The future of the oceans past

Abstract

Major macroevolutionary events in the history of the oceans are linked to changes in oceanographic conditions and environments on regional to global scales. Even small changes in climate and productivity, such as those that occurred after the rise of the Isthmus of Panama, caused major changes in Caribbean coastal ecosystems and mass extinctions of major taxa. In contrast, massive influxes of carbon at the end of the Palaeocene caused intense global warming, ocean acidification, mass extinction throughout the deep sea and the worldwide disappearance of coral reefs. Today, overfishing, pollution and increases in greenhouse gases are causing comparably great changes to ocean environments and ecosystems. Some of these changes are potentially reversible on very short time scales, but warming and ocean acidification will intensify before they decline even with immediate reduction in emissions. There is an urgent need for immediate and decisive conservation action. Otherwise, another great mass extinction affecting all ocean ecosystems and comparable to the upheavals of the geological past appears inevitable.

Figure 1.

Chronology of environmental and ecological changes in the coastal SWC over the last 10 Myr. (a) Ecological structure of biotic assemblages estimated by PCA axis 1, (b) per cent carbonate in sediments, (c) MART and (d) extinction rates for coral species and molluscan genera. Environmental change is concentrated in the period of the final closure of the Panamanian Strait about 4.4–3.5 Ma, whereas peaks in extinction lagged by 1–2 Myr. Horizontal error bars indicate 95% confidence intervals and vertical bars indicate maximum and minimum age estimates of collections. Adapted from O'Dea et al. (2007).

Figure 2.

Life histories of 24 common cupuladriid bryozoan species responded to environmental change (horizontal yellow bar) in the SWC. As planktonic productivity collapsed, species that survived significantly reduced their levels of clonal reproduction, while newly originated species were all predominantly aclonal. By contrast, species that failed to reduce levels of clonal reproduction became extinct 1–2 Ma after the environment changed, except for two species, indicated by asterisks in the figure, that survived in the eastern pacific (red). Thickness of the vertical range bar for each species represents the percentage of clonal colonies. Data for all species combined (grey/far-right bar) were calculated as the percentage of all clonal colonies irrespective of species. Note that 0% clonality is shifted slightly to the right to give entirely aclonal values some thickness. Adapted from O'Dea & Jackson (2009).