Alien species are non-indigenous organisms introduced into an ecosystem that is not their native habitat either by accident or intentionally. Measured by total counts of all invasive species according to data from the Global Invasive Species Database (GIRD).

For more details on the variable construction, see the original source:

Molnar, J. L., Gamboa, R. L., Revenga C., Spalding, M. (2008). Assessing the global threat of invasive species to marine biodiversity. Frontiers in Ecology and the Environment 6(485).

When using this variable, please cite both the OHI project and the original source.