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.