'%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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of colonies affected by bleaching in a given area).

These parameters can be calculated at the site or

regional level (including all coral species in one reef-

wide average) or calculated by species, at a variety of

scales.

The degree of bleaching can be categorized by severity

(e.g., AGRRA)3,8:

0 = No bleaching,

1 = Pale (discoloration of coral tissue),

2 = Partly Bleached (patches of fully bleached or white

tissue), and

3 = Bleached (tissue is totally white, no zooxanthellae

Melanie McField / WWF

visible).

Data Needs

Bleached corals can be monitored for subsequent

mortality or disease.

Coral bleaching data are available from the MBRS

and AGRRA websites, along with various monitoring

Usefulness

program reports and research publications, some of

which may not be readily accessible in the region.

The coral bleaching signal depends on when

observations are made (i.e., during or after an event).

Although several monitoring programs assess coral

If a bleaching event is not monitored over time, it may

bleaching in the MAR, we recommend developing

be difficult to determine the extent of resulting tissue

a BleachWatch program, modeled on the existing

mortality. Coral bleaching varies depending upon coral

programs in the Great Barrier Reef and Florida

species (e.g., some species bleach earlier, and some

Keys28,29. These programs provide training, planning,

tend to stay bleached longer), water depth, reef type,

and rapid response monitoring teams to track the

physical environment (e.g., water clarity, proximity to a

progression of coral bleaching events (including

channel) and disturbance history.

any delayed mortality associated with coral disease

outbreaks). This approach would provide regionally

Coral bleaching is not an early warning signal.

consistent data and a better indication of the impacts

However, NOAA HotSpot maps do provide a good

following a bleaching event. Collaboration and training

alert to water-temperature conditions that may cause

could involve marine tour guides and divemasters,

bleaching. (See Indicator D14 - Coral Bleaching Index).

who can act as "first responders" to alert managers

Coral bleaching may be a good indicator of climatic

and scientists of signs of a bleaching event.

changes.

More research is needed on the response and

Status

adaptability of corals and their algal symbionts,

bleaching effects on reproductive fitness and

The prevalence of coral bleaching will vary naturally

strategies of corals, and effects on calcification.

year to year. In summer 2000, which was not a mass

Additional research is needed on the resilience of reef

bleaching year, the average prevalence of bleaching in

areas to coral bleaching, and these findings need to

the MAR was 9%, with 11% bleached on the fore reef

be incorporated into MPA design and management.

and 7% on the reef crest9. This level is approximately

the amount expected for a non-bleaching-event year

In order to develop better benchmarks and targets

and may be related to a variety of smaller-scale

that encompass the ecological outcomes of bleaching,

stressors. However, the MBRS Synoptic Monitoring

the resiliency and potential susceptibility of various

Program (Mexico and Belize 2004/05, all habitats)

areas need to be evaluated, and an index similar to

found only 2.5% colonies bleached.

the "LD50" index of toxicology studies needs to be

developed for different levels of coral bleaching.

The most significant mass bleaching events in the

Such an index would encompass the severity (degree

MAR occurred in 1995 and in 1998 with ~50% to

of bleaching in each colony) and the prevalence

90% of corals bleaching in some areas25,26. Moderate

of bleaching (percent of corals affected in an given

bleaching (~30% to 40% of corals bleaching) occurred

area).

in some areas of the MAR in 200527.