long-term eutrophication (1980–2000) caused dramatic changes in the Mondego estuary (Portugal), leading
to a decline in seagrass beds and in species richness and
replacement of herbivores by detritivores (Cardoso et al.
2004). Meanwhile, during (1968–1971 and 1993), in shallow coastal areas of the Baltic Sea, eutrophication caused
significant change in the shoot density and biomass of
the sea grass Zostera marina, associated with significant
increase of total abundance and biomass of zoobenthos
(Boström et al. 2002)
In the southern Kattegat, the effects of eutrophication resulted in the change of macrophytes above halocline from
Fucus spp. to filamentous green algae and mortality of benthic macro fauna (mainly bivalves) in most years and seasons. Meanwhile, below the halocline, hypoxic conditions
caused the disappearance of fish, immobilization and/or
death of lobsters, and emergence of benthic infaunal species
from the sediment (Baden et al. 1990).
Increased macroalgal biomass and decreased oxygen concentrations in the bottom waters led to mortalities of benthic
animals and decreased fish catches in the Baltic, Swedish
and Danish coastal areas in the Kattegat and the Belt Sea
as well as in the Danish North Sea coast (Rosenberg 1985).
The hypoxia conditions induced by eutrophication inhibited growth of benthic animals, particularly sediment-dwelling invertebrates, such as the polychaete Nereis (Hediste) diversicolor, the bivalve Abra alba and the brittle star Amphiura filiformis (Hylland et al. 1996). In the lower York River,
Chesapeake Bay, USA, extensive hypoxia caused mass mortalities of benthic organisms on the inner continental shelves
of the New York Bight and the northern Gulf of Mexico off
Louisiana and Texas (Boesch and Rabalais 1991). In addition to mass mortality of the benthos in the Bay of Somme,
English Channel, anoxia conditions led to the disappearance
of the common cockle Cerastoderma edule and proliferation
of the polychaete Pygospio elegans as well as 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).
In Korean coastal waters, low dissolved oxygen and organic enrichment caused defaunation during summer hypoxia, with the persistence of the polychaetes, Sigambra
tentaculata, Mesochaetopterus sp., and Lumbrineris longifolia (Lim et al. 2006), while in the Aland Islands, northern
Baltic Sea, long-term eutrophication caused a drastic change
in abundance and biomass of the benthic communities and
the appearance of a new polychaete species Marenzelleria
viridis over the entire region, which became among the most
dominant benthic assemblages (Perus and Bonsdorff 2004).
Declined macroinvertebrate density and a more variable species composition under eutrophication were also reported in
Peel–Harvey Estuary and the Indian Ocean, associated with
proportionally less abundant crustaceans and high abundant
Polychaetes (Wildsmith et al. 2009).
Excessive nutrient loading has led to the decline and disappearance of rooted vegetation that is critically important to
the survival of animals such as certain zooplankton, finfish,
and/or shellfish which graze on algae (Anderson et al. 2002).
However, increase of algal growth/organic production rates
led to changes in the benthic community structure, such as
replacement of hermatypic corals with coralline algae, filamentous algae, macroalgae, and/or a variety of filter feeders
(Bell et al. 2007), and increase of bioerosion in some forms
(Hutchings et al. 2005).
Under the increase of drifting mats of annual algae in
the Baltic Sea, benthic community reduced significantly in
the species number and the dominance pattern, such as the
significant reduction (> 70 %) of the spat settlement of the
dominating bivalve Macoma balthica, complete disappearance of the dominating polychaetes Pygospio elegans and
Manayunkia aestuarina, and great increase in numbers of
the amphipod Corophium volutator (Bonsdorff 1992). Also,
rocky shore communities became dominated by single spe-