Effects of light on seagrass photosynthesis,growth and depth distribution |
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Institution: | 1. Western Ecology Division, US – EPA, 2111 SE Marine Science Dr., Newport, OR, USA;2. National Center for Ecological Analysis and Synthesis, 735 State St., Santa Barbara, CA, USA;1. Botany and Plant Science, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland;2. Seagrass Ecology Group, Oceanography Centre of Murcia, Spanish Oceanography Institute, Spain;3. Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Napoli, Italy |
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Abstract: | The relationships between light regime, photosynthesis, growth and depth distribution of a temperate seagrass, Zostera marina L. (eelgrass), were investigated in a subtidal eelgrass meadow near Woods Hole, MA. The seasonal light patterns in which the quantum irradiance exceeded the light compensation point (Hcomp) and light saturation point (Hsat) for eelgrass photosynthesis were determined. Along with photosynthesis and respiration rates, these patterns were used to predict carbon balances monthly throughout the year. Gross photosynthesis peaked in late-summer, but net photosynthesis peaked in spring (May), due to high respiration rates at summer temperatures. Predictions of net photosynthesis correlated with in situ growth rates at the study site and with reports from other locations.The maximum depth limit for eelgrass was related to the depth distribution of Hcomp, and a minimum annual average Hcomp (12.3 h) for survival was determined. Maximum depth limits for eelgrass were predicted for various light extinction coefficients and a relationship between Secchi disc depth and the maximum depth limit for survival was established. The Secchi disc depth averaged over the year approximates the light compensation depth for eelgrass. This relationship may be applicable to other sites and other seagrass species. |
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