Thoughts behind coral reef conservation

 In Biodiversité, Conservation, Coral reefs, Marine Biology

How can management monitoring help define the next step in conservation? 

The measure of management outcomes in coral reefs is made by monitoring key variables (indicators), that can give the most information about the achievement of any given goal. At the same time, this feedback gives information about what the most resource-efficient conservation measures are, in order to reach a large amount of goals with few resources (Harris et al, 2017). This is useful for prioritizing what to do next, where and how. 

Increasingly, in order to sustain ecosystems and their services they provide to human communities, coral reefs’ management is needed to consider multiple goals, including both biological and socio-economical components (Nörstrom et al, 2016).

 

The importance of thresholds in conservation management 

To help understand how successful management is, it is important to define the thresholds for each of the indicators, which will tell us how close the results are to what was expected or desired. 

In this sense, the use of reference conditions is very useful. In fact, reference conditions are defined as the values of a “model ecosystem” that can be compared to the management results. These can be set as the conditions in absence of human pressure (Borja et al, 2012) or under acceptable resource exploitation (MacNeil, 2013). They act as the direction for management measures, so they can be more or less ambitious, and this choice will change the interpretation of the outcomes (Cinner et al, 2020).

 

What is the importance of context in achieving management goals for coral reef conservation? 

When considering the management outcomes of several coral reef ecosystems on a larger scale, besides the examination of the individual management measures, it is key to also consider the respective surrounding conditions, since they can influence the processes and achievements. For example, biologically, if the coral reef is surrounded by seagrass meadows, the seascape’s heterogeneity may better sustain the richness of species and their abundance (Grober-Dunsmore et al, 2007).

On the other hand, regarding the human component, one way to analyse human pressure in the seascape is through the “gravity” metric (Cinner et al, 2018). It mainly consists in measuring the interaction between humans and reefs by considering the surrounding population size and travel time to the reef (Cinner, 2018).

 

Combining management effort, context and conservation gains for coral reefs 

In 2020 a team of scientists lead by Joshua Cinner from the ARC Center of Excellence for Coral Reef Studies in Australia published a paper in Science magazine aimed at describing under which context (in terms of human pressure and management efforts) coral reefs around the world reached multiple conservation goals. This gave an idea of which coral reefs have the best conservation achievements, and why. To do so, they assessed the conditions of 1,800 tropical coral reefs in 40 countries and territories.

As for conservation goals they considered three parameters: the fishable biomass in the reef (fish over 20 cm long), the scraping potential of parrotfish (the more parrot fish scrap, the less algae in the reef and therefore the easier corals can survive) and the diversity of species’ traits (characteristics of species linked to community’s processes: home range, diet and behaviour). The team sat reference conditions for such parameters with as well as “aspirational targets”: 25%, 50%, 75% of the reference conditions (the higher the number, the more ambitious it is).

As a first result, they found that only 5% of the analyzed reefs achieved the three considered indicators simultaneously at 75% of the reference conditions (the most ambitious goal), and these are spread in the Indian, Pacific and Atlantic Oceans (Figure 1).

 

Figure 1. Distribution of sites that simultaneously have biomass, parrotfish scraping potential and diversity of traits at >75% (purple), 50-75%, 25-50% (dark pink) and <25% (black) of reference conditions. Source: Cinner et al, 2020.

 

The next step in the analysis was to include the management efforts and the context (in terms of human pressure) to describe the probability of meeting the three goals at the different ambitiousness levels. 

Cinner’s team found that the areas with no fishing regulation (“Openly fished”, Figure 2) had very high probability to accomplish the lower standards of the three conservation goals (light pink line: 25 and 50% of reference conditions, Figure 2A). In more, they had low probabilities of achieving results close to the reference conditions, in both low and high human pressure scenarios (purple line: 75% of reference conditions, Figure 2A). 

In parallel, the Marine Protected Areas (MPAs) had a high likeliness to accomplish all goals at the most ambitious level (purple line: 75% of reference conditions, Figure 2E). The restricted fishing areas follow the same trends but with lower probabilities compared to the MPAs (Figure 2I). Furthermore, the likeliness of achieving the different goals in these areas decreased more rapidly in “high human pressure contexts” compared to the MPAs (Figure 2E, 2I), suggesting that the context is an important factor for the local management outcomes

Therefore, according to this analysis, the potential conservation gains will depend on the seascape context as well as in the ambitiousness of the goal. Less-pressure reefs have better probabilities of achieving conservation gains compared to the ones under high human pressure in the seascape, therefore where efforts should be placed.

 

                   

Figure 2. “Estimated probability of reef sites having 25, 50, 75% of reference conditions […] for the combination of fisheries sustain (biomass of fish >20 cm), parrotfish scraping potential and trait diversity” (light, dark pink and purple, respectively). A for openly fished areas (no restrictions), E for Marine Protected Areas and I for restricted fishing. In the x axis (horizontal) there is the gravity metric for human pressure : the closer to 0, the higher the human pressure. Source: Cinner et al, 2020.

 

Still, the prioritization of coral reefs’ conservation is a highly debated topic in marine sciences, since there are different positions. For instance, the team of Jill Harris of WWF and National Geographic Society proposed in their 2017 paper that coral reefs that were more intensely threatened by humans on a local scale should be prioritized for conservation. Therefore those under high human pressure contexts, where the pressure can actually be managed (Harris et al, 2017). 

 

In conclusion, Cinner’s team research contributes in giving a large scale overview of the gains of coral reef conservation considering multiple goals, both biological and socio-economic. Also, management measures and human pressure are important factors for the achievement of the goals under different levels of ambition. Still, each context should be considered individually to make decisions and prioritize areas, including the habitat structure of the surrounding seascape (Grober-Dunsmore et al, 2007; Weeks, 2017) and the level of dependency of local communities towards coral reefs (Harris et al, 2017).

 

To find out more : Cinner et al., (2020) Meeting fisheries, ecosystems function and biodiversity goals in human-dominated world. Science 368, pp. 307-311. DOI: 10.1126/science.aax9412 

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