36
M. M. Dorgham
The hypoxia conditions in the northern Barnegat BayLittle Egg Harbor Estuary appeared to be associated with decreased biomass, density, and areal cover of the submerged
aquatic vegetation from 2004 to 2006 (Kennish et al. 2008),
with a degradation of about 50–87.8 % (Kennish et al. 2007).
In contrast to the degrading effect, eutrophication may
play an enhancing role in the growth of seagrasses. A gradual
increase in seagrass distribution was reported since the 1950s
at Green Island owing to regional increase in anthropogenic
nutrient (Udy et al. 1999), while along the north Queensland
coast the tissue nutrient status of the seagrass Halophila ovalis has increased over a 20-year period with increasing fertilizer usage (Mellors et al. 2005).
Furthermore, eutrophication is a principal factor promoting massive accumulations of macroalgae worldwide, such
as in Tunis and Venice Lagoons (Sfriso et al. 1993), Saint
Brieuc Bay and other open coastal systems in France (Menesguen 1992), Waquoit Bay and other urbanized embayments
in the northeastern USA (Valiela et al. 1997) and the Peel
Harvey estuary in western Australia (McComb et al. 1981).
In an intertidal area of the German North Sea coast, eutrophication was associated with pronounced increase in the
macroalgae cover (Chlorophyta, Ulvaceae) in 1990–1992,
sometimes to 30–60 % of the tidal flats (Kolbe et al. 1995).
3.4.4 Effect on Coral Reefs
Eutrophication exhibited variable effects on the corals, such
as recruitment, diversity, collapse of coral reef community,
trophic structures, mortality, bioerosion, associated communities, decrease in skeleton density, misshaped aragonite
structure, and bioerosion. In the Whitsunday Islands, corals
could recruit in eutrophic areas, near the mouths of rivers,
but the recruits failed to survive (Cooper et al. 2007). Along
the leeward coast, west of Barbados, the effects of eutrophication processes were directly and/or indirectly affecting the
community structure of scleractinian coral assemblages (Tomascik and Sander 1987b), since eutrophication can restrict
coral growth and reproduction and may cause virtual extinction of some species, particularly sensitive to eutrophication,
such as Acropora palmata (Bell and Tomascik 1993), owing
to higher mortality of juveniles on the eutrophic reefs than
the less eutrophic reefs (Wittenberg and Hunte 1992). On
the other hand, under nutrient enrichment from upwelling
waters, juvenile scleractinian corals were outcompeted for
space by opportunistic algae and tunicates, resulting in reduced survivorship (Birkeland 1977).
The diversity of hard coral species and algal cover was
reduced in the region between Cardwell and Cape Flattery
owing to increased effect of land-based effluents (DeVantier
et al. 2006), as high nutrient levels may exhibit different impacts on coral communities (Fabricius 2007), such as collapse of coral reef community (Smith et al. 1981), bioerosion (Risk et al. 1995), altered biodiversity (van Woesik et al.
1999), reduced recruitment and modified trophic structures
(Fabricius 2005).
The organic compounds released from nutrient-induced
algal blooms promote microbial activity on coral surfaces
and cause coral mortality (Smith 2006), while synergistic
effect of both the dissolved organic matter and rates of bioerosion has a pronounced role in reef degradation (Kline
et al. 2006). In Kaneohe Bay, Hawaii, intensive biological
activities such as phytoplankton blooms associating eutrophication led to loss of live corals (Caperon et al. 1971) and
increase of filter and deposit feeders such as tube worms and
sponges (Kinsey and Devies 19) and increase in cryptofauna
biomass (Brock and Smith 1983).
Essential shifts in the physicochemical and biological
environment of coral reef ecosystems are usually associated with the eutrophication process (Tomascik and Sander
1987b) and cause environmental disturbance to coral reef
(Hoegh-Guldberg et al. 2007) resulting in reductions in live
coral cover, and concomitantly effects on the diversity and
abundance of other reef-associated communities (Pratchett
et al. 2008).
Nutrient enrichment causes the shift in species composition of the coral reef-associated community (Done 1992) as
larger, slow-growing organisms, surviving in nutrient-poor
waters are replaced by smaller, rapidly growing species in
elevated nutrient concentrations (Birkeland 1988). In addition, the intensive algal growth overgrows and outcompetes
corals for hard substratum and hinders coral growth (Larkum
and Steven 1994). In the Gulf of Oman, large-scale HABs
of the dinoflagellate Cochlodinium polykrikoides in October/
November 2008 caused the complete loss of the branching
corals, Pocillopora and Acropora spp., and substantial reductions in the abundance, richness, and trophic diversity
of the associated coral reef fish communities (Bauman et al.
2010).
Since numerous coral reefs prefer to grow in nutrient-poor
waters, eutrophication and siltation have severely stressed
many fringing and offshore reefs (Brown 1997), particularly on long-term scale (Kramarsky-Winter et al. 2009), and
caused physiological changes in growth and skeletal tensile
strength, decrease of reproductive effort, and a reduced ability to withstand disease (Loya 2007). On the other hand, high
levels of nutrients demonstrate a pronounced effect on the
coral community (Birkeland 1988) reflected on a number
of biochemical parameters (Larkum and Steven 1994) such
as changes in metabolism, density of the zooxanthellae and
chlorophyll concentration per cell (Muscatine et al 1989),
decrease in skeleton density, and misshaped aragonite structure (Strambler et al. 1991). In addition, high concentration
of phosphates can inhibit coral reef calcification by more
than 50 % (Kinsey and Davies 1979) and suppress benthic
M. M. Dorgham
The hypoxia conditions in the northern Barnegat BayLittle Egg Harbor Estuary appeared to be associated with decreased biomass, density, and areal cover of the submerged
aquatic vegetation from 2004 to 2006 (Kennish et al. 2008),
with a degradation of about 50–87.8 % (Kennish et al. 2007).
