Matthew Bracken1, Robin Fales2, Emily Jones3, Hannah Hall1, Susan Williams1
1University of California, USA - 2Soka University of America, USA - 3California State Polytechnic University, USA
Predicting the consequences of global change for species, communities, and ecosystems requires understanding the vulnerability of species to stressors and the contributions of those species to community interactions and ecosystem functioning. Here, we explore the use of seaweed traits to predict the functional consequences of an intertidal aerial heat wave. We observed severe impacts (e.g., bleaching, declines in cover) on intertidal seaweeds associated with several days of sunny, hot air temperatures that coincided with daytime low tides on the northern California coast (USA) during the spring of 2008. Even in the low zone on wave-exposed shores, maximum daytime air temperatures exceeded 30°C for four consecutive days; typical maximum daily air temperatures in wave-exposed plots averaged 20.6 ± 5.2°C [mean ± SD]). The heat wave disproportionately impacted ephemeral species with higher surface-area-to-volume ratios (SA:V) and lower thallus dry mass content (TDMC; e.g., Ulva), which declined in cover. In contrast, several perennial species with lower SA:V and higher TDMC (e.g., Mastocarpus, Pelvetiopsis) increased in abundance. These changes have the potential to alter ecosystem functioning, as maximum nitrate uptake and photosynthetic rates of ephemeral species were twice as high as those of perennials, and both nitrate uptake rates and photosynthetic rates were positively correlated with species’ susceptibility to heat-wave-induced bleaching. Seaweed traits may be an important predictor of vulnerability to global change, especially as the magnitude and frequency of heat wave events increase.
Biography
Matthew Bracken is a Professor of Ecology and Evolutionary Biology at the University of California – Irvine, where he studies the causes and consequences of changes in marine biodiversity. Current projects include taking a functional-trait approach to understanding seaweed diversity on rocky shores, evaluating responses of seaweeds to temperature changes and habitat loss, and merging trait-based and biomechanical approaches to measure responses of intertidal organisms to physical stressors.