Environmental forcing versus endogenous control of photosynthesis in intertidal epilithic microalgae

Abstract

Photoadaptation and photosynthetic capacity of an intertidal epilithic microflora were measured hourly over a period of 8 d. The algae were photoadapted to the dim light intensities experienced when submerged and showed little resistance to the extreme irradiances received when exposed. During neap tide when the community was permanently submerged, the photosynthetic response of algae collected hourly in the field followed a circad~an cycle. The endogenous control of this cycle was demonstrated by isolation experiments. During spring tide, photosynthet~c processes were photoinactivated at low tide when extreme irradiances reached the algae. These results lead to the general hypothesis that short-term variability in the photosynthetic capacity of intertidal epilithic microalgae is controlled primarily by endogenous phasing at neap tide and tidal forclng a t spring tide. Time senes of in situ production were reconstructed from solar irradiance measurements and hourly estimates of the parameters of the Photosynthesis-Irradiance curve. Despite the additional stress of low tide exposure, average daily production was comparable between spring and neap tides.

European-scale analysis of seasonal variability in limpet grazing activity and microalgal abundance

“…Examination of the relationship between physical variables and microalgal abundance can give valuable insight into where such studies should be focused. We found a significant inverse correlation of microalgal abundance with maximum monthly air temperatures at all locations, and with mean monthly sunshine hours in the south-west of England, indicating the potential importance to microalgal productivity of conditions during the period of emersion (see Aleem 1950, Castenholz 1963, Lamontagne et al 1989). Interestingly, there was no significant relationship between limpet grazing activity and standing stock at any location.…”

Physical Stress and Biological Control Regulate the Producer–consumer Balance in Intertidal Biofilms

“…Recent attempts to link biodiversity and ecosystem functioning have rekindled interest in a holistic interpretation of community structure (Loreau et al 2001, Naeem 2002 and highlighted the need to measure the relative importance of abiotic and biotic factors including bottom-up and top-down regulation of communities. There is, however, a growing realization that physicochemical factors, such as light or nutrients, can either stimulate the growth of primary producers (production) or constrain them (Lamontagne et al 1989, Menge 1992, Sundback et al 1996. Here, we unravel the relative contributions of bottom-up forcing, top-down regulation, and inhibition by environmental stressors on one of the major primary producers in the mid region of exposed North Atlantic rocky shores: photosynthetic biofilms (Hawkins et al 1992).…”

Annual bacterial production in relation to benthic microalgal production and sediment oxygen uptake in an intertidal sandflat and an intertidal mudflat

“…In addition, production was assumed to be negligible during submersion of the flats, but this may not always be the case, even with depths of 2 m at high tide (Leach 1970, Varela & Penas 1985. A third potential problem arose from the need to extrapolate gross production between sampling dates (Colijn & de Jonge 1984, Shaffer & Onuf 1985, Lamontagne et al 1989). The assumption made in this study was that productivity was never light-saturated; therefore, productivity on days between actual measurements was predicted from measured oxygen production per unit light and light available to the microalgae.…”