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Microbial Ecology Across a Land-Sea Gradient

Microbial communities and processes across a land-sea gradient in the hypermaritime coastal temperate rainforest.

Steven Hallam, William Mohn, Colleen Kellogg, David Levy-Booth

Microbial communities play a crucial role in mediating global biogeochemical cycles. Their importance is especially acute in productive coastal ecosystems, such as coastal temperate rain forest systems like Calvert Island, where large amounts of organic matter (OM) can be exported from land to sea. We hypothesize that this OM directly impacts marine nutrient cycling and trophic interactions and that complex microbial community interaction networks selectively refine and alter this organic matter pool during its seaward transit. We explore these concepts on Calvert Island and the surrounding waters using the powerful tools of environmental genomics. We have harmonized our sample collection with the ongoing freshwater and marine monitoring projects of the Kwakshua Watershed Program to generate multimolecular datasets including high-resolution ribosomal RNA gene sequence tags, paired metagenomes and metatrascriptomes, and single cell amplified genomes from six watersheds (626, 693, 703, 708, 819, 844) flowing into Kwakshua Channel and their associated nearshore and marine sites. On land, we are employing high-resolution ribosomal RNA gene sequence tags and metagenomics to examine microbial communities associated with organic and mineral soils in three watersheds (626, 703, 819).

This project establishes a baseline understanding of the microbial communities characteristic of the complex landscape and seascape of Calvert Island. Resulting datasets will be analyzed in conjunction with climate information, soil properties, water properties and hydrology, plant communities, and organic matter profiles to better constrain microbial controls on soil organic matter cycling on land, the influence of these degradation processes on organic matter exported to adjacent freshwater and marine environments, and the subsequent response of the marine microbial community. The balance of carbon fluxes into and out of this system has major consequences for global climate and these microbial transformations have critical implications for the magnitude of carbon stored on land as well as for the amount and composition of soil organic matter transported to the ocean.

Examining protist diversity and community dynamics across the land-sea gradient in the hypermaritime coastal temperate rainforest.

Thierry Heger and Patrick Keeling

Protists, also known as microbial eukaryotes, are extremely diverse and present in all habitats. They contribute to several key steps in the transfer of inorganic and organic carbon to higher trophic levels and the recycling of growth-limiting nutrients for other organisms. Yet, they remain relatively poorly characterized, particularly in soil ecosystems. In this project, we use high-throughput sequencing and microscopy-based techniques to assess protist diversity and temporal community dynamics from diverse terrestrial and aquatic habitats such as blanket bogs, bog woodlands, bog forests, zonal forests, streams and coastal marine environments. Preliminary results revealed distinct protists communities across gradients of terrestrial ecosystems and an impressive diversity of heterotrophic and phototrophic protists from the soil surface. Further analyses are underway to characterize and quantify protist community composition changes among aquatic and terrestrial ecosystems, and how they respond to abiotic and biotic factors. Combined with the data generated by the other members of the Kwakshua Watersheds Program, this data-set will contribute to a better understanding of how dissolved organic carbon (DOC) and other terrestrial exports affect coastal water food webs. Finally, this project will also allow us to evaluate the suitability of high-throughput sequencing to fully integrate protists into ecological studies and develop new biomonitoring approaches.

This photo illustrates one of a number of protist taxa occurring in the bogs of Calvert Island (Photo: T.Heger).

This photo of the testate amoeba Hyalosphenia papilio illustrates one of the numerous protist taxa occurring in the bogs of Calvert Island (Photo: T.Heger).