Spatial and temporal variation of diverse inter‐tidal algal assemblages in Southwest O‘ahu |
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| Authors: | Traci Erin Cox Heather L Spalding Michael S Foster |
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| Affiliation: | 1. Dauphin Island Sea Lab, Dauphin Island, AL, USA;2. Department of Botany, University of Hawai'i at Mānoa, Honolulu, HI, USA;3. Moss Landing Marine Laboratories, Moss Landing, CA, USA |
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| Abstract: | Spatial and temporal variation in tropical inter‐tidal communities is poorly known, making predictions about the effects of climate change and other anthropogenic disturbances difficult. Along Southwest O‘ahu, Hawai'i, local residents are concerned about the environmental effects of coastal development and the perceived loss of targeted algal species, which are collected for human consumption. To describe the coastal benthic community and better understand the processes that form and maintain it, the abundance and composition of macroalgae were sampled in the region's inter‐tidal zone from 2006 to 2015. Sixty‐six macroalgal species and two broad algal assemblages were identified that corresponded to substrate topography and sand influence at a similar tidal elevation. Along flat carbonate benches with a sand beach, Phaeophyceae and Rhodophytes occurred in almost equal proportions, while shores with slightly more topographic relief and angular substrate were dominated by Rhodophytes. Foliose or turf algal forms were most common. Surveys captured the local invasion of an alga, Avrainvillea sp. and significant declines in abundant macroalgae in 2015 after a period of unseasonably warm, calm water. Temporal changes in algal assemblages were related to maximum water temperature and wave height but not precipitation. Thus, algal assemblages appear to be structured by local beach morphology as they interact with sand and wave activity and episodically by unusual weather events. However, manipulation and continuous monitoring of the algal assemblages coupled to sensing of the localized environment is necessary to confirm factors related to assembly maintenance and recent species shifts. |
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| Keywords: | benthic ecology ‘ Ewa Beach sand influence topography tropical inter‐tidal zones warming event |
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