Background
In introducing their study, the authors note that sponges comprise a major component of coral reef macrofauna and that they play key ecological roles, including providing habitat for other invertebrates and complex microbial symbioses, citing Bell (2008). Thus, they are concerned that projected increases in air and sea surface temperatures of up to 4°C by 2100, as suggested in the IPCC (2007) report, will have a direct and significant impact on them and their holobionts.

What was done
In a series of laboratory experiments, Webster et al. "assessed the effect of elevated seawater temperature on bacterial communities in larvae of the Great Barrier Reef sponge, Rhopaloeides odorabile," in order to be able to "compare the thermal thresholds for the different life history phases of this model sponge species."

What was learned
Although R. odorabile adults had previously been observed to experience significant negative repercussions above 32°C, the four researchers found that their larvae exhibited "a markedly higher thermal tolerance," with no adverse health effects detected at temperatures up to 36°C, while their microbial communities "were conserved at temperatures up to 34°C."

What it means
In the words of the Australian scientists, "we demonstrated that sponge larvae maintain highly stable symbioses at seawater temperatures exceeding those that are predicted under current climate change scenarios." And given the high likelihood that both the sponge and its holobionts would experience considerable adaptive evolution between now and the end of the 21st century, it is safe to say that predicted global warming would have little to no impact on them in terms of their survival and normal functioning.

References
Bell, J.J. 2008. The functional roles of marine sponges. Estuarine, Coastal and Shelf Science 79: 341-353.

IPCC. 2007. Climate Change 2007: The Physical Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC, Geneva, Switzerland.