New Zealand Journal of Marine and Freshwater Research abstracts

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Contribution of photosynthetic gains during tidal emersion to production of Zostera capricorni in a North Island, New Zealand estuary

Anne-Maree Schwarz

National Institute of Water and Atmospheric
Research Limited
P.O. Box 11 115
Hamilton, New Zealand
email: a.schwarz@niwa.co.nz

Abstract  Photosynthetic characteristics of intertidal Zostera capricorni were measured under different tidal conditions in Whangapoua Harbour on the eastern Coromandel Peninsula, New Zealand, and compared with permanently submerged seagrass beds. Photosynthetic characteristics were measured using pulse amplitude modulated (PAM) fluorometry and oxygen (O2) electrode techniques. Gross light saturated photosynthesis measured as oxygen exchange averaged 5.74 and 5.36 mg O2 g^-1 dry weight (DW) h^-1 and leaf respiration rates averaged 1.22 and 1.38 mg O2 g^-1 DW h^-1, for intertidal and subtidal plants respectively. Photosynthesis of both intertidal and shallow subtidal plants was light saturated at between 195 and 242 µmol photons m^-2 s^-1, suggestive of acclimation to a high light environment. Despite the period of exposure at low tide clearly being an important time for photosynthetic gains for intertidal plants, when water clarity was sufficiently high, maximum rates of photosynthesis were also possible when the beds were submerged. If average water clarity was at the clearer end of a range measured for this site (Kd = 0.85 m^-1) then it was calculated that for intertidal seagrass beds growing at mean sea level in Whangapoua, c. 50% of above-ground production could occur while plants were submerged.

Keywords  intertidal seagrass; PAM fluorometry; photosynthesis

M03071; Online publication date 24 November 2004 Received 23 October 2003; accepted 8 August 2004
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38: 809–818
0028–8330/04/3805–0809 © The Royal Society of New Zealand 2004

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