Light intensity and the interactions between physiology, morphology and stable isotope ratios in five species of seagrass

• Published in: Journal of experimental marine biology and ecology 1996, Vol.195 (1), p.91-110
• Main Authors: Grice, A.M., Loneragan, N.R., Dennison, W.C.
• Format: Article
• Language: English
• Subjects: Carbon; Light; Marine; Nitrogen; Seagrass; Stable isotope ratio
• ISSN: 0022-0981; 1879-1697
• DOI: 10.1016/0022-0981(95)00096-8

The effects of light intensity on stable isotope ratios, physiology and morphology of five seagrass species were investigated in an outdoor, light controlled experiment. Seagrasses were maintained in flowing seawater aquaria, with each seagrass species exposed to different light regimes (5, 15, 20, 30, 50, and 100% full sunlight) using shade screens. After 30 days exposure to the various light regimes the five species of seagrass showed markedly different δ 13C signatures, with values ranging from −17.6 to −5.5%. Marked responses to light intensity were also shown by each species, with leaf δ 13C values becoming at least 3 to 4%. less negative in full sunlight. Other common responses to light intensity were: higher productivities, higher C:N ratios, larger lacunal areas and more root biomass under full sunlight compared with lower light intensities. Less negative δ 13C values at high light intensities could be primarily due to (a) increased uptake of 13C from the external C source or (b) increased internal recycling of CO 2 in the lacunae due to the increased lacunal size. The increase in size of lacunae may be related to the need to supply more oxygen to the increased root biomass occurring in seagrasses under high light conditions. In contrast to δ 13C, the δ 15N values of seagrass leaf tissue appeared to be affected by the site of collection, rather than the species of seagrass or light intensity. Higher δ 15N values were found at the more eutrophic site (western Moreton Bay = 8.6 to 8.8%.) than at the site further from anthropogenic influence (eastern Moreton Bay = 2.6 to 4.5%.).