Invasive algae can pose a serious threat to coral reefs by spreading and growing rapidly, smothering or outcompeting corals and other organisms. This can significantly alter the structure and function of the reef ecosystem. Four species of alien red algae have become invasive in Hawaiʻi: prickly seaweed (Acanthophora spicifera), hookweed (Hypnea musciformis), smothering seaweed (Kappaphycus spp.), and gorilla ogo (Gracilaria salicornia). Mangroves are an invasive alien species, introduced to Hawai‘i in the early 1900s, that rapidly colonize many nearshore environments, cause water quality issues, anoxic sediments, and provide habitat for invasive fish species.
A single data layer was created to represent presence-only of invasive algae species in nearshore waters and mangroves along the shoreline. Invasive algae data were from monitoring surveys in the Hawaiʻi Monitoring and Reporting Collaborative database (2000-2013) as well as invasive algae surveys conducted across the state in 2002 and 2004 by Dr. Jennifer Smith. Data consist of point locations of invasive algae presence that were subsequently converted to raster. To account for uncertainty in geographic position, the fragmentation and spread of algae, and expanded ranges, we estimated presence within a 1-km radius of observed invasive algae locations. Shorelines with invasive mangroves present were extracted from NOAA Environmental Sensitivity Index (2001) line data, converted to raster with a value of 1, and combined with invasive algae data. No buffering or focal statistics were applied with the assumption that mangroves do not extend further offshore than the footprint of the resulting 100 m raster pixels. These data are presence-only. The status in un-surveyed areas is unknown and there is the potential that a survey failed to observe an invasive species where it is actually present. Map units are presented as a normalized score from 0 - 1.