Substratum‐dependent responses of ciliate assemblages to temperature: a natural experiment in Icelandic streams

Abstract

1. Ciliate assemblages play a significant role in the microbial food web. The effects of environmental temperature on assemblage composition may be influenced by abiotic factors such as seasonality and disturbance, but the effects of temperature on ciliate assemblages found on different substrata have not been explored. Sandy bottoms and submerged rocks harbour dissimilar ciliate assemblages, and it might be expected that their ciliate assemblages will respond differently to temperature. 2. We studied how alpha diversity, beta diversity and total biomass of ciliate protist assemblages found on sandy bottoms and submerged rocks differed in 13 geothermally heated streams in Iceland whose mean temperatures range from 5 to 20°C. We recorded number of operational taxonomic units (OTUs) and measured the size of cells in ciliate assemblages from both substrata. 3. Effects of temperature on natural ciliate assemblages were substratum dependent. On rock surfaces, both total ciliate biomass and alpha diversity declined with increasing temperature, and beta diversity increased with increasing temperature difference due to OTU nestedness (assemblages from warm streams being composed chiefly of subsets of the OTUs found in colder streams). In sandy substrata, however, ciliate assemblage composition was independent of temperature. 4. Substratum-specific responses may be due to differences in mechanical disturbance, nutrient availability or exposure to invertebrate grazers. Rock-surface assemblages may be more exposed to the flow and retain less nutrient than those of sandy substratum; thus, they may be more strongly resource limited and more responsive to direct effects of temperature on metabolism. Alternatively, rocksurface assemblages may be more exposed to grazing by invertebrates, which intensifies with temperature. 5. Our study highlights the need to account for environmental context such as substratum type to fully understand the effect of temperature on microbial assemblages in streams. Future increases in global temperatures may affect fresh waters differently depending on their prevalent substratum. Those dominated by hard substrata may have their ciliate assemblages, and thus, food-web structures and ecosystem functioning more strongly affected by warming relative to systems dominated by soft substrata. 2 ABSTRACT 1. Ciliate assemblages play a significant role in the microbial food web, and the effects of environmental temperature on their composition can be influenced by abiotic factors such as seasonality and disturbance. The effects of temperature on ciliate assemblages found on different substrates, however, have not been explored. Different substrate types such as sandy bottoms and submerged rocks harbour dissimilar ciliate assemblages; thus we could expect ciliate assemblages from these two substrates to respond differently to temperature.2.We studied how alpha diversity, beta diversity, and total biomass of ciliate protist assemblages found on sandy bottoms and submerged rocks changed in 13 geother...

Unexpected biodiversity of ciliates in marine samples from below the photic zone

“…The distribution of ciliate assemblages throughout the water column may also be affected by temperature, which decreases with depth (range 5-23°C). The pattern we observe is consistent with a morphological study on the influence of temperature on benthic ciliates in freshwater environments with rocky substrates (Plebani et al 2015) and a molecular study of oligotrichs and choreotrichs along an estuarine salinity gradient .…”

“…The pattern we observe is consistent with a morphological study on the influence of temperature on benthic ciliates in freshwater environments with rocky substrates (Plebani et al . ) and a molecular study of oligotrichs and choreotrichs along an estuarine salinity gradient (Tamura et al . ).…”

“…These data suggest that release from predation pressure allows diversification within the ciliate community. Plebani et al (2015) suggest that the higher grazing rate negatively impacted the ciliate diversity in temperate freshwater environments. This makes it more difficult to disentangle the impact of abiotic and biotic factors on ciliate diversity.…”

Community coalescence: an eco-evolutionary perspective

“…The implications of coalescence for natural community structure and function is unclear, but could be particularly important in the context of environmental change [97]. Temperature changes alter eco-evolutionary dynamics, and could impact coalescence through range shifts, altering species interactions, and changing weather patterns [97][98][99][100]. Additionally, antibiotics and environmental pollutants disturb gut, soil and aquatic microbiomes with associated disease outbreaks and biodiversity loss [101][102][103].…”

Community responses to seawater warming are conserved across diverse biological groupings and taxonomic resolutions

“…Previous work on aquatic biofilms developed under different thermal regimes has shown that modest temperature increases of the order of 2-58C can have considerable effects on the development, structure and functioning of communities comprising bacteria and other single-celled organisms [3,38,[46][47][48]. Several studies have shown positive effects of warming, in that biofilms develop more quickly at elevated temperatures [3,47,49], while other studies have documented changes in the relative abundances of bacteria and protists [38,46,50].…”