Important Plant Species for Arboreal Snail Conservation Efforts across O‘ahu, Hawai‘i

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Informed conservation efforts for Hawaiian land snails are urgently needed. A critical step in this is identifying which native plants support arboreal snail populations. The objectives of this study were to (1) revisit a long-term study site at Mt. Ka‘ala Natural Area Reserve, O‘ahu to confirm that snail plant preferences persist over time, and (2) expand our sampling to eight additional (nine total) sites on O‘ahu to better inform conservation efforts across the island. Despite a decade between studies, snail preferences for plants at Mt. Ka‘ala remained consistent with Hydrangea arguta and Ilex anomala emerging as important species preferred by many arboreal snails. Across the nine sites on O‘ahu, 34 (25%) of the 135 plant species in our surveys were preferred by at least one snail species at one site, but only 16 plants (12%) were preferred (used more often than expected by chance) more often than they were avoided (used less often than expected by chance) — notably, Antidesma platyphyllum, I. anomala, and H. arguta. These results highlight that native plant species vary significantly in their value to Hawaiian arboreal snails and that our targeted, person-hour intensive field experiments yield critical ecological insights needed for effective conservation action. Snail conservation has historically been hindered by a lack of key ecological data, but the identification of host plants provides actionable guidance for habitat restoration and conservation planning aimed at reversing the decline of Hawai‘i’s critically endangered snail fauna and the habitats on which they depend.