Coral ecology ppt

ECOLOGY OF CORAL REEFS

VIJAYKUMAR, M.E,

Jitendra Kumar

I PhD, Dept. of FRM

jitenderanduat@gmail.com

Coral reefs are wave-

resistant structures notable

for their great species

richness,

ecological complexity and

remarkable beauty

They are unique in being

formed entirely by the

biological activity

Often called rain forests of the sea, due to

their richest biodiversity. They occupy less

than 0.1% of the world’s ocean surface, but

provide home for 25% of marine species

ORIGIN OF REEFS

Subsidence theory – (Darwin-Dana)

Solution theory – (Semper-Murray)

Submerged bank theory

Glacial epoch theory - Daly

It involves understanding biotic

and abiotic factors influencing the

distribution and abundance of

living things of coral community

DISTRIBUTION

Corals occur throughout the oceans, but

colonial reef-building (hermatypic) corals are

confined to the tropics and sub-tropics where

calcification rates are greatly enhanced

Reefs grow best in warm, marine, shallow,

clear, sunny and agitated waters

LIMITING FACTORS

Latitude

Temperature

Salinity

Turbidity & Sedimentation

Wave action

Aerial exposure

Coral reefs, just like any other ecosystem on our

planet, rely on a variety of biotic and abiotic

factors to keep them healthy and functional.

Without stable temperature, pH, light intensity,

water flow, salinity, and chemical composition of

sea water, coral reefs could not exist, but

without a stable trophic cascade, coral reefs

could not survive.

Biotic Factors

• Competitors

• Disease

• Predators

• Food availability

• Habitat availability

• Symbiotic relationships

Abiotic Factors

• pH

• Temperature

• Weather conditions

• Water availability

• Chemical composition of environment

• nitrates, phosphates, ammonia, O2, pollution

TYPES OF CORALS

Hard corals, also known as scleractinian and

stony coral, produce a rigid skeleton made of

calcium carbonate (CaCO3) in crystal form

called aragonite. Anatomic structures such

as septa, tentacles, and mesenteries are

found in sets of six, so hard corals are also

often termed hexa corals.

One of the characteristic feature of hermatypiccorals is the presence of unicellular algae(Symbiodinium microadriaticum) with in thegastrodermal tissue.

By their influence on coral growth andcalcification rates these symbiotic zooxanthellaeplay a fundamental role in the reef-buildingprocess

HARD CORALS

Brain coral

Stag horn coral

Foliose coral

MORPHOLOGICAL TYPES OF HARD

CORALS

Anatomy and Growth

SOFT CORALS

Soft coral, also known as Alcyonacea and ahermatypic coral,

do not produce a rigid calcium carbonate skeleton and do not

form reefs, though they may be present in a reef ecosystem.

Anatomic structures such as tentacles and mesenteries are

found in sets of eight, so soft corals are often called

octocorals.

DIVERSITY OF CORAL REEFS

Reefs are home to a large variety of organisms, including

fish, seabirds, sponges, cnidarians (which includes some types of

corals and jellyfish), worms, crustaceans (including shrimp, cleaner

shrimp, spinylobsters and crabs), mollusks (including

cephalopods), echinoderms (including starfish, sea

urchins and sea cucumbers), sea squirts, sea turtles and sea

snakes.

Aside from humans, mammals are rare on coral reefs, with

visiting cetaceans such as dolphins being the main exception.

A few of these varied species fed directly on corals, while others

graze on algae on the reef.

Reef biomass is positively related to species diversity.

CORAL REEF COMMUNITIES

NUTRITION

Corals have developed several unique ways

of feeding; they receive nutrients from

symbiotic algae, capture particles such as

plankton, and take up dissolved substances

from the water.

In order to fully appreciate the importance of a

balanced ecosystem such as a coral reef, we

must first understand its trophic structure; the

organisms that make up each trophic level, and

the functions of each level in the maintenance

of a healthy reef.

TROPHIC STRUCTURE

Coral reefs are complex ecosystems that require a balanced

trophic structure to function properly and efficiently.

Imbalances can occur in this intricate trophic cascade

from the top down or the bottom up. For an example of

bottom-up effects, nutrient-rich agricultural run-off can

cause a massive increase in primary productivity (e.g.

algal blooms), the effects of which often cannot be

buffered by consumers fast enough to prevent a coral

reef ecosystem from collapsing.

There are three categories of organisms in every ecosystem: producers, consumers, and decomposers.

Primary consumers are herbivorous, whereas secondaryconsumers prey on herbivores and tertiary consumers eatother carnivores.

Decomposers are responsible for breaking down deadand decaying plant and animal matter into componentsthat are once again usable for growth by producers.

None of these three categories of organisms can existwithout the others in order to complete the cycle ofproduction, consumption, and decomposition.

PRIMARY PRODUCERS OF CORAL REEF

ECOSYSTEM

zooxanthellae in corals

filamentous algal scum (turf algae)

coralline (calcareous) algae

non-coralline seaweed

filamentous algae growing through the

upper layers of the porous reef rock

(endolithic algae)

benthic and interstitial diatoms

phytoplankton

Tuft algae

Zoo xanthellae

Coralline red algaeCrustose coralline red algae

BENTHIC SEAWEEDS

BENTHIC DIATOMS

PHYTOPLANKTON

HERBIVORES

herbivorous fish

most parrotfish

surgeonfish

Pacific Gregory

(Stegastes fasciolatus)

tidepool blennies

herbivorous snails and

sea hares

most sea urchins

herbivorous crabs

green sea turtles

Chiton

Tiger cowrie

NATURAL CAPITAL: SOME COMPONENTS AND

INTERACTIONS IN A CORAL REEF ECOSYSTEM

Consumers

- primary consumers

Phytoplankton and other single-celled primaryproducers are eaten by primary consumers.

