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M. M. Dorgham
3.1 Introduction
Eutrophication is a complex process which occurs both in
fresh and marine waters, where excessive development of
certain types of algae disturbs the aquatic ecosystems and
becomes a threat to animal and human health (European
Communities 2002). It is one of the most anthropogenic
sources of hazardous effect on the aquatic ecosystems. Several definitions of eutrophication have been proposed. For
example, eutrophication is defined as an increase in the rate
of supply of organic matter to an ecosystem, which is typically reflected by an increase in the primary production of
the system (EEA 2001). It is the enrichment of water by nutrients, especially compounds of nitrogen and phosphorous,
causing an accelerated growth of algae and higher forms of
plant life to produce an undesirable disturbance to the balance of organisms and the quality of the water (CEC 1991).
Two criteria for the evaluation of eutrophication are known;
the first, applied in European countries, is based on nutrient
concentrations to differentiate between two conditions of the
water quality: poor and bad (EEA 1999), and the second criterion, applicable in USA, is based on high chlorophyll a and
low oxygen saturation (Bricker et al. 1999).
The threat of eutrophication was first reported in freshwater ecosystems (Vollenweider 1976), and later, since the
early 1970s, in the coastal and marine ecosystems (Smith
2006). Numerous parts of the world marine habitats suffered
from acute eutrophication, for example, Chesapeake Bay in
USA, Inland Sea of Japan, the Black Sea, Chinese coastal
waters (Anderson et al. 2002), and southeastern Mediterranean (Dorgham 2011). It is among the most detrimental
of all human activities in coastal ecosystems (Heckjr and
Valentine 2007), causing coastal hypoxia and food-web-altering in many threatened areas (Levin et al. 2009).
Eutrophication as an environmental problem is distributed worldwide; within a few decades, numerous pristine, oligotrophic estuarine, and coastal waters have transformed to
eutrophic conditions, which, in several occasions have been
accompanied by epidemic harmful algal blooms (HABs;
Smayda 1990).
The effect of eutrophication is not restricted only to the
biological and ecological characteristics of the aquatic habitat, but may extend to cause severe social-economic losses
(Kumagai 2008). The deleterious effects of eutrophication
on the abiotic and biotic ecosystems will be discussed in the
following parts.
in nitrogen and phosphorus metabolism in seagrass and consequently cause a change in
plant communities. Coral reefs are affected by eutrophication in different aspects. The organic compounds released from algal blooms promote microbial activity on coral surfaces
and cause coral mortality, while synergistic effect of both the dissolved organic matter and
rates of bioerosion has a pronounced role in reef degradation. Harmful algal blooms caused
a complete loss of the branching corals, and substantial reductions in the abundance, richness, and trophic diversity of the associated coral reef fish communities. Eutrophication
and siltation have severely stressed many fringing and offshore reefs that prefer to grow
in nutrient-poor waters, and cause physiological changes in growth and skeletal strength,
decrease of reproductive effort, and a reduced ability to withstand disease. In many marine
eutrophic habitats, zooplankton community experienced a decline in species richness and
abundance, change in structure, size, reproduction rate, and feeding habits. Size change in
zooplankton occurs owing to the replacement of small species by another relatively large
species of the same group, while the structure may change because of the trophic relationship of zooplankton with their prey (primary producers) and predators (fishes). Although
benthic foraminiferans have been widely used as indicators of eutrophication in coastal
marine ecosystems, low species diversity and high population densities of several benthic
foraminiferans were reported in eutrophic area. On the other hand, smaller opportunistic
benthic foraminiferal species dominate in the coral reef ecosystems and lead to a decline
of larger endosymbiont-bearing taxa, while the hypoxia-tolerant foraminiferan species increased in abundance against the disappearance of the more sensitive species.
