Growth of three subtropical mangrove species in response to varying hydroperiod in an experimental tank

Abstract

The effect of hydroperiod on the survival and growth of Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle seedlings under experimental conditions was investigated using a simulated tidal system. Seedlings of the three mangrove species were grown at four inundation levels. All levels were flooded every 12 h in order to create a simulated semi-diurnal tide cycle (i.e., two high tides and two low tides per day). Based on the hydroperiod for the study area, level 1 was flooded for 10 h, level 2 for 6 h, level 3 for 2 h, and level 4 for 6 min. After 570 days, the results showed that R. mangle presented the highest growth at level 1 and the lowest growth at level 4. The optimal growth of L. racemosa occurred at levels 2 and 3, but all the seedlings died at level 1, indicating that this species is highly sensitive to tidal regimes. Compared to L. racemosa and R. mangle, A. germinans had a moderate growth rate at all four levels. Mangrove growth differentiations were more prominent at levels 1 and 3, where the three species showed very different growth patterns. Studies of optimal growth using hydroperiod experiments are important in order to understand the physiological responses of mangrove forests to a possible sea level rise in the next decades, especially in subtropical environments where they are constantly exposed to stress.