Oliver et al (2004) Monitoring bleaching

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Appendix 2. Monitoring Variables Bleaching Clearly the most important variable to be recorded in all programs is the amount of bleaching and mortality that has occurred. Bleaching is not an “all or nothing” phenomenon. During bleaching, coral colonies lose their algae over a period of days to weeks and can exhibit a continuous range of colouration from a slight paling, to complete loss of colour resulting in a totally bleached white appearance. Furthermore, colonies do not lose colour uniformly over their entire surface. Upper surfaces bleach more rapidly and intensely than lower surfaces in some corals, while apparently random patterns of bleaching intensity can often be seen in other corals. Finally some coral can become pale as part of a normal seasonal response to changes in light intensity and water quality. Such corals can appear to be bleached even to experienced experts if they are not familiar with the area the normal colour variation of its corals. These features make it very difficult to quantify the intensity of bleaching both within coral colonies and over an entire reef. Consequently, for synoptic surveys we suggest that no attempt be made to grade the level of colony bleaching, and that only extremely pale or totally bleached colonies are recorded to be “bleached”. Bleaching severity for a reef area should be based on the proportion of the total living coral cover that is bleached. While this conservative approach may tend to miss early stages of a bleaching event it will avoid over reporting of “bleaching” caused by over-emphasizing the significance of slightly pale colonies which are either naturally pale, or only slightly stressed. An index of overall bleaching, based on the percentage of total coral cover that has bleached is presented in Appendix 3, Table 8 and should be used a minimum measurement for all studies. In addition to this, where time and resources permit, it is recommended: 1. Actual percentage of total coral cover be recorded directly and assigned to a category later during summary analysis 2. Bleaching percentage be broken into contributions from major taxonomic groups. Table 10 in appendix 2 shows different taxonomic levels which should be used depending on the skills and resources available. 3. Bleaching percentage should be measured using point, transect or direct area measurements if different measurements will be compared and differences of more than about 25% need to be detected 4. The size of bleached colonies be recorded (as length, width and height, or as size categories) if the ecological impact of bleaching is an important question. Colony Indices When fine scale monitoring is being conducted which permits measurements for individual colonies (using tagged colonies, quadrats or belt transects), more detail on the bleaching status can be recorded. The intensity of bleaching (whiteness) is difficult to measure precisely without resorting to sophisticated analyses of zooxanthellae density or spectrophotometer measurements. Calibrated colour cards could, in theory, be used to obtain semi-quantitative data on the degree of bleaching, but this method (see www.coralwatch.org) requires additional field testing and calibration in a variety of locations before it can be effectively used as a globally consistent index. Table 9 in Appendix 3 sets out a recommended bleaching index for individual colonies base on visual assessment. If time permits then individual assessments of level of bleaching and percentage mortality would be useful. These can be converted into the appropriate category if needed for comparison purposes later during data analysis. In addition the maximum length, width and height should be recorded using a transparent ruler in the field. Coral Mortality The ultimate level impact of coral bleaching on coral reefs will depend on whether corals recover from bleaching or die. If they recover, the impacts are likely to be minor, although there is some evidence to suggest that bleached corals can suffer from reduced reproductive output in following years, and growth rates are likely to be suppressed. However if most of the bleached corals die, this can have a 28
major effect not only on coral cover but on a range organisms (including humans) who depend on living corals for their habitat or food. Once a coral has died, it becomes rapidly overgrown by a succession of organisms. Recently dead corals can be identified by a thin coating of algae with the underlying white skeleton still clearly visible. Corals with this appearance are likely to have died within one or at most two months. Corals which have been dead for longer periods can have a variety of appearances depending on the types of organisms which have grown over the skeleton and the level of grazing that has. Unless they have been monitored regularly during and after the bleaching event, it is extremely difficult to determine how long such corals have been dead, and thus whether they died as a consequence of recent bleaching or some other cause at an earlier date. Thus the percentage cover of dead coral should only be used as and indictor of the impacts of bleaching for corals which are recently dead, and have died following an observed bleaching of corals in the area. If individual tagged colonies are monitored repeatedly during he bleaching event, however, changes in the percentage of its surface which are dead provide a good measure of the impacts of bleaching. Benthic Cover In cases where more details on the types of corals and other organisms which are bleached is desired, and where the longer term impacts on the distribution and abundance of major reef organisms is needed, the percentage cover of all major benthic organisms should be recorded. While it is possible to estimate some of the key cover categories, it is better to measure these objectively using standard benthic monitoring techniques. The Line Intercept Transect (LIT) is the most commonly used technique, however belt transects, quadrats and point intercept methods also yield satisfactory results. Since each method has it own set of errors and biases, it is important that only one method be used within a monitoring program so that comparisons between sites can be made with the greatest confidence. If you have no strong preference, selection of the LIT method will make your data directly comparable with a greater number of other programs. Benthic cover monitoring methods are well covered in Hodgson et al (2003), English et al (1998 and Rogers et al. (1994). Image recording – digital photography In the last few years digital cameras have become reasonably priced, offer high resolutions and a wide range of models. Many models have dedicated underwater housings and flash units. Increasingly, digital photography offers a range of advantages over conventional film photography, and very few disadvantages. A comparison of film vs digital cameras for coral reef monitoring is presented below. Table 1. Film vs Digital Photographs Advantages Disadvantages Film • Film offers the highest resolution • cameras and film are cheap and available everywhere • need to send film away for processing • cannot check exposure/focus until film is developed • maximum of 36 exposures per dive • film is heat and age sensitive resulting in altered colour balance for old or improperly stored film Digital • can take 50-100 photos in one session (or more - dependent only on size of memory card) • produces more consistent colour since its not dependent on variations in the dyes used in negatives and prints • can be quickly viewed and computer analysed without the extra step of developing and scanning prints or negatives • resolution is lower than film (but at 6-8 mega pixels, the difference becomes negligible) • digital cameras heat up when in use and can cause fogging on the inside of the housing lens port – this is a significant problem with some models • digital cameras and memory cards are 29
Page 1 and 2: Draft A Global Protocol for Assessm
Page 3 and 4: Introduction Coral bleaching occurs
Page 5 and 6: This protocol is designed to assist
Page 7 and 8: and easily, even if only part of so
Page 9 and 10: which has very poor power to answer
Page 11 and 12: Monitoring for different scenarios
Page 13 and 14: Sites within a Location Locations w
Page 15 and 16: • The initially random selection
Page 17 and 18: Recommended Manta Tows The manta to
Page 19 and 20: Anchor damage: Pictures: Comments:
Page 21 and 22: Buddy: Vessel: Depth: Replicate: Be
Page 23 and 24: Colonies can be tagged using large
Page 25 and 26: Appendices Appendix 1. Data Forms S
Page 27: WWF Bleaching Monitoring Program Ti
Page 31 and 32: the event. Electronic salinity logg
Page 33 and 34: mainly for landscape/seascape conse
Page 35 and 36: Table 10. Benthic codes Level 1 Lev

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