Keywords
Benthic life · Coral reefs · Eutrophication · Harmful algal blooms · Phytoplankton ·
Seagrasses · Trophic linkage · Zooplankton
M. M. Dorgham
3.1 Introduction
Eutrophication is a complex process which occurs both in
fresh and marine waters, where excessive development of
certain types of algae disturbs the aquatic ecosystems and
becomes a threat to animal and human health (European
Communities 2002). It is one of the most anthropogenic
sources of hazardous effect on the aquatic ecosystems. Several definitions of eutrophication have been proposed. For
example, eutrophication is defined as an increase in the rate
of supply of organic matter to an ecosystem, which is typically reflected by an increase in the primary production of
the system (EEA 2001). It is the enrichment of water by nutrients, especially compounds of nitrogen and phosphorous,
causing an accelerated growth of algae and higher forms of
plant life to produce an undesirable disturbance to the balance of organisms and the quality of the water (CEC 1991).
Two criteria for the evaluation of eutrophication are known;
the first, applied in European countries, is based on nutrient
concentrations to differentiate between two conditions of the
water quality: poor and bad (EEA 1999), and the second criterion, applicable in USA, is based on high chlorophyll a and
low oxygen saturation (Bricker et al. 1999).
The threat of eutrophication was first reported in freshwater ecosystems (Vollenweider 1976), and later, since the
early 1970s, in the coastal and marine ecosystems (Smith
2006). Numerous parts of the world marine habitats suffered
from acute eutrophication, for example, Chesapeake Bay in
USA, Inland Sea of Japan, the Black Sea, Chinese coastal
waters (Anderson et al. 2002), and southeastern Mediterranean (Dorgham 2011). It is among the most detrimental
of all human activities in coastal ecosystems (Heckjr and
Valentine 2007), causing coastal hypoxia and food-web-altering in many threatened areas (Levin et al. 2009).
Eutrophication as an environmental problem is distributed worldwide; within a few decades, numerous pristine, oligotrophic estuarine, and coastal waters have transformed to
eutrophic conditions, which, in several occasions have been
accompanied by epidemic harmful algal blooms (HABs;
Smayda 1990).
The effect of eutrophication is not restricted only to the
biological and ecological characteristics of the aquatic habitat, but may extend to cause severe social-economic losses
(Kumagai 2008). The deleterious effects of eutrophication
on the abiotic and biotic ecosystems will be discussed in the
following parts.
in nitrogen and phosphorus metabolism in seagrass and consequently cause a change in
plant communities. Coral reefs are affected by eutrophication in different aspects. The organic compounds released from algal blooms promote microbial activity on coral surfaces
and cause coral mortality, while synergistic effect of both the dissolved organic matter and
rates of bioerosion has a pronounced role in reef degradation. Harmful algal blooms caused
a complete loss of the branching corals, and substantial reductions in the abundance, richness, and trophic diversity of the associated coral reef fish communities. Eutrophication
and siltation have severely stressed many fringing and offshore reefs that prefer to grow
in nutrient-poor waters, and cause physiological changes in growth and skeletal strength,
decrease of reproductive effort, and a reduced ability to withstand disease. In many marine
eutrophic habitats, zooplankton community experienced a decline in species richness and
abundance, change in structure, size, reproduction rate, and feeding habits. Size change in
zooplankton occurs owing to the replacement of small species by another relatively large
species of the same group, while the structure may change because of the trophic relationship of zooplankton with their prey (primary producers) and predators (fishes). Although
benthic foraminiferans have been widely used as indicators of eutrophication in coastal
marine ecosystems, low species diversity and high population densities of several benthic
foraminiferans were reported in eutrophic area. On the other hand, smaller opportunistic
benthic foraminiferal species dominate in the coral reef ecosystems and lead to a decline
of larger endosymbiont-bearing taxa, while the hypoxia-tolerant foraminiferan species increased in abundance against the disappearance of the more sensitive species.
Keywords
Benthic life · Coral reefs · Eutrophication · Harmful algal blooms · Phytoplankton ·
Seagrasses · Trophic linkage · Zooplankton