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Temporal Variability in Chlorophyll Fluorescence of Back-Reef Corals in Ofu, American Samoa

Gregory a. Piniak^1,* and Eric K. Brown^2,

¹ USGS Pacific Science Center, 400 Natural Bridges Drive, Santa Cruz, California 95060
² Hawai‘i Institute of Marine Biology, P.O. Box 1346, Kne‘ohe, Hawaii 96744

^* To whom correspondence should be addressed, at NOAA Center for Coastal Fisheries and Habitat Research, 101 Pivers Island Road, Beaufort, NC 28516. E-mail: greg.piniak{at}noaa.gov

Current address: Kalaupapa National Historic Park, P.O. Box 2222, Kalaupapa, HI 96742. E-mail: Eric_Brown{at}nps.gov

Abstract. Change in the yield of chlorophyll a fluorescence is a common indicator of thermal stress in corals. The present study reports temporal variability in quantum yield measurements for 10 coral species in Ofu, American Samoa—a place known to experience elevated and variable seawater temperatures. In winter, the zooxanthellae generally had higher dark-adapted maximum quantum yield (F_v/F_m), higher light-adapted effective quantum yield (F/F'_m), and lower relative electron transport rates (rETR) than in the summer. Temporal changes appeared unrelated to the expected bleaching sensitivity of corals. All species surveyed, with the exception of Montipora grisea, demonstrated significant temporal changes in the three fluorescence parameters. Fluorescence responses were influenced by the microhabitat—temporal differences in fluorescence parameters were usually observed in the habitat with a more variable temperature regime (pool 300), while differences in F_v/F_m between species were observed only in the more environmentally stable habitat (pool 400). Such species-specific responses and microhabitat variability should be considered when attempting to determine whether observed in situ changes are normal seasonal changes or early signs of bleaching.

Abbreviations: F_v/F_m, maximum photosynthetic yield • F/F'_m, effective photosynthetic yield • rETR, relative electron transport rate • PAR, photosynthetically active radiation