I wanted to add a little to Ove’s continued defence against ‘The Australian’ on going war against science. Whilst most people see the Great Barrier Reef as being one large coral reef, it also contains an array of other habitats including seagrass meadows that are critical to the overall ecosystem. Seagrasses, amongst there many roles in the GBR, are critical in supporting biodiversity and fisheries productivity. These seagrass meadows, like coral reefs, are also under threat from increasing seawater temperatures.
The potential 4°C increase in global temperature by the end of the century, that the leader of the opposition recently described as “not a big moral challenge”, would have an enormous detrimental impact upon seagrass meadows, particularly the abundant intertidal meadows present throughout the GBR. Research published back in 2006 found how seagrasses of the GBR suffer irreparable effects from short-term or episodic changes in seawater temperatures as high as 40–45 °C. Although these temperatures sound high, intertidal pools can commonly approach and exceed these temperatures for short periods throughout the GBR, and seagrasses are observed to ‘burn’. If temperatures were to increase by 4°C, such ranges would be exceeded too regularly to allow for recovery, and seagrass meadows are likely to deteriorate with huge detrimental impacts upon fisheries and coastal productivity.
The Great Barrier Reef described to be “blue again” by ‘The Australian’ is under continued stress. Seagrasses although important in their own right make excellent ‘coastal canaries’ and their tissues are good time integrated indicators of the coastal nutrient environment. Monitoring throughout the GBR continues to find coastal seagrasses containing highly elevated C:N:P ratios, indicating rich and potentially eutrophic environments that are continuing to be enriched. Increasing nutrients onto the reef and into seagrass will continue to promote algae and reduce the resilience of coral and seagrass to future climate change and increasing temperatures. The combination of elevated nutrients and increased temperatures are of concern as greater temperatures increase metabolic rate, resulting in increased light requirements for seagrass. Such light requirements are not possible when increasing nutrients reduce light availability due to increased epiphytes and phytoplankton, resulting in eventual loss of the seagrass.
As Ove said previously, there exists no evidence to suggest that the GBR is “blue again”, and to the contrary, seagrass biomonitoring suggests nutrient conditions are continuing to deteriorate, with many coastal locations becoming increasingly eutrophic (see Figure 1 taken from the latest Seagrass-Watch magazine). The available evidence suggests that seagrasses and the coastal environment of the GBR are under increasing nutrient stress, reducing future resilience to climate change.