PARENT SESSION
OOS 4: Organisms as Ecosystem Engineers: Conceptual Progress, Limits and Challenges.
Organized by: JP Wright and CG Jones
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room E 146.
Environmental stress and engineering impacts: Lessons from hummocking plants in estuarine marshes.
Crain, Caitlin*,1, Bertness, Mark1, 1 Brown University, Providence, RI, USA
ABSTRACT- Because ecosystem engineers modify environments, community-level impacts of an engineer may vary predictably as a function of the background environment being transformed. To address this issue, we investigated mechanisms by which hummock-forming marsh plants engineer their environments and impact vegetative communities across an estuarine salinity gradient. In Northern New England estuaries, Triglochin maritima creates raised rings in salt marsh pannes, while Carex stricta grows in large tussocks in tidal freshwater marshes. In both of these habitats, the remaining vegetation is restricted almost exclusively to the tops of these physical structures. We conducted a series of hummock manipulations and transplant studies to determine how these engineers drive vegetative patterns. In the salt marsh, plants were restricted from the background mud by physiological stress (salinity and waterlogging), and the drained mounds created by T. maritima promoted increased species richness and abundance. In contrast, transplants in the tidal freshwater marsh were able to live in all environments except natural intertussock spaces buried in C. stricta wrack. In the benign and highly productive conditions of the fresh marsh, space and light are limiting resources and C. stricta wrack production indirectly limits the available habitat for other species, thereby negatively driving community patterns. Our results suggest that environmental modifications by engineers could lead to positive impacts on organisms in stressful environments and negative impacts under more benign conditions. The generality of this rule needs to be further investigated as it will add to a predictive understanding of when and where engineers should have large community impacts.
Key words: environmental stress, tidal freshwater marsh, estuarine salinity gradient, salt marsh