C O R A L S IZE FREQ UEN C Y
F3
What
What Is It?
BENCHMARK
Coral size refers to the overall size of an individual
No decrease in average coral size
No
coral head -- a measurement that is not entirely
(maximum diameter) from ~2000
straightforward, given the variety of shapes
values of 55 cm on fore reefs and 98
and irregularity of many coral species. Size can
cm on reef crests.
be characterized in terms of colony maximum
TA R G E T
diameter, perpendicular width, and height (x, y, and z
dimensions).
To be developed -- including size
frequency distribution targets by
Three useful metrics can be calculated from these
species.
species.
measurements:
RED FL AG
(1) average coral size (average maximum diameter)
(Preliminary) Average coral size of < 45
(Preliminary)
-- used in AGRRA until 2005, but now being replaced
cm (maximum diameter) on fore reefs,
by the more accurate:
< 80 cm on reef crests.
(2) average coral volume
(including maximum
characteristics of mortality, regeneration and
diameter, perpendicular width and height), and
survivorship. Coral size can often be measured
(3) coral size frequency distributions (i.e., numbers
even after a colony dies, thus providing the ability to
of coral heads in different size classes according to
hindcast previous populations' size structures (e.g.,
either maximum diameter or volume measurements).
acroporids).
Why
Why Do We Measure It?
High densities of large colonies ("old growth" stands)
suggest low disturbance or favorable growing
Coral size is used as a proxy for colony age, helping us
conditions.
to track general coral population dynamics. Scientists
often use colony size rather than age for population-
How Do We Measure It?
level studies of colonial organisms like corals, as size
A variety of methods can be used to measure coral
tends to correlate more closely with probabilities of
size. Most data from the MAR region (AGRRA, MBRS)
mortality and natality (birth rate) than does age in
rely on a diver to measure head size by using a 1-
these populations.
meter PVC bar marked off at 10-cm intervals. Each
Size frequency distributions, based on coral size
coral head encountered along a 10-m transect is
estimates and abundance, can be used to infer
characterized in terms of its maximum diameter (x),
width (y) and height (z)3,8.
Philip Kramer
The most basic and commonly used metric of average
coral size is the maximum diameter (x). This parameter
is measured directly, and is simply averaged by each
species or for the general coral population at a site by
pooling all species from that site.
The somewhat more accurate coral volume
measurement of size is currently being developed,
but will entail incorporation of the three-dimensional
measurements into a volumetric equation that may
differ for different growth forms (e.g., plate, head,
branching).
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