Identifying future hotspots for algal blooms: A multi-dimensional analysis evaluating impacts of potential land-based sources of pollution on the health of American Samoa’s coasts


Rosie Alegado, Assistant Researcher, University of Hawaii Manoa


National Institute for Water Resources, Water Resources Research Institute Program


3/1/2015 - 2/28/2016


Land-based sources of pollution (LBSP) drive coastal algal blooms, growth of opportunistic seaweeds that can persist for years and in many parts of the world. In tropical regions, blooms often have negative ecological and economic impacts, and are exacerbated by declines in grazers or loss of habitat. Using American Samoa as comparison for on-going studies of the Main Hawaiian Islands, we employed the first multi-dimensional assessment integrating geochemistry, nutrient measurements, and microbial community analysis with submarine groundwater discharge, to examine the potential for LBSP to impact reefs in Tutuila.

Our study aimed to identify areas vulnerable to blooms. We selected coastal sites along a human use gradient ranging from pristine to heavily impacted. Pristine sites had no residents within the watershed, little LBSP, few obstructions to water movement and sparse run-off. Impacted sites were downstream of dense residential areas and had substantial sediment loads and slowed water movement – pre-conditions for an algal bloom. At each site, we collected surface water for inorganic nutrients, δ15N, and planktonic microbial community, tissues of indicator algae, and characterized the benthic community.

Samples analyses are underway but much can be gained by examination of sites on our gradient. Microbial community analysis will be performed using high throughput Illumina sequencing. Algal tissues will be characterized by δ15N and %N analysis. We anticipate our results from pristine sites will show diverse benthic-plant communities, a microbial community that is indicative of a healthy watershed and low δ15N and %N in tissues of indicator algae. We anticipate our results from impacted sites will show declines in species numbers for the benthic communities, a shift in microbial communities with detection of pathogens, as well as elevated δ15N and % N in tissues of indicator algae. These data should help inform resource managers as to the threats to coastal regions.