Field biology of Halimeda tuna (Bryopsidales, Chlorophyta) across a depth gradient: comparative growth, survivorship, recruitment, and reproduction |
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Authors: | Peter S Vroom Celia M Smith James A Coyer Linda J Walters Cynthia L Hunter Kevin S Beach Jennifer E Smith |
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Institution: | (1) Deparment of Botany, University of Hawai'i at Manoa, 3190 Maile Way, Honolulu, HI, 96822, U.S.A.;(2) Present address: Kewalo Research Facility, National Marine Fisheries Service, 1125B Ala Moana Bvld., Honolulu, HI, 96814, U.S.A.;(3) Deparment of Botany, University of Hawai'i at Manoa, 3190 Maile Way, Honolulu, HI, 96822, U.S.A;(4) Department of Marine Biology, University of Groningen, Kerklaan 30, PO Box 14 9750 AA, Haren, The Netherlands;(5) Department of Biology, University of Central Florida, 4000 Central Florida Bvld., Orlando, FL, 32816, U.S.A;(6) Waikiki Aquarium, 2777 Kalakaua Ave., Honolulu, HI, 96815, U.S.A |
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Abstract: | Growth, survivorship, recruitment, and reproduction of Halimeda tuna, a dominant green alga in many reef systems of the Florida Keys, were monitored at a shallow back reef (4–7m) and deep reef slope (15–22 m) on Conch Reef. Despite lower light intensities and similar grazing pressures, amphipod infestations, and epiphyte loads at both sites, the deeper site exhibited significantly higher growth rates in summer months over a 4-year period than found for the shallow population, possibly because of higher nutrient levels at depth and photoinhibition of shallow plants. Sexual reproductive events occurred simultaneously across the entire reef, with up to 5% of the population at both sites developing gametangia. New upright axes formed from zygotes, asexual fragmentation, or vegetative runners. Plants appear to have persistent basal stumps that survive harsh environmental conditions, even if upright, photosynthetic axes are removed. Sexual reproduction and smothering by epiphyte overgrowth are hypothesized to be two causes of death for individuals. |
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Keywords: | Halimeda tuna coral reef alizarin Florida Keys Ericthonius brasiliensis Dictyota |
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