Abstract
Periphyton plays a vital ecological role in shallow, well-lit ecosystems which are vulnerable to rapidly changing environmental conditions, including raising temperature due to global warming. Nevertheless, little is known on the effect of increased temperatures on the taxonomic structure and functioning of periphytic communities. In this study, the influence of short-term temperature increase on the species composition and photosynthetic activity of the Baltic periphytic communities was investigated. The collected communities were exposed to increased temperature of 23 °C (ca. 4 °C above the summer average) for 72 h. After this time, species composition of the communities was studied under light microscope and their photosynthetic performance was evaluated using PAM fluorometry. Results showed that the biomass of cyanobacteria slightly increased. There were significant changes in the abundance of diatom species, among which Fragilaria fasciculata and Navicula ramosissima, were negatively affected by the elevated temperature and their cell number significantly decreased, whereas, Diatoma moniliformis and N. perminuta were stimulated by the increased temperature. Additionally, a shift towards higher abundance of smaller taxa was also observed. The higher quantum yield of photosystem II (PSII) (higher ΦPSII) accompanied by the lower value of non-photochemical quenching (NPQ) observed in communities kept at 23 °C showed more efficient photosynthesis. This was further confirmed by the changes in rapid light curves (higher photosynthetic capacity, rETRmax, and photoacclimation index, Ek). The obtained data constitute evidence that short periods of increased temperature significantly affect the structure and functioning of the Baltic periphyton.
Highlights
Periphyton assemblages can be found on a variety of substrata submerged in water
There was no change in community biomass (0.36 ± 0.02 μg chlorophyll a (Chla) ml−1) at the lower temperature (18 °C) on the third day of cultivation period compared to the starting day
In communities exposed to the higher temperature (23 °C) Chla concentration only slightly decreased (0.30 ± 0.06 μg Chla ml−1) compared to the communities maintained at the lower temperature (Student t-test; p > 0.05)
Summary
Periphyton assemblages (algal biofilms) can be found on a variety of substrata submerged in water. They can thrive on a solid surface-water interface by excreting extracellular polymeric substances. Periphyton can be responsible for majority of primary production especially in shallow well-lit habitats, in such aquatic environments as lakes, rivers, coastal waters etc. The environment is undergoing a dramatic change due to global warming, including continually increasing temperatures and the frequency and intensity of climate extreme phenomena such as heat waves (Vieira et al 2013). Recent studies proved temperature increase in the Baltic and have shown that in summer the average temperatures of ca. Occasionally short periods (several days) of temperatures above 23 °C can be observed (http://www. satbaltyk.pl)
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