'%Healthy Reefs for Healthy People - A Guide to Indicators of Reef Health and Social Well-being in the Mesoamerican Reef Region%'%by Melanie McField and PAtricia Kramer%

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CORAL DIVERSIT Y

What Is It?

BENCHMARK

Maintain species richness and diversity

Coral diversity is a measure of the variety of corals

living in a given area.

at current levels.

TA R G E T

Diversity can be assessed in many ways. Species

richness is the number of species present. Evenness

Diversity

Diversity indices equal to or greater

is a measure of how equal in number the different

than 1997 levels of ~1.7 (Shannon-

than

coral species are. Here, we consider coral diversity

Wiener) on fore reefs and > 30 species

Wiener)

in terms of both species richness and evenness.

per 225 m2 area.

per

(Formulas are given in Appendix 3: Technical Notes.)

RED FL AG

Any reduction in species richness.

WH Y DO WE ME A SURE IT ?

Melanie McField / WWF

Higher biodiversity is generally taken as a sign of

better ecosystem health (within a specific habitat).

We are especially interested in hard corals, as they

are the `structural engineers' of the reef. A decline in

coral species richness or diversity indicates a decline

in ecosystem health.

Reduced coral species richness or diversity makes

reefs more susceptible to natural and anthropogenic

disturbances, especially disease outbreak. Loss

of biodiversity can thus reduce the reef's overall

resilience to such disturbances.

Species diversity within key guilds or functional

groups (e.g., reef-building corals, herbivores) may be

of paramount importance.

HOW DO WE ME A SURE IT ?

In general, divers mark off an area of reef, then

count all species present. Species richness can be

measured in belt transects (long rectangular plots)4.

Diversity is then calculated from coral cover (indicator

S4), often using one of two common diversity indices

that incorporate species richness and evenness into a

single measure -- the Shannon Index. Technical notes

and formulas are provided in Appendix 3.

Usefulness

Usefulne s s

Biodiversity can be a powerful indicator of reef health,

but its application has some limitations. Diversity can

be easily calculated from coral cover data, but a larger

total sample area is generally needed to adequately

represent species richness in an area (thus increasing