The same level of human-caused stress will have varying levels of impact on different habitat types due to differences in their vulnerability. For this study we used 3 broad categories of benthic habitat to map cumulative impacts. Nearshore reef habitats were mapped for all MHI by the NOAA National Center for Coastal and Ocean Science in 2007 using high resolution satellite (IKONOS) and aerial imagery. This was the primary data source for the three nearshore habitats mapped in this project.

In addition to nutrient pollution from feed, other threats from aquaculture include risk of escape and genetic contamination of wild populations, disease, use of antibiotics and hormones, and attraction of animals. Two aquaculture map layers were developed for this project: ocean-based aquaculture and land-based aquaculture. 

In 2015, high resolution (2 cm) aerial imagery of the coastlines within the MHI were obtained. This imagery was analyzed to identify and quantify densities of marine debris on all shores across the State. Point locations of marine debris items by type and size-class were obtained from the Hawai‘i Division of Aquatic Resources.

Data on ship locations for a 1-year period (August 2011 – August 2012) from satellite-based Automatic Identification System (AIS) was obtained from the Pacific Islands Ocean Observing System (pacioos.org). Point locations were converted to ship track lines by connecting points with a common ship identification number in chronological order.

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).

Dredging was defined as activity involving physically removing substrate with machinery typically to allow for safe passage of vessels. Polygons for dredged areas were extracted from NOAA habitat maps, NOAA/USACE maintained channels, and NOAA ENCs available as of 2016. Point locations associated with recent dredging projects in which the USACE consulted NOAA in regards to essential fish habitat were buffered by 100 m (Data from NOAA PIRO, unpublished).

Coastal engineering consisted of shoreline armoring structures (e.g., seawalls, revetments, groins, break waters), artificial land (i.e., land fill), and piers. Artificial shoreline, rip rap, and artificial structures were extracted from NOAA Environmental Sensitivity Index (2001) line data and NOAA habitat maps (2007) and validated with high resolution imagery. Note that the above datasets include Hawaiian fishpond walls as artificial man made shoreline structures.

Benthic structures are artificial features in the offshore environment that disrupt benthic habitat and include moored buoys, channel markers, offshore cables and pipelines. The primary source of input data was NOAA Electronic Navigational Charts (ENC) available as of 2016. Point features for buoys, beacons, piles, etc. were extracted from a total of 21 ENC layers and merged together.

Direct human impact includes trampling, swimming, disturbance or displacement of wildlife, and any other effects of human bodies physically in or near the water. To approximate this across the MHI, the InVEST recreation model was run statewide at 1 km resolution for the years 2005 – 2014. This model uses publicly visible geotagged photos posted to the photo-sharing website Flickr to calculate the annual average number of photo users per day per grid cell.

A High Concentration Of Coastal Development And Population Density Results In Cumulative Impacts to the Ecosystem

The majority of visitor accommodations, local human population, and infrastructure are along the coastline in Hawaiʻi. This high concentration of coastal development and population density results in most human activities taking place in and adjacent to the nearshore environment.