Due to the large community of primary consumers oncoral reefs, phytoplankton levels in coral reef waterscan be 15-65% lower than in adjacent open oceanwaters.

Benthic grazers and some coral species feed byfiltering phytoplankton out of the water while othervertebrate and invertebrate grazers eat algae andseaweed; many species of parrotfish, surgeonfishand blennies have a diet that consists entirely ofcoralline, filamentous, and calciferous algae.

Secondary consumers

The animals in this trophic level feed on primaryconsumers and are consequently carnivorous.Secondary consumers in a reef ecosystem canbe divided into four main groups: (1) zooplankton feeders, (2) corallivores - organismsthat feed on coral tissue, (3) feeders on otherbenthic invertebrates, and (4) piscivores - fisheaters.

Plankton feeders can be small sessileinvertebrates like barnacles, corals like sunpolyps (Tubastrea sp.) and gorgonians, smalldamselfish or 15-ton whale sharks.

Corallivores can be sub-divided into polyp

eaters, coral scrapers, mucus feeders etc.

Many species of butterfly fish, damselfish

specialize in eating coral polyps

Some common coral scrapers are specific

species of triggerfish, parrotfish, blennies,

puffers, and butterfly fish.

Some animals that feed on coral mucus are

coral guard crabs and shrimps

Benthic invertebrates like mollusks,gastropods, worms, and crustaceans areeaten by many kinds of fish (e.g. goatfish,wrasses, triggerfish, etc.) and other largerinvertebrates

Piscivores are carnivores that eat fish; manyspecies of fish are piscivores as well assome mollusks and arthropods.

Tertiary (top) consumers

Tertiary consumers are large reef fish at the

top of the food chain that eat many smaller

fish. Some examples of top consumers in a

coral reef ecosystem are sharks, barracudas,

and moray eels. Marine mammals such as

dolphins and seals, and sea birds, if present,

are considered tertiary consumers, too.

Decomposers (and Detritivores)

Decomposers serve an extremely important function in allecosystems; they break down dead biological matter andwaste products and convert them into usable energywhile returning important materials to the environment.

The main decomposers in coral reefs are bacteria; thesebacteria play an integral part in the nitrogen cyclewhereby ammonia (NH4) is converted into nitrite (NO2)by bacteria in the genus Nitrosomonas, after which nitriteis then converted into nitrate (NO3) by bacteria in thegenus Nitrobacter.

The ultimate result is that levels of toxic wastes are keptvery low and that waste products are converted intocomponents that are available to producers in a readily-usable form.

Coral reefs are complex ecosystems thatrequire a balanced trophic structure to functionproperly and efficiently.

Imbalances can occur in this intricate trophiccascade from the top down or the bottom up.For an example of bottom-up effects, nutrient-rich agricultural run-off can cause a massiveincrease in primary productivity (e.g. algalblooms), the effects of which often cannot bebuffered by consumers fast enough to prevent acoral reef ecosystem from collapsing.

PRODUCTIVITY OF CORAL REEFS

The symbiotic arrangement between the algae

and corals results in nutrients being tightly

recycled with in coral reefs. This internal

nutrient cycling is of primary importance in

maintaining the productivity of the reef

The gross primary productivity ranges from

about 1500 to 5000 g.C/m2/year, values much

higher than those of open tropical Oceans

INTERNAL NUTRIENT RECYCLING

How can such rich community grow when the surrounding sea is unproductive?

IMPORTANCE OF CORAL REEFS

Protection from coastal erosion

Very high diversity = ecological stability

Source of important natural chemicals being researched as cures for cancer, arthritis, human infections, viruses, etc

Reef fisheries

Tourism

THREATS TO CORAL REEFS

There are two types of threats to coral reefs, anthropogenic and natural

Destructive and non-sustainable fishery practices

Coral bleaching – socio economic impacts, reef based tourism and fisheries

Coral mining – construction, lime industry, ornamental purposes

Pollution – agriculture, coastal development

Sedimentation - deforestation

CORAL BLEACHING

Coral bleaching

occurs when

symbiotic

zooxanthellae

algae is removed

or expelled

Associated with

high water

temperatures

Diseases – Black band, white band and red

band diseases were observed in corals

especially in shallow areas

In addition to the direct human interferences,

global climate change poses serious threat –

increase in temperature, and a possible

increase in the incidence of storms

Reefs are subjected to physical-erosion and bio-erosion

Physical erosion – intense wave action, currents, tropical storms

Bio erosion Removal of large no. of animals from reefs may

alter the ecology

Sea urchins graze up on the coral frame work

( fish, molluscs are over fished)

Crown of thorns star fish – Acanthasterplanci

( triton snail) Destruction of Great Barrier Reef

Others

As building material – Maldive islands

For ornamental purposes

Destructive fishing methods – dynamite, sodium cyanide

Anchoring – Reefs of Florida

Walking over the reef during low tide

Mangrove deforestation – Gulf of Kutch

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