Shifts in marine species distributions have attracted substantial attention, particularly over the last decade once it became clear that marine species were shifting rapidly but had been understudied relative to similar processes on land ( Murawski 1993, Perry et al.
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2012), again suggesting that species shifted to new locations and ran out of habitat. By contrast, low-latitude animals were more likely to go extinct during rapid and severe climate cooling during the Late Ordovician mass extinction (approximately 445 Mya) ( Finnegan et al. Extinctions recorded during end-Permian warming were disproportionately clustered among high-latitude taxa, strongly suggesting that they ran out of climatically habitable space ( Penn et al. During the end-Permian mass extinction (approximately 252 Mya), for example, ocean warming and other changes precipitated the worst catastrophe in the history of complex life, eliminating nearly 80% of marine animal genera ( Payne & Clapham 2012). The modern shifts in marine species distributions are not unprecedented, though the pace of change in recent decades is likely much faster than it was over geological time. Climate velocity-defined as the rate and direction that isotherms move across the seascape-has been a useful concept for explaining some of the variation in rates and directions of range shifts across species and regions ( Burrows et al. Existing records have been sufficient to document hundreds of species moving to higher latitudes and greater depths with warming ( Figure 1), though the complex mosaic of temperatures sometimes means that species have moved in other directions as they track preferred conditions ( Dulvy et al. Climate change is already driving poleward range edges of marine species to expand at an average of 72 km/decade, which is approximately an order of magnitude faster than observed rates on land ( Poloczanska et al. Perhaps ironically, Dana's publication came out right around the time that industrialization led to the emission of large quantities of the greenhouse gases responsible for these changes.Īny perception of stable marine biogeography has fallen away amid observations of dramatic shifts in species geographic distributions over timescales from years to decades, centuries, and millennia. Ocean warming is now accelerating, so both the rate and magnitude of future changes are likely to be even larger ( Cheng et al. Beyond that, human greenhouse gas emissions have driven ocean surface temperatures to rise 0.7☌ and pCO 2 to increase as well, with cascading effects on stratification, oxygen concentrations, pH (a 30% rise in hydrogen ion concentrations), primary productivity, circulation, and more ( Hartmann et al. Ocean conditions vary cyclically across temporal scales from years to decades, centuries, and beyond. The intervening decades of research, however, have shattered any sense of a stable ocean environment. More than 150 years ago, Dana (1853) laid out a biogeographic description of ocean life in terms of isocrymes (lines of equally cold winter temperatures), with the implicit suggestion that these maps of environment and biogeography would be relatively stable through time. Additional research is needed to understand how processes interact to promote or constrain range shifts, how the dominant responses vary among species, and how the emergent communities of the future ocean will function.
These differences suggest that species cope with climate change at different spatial scales in the two realms and that range shifts across wide spatial scales are a key mechanism at sea. Compared with species on land, marine species are more sensitive to changing climate but have a greater capacity for colonization. These shifts reassemble food webs and can have dramatic consequences. These shifts have their roots in fine-scale interactions between organisms and their environment-including mosaics and gradients of temperature and oxygen-mediated by physiology, behavior, evolution, dispersal, and species interactions. The geographic distributions of marine species are changing rapidly, with leading range edges following climate poleward, deeper, and in other directions and trailing range edges often contracting in similar directions.
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