Risk analysis using species distribution modeling to support public policies for the alien alga Kappaphycus alvarezii aquaculture in Brazil

The native tropical seaweed Kappaphycus alvarezii from the Indo-Pacific region has been introduced in many countries because it is the main source of raw material for the carrageenan industry. In Brazil, K. alvarezii aquaculture is allowed in 300km of the southeastern coast. The aim of this study was to analyze the risk of invasion of this species along the entire Brazilian coast to design public policies and to minimize environmental risks associated with aquaculture. The risk analysis was based on: K. alvarezii suitability models (GARP and MAXENT), coral reef presence, substrate preferences for establishment, and the probability of occurrence of nine species of herbivores that are potential feeders. An invasibility index was created from these parameters and published data of field experiments were used for calibration. The maximum values of suitability corresponded to regions with low temperature ranges, low nitrate availability, high irradiance, and high salinity. Three invasion risk classes were established. The areas of high risk are the eastern and northeastern regions, where the main Atlantic coral reefs are found. This is a priority area for global marine conservation. K. alvarezii introduction is not recommended in this area and the cultivation of native species must be prioritized. The area of medium risk is mainly in the northern region, where local field scale experiments are recommended before widespread introduction. The area of low risk is the southeastern region, where K. alvarezii farming has been established since 2004 with no evidence of invasion. However, considering the high capacity of acclimation of this species, permanent monitoring is recommended, even in areas having a low risk of invasion.We state the relevance of our paper in commercial aquaculture since we presented a consistent environmental risk analysis for K. alvarezii that according to FAO is the most cultivated seaweed in the world. Our aim is to contribute for development of sustainable seaweed aquaculture, subsiding data to minimize environmental risks associated with K. alvarezii introduction. This kind of analysis also can be adapted to other countries. Our results indicate safe areas to extend K. alvarezii cultivation, areas where the native seaweed should be cultivated and with those conclusions encouraging the expansion of the commercial seaweed aquaculture and highlight for high environmental risks in coral reef areas.