Oliver et al (2004) Monitoring bleaching

After onset of bleaching is observed (during peak of bleaching)
• Carry out extensive manta tow and/or timed swims to determine the extent/severity/variability
of bleaching.
• Determine if exiting sites adequately represent the areas bleached. If not add additional sites to
cover a range of levels of bleaching intensity
• Carry out belt transects (or LIT if the bleaching is very frequent) to get accurate estimates of
% of corals bleached at different levels of intensity
• Record condition of all tagged corals. If there is not a reasonable number of bleached corals at
each site (at least 10) then additional bleached corals should be tagged ant their condition
recorded. There is a great deal of additional work that could be done on these tagged colonies
(zooxanthellae counts and genetics, PAM fluorometry, reproductive studies). These might be
carried out by interested researchers at major Universities without much additional cost other
than collection time.
Further monitoring during and after bleaching
• Repeat synoptic surveys (manta tow or timed swims) at regular intervals. Suggested optimal
regime would be at , 2 months, 6 months, 12 months and 24 months after initial bleaching.
Full post-bleaching LIT surveys should be repeated once bleaching is not longer present and
all corals have either died or recovered. If resources permit, further recovery LIT surveys
using should be conducted annually or every two years.
Sampling Design Considerations
Deciding on the Spatial and Time Scale
For simple logistical reasons it is important to decide on the total area over which you wish to monitor
bleaching, and the overall time frame during which you will be monitoring. Given a fixed budget and
resources, larger spatial and time scales will usually mean less frequent, and fewer (less closely spaced)
samples. If you want to monitor a large area you will probably not be able to detect small scale
differences in bleaching pattern, and if you want to monitor for an entire year or for 5 years, then you
will probably be restricted to sampling at periods of 1-2 months and may not be able to detect the exact
timing of bleaching onset, recovery or mortality. These trade-offs needs to be carefully considered, and
choices should based on the specific issues which are important to you (as discussed in Step 1).
Before selecting a specific survey method, sampling sites and sampling frequency, it is important to
decide on the area over which you wish the program to be able to draw conclusions. Is the program
supposed to describe bleaching impacts globally, for a particular country, a single reef, or a single site
within a reef?
Deciding on the number, location and frequency of surveys (samples) is one of the most important and
difficult steps in a monitoring program. A clear understanding of the questions and the time a spatial
scales in which they will be addressed is crucial to the design of an effective sampling strategy. Some
general guidelines are provided below, however it is recommended that professional assistance is
sought in designing and sampling program and associated statistical analysis, especially if substantial
resources are to be invested in the monitoring.
Site and Sample Selection
A basic question which most monitoring programs will address is: what it the ext ent and severity of the
bleaching? In most cases the area over which this question is being asked is very large (10’s to 100’s of
kilometers or more), and thus sampling will need to cover as much of this area as possible, yet still
obtain sufficient quantitative information on specific variables to examine differences in intensity and
ecological impacts between sites. In such cases a nesting of sample locations and survey methods is
recommended. For instance, manta tow surveys could be used to obtain estimates of bleaching over the
entire area, while more detailed replicate line transects could be carried out at specific sites, nested
within locations around the entire area.
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