Abstract
Seaweed beds play a key role in providing essential habitats and energy to coastal areas, with enhancements in productivity and biodiversity and benefits to human societies. However, the spatial extent of seaweed beds around Japan has decreased due to coastal reclamation, water quality changes, rising water temperatures, and heavy grazing by herbivores. Using monthly mean sea surface temperature (SST) data from 1960 to 2099 and SST-based indices, we quantitatively evaluated the effects of warming seawater on the spatial extent of suitable versus unsuitable habitats for temperate seaweed Ecklonia cava, which is predominantly found in southern Japanese waters. SST data were generated using the most recent multiple climate projection models and emission scenarios (the Representative Concentration Pathways or RCPs) used in the Coupled Model Intercomparison Project phase 5 (CMIP5). In addition, grazing by Siganus fuscescens, an herbivorous fish, was evaluated under the four RCP simulations. Our results suggest that continued warming may drive a poleward shift in the distribution of E. cava, with large differences depending on the climate scenario. For the lowest emission scenario (RCP2.6), most existing E. cava populations would not be impacted by seawater warming directly but would be adversely affected by intensified year-round grazing. For the highest emission scenario (RCP8.5), previously suitable habitats throughout coastal Japan would become untenable for E. cava by the 2090s, due to both high-temperature stress and intensified grazing. Our projections highlight the importance of not only mitigating regional warming due to climate change, but also protecting E. cava from herbivores to conserve suitable habitats on the Japanese coast.
Highlights
Climate change is expected to alter species distribution ranges (e.g., Hoegh-Guldberg and Bruno 2010). long-term studies examining the effects of climate change on marine species, in comparison with terrestrial species, remain scarce (Rosenzweig et al.2008), several reports have documented distributional shifts/expansions for several species, including seaweeds (e.g., Wernberg et al 2011; Tanaka et al 2012), corals (e.g., Yamano et al 2011), and fishes (e.g., Perry et al.2005)
E. cava habitats around Japan were assessed in terms of rising water temperatures and grazing over the course of the 21st century
We used only SSTbased indices in this study, our model performance is consistent when compared with previous studies, which evaluated the effects of climate change on seaweeds (e.g., Jueterbock et al 2013)
Summary
Climate change is expected to alter species distribution ranges (e.g., Hoegh-Guldberg and Bruno 2010). Rising seawater temperatures can affect seaweeds, either directly through physiological impacts (e.g., a negative effect on photosynthesis) (Serisawa et al 2001; Tanaka et al 2008) or indirectly via prolonged grazing by herbivorous fish (Yamaguchi et al.2010) For these reasons, barren ground events are expected to become more frequent and severe around. For the first time, distributional shifts in the habitat of E. cava around Japan were assessed with regard to rising seawater temperatures over the course of the 21st century This analysis was based on SST outputs provided by multiple CMIP5 climate model projections forced with all four future emissions scenarios of the Representative Concentration Pathways (RCPs; Moss et al.2010). E. cava, may lead to cascading effects throughout the coastal marine ecosystem
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