This research aims to link land-based sources of nitrogen pollution to changes in limu (macroalgae) in Kaua‘i’s nearshore environments. Macroalgal species readily uptake nitrogen in the marine environment, and with lack of pressure from herbivore grazing can be strong competitors with corals. Limu, are used as nutrition for local communities, medicine, as well as for ceremonial purposes. On the island of Kaua‘i, there are concerns about outdated waste management systems, as well as fertilizer from farms, golf courses, and hotels entering the nearshore environment. Methods for monitoring nutrient inputs can be costly and technical, making it difficult for communities to monitor nutrient inputs and their effects on nearshore ecosystems. I focused three sites on the north eastern shorelines of Kaua‘i: Anini, Kalihiwai, and Moloa‘a. These sites once supported thriving fishing communities and were known for the diversity and health of their limu. I investigated potential sources of nitrogen pollution by collecting samples of ocean water, stream water, and macroalgae, then analyzing them using stable nitrogen isotope analysis. These results will be compared with land use maps of suspected sources of pollution. Limu species present today will be compared to lists of historically known species for these sites based on macroalgal herbarium specimens from Bishop Museum, and records from historical newspaper articles, and interviews.
Results/Conclusions
Macroalgal stable nitrogen isotope ratios show high values (above 7) at sites near outdated cesspools owned by vacation rentals, county park restrooms, and recently developed luxury housing. This research also found that although the standard drying method for this type of analysis includes drying samples in oven, drying with silica gel, salt, and herbarium pressing show no significant difference in their delta 15N ratios. This is particularly useful in remote conditions, research cruises, or community settings where using ovens can be challenging logistically. At these sites, there is a decline in the amount of algal species found at these sites over all (only 54% of historically recorded species). Some new species, not historically recorded, were identified at these sites, including more species of blue-green and other invasive algal. There was a noted decline in native species, especially those that are consumed or are historically known for the area, such as limu 'ele'ele (Ulva flexuosa) at Anini reef, and limu kohu (Asparagopsis taxiformis). This research pilots new and less expensive approaches for monitoring land-based sources of pollution which may aid in community-based management.