Stable carbon isotope variability in marine macrophytes and its implications for food web studies |
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Authors: | R L Stephenson F C Tan K H Mann |
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Institution: | (1) Department of Biology, Dalhousie University, B3H 4J1 Halifax, Nova Scotia, Canada;(2) Atlantic Oceanography Laboratory, Bedford Institute of Oceanography, P.O. Box 1006, B2Y 4A2 Dartmouth, Nova Scotia, Canada;(3) Marine Ecology Laboratory, Bedford Institute of Oceanography, P.O. Box 1006, B2Y 4A2 Dartmouth, Nova Scotia, Canada;(4) Present address: Marine Fish Division, St. Andrew Biological Station, E0G 2X0 St. Andrew, New Brunswick, Canada |
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Abstract: | Stable carbon isotope ratios ( 13C) of eelgrass Zostera marina and of kelp Laminaria longicruris showed considerable variation in time and space. The isotopic composition of Z. marina varied seasonally from a mean of-6 for leaves formed in June to a mean of-10 for leaves formed in February. The maximum range for individual leaves was from-5 to-11.4 . Once a leaf was fully formed, its isotopic composition appeared not to change. In L. longicruris there was no clear seasonal pattern of variation, but in any given blade there was a spatial pattern of variation, with the thickened central band tending to be least negative and the margins most negative. In one blade the range was from-12 to-20 . Since this range overlaps values that are found in various other macrophytes and in seston, the value of the stable carbon isotope ratio as a tracer in food webs involving macroalgae is questioned. For Z. marina, in which the values are seasonally predictable, the technique may be useful if interpreted with care. The most probable explanation of variation in the ratios is differential storage of biochemical components of different isotopic compostion. |
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