Dynamic model of the short-term variability of microphytobenthic biomass on temperate intertidal mudflats

Abstract

In the present paper, we list and document the relevant behavioral and physiological processes controlling primary productivity of epipelic microalgae on intertidal mudflats in order to develop a simplified model. We first propose, in an attempt to characterize the 'photosynthetically active biomass' of the epipelic community, a new approach to describe the photic environment at the sediment surface, by substituting a discrete 2-layer model in place of continuous vertical light distribution. This concept thus allows us to build a functional representation of the distribution of the photosynthetically active biomass in the sediment and, by then integrating the light and temperature forcing of the latter biomass, to predict the dynamics of the whole epipelic community on short-term time scales. The model then clearly reveals an oscillatory behavior of the total biomass at the surface of the sediment, consistent with field biomass daily measurements performed during a spring-neap tidal cycle. Biomass increases occur during the diurnal emersion phase, in alternation with decreases during the submersion and nocturnal emersion phases; the dynamics of intertidal microphytobenthos is thus controlled by the night/day cycle and tidal hydrodynamic forcing, which determines the fast changes in environmental conditions (light and nutrient availability, temperature) which epipelic microalgae experience. The similarity between model simulations and field observations leads us to conclude that the conceptual framework of the model is valid.

Does sediment grain size affect diatom grazing by harpacticoid copepods?

“…In addition to mobility restrictions, the proportion of silt determines the degree of sediment pore space Wlling, and thus the upper size limits of interstitial species (Schwinghamer, 1981). However, we expect diatom grazers to be mainly active at the sediment surface as a typical mudXat bioWlm is most pronounced near the sediment surface, where diatoms and other phototrophs give rise to an eYcient primary production (e.g., Decho, 2000;Guarini, Blanchard, Gros, Gouleau, & Bacher, 2000). In essence, the feeding eYciency of the two harpacticoid copepod species may be favoured when grain size is increasing, as seen in our experiment.…”

Hydrotaxis of Cyanobacteria in Desert Crusts

“…However, this suggests a close coupling between water content and cyanobacterial movements. Similarly, migration of benthic diatoms in tidal sediment is strongly influenced by the tide level [13,26], but the causes of the rhythm are not yet clearly understood [13]. The upward migration in the presence of water could simply be a relaxation of a tightly bound population that initiates a random walk; thus part of it reaches the surface in the absence of stimulus.…”

Endogenous versus environmental control of vertical migration by intertidal benthic microalgae

“…The vertical migratory behaviour of benthic microalgae also has ecological importance, as the large changes in microalgal biomass in the photic zone of sediments are a major factor in controlling short-term variation in biofilm-level photosynthetic rates (Pinckney & Zingmark, 1991;Guarini et al, 2000;Seroˆdio et al, 2001). Moreover, migratory rhythms cause changes in the photophysiology of the cells, which affects the photosynthetic efficiency of biofilms (Forster & Kromkamp, 2004;Seroˆdio, 2004;Seroˆdio et al, 2005;Perkins et al, 2010).…”