'%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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How Do We Measure It?

The most common way to estimate

partial mortality of a colony surface

is through visual observations

from a planar view perpendicular

to the axis of growth. Mortality for

each colony is distinguished as

"recent," "old," or "100% dead"

and presented as a percentage.

Details are given in the AGRRA

and MBRS methodologies3,8.

Usefulness

The use of partial coral mortality

as an indicator of reef condition is

well established.

Data on recent mortality are

particularly useful in the first

several months after major

disturbances such as hurricanes

or bleaching events. Such data

help researchers gauge the

ecological significance of these

events.

The mortality signal can be lost

or obscured due to such factors

as bioerosion, hurricanes, algal

overgrowth, predation and time

elapsed since death.

A complicating factor is the

WWF-Canon/Anthony B. Rath

variability in mortality signature

among different species. For

example, Acropora palmata (elkhorn coral) skeletons

24% and was higher on reef crests (32%) than on fore

retain their colony structure long after death (up to

reefs (21%)9.

15-20 years), while other, less robust skeletons do

The proportion of standing dead colonies in the

not. As a result of this variability, mortality data may

MAR averaged 7%. Standing dead corals were more

include an artifactual bias towards those species that

common on shallow reefs (24%) than on deep reefs

retain their mortality signature.

(3%), due to high numbers of dead Acropora palmata

Measures of partial mortality are relatively easy,

in the shallow areas9.

inexpensive and quick to obtain. Training is required for

Data Needs

Data

data collectors, to ensure consistency and accuracy.

Additional regional AGRRA data are currently (2006)

Status

being collected across the MAR and will complement

The average recent mortality (1998-2001 AGRRA)

existing MBRS SMP data.

in the MAR region averaged 2% (average percent of

These data should be used to examine the ability

colony with recently dead tissue), which was similar to

of reefs to absorb disturbances, resist phase shifts

normal background levels reported for the Caribbean9.

and recover from disturbances. Causes of mortality

In a 2001 WWF survey, recent mortality averaged

need further examination--particularly the roles of

1.7%, and ranged from a low of 0.2% (Coordillara, Sian

contaminants, human-induced nutrients and the

Ka'an) to a high of 4.4% (Pelican Cay, Belize Barrier)4.

impacts of degradation or conversion of adjacent

Old dead in the MAR (1998-2001 AGRRA) averaged

coastal and watershed habitats.