Periphyton development on artificial substrates across a biogeographical and trophic gradient

Periphyton plays an important role in the nutrient cycling, energy flow and food web of aquatic ecosystems. Variation in the biomass, biodiversity and taxonomic structure of the periphytic algae community can provide information on changes in environmental conditions and can serve as a tool for ecological assessment. Here, we assessed periphyton growth and diversity on two different artificial substrates (i.e., high-density polyethylene - HDPE, polyethylene terephthalate - PET) in freshwater mesocosms distributed across five locations in the Iberian Peninsula. The aim was to evaluate differences in biomass and community composition of phytobenthos for artificial substrates with different incubation depth since HDPE substrates floated in water while PET, being denser than water, sank. Over the 45 samples analyzed, we found 242 different species distributed in 145 genera. The 33.5% belong to the phylum Bacillariophyta, followed by Chlorophyta (26.4%), and Cyanobacteria (8.3%). We found some cosmopolite species, which were recorded in almost all the samples, like Aphanocapsa incerta (Lemm.) Cron. and Kom. or Cocconeis placentula Ehr. Overall, 20 species occurred exclusively in HDPE samples, while 17 species only in PET samples. However, in all the cases these species had a low recurrence, being identified at most in four different samples. The amount of biomass developed on substrates differed based on the polymer type, with higher biomass on PET substrate compared to HDPE. Artificial substrates may host many different species of microalgae, but we did not observe a dissimilarity in community composition based on the different incubation depths. Instead, geographic and altitudinal gradient and nutrient concentration seem to be the most crucial factors in driven species sorting of epiplastic community.