How does rising atmospheric CO2 affect marine organisms?

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The World's Longest-Running Tropical Sponge Study
Kelmo, F., Bell, J.J. and Attrill, M.J. 2013. Tolerance of sponge assemblages to temperature anonamalies: Resilience and proliferation of sponges following the 1997-8 El-Niņo Southern Oscillation. PLOS ONE 8: e76441.

Sponges, in the words of the authors, "are a major component of coral reef communities across the world," and they say they can "form important relationships with a range of microorganisms, which can facilitate high levels of benthic primary production and nutrient cycling." However, they state that "there is a paucity of information concerning the impacts of large-scale climate events on sponges or how future climate change is likely to influence sponge assemblages." And, hence, they conducted a lengthy study to help fill this void.

What was done
Focusing on four reefs in Bahai, Brazil - Abai (12°40'04"S, 38°04'47"W), Guarajuba (12°39'22"S, 38°03'18"W), Itacimirim (12°37'20"S, 38°01'40"W) and Praia do Forte (12°34'42"S, 37°58'59"W) - Kelmo et al. conducted a 17-year study in which they examined "changes in sponge assemblages from three different reef habitat types at four different locations spanning the 1997-8 ENSO event (and later smaller ENSO events) in order to assess assemblage-level impact and recovery patterns." And what did they find?

What was learned
The three researchers discovered that the reefs' sponges appeared to have been unaffected by the increase in seawater temperature, and that they actually increased in abundance after the major ENSO event, in what they said was a finding that stood "in stark contrast to all other benthic organisms in this study area that experienced mass mortalities, including foraminifera, corals, echinoderms, bryozoans and ascidians," as observed in the studies of Kelmo et al. (2003), Attrill et al. (2004), Kelmo et al. (2004), Kelmo et al. (2006), Atrill and Kelmo (2007) and Kelmo and Hallock (2013)."

What it means
In light of their findings, as well as those of the other cited studies, Kelmo et al. conclude that "of all reef taxa, sponges have the potential to be resilient to large-scale thermal stress events," and they thus go on to hypothesize that "sponges might be less affected by projected increases in sea surface temperature compared to other major groups of reef organisms," adding, therefore, that "identifying the potential mechanisms enabling sponges to deal with heat stress should be a focus of future investigations."

Attrill, M.J. and Kelmo, F. 2007. Opportunistic responses of Diadema antillarum (Echinodermata: Echinoidea) populations following the 1997-98 El Niņo event in Bahai, Brazil. Estuarine, Coastal and Shelf Science 73: 243-248.

Attrill, M.J., Kelmo, F. and Jones, M.B. 2004. Impact of the 1997-8 El Niņo event on the coral reef-associated echinoderm assemblage from Northern Bahia, NE Brazil. Climate Research 26: 151-158.

Kelmo, F., Attrill, M.J., Gomes, R.C.T. and Jones, M.B. 2004. El Niņo induced local extinction of coral reef bryozoan species from Northern Bahia, Brazil. Biological Conservation 118: 609-617.

Kelmo, F., Attrill, M.J. and Jones, M.B. 2003. Effects of the 1997/1998 El Niņo on the cnidarian community of a high turbidity coral reef system (Northern Bahia, Brazil). Coral Reefs 22: 541-550.

Kelmo, F., Attrill, M.J. and Jones, M.B. 2006. Mass mortality of coral reef ascidians following the 1997/1998 El Niņo event. Hydrobiologia 555: 231-240.

Kelmo, F. and Hallock, P. 2013. Responses of foraminiferal assemblages to ENSO climate patterns on bank reefs of northern Bahia, Brazil: A 17-year record. Ecological Indicators 30: 148-157.

Reviewed 22 January 2014