Abstract
Comparing populations across temperature gradients can inform how global warming will impact the structure and function of ecosystems. Shoot density, morphometry and productivity of the seagrass Posidonia oceanica to temperature variation was quantified at eight locations in Sardinia (western Mediterranean Sea) along a natural sea surface temperature (SST) gradient. The locations are spanned for a narrow range of latitude (1.5°), allowing the minimization of the effect of eventual photoperiod variability. Mean SST predicted P. oceanica meadow structure, with increased temperature correlated with higher shoot density, but lower leaf and rhizome width, and rhizome biomass. Chlorophyll a (Chl-a) strongly impacted seagrass traits independent of SST. Disentangling the effects of SST and Chl-a on seagrass meadow shoot density revealed that they work independently, but in the same direction with potential synergism. Space-for-time substitution predicts that global warming will trigger denser seagrass meadows with slender shoots, fewer leaves, and strongly impact seagrass ecosystem. Future investigations should evaluate if global warming will erode the ecosystem services provided by seagrass meadows.
Highlights
Shoot density Shoot morphometry # of leaves Leaf width Leaf length Necrotic leaf Shoot productivity # of scales Rhizome length Rhizome width Rhizome biomass
The abrupt decline experienced by P. oceanica from recent heatwaves[48], has seriously questioned its persistence for the coming decades[40]
Despite similar latitude, the western locations are generally cooler than the eastern sites, with differences in SST comparable to climate change scenarios for the twenty-first century for the Mediterranean Sea, making this space-for-time substitution informative for projections of trait changes over the decades
Summary
Shoot density Shoot morphometry # of leaves Leaf width Leaf length Necrotic leaf Shoot productivity # of scales Rhizome length Rhizome width Rhizome biomass. Plants from warm thermal environments were found to activate a suite of p hysiological[49] and molecular mechanisms[50,51,52] to tolerate simulated heatwave exposures, whereas phenological response to warming likely involves higher flowering[53] and denser m eadows[54]. This is a space-for-time substitution, a method for studying slow ecological processes, where the relationships between ecological variables are studied at sites that are assumed to be at different stages of development[55]. P. oceanica is currently in the EU Marine Strategy Framework Directive monitoring p rotocols[58]
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