Combined effects of high temperature and light on the photosynthetic parameters and recovery of temperate microphytobenthos in Browns River, Tasmania

Microphytobenthos (MPB) communities are responsible for most primary production in shallow intertidal mudflats. The effects of short-term changes in temperature and light (1200, 500 and 0 μmol photons m^-2s^-1) on the photosynthetic activity of intertidal MPB communities of Browns River, Tasmania, during winter (0, 5, 10 and 15 Celsius degree) and summer (20, 25, 30, 35 and 40 Celsius degree) were examined using a Pulse Amplitude Modulated (Water PAM) fluorometer. The MPB communities were primarily dominated by the diatom genera Navicula, Cocconeis and Amphora, with a difference in species dominance during seasons. During summer, Amphora coffeaeformis dominated communities were significantly impacted by temperatures above 30 Celsius degree regardless of light intensities. The MPB was able to photosynthesize at temperatures only up to 25 Celsius degree. The rETRmax at 25 Celsius degree, ranged from 39.18 +- 3.42 (500 μmol photons m^-2 s^-1) to 22.83 +- 1.05 (0 μmol photons m^-2 s^-1), which was lower than the values recorded at an equivalent irradiance in in-situ summer. However, if ambient temperature exceeds 25 Celsius degree in summer, it is likely that the photosynthetic capabilities of the MPB will be diminished and it will cause irreversible photoinhibition.