This raster data layer represents the presence of alien and invasive algal species within 1 km of an observation. Original data is from Jen Smith, based on MHI surveys in 2002, and invasive species data queried from the FERL biological survey database which is synthesized from NOAA, DAR, CRAMP, TNC, and other surveys (Smith et. al 2002; Hawaii Fish and Benthic Biological Synthesis Database). This data should be considered presence only. Areas with no presence may be due to lack of survey data, surveys that did not identify algae to the species level, or observed absence. Raster values of 1 represent areas within 1 km of positive invasive algae observations while values of 0 represent the remaining area. The cell size is 500 m and the AOI is from the shoreline of the MHI extending 5 km offshore and 1 km inshore. This layer was developed as part of a geospatial database of key anthropogenic pressures to coastal waters of the Main Hawaiian Islands for the Ocean Tipping Points project (http://oceantippingpoints.org/). Ocean tipping points occur when incremental changes in human use or environmental conditions result in large, and sometimes abrupt, impacts to marine ecosystems. The ability to predict and understand ocean tipping points can enhance ecosystem management. The goal of the Hawaii case study of the Ocean Tipping Points project was to gather, process and map spatial data on environmental and anthropogenic drivers of coral reef ecosystem states. Understanding direct anthropogenic drivers is critical for coral reef management and implementing policies to protect ecosystem services generated by coral reefs. This layer is presented in the WGS84 coordinate system for web display purposes. Downloadable data are provided in native coordinate system or projection.