2.3 Growth & Reproduction

Process of Reef Growth

Asexual budding

  • Growth is affected by light intensity, water motion, depth, turbidity, day length, water temp, plankton concentration, predation, competition

Fragmentation

  • storms and waves can commonly break coral colonies, causing genetically identical copies of a colony

  • often contributes to single-species domination of an area

  • rapid recolonization after a disturbance

Polyp Bailout

Skeletal growth

  • growth rate determined by skeleton density

  • Average growth 1mm upward and 8mm horizontally per year (marine life book)

  • depends on balance of deposition and removal of CaCO3

    • contributions form calcareous algae, colonial hydrozoans, skeletons of crustaceans, bryozoans, foraminifera, mollusks, echinoderms.

    • loss of CaCO3 can be caused by grazing/scraping urchins & fish, or etchers (bacteria, fungi, algae) that penetrate skeletons. Infaunal organisms (sponges, bivalves, worms) bore holes into skeletons.

Sexual Reproduction

  • strategy linked to taxonomy

  • Dioecious - only producing male or female gametes

  • hermaphroditic - possessing both male and female sex organs

Brooders

  • eggs remain in gastrovascular cavity where they are fertilized by motile sperm cells. developing zygotes are eventually released to settle nearby

  • commonly small-polyped species

Spawners

  • millions of gametes released into water column for external fertilization

  • commonly large-polyped species

Mass spawning events

  • induced by specific dark periods & the cycle of the moon

  • seasonality driven by temperatures

  • multi-speceis spawning may satiate predators by overwhelming them with food

Larvae & recruitment

  • planula larvae - at first they swim towards brighter light (stay at surface where currents can facilitate dispersal), then after some development they swim away from light to settle on sea floor

  • Single-polyp recruits metamorphose into a juveline byt developing a CaCO3 skeleton, mouth and tentacles

  • Develop to maturity in 7-10 years

References

See Morphology section for all growth papers

Harriott 1983

Reproductive ecology of four scleractinian species. Describes patterns of coral reproduction. Histology.

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