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Native and Invasive Macroalgae in Submarine Groundwater Discharge (SGD)

Linking watershed and groundwater management to groundwater dependent ecosystems (GDEs) and their ecological, cultural, and socio-economic values.

This project is a collaboration between The University of Hawai‘i Economic Research Organization (UHERO), Water Resources Research Center (WRRC), the School of Life Sciences, the School of Earth Sciences, and the Hawai‘i Institute of Geophysics and Planetology (HIGP).

Our multi-disciplinary team of scientists sought to use physiological data from native and invasive algae with predictive models—together with hydrological data from Kona—to project habitat suitability for our native Ulva lactuca and invasive Hypnea musciformis in specified climate change and urban development scenarios.

The project began with the development of a land-sea model that allowed us to predict how climate change, future urban development, and native forest protection would affect groundwater quality and quantity and how the resulting water quality would impact native limu and invasive algae in coastal Kona, Hawai‘i. Our results were recently published in Water Resources Research

The manipulative experiments used six salinty/nutrient combinations that follow a natural oceanic to SGD gradiant. This created an opportunity to gather growth and photosynthesis data for these two macroalgal species in a range of treatments and temperatures. The growth data was used to inform the predictive models as mentioned above. The photosynthesis data included values of saturated irradiance (Ek) paired with actual logged irradiance to derive a little-used but highly intuitive parameter; time in saturated irradiance (Hsat). We further developed a new parameter—diurnal saturated photosynthesis index (DSPI)— using individual Hsat values with their maximal values of photosynthesis (Pmax). DSPI thus gives us a maximum daily photosynthetic gain and our results suggest that the invasive H. musciformis does not tolerate salinities below ~28 ppt despite significant nutrient subsidies. See our results published in Scientific Reports.

Clockwise from top left: individual algae in experimental jars, field validation in Kona, transect, researcher in Kona, H. musciformis in lab, U. lactic during data collection.