Effects of Way-Above-Average Warming on Tasmanian Reefs

Stuart-Smith et al. write that "despite increasing scientific and public concerns [about] the potential impacts of global ocean warming on marine biodiversity, very few empirical data on community-level responses to rising water temperatures are available." In an effort designed to help fill this important data void, the authors undertook, as they describe it, "a study of sub-tidal reef communities over a decadal time scale, comparing data on fishes, macroinvertebrates and macroalgae collected at 136 sites, spanning hundreds of kilometers around the island of Tasmania (southeastern Australia) in the early to mid 1990s, with data from the same sites in 2006/2007." This region, in their words, "has experienced relatively rapid warming during the last century as a consequence of a strengthening of the warm East Australian Current (Ridgway, 2007)," such that there has been "an increase in sea surface temperature of 2.28 ± 0.35°C per century for the period 1944-2002 (Ridgway, 2007), which is considerably more rapid than the global mean of 0.6 ± 0.2°C per century estimated by Smith and Reynolds (2003), and a mean increase in surface air temperature of 0.6-0.8°C (Salinger, 2005; Hansen et al., 2006)." In fact, the warming around this part of Tasmania has been more than three times greater than that of the global mean. So what did they learn?

Contrary to what they had expected to find, the four researchers discovered that "Tasmanian shallow rocky reef communities have been relative stable over the past decade," in spite of the "substantial rise in sea surface temperature over this period" and the "continuation of a considerable warming trend in oceanographic conditions over the last 50 years." Indeed, they report that "the northeast and southeast bioregions, which are most influenced by the East Australian Current and hence have experienced the greatest warming over the last century, appeared to have actually changed very little," adding that "not only were Tasmanian reef communities remarkably similar between 1994 and 2006 in a multivariate sense, but univariate community characteristics such as species richness and total fish abundance were also consistent." Thus, contrary to many people's expectations, as well as their own initial thoughts on the subject, the Australian scientists found very little evidence to support the "doomsday" scenarios of the IPCC, who foresee continued global warming decimating earth's highly productive costal marine ecosystems.

Additional References
Hansen, J., Sato, M., Ruedy, R., Lo, K., Lea, D.W. and Medina-Elizade, M. 2006. Global temperature change. Proceedings of the National Academy of Sciences USA 103: 14,288-14,293.

Ridgway, K.R. 2007. Long-term trend and decadal variability of the southward penetration of the East Australian current. Geophysical Research Letters 34: 10.1029/2007GL030393.

Salinger, M. 2005. Climate variability and change: past, present and future -- an overview. Climatic Change 70: 9-29.

Smith, T.M. and Reynolds, R.W. 2003. Extended reconstruction of global sea surface temperatures based on COADS data (1854-1997). Journal of Climate 16: 1495-1510.