Anchialine Pools Climate Vulnerability Assessment and Adaptation Strategies for Hawai‘i AT VULNERABILITY HABITAT DESCRIPTION Anchialine pools are landlocked bodies of water found in young lava flows and . These pools are characterized by subsurface hydrological connectivity, but lacking surface connection to the . Pools vary in salinity, dissolved oxygen levels, and water level depending on distance to the sea, tidal fluctuations, groundwater input, and rainfall. The Hawaiian have the largest concentration of anchialine pools in the world. The of Hawai‘i supports 80% of the world’s known anchialine pools.

HABITAT VULNERABILITY

Anchialine pools are sensitive to climatic factors that reduce Low Moderate High groundwater levels and surface runoff, which impacts pool depth and salinity. Sea level rise and saltwater intrusion may also change Drivers of Habitat Vulnerability pool size and salinity, as as influence pool abundance and • Climatic factors and disturbance landscape distribution. Shifts in pools salinity, depth, distribution, regimes: Drought, precipitation amount & and temperature will impact anchialine pool fauna. Non-climate timing, extreme precipitation events, stressors further impact anchialine pool biotic communities and tropical storms/hurricanes, sea level rise, structure by affecting water quality, water depth, competition and coastal flooding, saltwater intrusion, sea predation, and elevating disturbance. Development and roads will surface temperature reduce opportunities for new pool formation as sea levels rise. • Non-climate factors: Invasive species, Anchialine pools are abundant on Hawai’i and pristine habitat areas groundwater development, water still remain, but managers have limited funding, and these habitats diversions, roads/highways/trails, will continue to compete with coastal development pressures. residential & commercial development, pollution & poisons, recreation PROJECTED FUTURE POTENTIAL IMPACTS ON ANCHIALINE POOL CHANGES HABITATS ADAPTIVE CAPACITY • Changes in Drier conditions restrict pool precipitation; distribution and lower water levels, potentially increasing salinity and Factors that enhance adaptive capacity: increased drought impacting community composition + risk in low- and structure High habitat extent elevation leeward + Some pristine habitat areas remain (e.g., areas Manukā coastline) + High subsurface pool connectivity may • Altered water levels, impacting salinity Increased frequency promote wildlife colonization of new or and strength of and pool community structure and tropical storms/ composition restored pools hurricanes; uncertain • Storm surge may introduce marine + Moderate-high public value change in extreme fauna + Some habitats are protected precipitation events • Storm waves may temporarily increase + Restoration and pool creation efforts pool salinity and sedimentation have been successful Sea level rise (SLR); • <1 m (3.28 ft) of SLR will increase pool increased coastal size; 1 m or more of SLR will cause pool loss to inundation and potential flooding & saltwater Factors that undermine adaptive capacity: intrusion pool creation in low-lying areas with +0.4 m (1.3 ft) to +3.3 m appropriate substrate - Variable habitat integrity (e.g., some (10.8 ft) of SLR by 2100 • Increased surface connectivity pools have been lost on western ) between pools and man-made water - Some human-driven ecological changes features, which may increase vulnerability invasion may be irreversible - • Increased sub-surface salinity, Low diversity and presence of threatened particularly if groundwater levels and endangered species increases decline vulnerability to impacts Increased sea • Two shrimp species (Halocaridina - Managers need more funding to manage surface temperature rubra, Metabetaeus lohena) are climate change impacts +1.3°C (2.3°F) to +2.7°C adapted to variable and high - Face competing interests with coastal (4.9°F) by 2100 temperatures; other shrimp species may be more vulnerable development ADAPTATION STRATEGIES FOR ANCHIALINE POOLS Types of Adaptation Approaches Adaptation Strategy Specific Action Resistance: Prevent climate change Maintain/improve • Provide incentives for Hawaiian field systems to from affecting a resource. water quantity and not be developed or grazed by cattle Near-term approach quality • Investigate and reduce non-point source pollution • Maintain by ensuring native forest cover Resilience: Help resources weather Preserve water • Use Hawaiian field system to slow water, increase climate change by avoiding the supplies by recharge, and benefit anchialine pools effects of or recovering from changes increasing water use • Improve rainfall capture to decrease Near- to mid-term approach efficiency groundwater withdrawals Response: Intentionally Protect and • Establish shoreline setbacks accommodate change and future habitat • Identify and protect low-lying areas where adaptively respond to variable anchialine pools can migrate conditions Long-term approach Knowledge: Gather information Increase • Increase understanding of groundwater influence about climate impacts and/or understanding of on anchialine pools management effectiveness in water resources and • Increase knowledge of water needs of native addressing climate challenges their values and species and the impacts of water Near- to long-term approach withdrawals on these resources Collaboration: Coordinate efforts Create new/improve • Review existing monitoring programs across and capacity across landscapes and partnerships to jurisdictions to identify overlaps and avoid agencies increase capacity duplication of effort Near- to long-term approach

Low F/High E Use Hawaiian field system to slow High F/High E down water, increase recharge, and Identify and protect low-lying

benefit anchialine pools areas where anchialine pools can High

migrate Provide incentives for Hawaiian field systems to not be developed Investigate and reduce non-point

S or grazed by cattle source pollution

S

Mod F/Mod E Establish shoreline setbacks

CTIVENE Improve rainfall capture to E decrease groundwater withdrawals Moderate

EFF Maintain aquifers by ensuring native forest cover

Likelihood of reducing vulnerabilities Likelihood of reducing Increase understanding of groundwater influence on anchialine Review exiting monitoring pools programs across jurisdictions to

Increase knowledge of water needs identify overlaps and avoid of native ecosystems and species duplication of effort

Low and the impacts of water withdrawals Low F/Low E on these resources High F/Low E Low Moderate High FEASIBILITY Ease of action implementation Further information and citations can be found in the Hawaiian Islands Climate Vulnerability and Adaptation Synthesis and other products available online at www.bit.ly/HawaiiClimate. Reynier WA, Gregg RM. 2018. Anchialine Pools: Vulnerability and Adaptation Brief for Hawai‘i. EcoAdapt, Bainbridge Island, WA. Produced in cooperation with the Pacific Islands Climate Change Cooperative, with funding from the U.S. Fish and Wildlife Service.