Photosynthetic activity and community shifts of microphytobenthos covered by green macroalgae

Abstract

Summary Macroalgae blooms, a frequent consequence of eutrophication in coastal areas, affect the photosynthetic activity of sediments dominated by microphytobenthos (MPB). Light spectra, steady‐state (after 1 h) microprofiles of O2, gross photosynthesis (Pg), community respiration in light (RL) and net community photosynthesis (Pn) were measured in diatom‐ and cyanobacteria‐dominated communities below increasing layers of Ulva. Photosynthetic photon flux (PPF) decreased exponentially with increasing layers of algae and the light spectrum was increasingly enriched in the green and deprived in blue and red regions. Sediment Pg, Pn and RL decreased as the number of Ulva layers increased; however, 1.6 times higher macroalgal density was necessary to fully inhibit cyanobacteria Pg compared with diatoms, indicating that cyanobacteria were better adapted to this light environment. Long‐term (3 weeks) incubations of diatom‐dominated sediments below increasing layers of Ulva resulted in a shift in the taxonomic composition of the MPB towards cyanobacteria. Hence, changes in the light climate below macroalgal accumulations can negatively affect the photosynthetic activity of sediments. However, spectral niche differentiation of MPB taxonomic groups and concurrent changes in the MPB community may provide sediments with increased resilience to the detrimental effects of eutrophication.

Water column dissolved silica concentration limits microphytobenthic primary production in intertidal sediments

“…Chlorophyll a content was within the range reported previously for the inner Cádiz Bay (García‐Robledo and Corzo , García‐Robledo et al. , ). MPB cell density almost doubled compared to initial values, at least in the treatment with 45 μmol · L DSi −1 added.…”

“…Key index words: Bay of Cadiz; dissolved silica limitation; inorganic nutrients; intertidal sediments; microelectrodes; microphytobenthos; primary production Abbreviations: C org , organic carbon; DSi, dissolved silica; MPB, microphytobenthos; OM, organic matter; P g A , areal gross primary production; P g , gross primary production; P n , net primary production; R D , dark respiration; R L , light respiration Microphytobenthos (MPB), the phototrophic community inhabiting the first millimeters of euphotic sediments, exhibits high rates of primary production (Middelburg and Soetaert 2004, Underwood et al 2005, Garc ıa-Robledo et al 2012. MPB activity has a strong impact on the oxygen exchange (Revsbech et al 1980, Glud et al 1992, Glud 2008, as well as on the fluxes of inorganic nutrients across the sediment-water interface (Laima et al 2002, Dalsgaard 2003, affecting in this way the biogeochemistry of both sediment and the water column.…”

Diel patterns of microphytobenthic primary production in intertidal sediments: the role of photoperiod on the vertical migration circadian rhythm

“…which represented >95% cells and some minor amounts of cyanobacteria (short chains of Oscillatoria sp.). This community was similar to that found in previous studies on MPB in Cádiz Bay 66 .…”

Dynamics of Inorganic Nutrients in Intertidal Sediments: Porewater, Exchangeable, and Intracellular Pools

“…Silicate in particular seems act as a limiting nutrient in the Bay of Cadiz; in addition to the aforementioned relation between NDP and water column silicate, sediment pigments content correlated with . Given that the intertidal MPB community in the Bay of Cadiz is usually dominated by diatoms (García-Robledo et al, 2012 ), silicate seems to control to a large extent the MPB dynamics in the area due to its role for diatom growth.…”