Oliver et al (2004) Monitoring bleaching

Colony level monitoring
The following techniques should be used if you are asking a question which requires the fate of
individual colonies to be tracked. Video recording along line transects or still images along a belt
transect can also provide the relevant data for subsequent provided the imagery captures the same area
of bottom on each visit. Tagged colonies have the advantage that they can be located in the field
quickly without having to refer to the previous image. This allows tissue samples to be taken to track
actual abundances of zooxanthellae (by clade if needed) or concentrations of Chlorophyll.
Hybrid technique
Currently WWF is employing a hybrid of LIT and Quadrat technique for some of its field
projects. This method involves establishing a permanent 20m transect (marked at one end with a
temperature data logger) and taking digital photographs of a 0.5 x 0.75m quadrat set along the transect
every 0.5 m, alternating sides of the transect. This results in 40 photos. Additionally the quadrat is
arbitrary tossed on the benthos in the area that would consist of the arc of the circle created by the
transect line. Fifteen of these arbitrary tosses are made and a digital photo is taken of each. Digital
photo resolution is maintained at 2272 x 1704 pixels using a 4 megapixel camera. Photos are then
analysed by counting all of the colonies and assessing how many bleaching and to what degree.
Tagged Corals
The use of tagged colonies permits accurate assessment and ongoing monitoring of the health of
specific colonies. In particular, the tracking of a population of corals from the onset of bleaching until
mortality or full recovery has occurred, will provide the best measure of mortality that can be
unambiguously related to bleaching. In other methods, mortality can only be inferred from a decrease
in coral cover between sampling events. Tagged colonies are also particularly appropriate for
investigating the relationship between the severity of coral bleaching and subsequent
mortality/recovery, or the susceptibility of coral which have previously bleached and recovered to
bleach in subsequent years (adaptation). Tagged coral are also essential for time series studies of
physiological aspects of bleaching such as zooxanthellae density, changes in concentrations of UV
protective compounds and responses and population shifts in zooxanthellae strains.
If the above questions are of importance to the program at a particular location then one or more
representatives sites should be chosen in which to tag several colonies for a range of species. It is
recommended that a minimum of 20 (up to 50) colonies should be tagged for each species. If the
objective of the study is to obtain detailed information on mortality and bleaching susceptibility of the
coral community then species from several families should be chosen. In general, species from the
most abundant families should be selected: Pocilloporidae, Acroporidae, Faviidae, Poritidae, but in
areas where species from other families predominate, then these should also be tagged. Ultimately the
number of species and fami lies tagged will depend on time and resources. It is better to sample
adequately (~30) from a few species than to obtain inadequate sample sizes from a large number of
species.
During the initial survey (and at yearly intervals) the colony should be measured (length x height x
width) and for all surveys its condition should be scored in terms of bleaching, and optionally disease
and physical damage. A 4-point score should be used (Table 9 in Appendix 3) for bleaching, and a 3
point score for other types of stress.
Where possible colonies should be tagged in a well defined area which can be easily resurveyed
without having to swim over large distances. Colonies should be selected haphazardly and cover a
range of sizes. If repeated samples are to be taken from the colony for laboratory analysis then larger
colonies are essential. In order to facility relocation of tagged colonies, a rough map of the area should
be drawn whilst underwater, showing major landmarks (e.g. large or unusually shaped colonies; sand
patches; general reef features such as ridges, depressions, indentations and protrusion of the reef edge)
in relation to each tagged colony. Alternatively, if visibility is usually low at the site, a nylon line can
be strung from one colony to another to create a trail. This should be avoided in areas where other
divers and tourists are likely to visit as it is both unsightly and likely to be removed.
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