Foundation species are disproportionately important to the structure of their associated communities (Dayton 1972, Bruno and Bertness 2001) and are evident in both terrestrial and marine systems (e.g., mangroves, redwood trees, kelps, hermatypic corals). Through the direct provisioning of energy and habitat, foundation species facilitate the maintenance of community structure in different ways than keystone predators (e.g., sea otters, wolves) and ecosystem engineers (e.g., termites, beavers), although these terms are sometimes (and incorrectly) used interchangeably in the literature. Keystone predators actively regulate species interactions (Paine 1969a, Paine 1969b), while ecosystem engineers provide habitat architecture and modify the physical environment (Jones et al. 1994, Hastings et al. 2007). Like these critical species, however, the loss of foundation species from a system generally causes conspicuous declines in local biodiversity, productivity, and ecosystem functioning (Knowlton 2001, Graham 2004, Ellison et al. 2005). The utility of the foundation species concept is that variability in productivity and population dynamics of foundation species may be directly proportional to community characteristics and ecosystem function. Therefore, studies of the ecophysiology of foundation species are critically important for forecasting subsequent variability in associated communities and ecosystems. Because the role of foundation species may be context dependent (Hughes 2010), a

Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA, USA, 95039. * Corresponding author: [email protected]

detailed understanding of how macrophyte foundation species respond to external stressors and environmental conditions is paramount for developing successful management strategies, maintaining key ecosystem services, and promoting natural resilience in marine systems.