In contrast to the degrading effect, eutrophication may
play an enhancing role in the growth of seagrasses. A gradual
increase in seagrass distribution was reported since the 1950s
at Green Island owing to regional increase in anthropogenic
nutrient (Udy et al. 1999), while along the north Queensland
coast the tissue nutrient status of the seagrass Halophila ovalis has increased over a 20-year period with increasing fertilizer usage (Mellors et al. 2005).
Furthermore, eutrophication is a principal factor promoting massive accumulations of macroalgae worldwide, such
as in Tunis and Venice Lagoons (Sfriso et al. 1993), Saint
Brieuc Bay and other open coastal systems in France (Menesguen 1992), Waquoit Bay and other urbanized embayments
in the northeastern USA (Valiela et al. 1997) and the Peel
Harvey estuary in western Australia (McComb et al. 1981).
In an intertidal area of the German North Sea coast, eutrophication was associated with pronounced increase in the
macroalgae cover (Chlorophyta, Ulvaceae) in 1990–1992,
sometimes to 30–60 % of the tidal flats (Kolbe et al. 1995).
3.4.4 Effect on Coral Reefs
Eutrophication exhibited variable effects on the corals, such
as recruitment, diversity, collapse of coral reef community,
trophic structures, mortality, bioerosion, associated communities, decrease in skeleton density, misshaped aragonite
structure, and bioerosion. In the Whitsunday Islands, corals
could recruit in eutrophic areas, near the mouths of rivers,
but the recruits failed to survive (Cooper et al. 2007). Along
the leeward coast, west of Barbados, the effects of eutrophication processes were directly and/or indirectly affecting the
community structure of scleractinian coral assemblages (Tomascik and Sander 1987b), since eutrophication can restrict
coral growth and reproduction and may cause virtual extinction of some species, particularly sensitive to eutrophication,
such as Acropora palmata (Bell and Tomascik 1993), owing
to higher mortality of juveniles on the eutrophic reefs than
the less eutrophic reefs (Wittenberg and Hunte 1992). On
the other hand, under nutrient enrichment from upwelling
waters, juvenile scleractinian corals were outcompeted for
space by opportunistic algae and tunicates, resulting in reduced survivorship (Birkeland 1977).
The diversity of hard coral species and algal cover was
reduced in the region between Cardwell and Cape Flattery
owing to increased effect of land-based effluents (DeVantier
et al. 2006), as high nutrient levels may exhibit different impacts on coral communities (Fabricius 2007), such as collapse of coral reef community (Smith et al. 1981), bioerosion (Risk et al. 1995), altered biodiversity (van Woesik et al.
1999), reduced recruitment and modified trophic structures
(Fabricius 2005).
The organic compounds released from nutrient-induced
algal blooms promote microbial activity on coral surfaces
and cause coral mortality (Smith 2006), while synergistic
effect of both the dissolved organic matter and rates of bioerosion has a pronounced role in reef degradation (Kline
et al. 2006). In Kaneohe Bay, Hawaii, intensive biological
activities such as phytoplankton blooms associating eutrophication led to loss of live corals (Caperon et al. 1971) and
increase of filter and deposit feeders such as tube worms and
sponges (Kinsey and Devies 19) and increase in cryptofauna
biomass (Brock and Smith 1983).
Essential shifts in the physicochemical and biological
environment of coral reef ecosystems are usually associated with the eutrophication process (Tomascik and Sander
1987b) and cause environmental disturbance to coral reef
(Hoegh-Guldberg et al. 2007) resulting in reductions in live
coral cover, and concomitantly effects on the diversity and
abundance of other reef-associated communities (Pratchett
et al. 2008).
Nutrient enrichment causes the shift in species composition of the coral reef-associated community (Done 1992) as
larger, slow-growing organisms, surviving in nutrient-poor
waters are replaced by smaller, rapidly growing species in
elevated nutrient concentrations (Birkeland 1988). In addition, the intensive algal growth overgrows and outcompetes
corals for hard substratum and hinders coral growth (Larkum
and Steven 1994). In the Gulf of Oman, large-scale HABs
of the dinoflagellate Cochlodinium polykrikoides in October/
November 2008 caused the complete loss of the branching
corals, Pocillopora and Acropora spp., and substantial reductions in the abundance, richness, and trophic diversity
of the associated coral reef fish communities (Bauman et al.
2010).
Since numerous coral reefs prefer to grow in nutrient-poor
waters, eutrophication and siltation have severely stressed
many fringing and offshore reefs (Brown 1997), particularly on long-term scale (Kramarsky-Winter et al. 2009), and
caused physiological changes in growth and skeletal tensile
strength, decrease of reproductive effort, and a reduced ability to withstand disease (Loya 2007). On the other hand, high
levels of nutrients demonstrate a pronounced effect on the
coral community (Birkeland 1988) reflected on a number
of biochemical parameters (Larkum and Steven 1994) such
as changes in metabolism, density of the zooxanthellae and
chlorophyll concentration per cell (Muscatine et al 1989),
decrease in skeleton density, and misshaped aragonite structure (Strambler et al. 1991). In addition, high concentration
of phosphates can inhibit coral reef calcification by more
than 50 % (Kinsey and Davies 1979) and suppress benthic