Abstract
The Government of Madagascar plans to increase marine protected area coverage by over one million hectares. To assist this process, we compare four methods for marine spatial planning of Madagascar's west coast. Input data for each method was drawn from the same variables: fishing pressure, exposure to climate change, and biodiversity (habitats, species distributions, biological richness, and biodiversity value). The first method compares visual color classifications of primary variables, the second uses binary combinations of these variables to produce a categorical classification of management actions, the third is a target-based optimization using Marxan, and the fourth is conservation ranking with Zonation. We present results from each method, and compare the latter three approaches for spatial coverage, biodiversity representation, fishing cost and persistence probability. All results included large areas in the north, central, and southern parts of western Madagascar. Achieving 30% representation targets with Marxan required twice the fish catch loss than the categorical method. The categorical classification and Zonation do not consider targets for conservation features. However, when we reduced Marxan targets to 16.3%, matching the representation level of the “strict protection” class of the categorical result, the methods show similar catch losses. The management category portfolio has complete coverage, and presents several management recommendations including strict protection. Zonation produces rapid conservation rankings across large, diverse datasets. Marxan is useful for identifying strict protected areas that meet representation targets, and minimize exposure probabilities for conservation features at low economic cost. We show that methods based on Zonation and a simple combination of variables can produce results comparable to Marxan for species representation and catch losses, demonstrating the value of comparing alternative approaches during initial stages of the planning process. Choosing an appropriate approach ultimately depends on scientific and political factors including representation targets, likelihood of adoption, and persistence goals.
Highlights
While climate change, overfishing and land use change negatively impact the biodiversity and ecological function of marine ecosystems worldwide [1,2], increasing evidence shows that effective conservation and management can recover the resource base, conserve biodiversity, and increase fisher’s incomes [3,4,5,6,7]
We produced two maps of biodiversity value, one based on the estimated numbers of fish species (Figure 4a) and one with biodiversity value calculated by the first run of the Zonation algorithm on biodiversity features alone (Figure 4b)
The map produced by Zonation highlights many of these same areas for high biodiversity value (Figure 4b), with some key differences, notably higher estimates for the Banc de Leven some 40 km westnorthwest of the Nosy Mitsio group, and the large shallow banks southwest of Cap Sainte Marie
Summary
While climate change, overfishing and land use change negatively impact the biodiversity and ecological function of marine ecosystems worldwide [1,2], increasing evidence shows that effective conservation and management can recover the resource base, conserve biodiversity, and increase fisher’s incomes [3,4,5,6,7]. In this paper we compare four alternative methods of successive technical complexity for identifying conservation and management priorities across Madagascar’s west coast, a regionally and globally important tropical coral reef ecosystem [10,11]. The waters of the West Coast of Madagascar are home to 90% of Madagascar’s coral reefs, large-scale export fisheries for shrimp, octopus, sea cucumbers, and tuna, and important artisanal fisheries. Few additional areas are under formal marine management across a region spanning thousands of kilometers of coastline and home to nearly two million people, many of whom are dependent on marine resources as an important protein source for local consumption and as a source of cash from export or sale [13,14]. Large areas of the region’s coral reef ecosystems are chronically stressed [17]
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