Abstract
This research evaluated the effect of flooding on the microphytobenthos community structure in a microbial mat from a tropical salt flat. Field samples were collected during four consecutive days: on the first three days the salt flat was dry, on the fourth day it was flooded by rain. In order to evaluate the community maintained in flood conditions, samples from this area were collected and kept in the laboratory for 10 days with sea water. The results of total abundance of microphytobenthos varied from 4.2 × 108 to 2.9 × 109 organisms L-1, total density increased one order of magnitude under the effect of water for both situations of precipitation in the salt flat and in experimental conditions, an increase due to the high abundance of Microcoleus spp. Shannon index (H') was higher during the desiccation period. Our data suggest that changes in the abundance of organisms were due to the effect of water. The dominance of the most abundant taxa remained the same under conditions of desiccation and influence of water, and there is probably a consortium of microorganisms in the microbial mat that helps to maintain these dominances.
Highlights
Benthic microalgae are the main primary producers in tropical salt flats (Stal, 2001; Adame et al, 2012), where hypersaline conditions preclude the presence of most plants
Microbial mat color changes were observed in the Guaratiba salt flat; during the days that preceded the rain, the microbial mat appearance was that of a dead community, with a dark color which was simultaneously whitened by the salt
Benthic microalgae from salt flat microbial mats were dominated by Microcoleus spp., Leptolyngbya spp. and Lyngbya sp
Summary
Benthic microalgae are the main primary producers in tropical salt flats (Stal, 2001; Adame et al, 2012), where hypersaline conditions preclude the presence of most plants. Salt flat benthic communities are usually established in the superficial layers of microbial mats, mostly composed by cyanobacteria and sometimes by a film of diatoms (Stal, 2001; 2012). Many species that form a cyanobacteria mat in salt flats are well adapted for diazotrophic growth, because this environment is usually N limited (Adame et al, 2012; Stal, 2012). Microphytobenthic or benthic microalgae from microbial mats are commonly enveloped in exopolimeric substances (EPS), like proteins, nucleic acids, polysaccharides, and other substances, that protect these organisms from desiccation.
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