Bleaching, or the paling of zooxanthellate invertebrates, occurs when (i) the densities of zooxanthellae decline and/or (ii) the concentration of photosynthetic pigments within the zooxanthellae fall (Kleppel et al. 1989). Most reef-building corals normally
contain around 1-5 x 106 zooxanthellae cm-2 of live surface tissue and 2-10 pg of chlorophyll a per zooxanthella. When corals bleach they commonly lose 60-90% of their zooxanthellae and each zooxanthella may lose 50-80% of its photosynthetic pigments (Glynn, 1996). The pale appearance of bleached scleractinian corals and hydrocorals is due to the cnidarian’s calcareous skeleton showing through the translucent tissues (that are nearly devoid of pigmented zooxanthellae, see Figure 3.13). If the stress-causing bleaching is not too severe and if it decreases in time, the affected corals usually regain their symbiotic algae within several weeks or a few months. If zooxanthellae loss is prolonged, i.e. if the stress continues and depleted zooxanthellae populations do not recover, the coral host eventually dies (Buchheim, 1998). Three hypotheses have been advanced to explain the cellular mechanism of bleaching, and all are based on extreme sea temperatures as one of the causative factors (Buchheim, 1998). High temperature and irradiance stressors have been implicated in the disruption of enzyme systems in zooxanthellae that offer protection against oxygen toxicity.
The first major coral bleaching event ever recorded for Ningaloo Reef occurred in winter (July) of 2006. The combination of cold air temperatures and aerial exposure of corals due to a low spring tide and a high pressure system appeared to cause bleaching of exposed corals. Submerged corals appeared to remain unbleached.
Observations made during an aerial survey indicated that bleaching had occurred along most of the Ningaloo Reef. The most severe bleaching was recorded at Pelican Point, where approximately 81% of live hard coral was bleached. Bleaching was restricted to shallow-water corals of back-reef and patch reef environments dominated by plate and corymbose acroporids (Armstrong et al., 2008).
Figure 3.13 Bleaching hard coral on Great Barrier Reef. PhotoCourtsey by GefCoral
Photosynthesis pathways in zooxanthallae are impaired at temperatures above 30 degrees C, this effect could activate the disassociation of coral / algal symbiosis (Dubinsky and Stambler, 1996) Low- or high-temperature shocks results in zooxanthellae low as a result of cell adhesion dysfunction. This involves the detachment of cnidarian endodermal cells with their zooxanthellae and the eventual expulsion of both cell types.
It has been hypothesized that bleaching is an adaptive mechanism which allows the coral to be repopulated with a different type of zooxanthellae, possibly conferring greater stress resistance. Different strains of zooxanthellae exist both between and within different species of coral hosts, and the different strains of algae show varied physiological responses to both temperature and irradiance exposure (Gleason and Wellignton, 1993). The coral/algal association may have the scope to adapt within a coral’s lifetime. Such adaptations could be either genetic or phenotypic. As coral reef bleaching is a general response to stress, it can be induced by a variety of factors,
alone or in combination. It is therefore difficult to unequivocally identify the causes for bleaching events.
A major trigger for coral bleaching is an extended period of excessively hot, calm and clear conditions that damages the photosynthetic pathways of the zooxanthellae and causes their expulsion en masse. The bleached coral’s capacity to build new skeleton is compromised, its tissues are damaged, and its reproduction is reduced, if not suspended (Michalek-Wagner and Willis 2000; Ward et al. 2002). A bleached coral may die, in part, or entirely (Baird and Marshall, 2002). Alternatively, a bleached coral may fully recover its colour and the energy contribution of its zooxanthellae within months.
Recent increases in the incidence of coral bleaching on the Great Barrier Reef have been correlated with warming sea temperatures (Done et al., 2003).
3.9 Conclusion
Although protected through Commonwealth and State legislation, Ningaloo Marine Park is a rich but fragile environment exposed to environmental and human threats.
