Microbenthos in a hypersaline tidal lagoon: factors affecting microhabitat, community structure and mass exchange at the sediment-water interface

Abstract

Three benthic microbial communities from a hypersaline lagoon with tidal influence were studied: a compact microbial mat, a 'fluffy' microbial mat and a non-cohesive diatom-dominated sediment. In each community, qualitative and quantitative analyses of phototrophs, meio-and macrofauna were done. Vertical profiles of oxygen, sulfide and pH were measured at the sediment-water interface using microelectrodes. Physico-chemical properties of the water column were also assessed. The most compact mat, dominated by Microcoleus chthonoplastes, had the highest photosynthetic biomass, while meio-and macrofauna were nearly absent. The compact mat showed the steepest physico-chemical microgradients and the highest fluxes of oxygen and sulfide. The 'fluffy' mat had an areal amount of chl a similar to the compact mat and contained a higher abundance of meiofauna. This mat showed the deepest oxic layer. The diatom-dominated sediment comprised a high abundance of macrofauna, but meiofauna were very scarce. This community presented relatively smoother microgradients and intermediate values of internal fluxes of oxygen. Our results show the close relationship between the structure of the microbenthic communities, net metabolism, and the exchange of mass at the water-sediment interface. Changes in biotic and abiotic factors determined the spatial distribution of each microbial community. KEY WORDS: Microbenthic community · Microbial mat · Meiofauna · Macrofauna · Microelectrodes · Biotic factors · Abiotic factors Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 38: [53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69] 2005 ments. Nitrogen fixation (Dubinin et al. 1992), fermentation (Moezelaar et al. 1996), the use of sulfide as an electron source (de Wit & van Gemerden 1989, van den Hoek et al. 1995, and the presence of some UV-protective substances (Garcia-Pichel & Castenholz 1991) have been demonstrated in some cyanobacteria, allowing these microorganisms to survive under very stressful and dynamic conditions (high irradiance, salinity, temperature). However, these physiological adaptations do not explain why microbial mats are usually absent in more moderate environmental conditions. Meio-and macrofauna can also play an important role in controlling microbial mat development in coastal environments. Under moderate environmental conditions, e.g. coastal environments, meio-and macrofauna reduce primary producer concentration due to a high grazing activity (Hargrave 1970, Connor et al. 1982, and thus these mild conditions prevent mat accretion , Awramik 1984. It has been classically postulated that extreme conditions like high salinities in hypersaline environments (Pierson et al. 1987, Wieland & Kühl 2000, periodic dryings (Lassen et al. 1992), or high temperatures from thermal sources (Castenholz 1984) can limit meio-and macrofauna growth, allowing the development of microbial mats. However, few studies have quantified meio-and macrofauna in microbial mat...

Effects of macroalgal blooms on carbon and nitrogen biogeochemical cycling in photoautotrophic sediments: An experimental mesocosm

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Factors Affecting Macrobenthic Fauna in a Tropical Hypersaline Coastal Lagoon in Ghana, West Africa

“…The extreme hypersaline conditions possibly accounted for the low faunistic densities recorded ( Table 2). The density of the polychaetes for instance (Table 2) in the lagoon was extremely low compared to 1.17×10 4 individuals per square meter recorded in other hypersaline lagoons (García de Lomas et al 2005). Gordon (2000) has also reported low numbers of benthic macroinvertebrates in the hypersaline Muni lagoon in Ghana.…”

Photosynthetic activity and community shifts of microphytobenthos covered by green macroalgae

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