Research

Effects of an introduced eelgrass (Zostera japonica) on sediment microbial communities and processes

Funding: Royalty Research Fund, UW and the Padilla Bay National Estuarine Research Reserve

Widespread biological invasion represents a significant component of human-induced global change. While the effects of plant invasions on above-ground plant communities are well documented, we know relatively little about impacts on below-ground microbial communities. We are interested in understanding the influence of introduced plant species versus native plant species on sediment microbial communities and the biogeochemical processes they mediate. We are focusing on microbes that mediate steps in the nitrogen cycle. In particular, we are examining differences in the denitrifying community of microbes in the rhizosphere of a native and an introduced eelgrass in Padilla Bay, Washington. We are also looking at rates of denitrification in these sediments to see if community or abundance differences are related to process differences. Padilla Bay, Washington, supports one of the largest eelgrass meadows on the west coast of North America. Habitat censuses reveal that the invasion of non-native Z. japonica in Padilla Bay is actively progressing, both colonizing previously bare mudflat and displacing areas of the native eelgrass, Z. marina. We are interested in expanding this work to think about management implications and future restoration work for this system as well as other invaded systems.

Living in the dead zones: Spatial and temporal patterns of microbial community composition in Hood Canal, Washington

Co-PI: Gabrielle Rocap
Funding: ICoMM and Hood Canal Dissolved Oxygen Project

The phenomenon of hypoxia/anoxia is widespread, occurring in the waters of 16 of the 21 coastal states of the USA. In the most well known case, the Gulf of Mexico, the hypoxic area along the Louisiana and Texas coasts measured 20,700 km² in the summer of 2001. Where dissolved oxygen is greatly reduced (hypoxia, < 2 mg/L) or eliminated (anoxia, 0 mg/L), these so-called “dead zones” exclude fish, shrimp and benthic organisms and eliminate important habitat for many commercially and recreationally important marine species. Dead-zones, however, are far from dead. Hypoxic and anoxic zones support an active community of anaerobic and hypoxia-adapted organisms including bacteria, archaea, protists and viruses. Despite the increase in the number of hypoxic and anoxic regions world-wide and the impact these low oxygen regions can have on biological communities and commercial fisheries, we know relatively little about the microbes driving these processes and living in the “dead zones.”

Hood Canal is a glacial fjord in Puget Sound located about 80 miles from Seattle, WA. The long narrow shape of Hood Canal results in a classic estuarine circulation pattern and a stratified water column throughout much of the year. Hood Canal has also been shown to be more susceptible to eutrophication than other areas of Puget Sound. Low oxygen concentrations have been documented in Hood Canal as far back as the 1950s, but over the last decade the problem has worsened dramatically. In the 1950s and 1960s low oxygen concentrations were confined to the southern, and shallowest, part of Hood Canal and lasted only three to six months of the year. In contrast, recently southern Hood Canal has experienced up to twelve months of hypoxia, and northern stations have also exhibited oxygen levels below 5 mg/L, the level at which biological stress begins to occur. Severe fish kills brought on by hypoxia occurred in 2002, 2003 and 2006. Our work is part of a larger community effort to examine the dynamics in Hood Canal through coordinated studies of biological, chemical and physical factors and thus will inform discussions with managers and policy makers.

We have an ongoing study in Hood Canal (2+ years of monthly sampling at six stations) in which we are examining relationships among bacterial communities (using ARISA, primarily), phytoplankton communities and environmental characteristics, including primary production, respiration, nutrients and dissolved oxygen in Hood Canal. We are also working with ICoMM to apply the 454 V6 tag sequencing using Bacterial primers to a subset of water column samples from the larger, ongoing study of microbial community changes in space and time in Hood Canal. This work will allow us to examine the influence of rare community members on spatial and temporal patterns of diversity and composition as well as to examine the influence of undersampling on observed diversity patterns. Together, these two projects will lend insight into the relative importance of biotic and abiotic factors in determining bacterial community composition and abundance.

Biogeography of microbes

Co-PI: Jennifer Martiny

We have a number of ongoing projects examining spatial patterns of microbial diversity at a range of spatial scales, at different taxonomic resolutions and in different systems. In previous work, we found that the distribution of sediment beta-Proteobacteria within a salt marsh follows a taxa-area relationship. Moreover, we showed that this relationship was driven by abiotic environmental factors, rather than plant distributions or dispersal limitation. We are currently completing work that examines whether microorganisms follow a taxa-area relationship at a global scale, and whether this relationship changes over scales from within a marsh to across continents. We have sampled sediments from thirteen salt marshes around the world and are examining beta-Proteobacteria in general and ammonia oxidizers within the beta-Proteobacteria. We are testing whether organisms within one functional group follow a taxa-area relationship at large scales, whether the slope of this relationship changes over different geographic scales, and whether the genetic resolution of targeting that functional group matters.

In a series of smaller projects, we are examining spatial patterns of bacterioplankton in the Pacific and the Atlantic as well as of ammonia-oxidizing bacteria in terrestrial ecosystems across North America.