The lack of low temperature tolerance of tropical seagrasses strongly restricts their geographical distribution

Abstract

Temperature is considered to be the main factor controlling the growth and eco-distribution of seagrasses. In this study, the joint effects of temperature (27, 24, 21, 18 and 15 °C) combined with three light intensities (0, 200 and 800 μmol m^-2 s^-1) on chlorophyll fluorescence and activities of antioxidative enzymes were examined for three tropical seagrasses Enhalus acoroides, Thalassia hemperichii and Cymodocea rotundata. The results showed that low temperature could damage the PSII donor side, PSII reaction centers and end electron acceptor pool, thereby directly injured their photosynthetic performance. Furthermore, the lower the temperature and the higher the light intensity, the greater the damage incurred. The antioxidant defense system of seagrass cannot sufficiently counter low temperature stress (for temperatures below 21 °C) under high light. These results help explain why the ecological distribution of these three tropical seagrasses is limited to the low tidal coastal area of warm tropical regions.

Keywords: Cymodocea rotundata; Distribution; Enhalus acoroides; Seagrass; Temperature; Thalassia hemperichii; Tropical.