'%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 COVER

ORITY ON

C O R A L : A L G A E R AT I O

S FOR HEAL

What Is It?

What

BENCHMARK

The general term benthic reef cover refers to the

An increase in the regional average

living organisms covering the reef surface. Coral and

coral cover of at least 5% in the next 5

macroalgae are key components of benthic cover.

years, with a coral:macroalgae ratio no

less than 1.

Benthic cover is often expressed in terms of the

amount of living coral cover relative to other functional

TA R G E T

groups such as algae, sponges, dead corals, and other

A 25-30% increase (vs. ~2000 levels) in

sessile (attached) invertebrates. Two closely related

indicators are important in describing benthic cover:

coral cover over the next 10 years.

A 30-40% increase (vs. ~2000 levels) in

(1) Coral cover -- the amount of live stony coral tissue,

coral cover over the next 25 years.

and

A coral:macroalgae ratio no less than 2.

(2) Coral:algae ratio -- the proportion of live coral cover

to macroalgal cover.

RED FL AG

Any

Any decrease in coral cover of 5% or

Why Do We Measure It?

more in one year.

Reef-building corals are the main contributors to a

A coral:macroalgae ratio of 0.5 or lower.

reef's three-dimensional structure -- the structure

that provides critical habitat for many organisms.

Coral cover is therefore a good indicator of general

reef health.

dominated by turf and fleshy algae--which can lead to

coral loss, decline in reef structure and function.

The coral:macroalgae ratio provides a good indication

How Do We Measure It?

How

of "Who's winning?" in the ongoing competition for

space between corals and macroalgae -- a primary

Usually, a diver or snorkeler swims along a pre-defined

concern when looking at overall reef health.

transect, identifying and measuring organisms

A "healthy reef" can be characterized as one with a

under the line, at specific intervals along the line, or

relatively high cover of live corals (for the habitat type);

sometimes videotaping the transect for later analysis.

moderate levels of crustose coralline, calcareous and

Details of each of these options are provided in

short turf algae; and low cover of fleshy macroalgae. A

the AGRRA protocol16, MBRS protocol17, and other

sign of an "unhealthy reef" is benthic cover dominated

publications4,18.

by fleshy macroalgae instead of live coral.

Alicia Medina / WWF

A shift from coral-dominated reefs to reefs dominated

by turf and fleshy algae can lead to eventual loss of

reef framework. Changes in the abundance of fleshy

macroalgae and live coral cover may be a sign of

human stressors at work, although it is difficult to

distinguish among the many potential influences,

including natural variability.

We are concerned about benthic cover in the MAR

because there has been a drastic reduction in live reef-

building coral, presumably due to a combination of

factors. Likely candidates include disease, bleaching,

hurricanes, overfishing, nutrient enrichment and other

forms of pollution stress. Extensive loss of corals has

resulted in a shift from coral-dominated reefs to reefs