Geoscience Reference
In-Depth Information
2005) that the majority of existing coral reef ecosystems are likely to disappear
in average global temperature rises much above 1.5°C above the preindustrial
values. These studies are also complemented by similar conclusions for the
Indian Ocean (Sheppard, 2003), Pacific Ocean (Hoegh-Guldberg, 2000) and the
Coral Triangle (Hoegh-Guldberg et al., 2009).
Australian marine resources in 2°C and 4°C worlds
Using this information, it is possible to construct credible scenarios of what might
happen to Australian marine resources under conditions associated with average
global temperature increases of 2°C and 4°C above the pre-industrial period. As
noted earlier, based on observations of more than 40 years, marine organisms are
moving polewards and are changing their seasonal behaviour (e.g. reproduction,
migratory timing). The fact that this has occurred with an increase in average
global temperature of 0.7°C (IPCC, 2007) should give us extreme concern
over increases in average global temperature that may involve 4°C or more of
warming above the pre-industrial period. Ongoing, these changes are likely to
drive us into a world that will be unrecognizable in terms of the organisms and
ecosystems that will be present. Unfortunately, those ecosystems that will be
winners in this world will not be spectacular like the coral reefs and kelp forests
of our current world. Will tourists want to see the Great
Cyanobacterial
Reef of
Australia?
Shifts in distributions (and aspects such as behavioural timing or phenology)
of species could result in major rearrangement of marine ecosystems. One of the
key challenges that marine organisms will face is that the new environments are
likely to have different characteristics (e.g. light, pH, available habitat) and may
be suboptimal. For example, reproduction for many marine species is linked to
the appearance of phytoplankton within the water column at specific times of
the year (Cushing, 1989). The appearance of phytoplankton is matched to high
levels of solar radiation and the seasonal appearance of nutrients within the
water column. If spawning times shift toward earlier times in the year, they are
likely to occur when food (i.e. phytoplankton) is not yet available and conse-
quently emerging organisms will potentially starve. Given that over 90 per cent
of marine organisms depend on pelagic resources such as phytoplankton, the
impacts of this simple, rapid shift in timing is likely to have widespread conse-
quences for benthic as well as pelagic marine organisms, and would play havoc
with marine resources that are currently providing important fisheries income for
Australia.
Similar issues surround the potential for movement of organisms to higher
latitudes. There has been speculation that the Great Barrier Reef will simply
shift polewards (Hughes et al., 2012). The speed at which this would have
to occur can be calculated as follows. Most corals at the northern end of the
Great Barrier Reef are adapted to sea temperatures some 2°C warmer than at
its southern end, some 2,000 km away. If the Great Barrier Reef were to keep
pace with a 2°C rise in sea temperature over the next 100 years, it would have
