School of Life Sciences, University of Hawai'i at Mānoa, Honolulu, HI, USA.
University of Hawai'i Economic Research Organization, University of Hawai'i at Mānoa, Honolulu, HI, USA.
Sci Rep. 2023 Aug 26;13(1):13984. doi: 10.1038/s41598-023-40854-7.
Marine macroalgae are important indicators of healthy nearshore groundwater dependent ecosystems (GDEs), which are emergent global conservation priorities. Submarine groundwater discharge (SGD) supports abundant native algal communities in GDEs via elevated but naturally derived nutrients. GDEs are threatened by anthropogenic nutrient inputs that pollute SGD above ambient levels, favoring invasive algae. Accordingly, this case study draws on the GDE conditions of Kona, Hawai'i where we evaluated daily photosynthetic production and growth for two macroalgae; a culturally valued native (Ulva lactuca) and an invasive (Hypnea musciformis). Manipulative experiments-devised to address future land-use, climate change, and water-use scenarios for Kona-tested algal responses under a natural range of SGD nutrient and salinity levels. Our analyses demonstrate that photosynthesis and growth in U. lactuca are optimal in low-salinity, high-nutrient waters, whereas productivity for H. musciformis appears limited to higher salinities despite elevated nutrient subsidies. These findings suggest that reductions in SGD via climate change decreases in rainfall or increased water-use from the aquifer may relax physiological constraints on H. musciformis. Collectively, this study reveals divergent physiologies of a native and an invasive macroalga to SGD and highlights the importance of maintaining SGD quantity and quality to protect nearshore GDEs.
海洋大型藻类是健康近岸地下水依赖型生态系统（GDE）的重要指标，这些生态系统是新兴的全球保护重点。海底地下水排泄（SGD）通过升高但自然产生的养分来支持 GDE 中丰富的本地藻类群落。GDE 受到人为营养输入的威胁，这些输入会污染 SGD，使其超过环境水平，从而有利于入侵藻类。因此，本案例研究借鉴了夏威夷科纳的 GDE 条件，我们评估了两种大型藻类的每日光合作用产量和生长情况；一种是具有文化价值的本地种（绿藻）和一种是入侵种（Hypnea musciformis）。为了应对科纳未来的土地利用、气候变化和水利用情景，我们设计了操纵性实验，以在自然 SGD 养分和盐度范围内测试藻类的反应。我们的分析表明，绿藻的光合作用和生长在低盐度、高养分水中最佳，而 Hypnea musciformis 的生产力似乎仅限于较高的盐度，尽管有较高的养分补贴。这些发现表明，气候变化导致的 SGD 减少，如降雨量减少或含水层用水增加，可能会减轻 Hypnea musciformis 的生理限制。总的来说，这项研究揭示了本地和入侵大型藻类对 SGD 的不同生理特性，并强调了维持 SGD 数量和质量以保护近岸 GDE 的重要性。
