177
Getting into a stressed state due to some kind
of external effect corals dump their symbiont
companion making their body transparent and
their snow-white skeleton visible through their
tissues. Without algae corals can neither grow nor
breed thus they will die. As a result the building
of the calcareous skeleton will be stopped as well
and the entire living system will decay. Fading
corals do not mean the final death of the entire
colony. According to observations their regenerating capability is very high; however, this does
not mean that they could bear any strong effects.
Since the 1980s fading—a local problem at that
time—has been observed in almost every coral
region of the world. The main reasons behind
coral decline are discussed below based on Bright
(2000) and WWF (2015).
Since water temperature measurements at
coral regions yielded consecutively higher values
climate change was made responsible for coral
decline fairly soon. Water temperatures rose
above 28 °C first in the tropical areas of the
Pacific Ocean in the beginning of the 1980s and
this caused mass fading in coral reefs and the
process continued in the Indian Ocean as well.
Further research, however, proved that temperature change alone could not cause such
degree of coral reef fading. The primary suspect
was tropical rainforest clearing then.
Deforestation became very intense in the entire
tropical zone in recent years resulting in intensified soil erosion. Due to the increased load
brought by rivers, the amount of fine sediment
deposited on nearshore coral reefs also increased
abruptly. Corals tried to get rid of the sediments—
not always successfully—as sediment grains prevented light from reaching the algae living in
symbiosis with the corals. As a result photosynthesis ceased leading to the death of corals.
Especially clearings in mangrove forests
caused significant damage to coral reefs since
those forests developed along the coast and provided natural shelter from the erosion of waves.
Between 1980 and 2005 the area of mangrove
forests decreased by 19% (WWF 2015). The
most serious consequences were brought about
by forest clearings eliminating both mangrove
forests and rainforests in the catchment area of
rivers and streams flowing into the sea. For example, tree cutting in the catchment area and shores
of a bay in the Philippines increased erosion to
200-fold.
While it was proved that one of the main reasons of coral fading is forest clearing in certain
regions, many other harmful effects were also
revealed.
Coral decline was also contributed by economic development and associated settlement
growth on the coast and also by the lack of
municipal and industrial sewage treatment. Water
pollution in the vicinity of major cities on the
coast reduced the distance of sight in the water in
places to a quarter than before. This strongly
reduced the photosynthesis of algae living
together with the corals and even hindered it in
water layers deeper than 5–6 m.
Sometimes plant nutrients trigger the process
of cultural eutrophication. This could result in the
over proliferation of free algae (not living in symbiosis) reducing the amount of sunlight reaching
the corals.
Coral reefs along busy sea routes suffer from
oil pollution and occasionally from the toxic
effect of chemicals used for diffusing oil flowing
into the sea. These pollutants regularly get into
the ocean in the Persian Gulf, the Red Sea, the
Gulf of Mexico and in the vicinity of the straits
among the islands of Indonesia, etc. Shipping
may destroy some coral reefs with their anchors
demolishing them.
Although it has been banned worldwide, in
some countries blast fishing is still practiced
along the shores of the Pacific Ocean. This
extremely brutal method kills not only species to
be fished but every other living being and destroys
entire coral colonies. According to an estimation
this method has damaged 15–20% of the coral
reefs around the Philippines.
Other, much more indulgent ways of fishing
may damage the communities of coral reefs as
well. For example, trawling destroys the breeding and/or hiding places of many marine living
beings.
In many coastal countries and islands coral
reefs are mined for their building material. In Sri
Lanka and around the coasts of India and in
4.4 Changes in the Biosphere
Getting into a stressed state due to some kind
of external effect corals dump their symbiont
companion making their body transparent and
their snow-white skeleton visible through their
tissues. Without algae corals can neither grow nor
breed thus they will die. As a result the building
of the calcareous skeleton will be stopped as well
and the entire living system will decay. Fading
corals do not mean the final death of the entire
colony. According to observations their regenerating capability is very high; however, this does
not mean that they could bear any strong effects.
Since the 1980s fading—a local problem at that
time—has been observed in almost every coral
region of the world. The main reasons behind
coral decline are discussed below based on Bright
(2000) and WWF (2015).
Since water temperature measurements at
coral regions yielded consecutively higher values
climate change was made responsible for coral
decline fairly soon. Water temperatures rose
above 28 °C first in the tropical areas of the
Pacific Ocean in the beginning of the 1980s and
this caused mass fading in coral reefs and the
process continued in the Indian Ocean as well.
Further research, however, proved that temperature change alone could not cause such
degree of coral reef fading. The primary suspect
was tropical rainforest clearing then.
Deforestation became very intense in the entire
tropical zone in recent years resulting in intensified soil erosion. Due to the increased load
brought by rivers, the amount of fine sediment
deposited on nearshore coral reefs also increased
abruptly. Corals tried to get rid of the sediments—
not always successfully—as sediment grains prevented light from reaching the algae living in
symbiosis with the corals. As a result photosynthesis ceased leading to the death of corals.
Especially clearings in mangrove forests
caused significant damage to coral reefs since
those forests developed along the coast and provided natural shelter from the erosion of waves.
Between 1980 and 2005 the area of mangrove
forests decreased by 19% (WWF 2015). The
most serious consequences were brought about
by forest clearings eliminating both mangrove
forests and rainforests in the catchment area of
rivers and streams flowing into the sea. For example, tree cutting in the catchment area and shores
of a bay in the Philippines increased erosion to
200-fold.
While it was proved that one of the main reasons of coral fading is forest clearing in certain
regions, many other harmful effects were also
revealed.
Coral decline was also contributed by economic development and associated settlement
growth on the coast and also by the lack of
municipal and industrial sewage treatment. Water
pollution in the vicinity of major cities on the
coast reduced the distance of sight in the water in
places to a quarter than before. This strongly
reduced the photosynthesis of algae living
together with the corals and even hindered it in
water layers deeper than 5–6 m.
Sometimes plant nutrients trigger the process
of cultural eutrophication. This could result in the
over proliferation of free algae (not living in symbiosis) reducing the amount of sunlight reaching
the corals.
Coral reefs along busy sea routes suffer from
oil pollution and occasionally from the toxic
effect of chemicals used for diffusing oil flowing
into the sea. These pollutants regularly get into
the ocean in the Persian Gulf, the Red Sea, the
Gulf of Mexico and in the vicinity of the straits
among the islands of Indonesia, etc. Shipping
may destroy some coral reefs with their anchors
demolishing them.
Although it has been banned worldwide, in
some countries blast fishing is still practiced
along the shores of the Pacific Ocean. This
extremely brutal method kills not only species to
be fished but every other living being and destroys
entire coral colonies. According to an estimation
this method has damaged 15–20% of the coral
reefs around the Philippines.
Other, much more indulgent ways of fishing
may damage the communities of coral reefs as
well. For example, trawling destroys the breeding and/or hiding places of many marine living
beings.
In many coastal countries and islands coral
reefs are mined for their building material. In Sri
Lanka and around the coasts of India and in
4.4 Changes in the Biosphere