Pristine or polluted? Comparison of tropical nearshore macroalgal communities and environmental parameters at Majuro and Arno Atolls

In the Republic of the Marshall Islands, marine resource managers have identified a critical need to explain and mitigate the occurrence of macroalgal blooms along urbanized coastal areas.Nutrient loading from sewage and overfishing of herbivores may cause algal blooms or shifts in macroalgal communities. To better understand the ecology of macroalgae in shallow water (<4 m) with different surrounding population densities, seven sites were studied around the Majuro Atoll lagoon and one on the ocean-side of Arno Atoll. At each site, macroalgae and seagrasses were identified, benthic cover was quantified, algal biomass was measured, and water quality parameters were measured. To examine the presence of different sources of nutrients, the tissue C, N and δ¹⁵N of macroalgal species at each site were compared. This information will be provided to managers to predict algal blooms and community composition shifts with changes in nutrient inputs.