A fundamental question that one asks when using Chaetodontidae, or for that reason any species as biomonitors is: why use an organism when sophisticated machines are available to detect very small quantities of pollution in short space and time? One might think that biomonitoring has become redundant because of these machines, but the opposite is true, chemical monitoring tells us what is there, but not its effects – especially long term effects on ecosystems therefore biomonitoring has become a preferred method of assessing ecosystems (Spellerberg 1993).
The conditions required for healthy coral reef growth as well as factors ausing damage to reefs are well understood (Reese 1981). Usually acute environmental impacts on coral reefs can be easily assessed (Brown 1988). However it is not as simple when it comes to chronic sublethal factors. Using conventional methodologies the overall health of a coral reef can be determined against a baseline study (Brown 1988).
But it is of no-use because the damage has already been done, that is why indicators of sublethal are urgently required so stress can be detected early, and counter-measures put forth (Brown 1988, Reese 1981, Hourigan et al 1988). In this essay the use of Butterflyfishes as indicators of reef health will Butterflyfishes are consipicious, largly dirunal fishes ranging typically from 10 – 20 cm in length (Sale 1991). There are 114 species of Butterflyfishes world-wide (Crosby & Reese 1996), thirty five found in Fiji (Seeto 1999).
The name Chaetodontidae is derived from Greek “khaite”, meaning hair and “odont-” meaning tooth (Allaby 1991). They are, perhaps with some disagreement, the most beautiful fishes on coral reefs. Watching a Butterflyfish on the reef is an awesome acrobatic like performance! Their sheer colourfullness, beauty and apparent will to let people come physically close to them make this group of fishes rather special (personal The body shape helps Butterflyfishes escape from predators (Seeto 1999, Allen at al 1998).
When Butterflyfishes are viewed from the side, the impression one gets is that they are comparatively large, but as the fish move to front view they almost disappear because their bodies are so compressed (personal observations and experience). Its significance is that Butterflyfishes are able to live relatively long lives partly because of ack of predators (Seeto 1999), making them even better indicators of reef Furthermore Butterflyfishes are either home-ranging or territorial (Reese 1989).
What this means is that the Butterflyfishes live out their lives in the same area of coral reefs unless there is any stress. Butterflyfishes have a life span up to 10 – 12 years depending on species and have been observed on the same territories for seven to eight years (Reese 1991). Its significance is that since the Butterflyfishes are always relatively in the same area they will “feel” the stresses and respond accordingly (Crosby & Why use Butterflyfishes as Biomonitors?
There are many species of Butterflyfishes that have co-evolved with corals and are obligate corallivores (Reese 1981, 1991 Harmelin-Vivien & Bouchon-Navaro 1983). The metabolic or energy demand of these species are so “intimately linked” to the health of the corals that these species have excellent potential as indicators of changes on coral reefs (Crosby & Reese Crosby and Reese (1996) have described four important reasons why Chaetodontidae are potentially good indicators: Scientific names of corals and fishes are not required to be known by the data collectors.
Suggested species for Fiji are in Appendix 1. Information collection can be stepwise, example, the first step could be counting the Butterflyfishes along the transect and the next step could be counting the corals. This method allows the matching of time, recourses and personal available. Butterflyfishes are best used where there is gradual, chronic (sublethal) disturbances which would be difficult to measure by alternative methods, example, collection of tissue and water samples for analysis. However this method is not appropriate for catastrophic disturbances, example, oil spills, storms, etc.
Lastly, it is environmentally friendly, relatively cheap, nondestructive and non-consumptive method that does not require technical scientific training thus can be used by volunteers, local Practical Application of Butterflyfishes as Indicator Species Crosby and Reese (1996) propose a 8 step process in the application of this method. Firstly the problem has to be assessed, the question asked clearly identified and the goals of the monitoring program stated. The second is field observations, since the Butterflyfishes are directly observed – it is necessary to have scuba diving equipment.
The third step involves the establishing of transect lines. Transect lines are placed in sections of approximately 30m. They are placed purposefully in areas of high coral cover since change in living coral cover and behavior of Butterflyfishes are of interest. The data is recorded on underwater paper. Usually data sheets are photocopied on underwater paper to make recording of data easier. However sometimes the underwater paper has to be run through the copy-machine twice (See appendix 2) to get a good result (Reese 1999).
Step four involves counting and recording the numbers of each species of Butterflyfish within five meters of the transect lines (See Appendix 2). This method is known as the Belt Transect Census Method and is reviewed by Step five involves the estimation of coral cover along the transect lines. Data is again recorded on underwater data sheets (see Appendix 3). In the sixth step the territory boundary is marked and the chasing behavior measured (see Fig 2 and appendix 4). The seventh step is the measuring of the feeding behavior and the size of the territory (see appendix 5 & 6).
The size of the territory is estimated by measuring the territories to the left and right of the transect line and hen the area in square meters is calculated (see appendix 6). The eight step is like a clean-up operation, all the equipment (transect lines, colour-tagged nails, etc) are removed. However in order to return to the same site, accurate coordinates must be recorded. The final step is the analysis of the data. A comprehensive data analysis description with examples can be found in Crosby and Reese (1996). However correct data analysis depends on an understanding of the design of the monitoring program (Crosby and Reese 1996).
However in a nutshell under stressful conditions some of the behavioral hanges that is expected: The amount of chases will increase because the Butterflyfishes will try to find more food in their neighbors territories, the territory sizes will change and also the feeding rates will change The one major conclusion that can be made from this study is that the use of Butterflyfishes as indicators of coral reef health may be an excellent tool for the assesment of reefs in the South Pacific Region. This is because the use of Butterflyfishes for this purpose is cheap and requires relatively less resources than other methods.