Photosynthetic response of natural assemblages of marine benthic microalgae to short- and long-term variations of incident irradiance in Baffin Bay, Texas.

This study was designed to understand the high variability characterizing primary production rates of microphytobenthos. The photosynthetic efficiency (αB) and photosynthetic capacity (PBmax) of the microphytobenthos were measured at different times of the day on two different dates (8 May and 7 July 1990). In July, unusually low light conditions were caused by the development of a brown tide (chrysophytes). Both light-limited and light-saturated photosynthesis changed at hourly and monthly scales. There was a linear relationship between αB and PBmax, suggesting a common response to environmental factors [αB= 0.0075(±0.00063)·PBmax+ 0.00097(±0.0071), R2= 0.94]. Incident irradiance at the sediment-water interface was the primary physical factor that explained variability of both αB (84%) and PBmax (92%). Temperature had a negative but minor effect that explained an extra 8% and 2% of the variance, respectively. There was no diel rhythm of αB and PBmax and incident irradiance was regulated by wind-induced currents. Therefore, microphytobenthos photosynthesis seemed to be primarily controlled by wind events in Baffin Bay