Seminar Abstract

Ron Thom

Tuesday, October 11, 2005

"Climate-forced variation in eelgrass (Zostera marina) abundance: Can eelgrass be a conveyor of carbon from the atmosphere to an ocean carbon sink?"


Juvenile salmon as well as a vast number of other fish and invertebrate species inhabit eelgrass meadows. For juvenile salmon, eelgrass provides food resources and refuge from predation during their outmigration to the North Pacific. Pacific herring are known to spawn on eelgrass. For these and other reasons, eelgrass habitat is considered extremely important to the maintenance of fish populations.

Our work since 1982 illustrates that eelgrass abundance can vary dramatically between years. Between 1998 and 2001, annual variation in summer growth rate and abundance was correlated with variations in water temperature. In addition, annual variations in growth rate measured in most summers between 1991 and 2005 correlated with metrics commonly used to characterize climate variability, including the El Nino Southern Oscillation index and the Pacific Decadal Oscillation index. There was also a strong correlation between average monthly mean sea level anomaly and eelgrass growth rate during that period. Modeling of bottom current velocities has shown that changes in mean sea level also dramatically affect bottom circulation rates on a scale that could affect eelgrass survival. Further, a numerical model of light penetration predicted substantial variations in eelgrass abundance in Puget Sound driven by long-term sea level variations.

We present a conceptual model illustrating how variations in temperature and water depth control the interannual variation in abundance and productivity of eelgrass in Puget Sound and coastal estuaries in the Northwest. Underwater video surveys revealed that a substantial proportions of the massive annual production of eelgrass organic matter is probably exported to deeper areas of Puget Sound and the outer coast. We speculate that this presents a small but important carbon sink. A shift in weather and mean sea level under a global climate change scenario in the region would predictably affect eelgrass production, distribution and export to deeper areas.

Speaker bio:

Ron Thom is an Engineer with the Marine Sciences Division at Battelle Marine Sciences Laboratory in Sequim, WA. A list of selected publications is available here.