Abstract
Despite widespread climate-driven reductions of coral cover on tropical reefs, little attention has been paid to the possibility that changes in the geographic distribution of coral recruitment could facilitate beneficial responses to the changing climate through latitudinal range shifts. To address this possibility, we compiled a global database of normalized densities of coral recruits on settlement tiles (corals m-2) deployed from 1974 to 2012, and used the data therein to test for latitudinal range shifts in the distribution of coral recruits. In total, 92 studies provided 1253 records of coral recruitment, with 77%origi nating fromsettlement tiles immersed for 3-24 mo, herein defined as long-immersion tiles (LITs); the limited temporal and geographic coverage of data from short-immersion tiles (SITs; deployed for <3 mo) made them less suitable for the present purpose. The results fromLITs show de clines in coral recruitment, on a global scale (i.e. 82%from1974 to 2012) and throughout the tropics (85% reduction at 20° latitude). These trends indicate that a global decline in coral recruitment has occurred since 1974, and the persistent reduction in the densities of recruits in equatorial latitudes, coupled with increased densities in sub-tropical latitudes, suggests that coral recruitment may be shifting poleward.
Highlights
Organismal thermal tolerance drives biogeographic variation in the distribution of plants and animals on land and in the sea (Somero 2002, 2005), and as the Earth is warming through climate change, these distributions are changing (Parmesan & Yohe 2003, Pinsky et al 2013)
For reefs that do recover from major disturbances, a critical factor supporting recovery is the capacity for high coral recruitment supported by larvae produced through sexual reproduction (Bramanti & Edmunds 2016, Mumby et al 2016)
While an extensive poleward range shift of tropical corals is likely to be limited by the underwater availability of light, during winter months (Muir et al 2015), even a modest latitudinal range shift could provide an ecologically meaningful refuge against adverse conditions likely to occur in tropical seas
Summary
Organismal thermal tolerance drives biogeographic variation in the distribution of plants and animals on land and in the sea (Somero 2002, 2005), and as the Earth is warming through climate change, these distributions are changing (Parmesan & Yohe 2003, Pinsky et al 2013). Latitudinal or elevational range shifts have allowed many mobile terrestrial and marine organisms to escape increasing temperatures associated with global warming (Sorte et al 2010, Chen et al 2011, Beaugrand 2015), but for sessile marine organisms such as corals and sponges, temperaturemediated changes in distribution are more difficult to detect These difficulties arise from the lag in time between the dispersion of larval stages and the time necessary for them to grow to adults, and the high likelihood that temporal trends in distribution are expressed over regional scales (i.e. 200−4000 km; sensu Mittelbach et al 2001, Wernberg et al 2011) instead of the local scale on which most research operates. While an extensive poleward range shift of tropical corals is likely to be limited by the underwater availability of light, during winter months (Muir et al 2015), even a modest latitudinal range shift could provide an ecologically meaningful refuge against adverse conditions likely to occur in tropical seas (van Hooidonk et al 2014)
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