CORAL REEFS
'
165
nutrient salts.
These substances are produced as a result
of normal breakdown in the animal tissues.
But. corals
can exist without plants ; they may occur in dark places
under boulders without plants, which cannot exist in dark—
_
’ness.
It has been suggested that corals may feed upon the
-zooxanthellæ if animal plank_ton is searce, but experiments
carried out during the Great Barrier Reef Expedition failed
to conrm this.
But it is certain that the plants automati—
cally remove wast‘e' matter produced in the bodies of the
corals.
In this way, by increasing the efciency of the corals,
they may be an indispensable factor" in the necessarily excep—
tional powers of growth and repair possessed by coral reefs. ‘
It is difcult to estimate the gr0wth of corals, for this depends so much on conditions, especially temperature and the
supply of food, but it- has
thatthe branches of
'
Acropora may increase by one or two inches in length per an—
num, while a mass of Porites increased its diameter by thirty
inches in twenty—three years. Other estimations'have Shown
that a shallow—water reef might, under favoura‘ble conditions, grow upwar‘dsat a rate of ab0ut one foot in eleven and
a half years,or fourteenand a-half fathoms in one thousand
,
_
years.
In Samoa, Dr. Mayor came to the conclusion that the
corals added'æme
limestone to the reef
annually, although about four times this amount is removed
in the same period by cui‘rents, sea cucumbers and other
coral—boring animals. This'is not the only evidence we pos—
_
,
sess which indicates that coral reefs, in some areas at any
rate, may, at the-present day,‘be decreasing rather than
'
increasing.
'
'
'
‘
The Nulp0res or 'calcare‘ous se‘aWeeds grow as sheets
_
(Plate 61), usually comparatiÿely thin, though masses two
‘
feet thick have been reported “from the Indian Ocean.
They
va.ry in abundance from place to place, being clearly ofrstrate imp0r‘tauCe in- some areas, such as the Maldive. and
'
165
nutrient salts.
These substances are produced as a result
of normal breakdown in the animal tissues.
But. corals
can exist without plants ; they may occur in dark places
under boulders without plants, which cannot exist in dark—
_
’ness.
It has been suggested that corals may feed upon the
-zooxanthellæ if animal plank_ton is searce, but experiments
carried out during the Great Barrier Reef Expedition failed
to conrm this.
But it is certain that the plants automati—
cally remove wast‘e' matter produced in the bodies of the
corals.
In this way, by increasing the efciency of the corals,
they may be an indispensable factor" in the necessarily excep—
tional powers of growth and repair possessed by coral reefs. ‘
It is difcult to estimate the gr0wth of corals, for this depends so much on conditions, especially temperature and the
supply of food, but it- has
thatthe branches of
'
Acropora may increase by one or two inches in length per an—
num, while a mass of Porites increased its diameter by thirty
inches in twenty—three years. Other estimations'have Shown
that a shallow—water reef might, under favoura‘ble conditions, grow upwar‘dsat a rate of ab0ut one foot in eleven and
a half years,or fourteenand a-half fathoms in one thousand
,
_
years.
In Samoa, Dr. Mayor came to the conclusion that the
corals added'æme
limestone to the reef
annually, although about four times this amount is removed
in the same period by cui‘rents, sea cucumbers and other
coral—boring animals. This'is not the only evidence we pos—
_
,
sess which indicates that coral reefs, in some areas at any
rate, may, at the-present day,‘be decreasing rather than
'
increasing.
'
'
'
‘
The Nulp0res or 'calcare‘ous se‘aWeeds grow as sheets
_
(Plate 61), usually comparatiÿely thin, though masses two
‘
feet thick have been reported “from the Indian Ocean.
They
va.ry in abundance from place to place, being clearly ofrstrate imp0r‘tauCe in- some areas, such as the Maldive. and