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Comparison of photosynthetic characteristics of the seagrasscongeners Zostera marina L. and Zostera japonica Ascher. & Graeb.
Citation:
Shafer, D. AND J. E. KALDY, III. Comparison of photosynthetic characteristics of the seagrasscongeners Zostera marina L. and Zostera japonica Ascher. & Graeb. MARINE ECOLOGY PROGRESS SERIES. Inter-Research, Luhe, Germany, 112:91-97, (2014).
Impact/Purpose:
On the Pacific coast of North America two seagrass species in the genus Zostera co-exist; the native species Zostera marina, and an introduced species, Z. japonica.
Description:
On the Pacific coast of North America two seagrass species in the genus Zostera co-exist; the native species Zostera marina, and an introduced species, Z. japonica. These two species typically occupy separate habitat niches, with Z. marina occupying the lower intertidal and shallow subtidal zones, and Z. japonica occupying the mid- to upper intertidal zone. This study was designed to explicitly test the hypothesis that Z. japonica has higher light requirements than Z. marina. Nursery pots containing Z. japonica and Z. marina were grown intermixed in replicate mesocosm tanks at two different light levels. Photosynthetic characteristics were measured after 18 d exposure. Using PAM fluorometry, we detected no diel patterns of effective quantum yield (Y) in either seagrass examined. We evaluated photosynthetic parameters derived using O2 evolution techniques. Z. japonica maximum rates of photosynthesis were 3-6 times higher than Z. marina, while respiration rates were similar. The measured compensation irradiance (Ic), respiration and chlorophyll normalized photosynthetic efficiency (α) of the introduced Z. japonica were similar to that of the native Z. marina. Estimates of the maximum colonization depth calculated using measured Ic for each species and seasonal light attenuation coefficients (kd), indicate that Z. japonica should grow at least as deep as Z. marina. Consequently, we suggest that Z. japonica has a competitive advantage with regard to carbon balance and that light is not the factor controlling the lower depth distribution of Z. japonica in North America.