There are currently large gaps in the knowledge about the marine communities, species and ecosystem processes in Ningaloo Marine Park, particularly in the deeper waters. Improving knowledge of these aspects is critical to improving management of the Marine Park. One of the key gaps in knowledge and research is in the geological origins of the Ningaloo Reef and the emergent flanks of the Cape Range and other anticlines of the region. The presence of deep (50 to>500 m) water over most of the Commonwealth Waters portion of the Ningaloo Marine Park imposes restrictions on research due to technical limitations and high costs. Research in deep
open waters requires the use of larger vessels, heavy sampling and sophisticated technical equipment such as side-scan sonar and remotely operated vehicles. Even aerial surveys of migratory animals such as whales and whale sharks are more expensive due to restrictions on the use of single engine aircraft that necessitate the use of twin engine aircraft at significantly higher cost (Le Provost Dames and Moore, 2000). Coupled with the fact that most of the recognised pressure on the resources of the Park occurs in shallow waters, it is a natural outcome that most research and most of the available funding are being expended in those areas.
While the mechanism itself needs to be further investigated, there is a need for further evaluation of physical and chemical oceanographic processes in order to evaluate the potential effects of development within or adjacent to the Park. This will assist in assessing the potential for ‘trapping’ or recirculation of nutrients and other contaminants which may be discharged into the waters from the land, and for modelling the trajectory of potential oil spills that may enter the Park as a result of a shipping or oil production accident. The available information on the deepwater habitats of the Marine Park is drawn mainly from a small number of oceanographic and fisheries resource surveys. There is a need for a more detailed investigation of the deeper waters, including mapping and characterisation of offshore benthic habitats and identification of any significant geomorphological features which may be present. The potential impact of demersal fishing, particularly trawling, on the seabed means that there is a need for additional information on benthic habitats and the sessile flora and fauna which they support and which are susceptible to trawling impacts.
There is also a need for a better understanding of the population dynamics and reproductive biology of the target and bycatch species.
In the next chapter I focus the attention on these knowledge gaps in coral reef ecosystems. Ecological research is a key strategy critical for the effective management of marine conservation reserves. Research provides key information on
the ecological environment of Ningaloo, an improved understanding of what is
“natural” as a benchmark for monitoring programs, and facilitates a better understanding of the short and long-term impacts of human activities. Research programs should, ideally, be designed to fill key gaps in current knowledge of most use to management. Despite the need and importance of such research, there has been traditionally very little funding available. The aims of this thesis is to estimate the monetary value people place on the reef and examine how this can be translated into ways of increasing its conservation and the knowledge about its ecological importance.
Chapter IV
Review of the Environmental Economic Valuation Literature Non-use value analysis
4.1 Introduction
While the scale and severity of environmental problems continue to grow, the deployment of scarce resources to mitigate these negative trends via environmental conservation highlights a fundamental valuation question. How much environmental conservation should there be, and therefore what is nature’s value?
Conventional economics couches its answer in terms of human individual preferences for particular things (including the environment) and the argument that something is of instrumental value to the extent that some individual is willing to pay for the satisfaction of a preference. Underlying this approach is the axiomatic assumption that individuals almost always make choices (express their preference) which benefit (directly or indirectly) them or enhance their welfare (Turner, 1999).
Utilizing a cost-benefit approach, economists then argue that nature conservation benefits should be valued and compared with the relevant costs. Conservation measures should only be adopted if it can be demonstrated that they generate net economic benefits.
Some environmentalists (including a minority of economists, such as environmental economists), on the other hand, either claim that nature has non-anthropocentric intrinsic value and non-human species possess moral interests of rights, or that while all values are anthropocentric and usually, but not always, instrumental the economic approach to environmental valuation is only a partial approach (Katz, 1996; Brennan, 1998; Light, 2002).
These environmentalist positions lead to the advocacy of environmental sustainability standards or constraints, which to some extent obviate the need for the valuation of specific components of the environment. Some ecocentrists seem to be arguing that all environmental resources should be conserved regardless of the costs of such a strategy, i.e. that environmental assets are infinitely valuable and the environmental standards are absolute (Hargrove, 1992).
The objective of this literature review is to illustrate the concept and the nature of the environmental values with a focus on marine biodiversity, the techniques that have been used and the results that have been achieved in empirical studies relevant to marine and coral reef biodiversity valuation. The reason why I focus the attention on marine biodiversity is based on the case study, that involve an economic evaluation of biodiversity in Ningaloo Marine Park. It also helps to understand the scenario of coral reef ecosystems which as outlined in previous chapters are very complex and completely different from any sort of terrestrial case study.
I then set out an expanded values classification in order to define the limits of the conventional environmental economics concept of total economic value (use plus non-use values). Particular attention is paid to the Contingent Valuation Methodology and Choice Modelling approach to value environmental goods, because they represent the two most relevant and tested methodologies.