Coral reef ecosystems
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Coral Reef Ecosystems. Coral biology Reproduction: sexual and asexual Production and symbiosis Reef formation and habitats Factors affecting coral reef distribution Physical Zoogeographic Corals and sponges as biodiversity and habitat Diversity in fishes Reproduction and larval dispersal

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Coral Reef Ecosystems

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Coral Reef Ecosystems

  • Coral biology

    • Reproduction: sexual and asexual

    • Production and symbiosis

    • Reef formation and habitats

  • Factors affecting coral reef distribution

    • Physical

    • Zoogeographic

  • Corals and sponges as biodiversity and habitat

  • Diversity in fishes

    • Reproduction and larval dispersal

    • Diel activity rhythms and migrations

Basic biology of corals

  • Corals are cnidarians in the class Anthozoa (including anemones and gorgonians); other classes are Scyphozoa (jellyfish) and Hydrozoa (hydroids, fire coral, etc.)

  • May be colonial or solitary, reef-building (hermatypic) or non-reef building

  • Most hermatypic corals are colonial but some (e.g., mushroom coral) are not

  • Reproduce asexually (by budding)and sexually

  • Sexual reproduction: can be hermaphroditic or dioecious. Sperm are released into the water, taken in by polyps, fertilization occurs in the female’s gastrovascular cavity, and planula larvae are released, often synchronously.


  • The coral animal lives symbiotically with zooxanthellae: dinoflagellates. Coral polyps feed at night on plankton but meet only a fraction of their nutritional requirements. Zooxanthellae provide the balance of the coral’s nutrition by photosynthesis and transfer to the coral. Corals kept in the dark feed but do not grow whereas those not fed but in the light can grow. Tropical marine waters are very unproductive (18-50 g C/m /yr) but the reefs can be very productive because the primary production is linked to the coral.


Star coral

Brain coral

Mushroom coral

Branching hydroid; a hydrozoan, not a coral

Physical Factors Affecting Hermatypic (reef-building) coral

  • Temperature: ~ 18-30

  • Depth: Light needed for symbiotic algae < 25 m (some to 70 m)

  • Salinity ~ 32-35 ppt (to 42 in Persian Gulf)

  • Sediment: smother coral and block light

  • Wave-action: oxygenates, supplies plankton, removes sediment

  • Air: prolonged exposure kills coral

Global distribution of corals

Tropic of Cancer 23.5 o N

Tropic of Capricorn 23.5oS

Coral zone

Global diversity of reef building coral species

Number of Species

300200 100 50 10

Coral Biology


Coral Reef Habitats


  • Supratidal pools

  • Intertidal pools

  • Grass beds

  • Patch reefs

  • Back reef flats, channels

  • Reef crest – breaker zone

  • Buttress zone

  • Fore-reefs

  • Drop-off









Micro-habitats: Coral , sponges

Temporal Structure: Day-Night

Larval Dispersal – Recruitment

pillar coral

pillar coral

Sand diver or lizardfish



basket star on star coral

basket star

Giant feather duster worm on finger (Porites) coral

Giant feather duster

brain coral

Christmastree worm on brain coral

flamingo tongue feeding on scratchy sea whip (a gorgonian)

flamingo tongue feeding on purple sea fan (gorgonian)

barrel sponge

In addition to corals, sponges constitute both a major part of the biodiversity of coral reef systems but they also join with corals to provide much of the three-dimensional structure in reefs. As such they provide critical habitat for many fish and invertebrate species.

Brittle star on an azure vase sponge

arrow crab and azure vase sponge

arrow crab

arrow crab

Brittle star on brown tube sponge

Brittle star on brown volcano sponge

Families of Coral Reef Fishes

Labridae - Wrasses

Chaetodontidae - Butterflyfishes

Scaridae - Parrotfishes


Families of Coral Reef Fishes







Families of Coral Reef Fishes

Balistidae – Triggerfishes and Filefishes



Moorish idol

Families of Coral Reef Fishes

Pomacentridae - Damselfishes

Diodontidae - Porcupinefishes

Tetraodontidae - Puffers

Ostraciontidae - Boxfishes


clown fish

Reproduction and larval dispersal

Bluehead wrasse

Many coral reef fishes are sequential (often protogynous rather than protandrous) or even simultaneous hermaphrodites. In addition to this consideration, species may broadcast planktonic eggs or deposit them in nests. The dispersal patterns are important for recruitment.

Nassau grouper

Coral Reef Ecosystems

Larvae from pelagic eggs

Larvae from non-pelagic eggs

Relative abundance (%)

0 20 40 60 80 100

Bay channel 0-5 5-2 2-8 10-12 12 km

Distance from Hawaiian Island of Oahu

Leis in Sale (ed.) 1991

Coral Microhabitat



Coral Microhabitat




sleeping parrotfish

glasseye sweeper


white grunt: solitary, diurnal

post-larval grunts:

schooling, diurnal

Juvenile French and white grunts: aggregate on reefs in the daytime

grunts in the evening

grunts migrating at dusk

Grunts migrate to grassbeds and feed at night as solitary individuals

migrating grunts re-aggregate and return at dawn

Sand divers (lizardfish) prey on migrating grunds

migrating grunts: back to the safety of the reef

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