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Biological Notes

    Naturevolume 43pages6566 (1890) | Download Citation



    RATE OF GROWTH IN CORALS.—But little is as yet known as to the rate of growth of corals under different conditions. In the third edition of Dana's “Coral and Coral Islands,” a résumé will be found of all that is known about this subject up to 1890, but some very interesting details have been published by Alexander Agassiz in the August number of the Bulletin of the Museum of Comparative Zoology at Harvard College. A series of specimens are figured, which have been taken off the telegraph cable laid between Havana and Key West, in June 1888, from a portion that was repaired in the summer of 1881; so that the growths could not be more than about seven years old. It is to be observed that this portion of the cable was laid at a depth of only from six to seven fathoms, and that the district in which it was laid was most favourably situated as regards food supply to the corals. Some of the specimens belong to species whose rates of growth have not yet been recorded; they are as follows:— Orbicetta annularis, figured on plates 1 and 2. Verrill mentions that the thickness of this coral formed in sixty-four years was not more than about 8 inches; the specimens from the Havana cable grew to a thickness of 2½ inches in about seven years. Manicina areolata, Ehrenb., figured on plate 3, has grown to a thickness of I inch; while Isophytta dipsacea, Ag., figured on plate 4, shows a still more rapid growth, projecting 2½ inches above the cable. Of course it is quite possible that these corals are of less than seven years' growth, but it is not probable that more than a short time passed before some of the swarms of pelagic coral embryos which must have floated past the cable found a place of attachment thereon.

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