Long-term spatial-temporal eelgrass (Zostera marina) habitat change in the Salish Sea (1932-2016)

Eelgrass (Zostera marina) is a critical nearshore marine habitat for juvenile Pacific salmon (Oncorhynchus spp.) as they depart from their natal streams. Given the poor marine survival of Coho (O. kisutch) and Chinook (O. tshawytscha) salmon juveniles in recent decades, it is hypothesized that deteriorating eelgrass habitats could contribute to their low survival. For three small estuaries in the Southern Gulf Islands of British Columbia, changes in eelgrass area coverage and shape index over the period of 1932-2016 were assessed using historic aerial photographs and Unmanned Aerial Vehicle (UAV) imagery. In addition, changes in eelgrass area and shape index were evaluated in relation to landscape level coastal environmental indicators, namely shoreline activities and alterations and residential housing density. All three eelgrass meadows showed a deteriorating trend in eelgrass condition; on average, eelgrass area coverage decreases by 41% while meadow complexity as indicated by the shape index increases by 76%. Shoreline activities (number of boats, docks, log booms, bulkhead) and residential housing density increase dramatically at all sites over the study period, which are moderately to very strongly correlated to eelgrass area coverage and shape index. Changes in these landscape level indicators over this time period corroborate the observed decline in eelgrass habitat condition as they suggest an overall deterioration of coastal environmental health in the Salish Sea due to increased use of the coastal zone as well as declines in water quality due to urbanization

Long-term Trends in Eelgrass Distribution and Coastal Development of the Salish Sea

In the Salish Sea, eelgrass meadows provide structurally complex habitat for a myriad of fish and invertebrate species, supporting marine ecosystems and stabilizing coastal sediments. Seagrasses of all species however, are in worldwide decline as increasing coastal development threatens the function and diversity of nearshore marine ecosystems. Long-term studies of the spatio-temporal dynamics of eelgrass in the Salish Sea are an important step in identifying contributing factors to eelgrass decline, and developing effective conservation and restoration strategies. One such dynamic to quantify are the impacts of coastal development on the distribution and trends of eelgrass ecosystems. Utilizing a historic aerial photography dataset covering the Southern Gulf Islands, BC over the years of 1932 to 2014, eelgrass beds were mapped using digital image classification methods for selected sites within the region. Through the application of a GIS change analysis, trends in eelgrass distribution were characterized and compared to changes in shoreline development and land use change in adjacent catchment areas. The results of this analysis can be applied to education, conservation, and restoration practices to prevent further eelgrass decline in the Salish Sea and beyond

Benefits and challenges of UAV imagery for eelgrass (Zostera marina) mapping in small estuaries of the Salish Sea

Seagrasses are a fundamental component of nearshore marine habitats and as such, concerted effort has been put into developing remote sensing methods for mapping and monitoring these important habitats. However, in the small coastal bays of the Salish Sea, traditional aerial or satellite remote sensing can be cost-prohibitive or lack sufficient spatial resolution to detect the small, fringing, and often patchy eelgrass (Zostera marina) meadows. Bridging the gap between remotely sensed data and ground-based mapping techniques, aerial imagery collected by Unmanned Aerial Vehicle (UAV) is revolutionizing the study of fine-scale ecological phenomena. This paper presents a method for collection and processing of UAV imagery to map eelgrass (Zostera marina) at three small coastal estuaries in the Salish Sea of British Columbia. A quad-copter style XAircraft X650 UAV equipped with a rectilinear GoPro Hero 3+ was used to acquire images with a ground resolution of 2 cm. Pix4D Pro software was used to orthorectify, georeference, and mosaic UAV imagery into continuous orthomosaics. To delineate eelgrass, a manual classification approach of segmented image objects was used on an eelgrass presence or absence basis using ground reference data collected in the form of underwater videography collected by kayak. Mapping accuracies of 95.3%, 88.9%, and 90.1% were achieved for Village Bay, Horton Bay, and Lyall Harbour respectively. The benefits (flexible acquisition, high resolution) and challenges (inconsistent radiometry, small footprint) of UAV mapping of seagrasses are compared to the use of conventional remote sensing technologies

Geomorphic and geologic controls of geohazards induced by Nepal's 2015 Gorkha earthquake

The Gorkha earthquake (magnitude 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9000 people and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of the earthquakes' induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions