Abstract
Temporary Mediterranean ponds are complex ecosystems which support a high diversity of organisms that include heterotrophic microorganisms, algae, crustaceans, amphibians and higher plants, and have the potential to supply food and a resting place to migratory birds. The role of heterotrophs at the base of the food web in providing energy to the higher trophic levels was studied in temporary ponds in Central and Southern Portugal. The relative quantification of the hetero and autotrophic biomass at the base of the food web in each pond was derived from the polar fatty acid (PLFA) composition of seston through the application of the matrix factorization program CHEMTAX that used specific PLFA and their relative proportion as markers for e.g., classes of bacteria, algae and fungi. The species composition of the culturable microbial communities was identified through their fatty acid profiles. The biomass in the lower trophic level of some ponds presented an even proportion of auto to heterotrophic organisms whilst either bacteria or algae dominated in others. In a selected subset of ponds, the incorporation of bacterial fatty acids was observed to occur in potentially herbivorous zooplankton crustacean. Zooplankton consumed and incorporated bacterial fatty acids into their body tissues, including into their phospholipids, which indicates that energy of heterotrophic origin contributes to the aquatic food webs of temporary ponds.
Highlights
Temporary Mediterranean ponds are lentic ecosystems during the winter flooding period and dry during the summer when they typically support a wetland/terrestrial community
Organic matter originating from allochthonous sources or from excreted metabolites and/or biomass decay may be used as substrate for heterotrophic microorganisms such as bacteria and fungi [8,9], and this mass and energy may further be transferred to metazoans in the food web through the microbial loop [10,11]
The polar fatty acid (PLFA) analysis indicate that the temporary ponds located at the FFR of Alcochete (CTA2-5) and at PNSACV, Sector B (B20, B26 and B27) contained over 30% of proteobacteria, ca. 20% green algae and 4%–10% diatoms
Summary
Temporary Mediterranean ponds are lentic ecosystems during the winter flooding period and dry during the summer when they typically support a wetland/terrestrial community. These ponds are likely to receive material and energy subsidies from the autochthonous source of detritus supplied by the summer vascular plant production, and may receive allochthonous detritus either by runoff from the surrounding drainage basin or by dust deposition. Planktonic algae, including cyanobacteria and diatoms, use inorganic nutrients dissolved in water and capture CO2 that is converted into biomolecules. These biomolecules directly fuel the aquatic food webs or may enrich sediments with organic carbon [3] (cyanobacteria are capable of nitrogen fixation [4]). Organic matter originating from allochthonous sources or from excreted metabolites and/or biomass decay may be used as substrate for heterotrophic microorganisms such as bacteria and fungi [8,9], and this mass and energy may further be transferred to metazoans in the food web through the microbial loop [10,11]
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