It gets cold out there. Seagrass Watch has a number of temperature monitors (iButtons) out in the field. A recent check on data generated by the monitor at SGW site AB1 on the Amity Banks found that temperatures got down to 11ºC to 13ºC on some days. The graph below gives a snapshot of those temperatures. The spikes in the data are a result of the monitor being exposed at low tide (see the red lines) so this means water temperatures were still between 18°C and a cool 15°C. These low temperatures have an impact on species and in particular impacts on dugongs which solely feed on seagrass. Dugongs in Hervey Bay and Moreton Bay in Queensland, as well as Shark Bay in Western Australia (Marsh et al., 1994), seem to respond to a water temperature threshold of 17–18 °C, below which they undertake meso-scale thermoregulatory movements. In Moreton Bay, Queensland, dugongs make microscale movements of about 10 km to escape the cold winter temperatures in the bay. During winter in 1988 –1989 tracked dugongs left the bay at some stage and moved through South Passage to where the waters of the East Australian current were >5 °C warmer than the 17–18 °C water in the bay (Sheppard et al, 2006).
Marsh, H., Prince, R.I.T., Saalfeld, W.K., Shepherd, R., 1994. The distribution and abundance of the dugong in Shark Bay, Western Australia. Wildl. Res. 21, 149-161.
Sheppard, J. K., Preen, A. R., Marsh, H., Lawler, I. R., Whiting, S. D. & Jones, R. E. 2006. Movement heterogeneity of dugongs, Dugong dugon (Muller), over
large spatial scales. J. Exp. Mar. Biol. Ecol. 334, 64–83.