Producción primaria del microfitobentos intermarealefectos del fotoperiodo y las mareas

Resumen

Microphytobenthos (MPB) is the photosynthetic community that inhabits euphotic sediments such as the intertidal zone. The primary production of MPB contributes significantly to the total primary production in estuaries. The photosynthetic biofilm or microbial mat formed by MPB grows at the sediment-water interface. Therefore, this community is strongly influenced by tidal state (immersion-emersion) and light/dark cycles. In the present thesis, we aimed to clarify aspects related to the effects of such physical forcing on the net production of MPB intertidal communities. Despite the higher incident irradiance in emersion, conserved energy via photosynthesis did not increase in parallel; in fact, less than 1 % of the incident light was conserved in any of the two tidal states. Of the absorbed light energy, 97 % was dissipated as heat in the sediment, however, the heat dissipation flux was directed mainly towards the water column during immersion, and toward deeper sediment layers during emersion. Thus, under emersion, sediment temperature increased notably at high irradiances. Light use efficiency was always slightly lower in emersion in comparison to immersion. MPB primary production in intertidal sediments showed a diel pattern with maximum production at 4-6 hours after initiation of daylight. In the absence of a tidal signal, it seems that this pattern is due to a vertical migration circadian rhythm entrained mainly by photoperiod. The existence of this pattern has to be considered when making measurements of MPB primary production to properly estimate diel primary production rates. In addition to diel oscillations, seasonal and spatial changes were observed along intertidal gradient with maximum peaks of biomass or production being observed in winter but without a clear spatial pattern. In the inner Cadiz Bay, MPB distribution and primary production along intertidal zone was conditioned by seasonality and environmental heterogeneity of morpho-hydrodynamic conditions. Overall, microbenthic metabolism of bare sediments in Cadiz Bay was net autotrophic with a net annual production of 76 g C m-2 yr-1, comparable to that of other similar intertidal flats in Europe. MPB production can contribute up to 41 % of the total benthic production of the intertidal zone in inner Cadiz Bay.