Carbon Pathways Through the Food Web of a Microbial Mat From Byers Peninsula, Antarctica

Abstract

Microbial mats are complex communities that represent a large biomass fraction in non-marine Antarctic ecosystems. They confer structure to soils and constitute, by themselves, intricate microecosystems, where a great variety of microorganisms and microfauna contributes to the ecosystem functions. Although in recent years Antarctic microbial mats have been thoroughly investigated, trophic relationships within the communities remain unresolved. We therefore conducted a study of the trophic relationships of a microbial mat from Byers Peninsula, Antarctica, using DNA analysis and stable isotopes as trophic tracers. Our results suggested, based on a Bayesian mixing model, that at least four trophic levels are present within this microecosystem: primary producers (cyanobacteria and diatoms), primary consumers (rotifers and tardigrades), secondary consumers (nematodes) and decomposers (fungi). Nematodes would play a key role as top consumers of the community, connecting the two carbon inputs described into the system, as omnivores at the secondary trophic level. In addition, carbon pathways from primary trophic level to consumers take place quickly during the first 24 h after its incorporation in the primary producers, dispersing across all the trophic levels and reaching secondary consumers in less than 11 days. This suggests that, given the changing physical conditions and presumably short periods of activity, there is a fine temporal coupling among the organisms in the community, minimizing the redundancy in function performance among trophic levels.

Keywords: Antarctica; carbon pathways; cyanobacteria; eukaryotic community; microbial mats; prokaryotic community; stable isotopes; trophic web.

FIGURE 1

(A,B) Location details of Byers Peninsula at Livingston Island in the South Shetland Islands, Antarctica. (C) Picture showing common microbial mat types from Byers Peninsula. The symbol “^∗” indicates where exactly enrichment experiments were conducted.

FIGURE 2

Relative abundance of the studied taxa, including microbial and eukaryotic community, in a microbial mat from Byers Peninsula (South Shetland Islands, Antarctica).

FIGURE 3

Bivariate model plot of isotopic signatures (δ¹³C and δ¹⁵N), of organisms in the community and potential food sources of a microbial mat from Byers Peninsula, Antarctica. For sources, points are mean trophic enrichment factor, and error bars are ±1 standard deviation of the trophic enrichment factor. For consumers, shapes around the plots represent the average of each group.

FIGURE 4

¹³C signal through the different organisms along time in a microbial mat from Byers Peninsula, Antarctica. Lines represent ¹³C data adjusted to a quadratic function. Dashed lines represent primary producers and solid lines consumers.

FIGURE 5

Results of SIAR Bayesian mixing model showing the contribution of each C source to the different fractions of the microbial mat community from Byers Peninsula, Antarctica. Different gray colored boxes indicate confidence intervals of 25, 75, and 95%. (A) Results for tardigrades and rotifers by their main sources diatoms, Particulate Organic Matter fraction <30 μm and POM fraction between 0.5 and 5 μm, of the microbial mat community. (B) Results for fungi by their main C sources diatoms, POM fraction <30 μm and POM fraction between 0.5 and 5 μm. (C) Results for nematodes by their main C sources, where the entire community was included as potential C source.