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Size frequency distributions can also be constructed

Details for dealing with these issues are provided in

for each species by summing the number of corals

the AGRRA methodology and in training sessions that

within each size class (with size classes being binned

all data collectors should attend.

at 10- to 20-cm intervals for maximum diameter

The single "average size" parameter provides an

measurements). Size frequency data from two or more

adequate proxy for the coral's age, provided one

sites may be combined in order to attain an adequate

accounts for variations in growth in different species.

sample size for each species (minimum of 50 coral

A more comprehensive equation for average size

heads per species).

estimates is currently being developed by the AGRRA

Usefulness

Usefulness

partnership.

Coral size is easy and inexpensive to measure, but

Size frequency data provide a population charcteriza-

consistency training is required for data collectors.

tion that integrates over a relatively long time frame.

On a typical reef, these data will include measure-

First, it is important to define and distinguish an

ments of corals that are less than a year old and cor-

individual colony. Here, a colony is defined as any

als that are more than 100 years old.

free-standing coral skeleton that is identifiable to

Status

Status

genus level (preferably to species level) based on the

presence of living tissue or identifiable corallites.

The average coral size (maximum diameter) in the MAR

is 60 cm9. The MAR average is similar to the average

Coral size varies naturally by coral species, reef type,

Caribbean value (61 cm ­ maximum diameter). MAR

depth and disturbance history. Coral colonies are

reef crests tend to host corals of larger average size

susceptible to partial mortality and bioerosion, which

(98 cm). Average size on fore reefs is considerably

may affect size estimates. Some species are able to

smaller (55 cm)9.

retain their size "signature" longer than other species

(e.g., species with dense skeletons). Average coral

Recent disturbances (1998 disease and bleaching)

size is not an early warning signal and may not change

resulted in the loss of many large corals (e.g.,

immediately after a disturbance.

Montastraea spp.). Recovery of these corals has not

been observed, nor has replacement by other corals.

As corals grow larger, they may be exposed to

disturbances that result in partial mortality (that

Fewer large corals are present on reef crests now

is, in tissue loss that exposes coral skeleton).

versus several decades ago, due to the loss of large

Partial coral mortality can result in isolated tissues

elkhorn corals in the 1980s, recent bleaching events

reducing the apparent original size of a colony. (For

(e.g., 1995, 1998) and hurricanes (e.g., Mitch in

more information, see indicator F5 - Coral Mortality).

1998)9,13.

Alternately, fusion of separate colonies of the same

species can result in an apparently larger coral size.

Data Needs

Data

The 2006 regional AGRRA survey included three-

dimensional data (x, y, and z planar measurements),

which are being analyzed to develop appropriate

calculations  for  volume  measurements.  This

undertaking will greatly improve the quality of the data

available on coral sizes, by adding the new volumetric

measures.

Population models and size frequency distributions

have not been developed for most coral species, thus

making it difficult to develop projections of minimum

viable population sizes.

More information on how pesticides and other

potential contaminants affect growth, mortality and

reproduction is needed.

F3

Shalini Cawich / WWF

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