Studying the Ecophysiological Responses of Native Hawaiian Macroalgae in a Changing World

Abstract

In the Hawaiian flora, approximately 550 species of algae or limu are identified, yet little is known about their physiological ecology: growth rates, photosynthetic capacities, or other features of biology, even for common native species. Culturally, Native Hawaiians as with many Pacific Islanders gather marine plants for nourishment, use in medicine, hula, and other traditional ceremonies. Ecologically, the limu are the primary producers of coastal reefs, provide refuge, and food for a wide range of herbivores and omnivores, and thus are of critical importance to nearshore marine food web. In this study, I 1) analyzed the biodiversity, species composition, and photosynthetic rates of a 2-year-old benthic plant community under future climate change conditions, 2) explored how irradiance and temperature affect the growth and photosynthesis of the native macroalga Microdictyon setchellianum, and 3) cultivated Sargassum aquifolium germlings on limestone tiles to characterize their early life stages and explored the effects of shading. Results reveal that 1) the biodiversity, species composition, and total photosynthetic rates did not dramatically change under predicted climate change conditions suggesting that our limu community may be resilient to changes in coastal acidification and increasing temperatures of coastal waters, 2) M. setchellianum fulfilled expectations for a broadly distributed alga in terms of depth as well as biogeography, had lower growth rate under shaded conditions, but still photoacclimated under both low and high irradiance levels in a short period of time which is consistent with the physiological adjustments for an alga that can be found in the intertidal to deep water communities, 3) and young Sargassum germlings successfully grew on tiles, had high rates of photosynthesis, and an ability to recover after being shaded with physiological expectations for germlings that grow under deep shade of dense, moving canopies of adult Sargassum. This research provides valuable insight into the physiological capabilities of two abundant Native Hawaiian limu, as well as the community of 32 species that developed in experimental mesocosms. In sum, single species studies reveal remarkable abilities that sustain their abundance in current reefs and give insight into changes in our future reefs. Analysis of communities that develop under future scenarios reveals hope for the stability of primary producer communities, at least in the Hawaiian islands. Further research to provide other crucial data will help estimate the ecological success of our benthic community and build restoration tools to help rehabilitate native limu populations such as Sargassum, as interest is building to restore native species on our reefs. Overall, this dissertation fills in biological data gaps for important native Hawaiian algal species and describes a cultivation tool that serves as a step towards replenishing the population of Sargassum on the reefs.