FACTORS AFFECTING THE GROWTH OF CORAL

REEFS

VIJAYKUMAR, M.E,

DFK – 1304

I PhD, Dept. of FRM

Latitude

Temperature

Light

Salinity

Turbidity & sedimentation

Wave action

Aerial exposure

Firm substrata

Growth

Abiotic factors Biotic factors

Species

interactions

(mutualism,

competition,

predation

Growth of reef corals is affected by both abiotic and biotic factors

LATITUDE

High calcification rates are limited to warm

waters. Consequently, coral reefs are restricted

to tropical seas, generally between 250 N and

250 S latitudes.

Temperature

Reef building corals cannot tolerate water

temperatures of less than180C (except as in

the Florida Keys of the United States),

although some corals tolerate temperatures

of up to 400C , optimum growth usually

occurs between 230C and 290C.

Light

After temperature, light is probably the most

important limiting factor to well-developed

coral reefs because of the symbiosis

between hermatypic scleractinian corals

and zooxanthellae

Since light intensity decreases exponentially

with depth, active reef building rarely occurs

below about 20-30m.

PAR

Salinity

Hermatypic corals seem to require open-ocean salinity

Well-developed reefs are not generally found in estuarine

or excessively hypersaline conditions(Persian Gulf reefs,

however, develop in salinities of more than 40ppt)

The absence of reefs along much of the tropical coastline

of the Atlantic coast of South America is due to the

influence of large rivers such as the Amazon and Ornico

High rains, resulting in excessive runoff, cause extensive

damage to corals close to river mouths

Turbidity & Sedimentation

High turbidity and sedimentation rates strongly

inhibit reef growth.

Turbidity reduces light penetration whilst, settling

silt particles smother the feeding structures of the

delicate coral polyps.

Rivers carry a large suspended sediment load to

the coastal areas periodically, which is

detrimental to corals

Wave action

Coral reefs thrive in regions of strong water

movement.

Wave action prevents sedimentation and keeps

the water well oxygenated.

Although the rigid calcareous skeletons of most

hermatypic corals are particularly resistant to

wave shock, severe storms do occasionally

cause extensive damage.

Storm damage can, in fact, be a mechanism of

coral dispersal, for pieces of living colonies

transported to new sites may survive to cement to

the bottom and establish a permanent new colony

Aerial exposure

Corals are unable to withstand prolonged aerial

exposure and rarely grow much above the low

spring-tide level.

The upward growth of a reef is restricted to the

level of lowest tides, as exposure to air for

more than several hours kills corals

FIRM SUBSTRATA

New reefs are initially formed by the

attachment of meroplanktonic coral larvae

(planulae) to a hard substrate, so a firm

platform is always necessary for

establishment and growth

MUTUALISM

Symbiotic relationships are especially important in

structuring coral-reef communities.

between Zooxanthellae, coral polyp

Carbondioxide, ammonium phosphate

Oxygen, photosynthate

COMPETITION

Competition for limited living space on coral reefs is

potentially severe

Fast - growing branching corals are capable of

overtopping slow – growing encrusting or massive

forms

Coexistence is facilitated however by the combined

effects of physical disturbance (storms) and

aggressive behaviour (tissue necrosis) of the

slower – growing species

PREDATION

The major groups of coral predators are star fish,

sea urchins and fish

Acanthaster planci

giant triton (Charonia tritonis)

Fish species that feed directly on coral polyps

(puffer fish, file fish, trigger fish)

Surgeon fish, parrot fish digests the algae and

endolithic fauna

NATURAL SOURCES OF STRESS ON CORAL

REEFS

intense storms

El Niño

disease

volcanic eruptions

predator population explosions

natural stream and river runoff

exceptionally low tides

STORM WAVE DAMAGE

Before After

STORM DAMAGE

CROWN-OF-THORNS OUTBREAKS

STREAM AND RIVER RUNOFF

LOW TIDES

Acid Rain in Marine Environment

• reduces ability of marine

organisms to utilize calcium

carbonate

• Coral calcification

rate reduced

15-20%

• Skeletal density

decreased,

branches thinner

NUTRIENTS AND ALGAE GROWTH

SEDIMENTS

BLEACHING

SOME LOCAL HUMAN IMPACTS

thermal effluents

sewage discharges and agricultural runoff

mechanical damage to reefs

sedimentation

destructive resource extraction practices

introduced species

GLOBAL HUMAN IMPACTS

Global warming

UV radiation

Ocean acidification

CORALS AND UV RADIATION

decreased growth

decreased rates of calcification

transplantation experiments (deep corals brought to the

surface) demonstrate corals may be UV-sensitive (exhibit

bleaching and increased mortality)

coral sperm appears to be UV-sensitive (note spawning

normally takes place at night)

POSSIBLE CONSEQUENCES OF STRESSES AND

IMPACTS ON CORALS AND CORAL REEFS

outright mortality of coral tissues

breakage of coral colonies

bleaching

diseases

slower growth

reduced reproduction and recruitment

competitive exclusion by other organisms

increased reef erosion

MODERN USES OF CORAL REEFS Seafood

Food Additives and Toiletries

Health and Medicine Products

Research and Education

Jewelry and Art

Marine Aquarium Specimens

New Land

Cement & Other Building Supplies

Shoreline Protection

Recreation

THANK YOU