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Eduncle posted an MCQ
October 19, 2019 • 17:07 pm 0 points
  • IIT JAM
  • Geology (GG)

Hermatypic corals are typically found in

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    Eduncle Best Answer

    Hermatypic corals live in shallow, warm, normally saline sea water, clear of fine suspended sediments. More precise requirements are as follows :
    Depth of Water : In very clear water, reefs may form even at depths of 90 metre. They, however, grow better at 40-50 metre depth. Most reef-forming genera and species live most successfully at depths of 15 metre or less.
    Temperature : Reefs form in warm water at average temperatures between 36ºC and 22ºC; 25ºC-29ºC range appears to be the optimum; a few genera and species may survive for a brief span at 17ºC-18ºC.
    Latitude Dependance : Most coral reefs are restricted to the tropical belt between 30ºN and 30ºS latitudes. This is rather due to the suitable temperature and availability of planktons, food for corals.
    Salinity : Corals are strictly marine. Of them, hermatypic corals live best within 1 or 2 parts of salinity of normal marine water of average 35 per cent salinity; reefs may form, however, between 27 per cent and 40 per cent.
    Clearness of sea water, sunlight and symbiosis between corals and algae : Coral reefs grow best in well-lighted sea water. In clear coastal water, sunlight penetrates upto about 200 metre depth, though in more turbid water near river mouths with high amount of suspended fine sediments, sunlight does not reach that depth. Here the sediments also clog the hollow space within corallites causing animals to suffocate and reef growth stalled. In clearest ocean water, sunlight may penetrate even beyond 1000 metre.
    Restriction of coral reefs to lighted water, rather the photic zone is more because of symbiosis between a photosynthetic dinoflagellate Zooxanthellae (loosely called brown algae) and reef-forming corals. The former lives in endoderm cells of coral polyps and through photosynthesis, consumes carbon dioxide to give oxygen. Corals take in that oxygen and give out in turn carbon dioxide for Zooxanthellae to consume. The process helps corals to live in proliferation.

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