Threats
 |
| Photographs
show coral that was healthy in 1975
are visibly sick by 1985, and dead
and broken by 1995. (Photographs
courtesy Phillip Dustan, College
of Charleston) |
Human activity continues
to represent the single greatest threat
to coral reefs living in Earth's oceans.
In particular, pollution and over-fishing
are the most serious threats to these
ecosystems. Physical destruction of
reefs due to boat and shipping traffic
is also a problem. The live food fish
trade has been implicated as a driver
of decline due to the use of cyanide
and other chemicals in the capture of
small fishes. Finally, above normal
water temperatures, due to climate phenomena
such as El Niño and global warming,
can cause coral bleaching. According
to The Nature Conservancy, if destruction
increases at the current rate, 70% of
the world’s coral reefs will have
disappeared within 50 years. This loss
would be an economic disaster for peoples
living in the tropics. Hughes, et al,
(2003), writes that "with increased
human population and improved storage
and transport systems, the scale of
human impacts on reefs has grown exponentially.
For example, markets for fishes and
other natural resources have become
global, supplying demand for reef resources
far removed from their tropical sources".
Currently researchers
are working to determine the degree
various factors impact the reef systems.
The list of factors is long but includes
the oceans acting as a carbon dioxide
sink, changes in Earth's atmosphere,
ultraviolet light, ocean acidification,
biological virus, impacts of dust storms
carrying agents to far flung reef systems,
various pollutants, impacts of algal
blooms and others. Reefs are threatened
well beyond coastal areas and so the
problem is broader than factors from
land development and pollution though
those are too causing considerable damage.
Land
development and pollution
Extensive and
poorly managed land development can
threaten the survival of coral reefs.
Within the last 20 years, once prolific
mangrove forests, which absorb massive
amounts of nutrients and sediment from
runoff caused by farming and construction
of roads, buildings, ports, channels,
and harbors, are being destroyed. Nutrient-rich
water causes fleshy algae and phytoplankton
to thrive in coastal areas in suffocating
amounts known as algal blooms. Coral
reefs are biological assemblages adapted
to waters with low nutrient content,
and the addition of nutrients favors
species that disrupt the balance of
the reef communities. Both the loss
of wetlands and mangrove habitats are
considered to be significant factors
affecting water quality on inshore reefs.
Poor water quality
has also been shown to encourage the
spread of infectious diseases among
corals.
Copper, a common industrial
pollutant, has been shown to interfere
with the life history and development
of coral polyps.
Fish trade
The hobby of keeping saltwater aquaria
has experienced an increase in world popularity
since the 1990s. Beyond sales of aquaria,
air pumps, food, medications and other
supplies, the primary product of the aquarium
industry is fish. However, the world market
is limited in the diversity of collected
species. For example, among 4000 coral
reef fish species, only 200–300
are exploited. Selection of species results
from a demand for fish being highly colorful
and being able to be maintained and fed
in aquaria. The last point is very important
in the choice of imported species.
Although a few fish
species (e.g. Pomacentridae) can be
reproduced in aquaria, 95% of exploited
fish are directly collected in the coral
environment. Intense sampling of coral
reef fish, especially in South-East
Asia (including Indonesia and the Philippines),
has caused great damage to the environment.
A major catalyst of cyanide fishing
is poverty within fishing communities.
In areas like the Philippines where
cyanide is regularly used to catch live
aquarium fish, the percentage of the
population below the poverty line is
40%. In such developing countries, a
fisherman might resort to such unethical
practices in order to prevent his or
her family from starving.
Most, 80–90%,
of aquarium fish exported from the Philippines
are captured with sodium cyanide. This
toxic chemical is dissolved in sea water
and released into fish shelters. It
has a rapid narcotic effect on fish,
which are then easily captured. However,
most fish collected with cyanide die
a few months after capture from extensive
liver damage. Moreover, other fish species
that are not interesting for the aquarium
market also die in the field.
Dynamite fishing
Dynamite fishing is another extremely
destructive method that fishermen use
to harvest small fish. Sticks of dynamite,
grenades, or home-made explosives are
lit or activated and thrown in the water.
Once the dynamite goes off the explosion
brings about an underwater shockwave,
causing the internal organs of fish
to liquefy, killing them almost instantly.
A second blast is often set off after
the first to kill any larger predators
that are attracted to the initial kill
of the smaller fish. This method of
fishing not only kills the fish within
the main blast area, but also claims
the lives of many reef animals that
are not edible or wanted. Also, many
of the fish do not float to the surface
to be collected, but sink to the bottom.
The blast also kills the corals in the
area, eliminating the very structure
of the reef, destroying the habitat
for fish and other animals important
for the maintenance of a healthy reef.
Areas that used to be full of coral
become deserts, full of coral rubble,
dead fish and little else after dynamite
fishing. This has made many fish start
to die out.
Bleaching
During the 1998 and 2004 El Niño
weather phenomena, in which sea surface
temperatures rose well above normal,
many tropical coral reefs were bleached
or killed. Some recovery has been noted
in more remote locations, but global
warming could negate some of this recovery
in the future. High seas surface temperature
(SSTs) coupled with high irradiance
(light intensity), triggers the lose
of zooxanthallae, a symbiotic algae,
and its dinoflagellates pigmentation
in corals causing coral bleaching. Zooxanthallae
provided 95% of the energy to the coral
host.
