Greening of the boreal peatland food web: Periphyton supports secondary production in northern peatlands

Abstract

Characterizing spatial and temporal variability of food web dynamics is necessary to predict how wetter and more nutrient-rich conditions expected with climate change will influence the fate of organic matter within northern peatlands. The goals of this study were to (1) document spatial and temporal variability in the contribution of periphyton to peatland food webs using isotope analysis ( 13 C and 15 N), and (2) quantify the influence of increased nutrient availability on primary and secondary production across a gradient of rich, moderate, and poor fen peatlands common to the northern boreal biome. We established replicate m 2 plots within each fen located in interior Alaska to quantify periphyton (algae and bacteria) and macroinvertebrate biomass with and without nutrient addition throughout a growing season (May-August). Stable isotope analysis showed that periphyton contributedx = 65% of organic matter to the food web over time and across fens compared to x = 7% from plants or detritus. The transfer of basal resources was reflected in an increase in herbivore biomass as algal biomass increased over time in all fens, followed by an increase in predatory macroinvertebrates during the latter part of the growing season. Furthermore, all measures of periphyton and macroinvertebrate biomass were enhanced by nutrient addition. These data provide insight into patterns of natural variation within the aquatic food web of boreal peatlands and show that basal resources within this ecosystem, which are generally considered to be "detritus-based," are actually driven by periphyton with minimal input from plant detrital pathways.

Cascading effects of predators on algal size structure

“…A detailed description of the site's physical and chemical characteristics has been provided in Wyatt et al (2021). This fen has a top-down food web with three trophic levels (Ferguson et al 2021); algal biofilm, herbivores, and predatory macroinvertebrates (most of which are insect larvae). Common aquatic herbivore fauna (i.e., grazers) include wood frog tadpoles (Lithobates sylvaticus), snails (Lymnaea), tadpole shrimp (Notostraca), chironomid larvae (Diptera), and caddisfly larvae (Limnephilus).…”

“…During periods of inundation (i.e., the wet phase), the energy balance shifts to phototrophic microbes (i.e. algae) that form on peat surface layers (van Duinen et al 2013, Vesterinen et al 2016, Ferguson et al 2021. In contrast to recalcitrant plant material (e.g., mosses), this algae-based food web is susceptible to trophic regulation (DeColibus et al 2017.…”

“…In contrast to recalcitrant plant material (e.g., mosses), this algae-based food web is susceptible to trophic regulation (DeColibus et al 2017. Consequently, hot spots of algal productivity have been shown to play a significant role in sustaining secondary production during wet periods (Ferguson et al 2021), which are expected to increase in frequency and duration with environmental change occurring at northern latitudes (Kendrick et al 2018, Douglas et al 2020.…”

Restoring aquatic food webs bottom-up : Improving trophic transfer through lake restoration project Marker Wadden

“…The high gastropod density under sheltered conditions may be attributed to high food availability, especially the presence of macrophytes. Higher macrophyte biomass in the sheltered treatments can be grazed directly by gastropods but can also function as substrate to support periphyton growth, which is an important food resource for gastropods (Ferguson et al 2021). Although the periphyton biomass in the shelter treatment was significantly lower compared with the no shelter treatment, this may be explained by a high trophic transfer efficiency between periphyton and gastropods -supporting a high density of gastropods under sheltered conditions.…”

“…I have shown that benthic algae (Chapter 3) or macrophytes (Chapter 4) were the dominant primary producers under sheltered conditions, which both could be grazed by gastropods (Schuler et al 2020, Chen et al 2020, Liu et al 2021. Moreover, higher macrophyte biomass under the sheltered conditions can not only serve as food and thereby directly benefit gastropods, but can also function as substrate to support periphyton growth, further provisioning food for gastropods (Ferguson et al 2021). Furthermore, the gastropods may also directly benefit from the calm conditions in the sheltered treatments as wind induced turbulence may increase their mortality and/or dislodgement Quinn 1988, Etter 1989).…”