Abstract
Characterizing the response of ecosystems to global climate change requires that multiple aspects of environmental change be considered simultaneously, however, it can be difficult to describe the relative importance of environmental metrics given their collinearity. Here, we present a novel framework for disentangling the complex ecological effects of environmental variability by documenting the emergent properties of eelgrass (Zostera marina) ecosystems across ∼225 km of the Atlantic Coast of Nova Scotia, Canada, representing gradients in temperature, light, sediment properties, and water motion, and evaluate the relative importance of different metrics characterizing these environmental conditions (e.g., means, extremes, variability on different time scales) for eelgrass bioindicators using lasso regression and commonality analysis. We found that eelgrass beds in areas that were warmer, shallower, and had low water motion had lower productivity and resilience relative to beds in deeper, cooler areas that were well flushed, and that higher temperatures lowered eelgrass tolerance to low-light conditions. There was significant variation in the importance of various metrics of temperature, light, and water motion across biological responses, demonstrating that different aspects of environmental change uniquely impact the cellular, physiological, and ecological processes underlying eelgrass productivity and resilience, and contribute synergistically to the observed ecosystem response. In particular, we identified the magnitude of temperature variability over daily and tidal cycles as an important determinant of eelgrass productivity. These results indicate that ecosystem responses are not fully resolved by analyses that only consider changes in mean conditions, and that the removal of collinear variables prior to analyses relating environmental metrics to biological change reduces the potential to detect important environmental effects. The framework we present can help to identify the conditions that promote high ecosystem function and resilience, which is necessary to inform nearshore conservation and management practices under global climate change.
Highlights
Coastal vegetated marine habitats, such as seagrass, seaweed, and salt marsh ecosystems are vulnerable to changing environmental conditions and anthropogenic stressors, leading to widespread declines over the past several decades (Lotze et al, 2006; Waycott et al, 2009; Krumhansl et al, 2016)
To support a more detailed understanding of temperature effects on seagrass emergent properties, we examine the relative importance of a variety of temperature metrics, including those that characterize the mean conditions, as well as temperature extremes and variability over different time scales
Our results demonstrate the strong interacting roles of temperature, light, water movement, and sediment characteristics in shaping metrics of eelgrass (Zostera marina) productivity and resilience across a broad range of biological scales
Summary
Coastal vegetated marine habitats, such as seagrass, seaweed, and salt marsh ecosystems are vulnerable to changing environmental conditions and anthropogenic stressors, leading to widespread declines over the past several decades (Lotze et al, 2006; Waycott et al, 2009; Krumhansl et al, 2016). Understanding how environmental conditions impact the functioning of marine ecosystems, as well as their susceptibility to disturbance, is critical for decision making processes related to nearshore conservation and management (Unsworth et al, 2015). Identifying the environmental conditions under which marine macrophyte communities remain resilient within the context of climate change is critical for maximizing the effectiveness of conservation strategies. An alternative approach is to investigate emergent properties of ecosystems, which represent the cumulative effects of the full suite of relevant environmental variables and associated processes over varying time scales (Odum and Barrett, 1971). Investigating emergent properties of seagrass communities at sites spanning environmental gradients and levels of stress can provide insights into how these ecosystems respond to environmental change, and the relative importance of different environmental variables for driving a biological response
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