Assessing the potential for mangrove oyster aquaculture in an estuarine system of the southeastern coast of Brazil : a geographic information system approach
Date
2008-04-10T06:01:45Z
Authors
Barroso, Gilberto Fonseca.
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Abstract
Coastal aquaculture is among the fastest growing sectors of the food producing industry. Bivalve farming is a promising activity in low income countries were mollusk could be cultured under low technology and budget, contributing to reduce poverty and assuring food security. Site selection has been considered as a key process in successful aquaculture developments. A suitability model for mangrove oyster farming in the PiraquC-aqu/PiraquC-mirim estuarine system - PAPMES (Espirito Santo, Brazil) was developed. The suitability model is based on Multi-criteria Evaluation (MCE) which consists of selecting criteria, define their acceptable and optimum ranges, assign their weights of relative importance, and combine suitability criteria under a decision rule. A georeferenced database was created with 8 water quality variables considered related to the habitat requirements of mangrove oyster, with 19 field sampling campaigns on 6 samplings sites embracing an area of 51 lha. Low salinity and dissolved oxygen levels were detected in the upper estuarine sections. Using the geographic information system (GIs) Idrisi32, point data were converted to continuous surface models using secondorder polynomial fit. The normalization process aimed at standardizing the set criteria considering a single scale ranging from low (i.e., 0) to high suitability (i.e., 255). Through pairwise comparison technique weights were assigned to each criteria. Salinity and dissolved oxygen were considered the most important criteria because of their relationship to oyster short-term survival. A weighted linear combination and two constraints (i.e., fecal coliform > 43 MPN1100mL and navigation channel) were applied as the MCE decision rule. An area of 75ha (14.6% of the PAPMES) was considered constrained for mangrove oyster fanning. Two suitability models were performed using average and low salinity values. Suitability maps developed onto the 0 - 255 range were reclassified in 4 categories: unsuitable, moderately suitable, suitable, and very suitable. In both models, no area was indicated as unsuitable. Although the low salinity model could be considered more restrictive, it yielded a very suitable area 26% larger than the average salinity model. The combination of the two models could bring together risk taking and risk-averse perspectives, respectively. The output of such combination is a map locating 80ha of very suitable areas for mangrove oyster farming, with 9.5ha preferentially designated for intertidal farming using racks. Aquaculture zones are discussed in terms of their interactions with other systems at higher spatial scales, such as the watershed and the coastal zone. GIs can serve as an integrative environment to integrate complex variables in multiple scales. It is only through its integration in multisectoral development plans and programs for the watershed and coastal zone realms that coastal aquaculture will be recognized as sustainable enterprise.