28 October: Sponges will thrive as many corals decline from ocean acidification

Sponges will thrive as many corals decline from ocean acidification

28th October 2014

AIMS scientists have revealed that some sponges may be able to adapt to ocean acidification while many corals may struggle to survive. The research was published in a new study this week in the Nature journal, International Society for Microbial Ecology (ISME). The study focused on the analysis of microorganisms that have a symbiotic relationship with sponges and corals at naturally-occurring volcanic seeps in Papua New Guinea, a site where there is a higher partial pressure of carbon dioxide (pCO₂) compared to other parts of the world’s ocean.

“Our study showed that the microorganisms living in close association with corals do not particularly like ocean acidification. Shifts in the coral-associated microbes likely have detrimental effects on coral health at the seep sites. However, other animals such as sponges, which do not calcify and make hard skeletons, may actually benefit from the high carbon dioxide levels, by using the by-products produced by their microbes to their benefit. For example, some cyanobacteria found in the sponge tissues likely consume the extra carbon dioxide, which improves their photosynthetic efficiency and passes more beneficial nutrients to the sponge” said AIMS scientist, Dr Kathleen Morrow.

Morrow explained that because of ocean acidification, where more carbon dioxide is being absorbed by the oceans, marine organisms and their microbial helpers will need to survive under conditions that are also more acidic (i.e. a lower pH).

“For many marine organisms such as corals that need to create their own skeleton, a lower surrounding pH makes this task much harder, thereby risking their long term growth and survival,” added Morrow.

The researchers found that some reef sponges (C. singaporensis and Cinachyra sp.) can survive in conditions with higher levels of carbon dioxide likely due to an increase in beneficial microbes. However, another sponge species (S. massa) and both study corals (A. millepora and P. cylindrica corals) do poorly at the CO₂ seep sites, which suggests they are more vulnerable to the long-term effects of ocean acidification.

These results provide important insights into how reefs may look in the future if human beings continue to burn fossil fuels at the current rate. This research, coupled with previous studies at the CO₂ seeps by researchers at AIMS (Fabricius et al. 2011 and 2013), suggests that there will be a loss of hard corals and a shift to other marine species such as sponges and macroalgae that can better take advantage of future environmental conditions.

Journal: International Society for Microbial Ecology (ISME)

Title: Natural volcanic CO₂ seeps reveal future trajectories for host–microbial associations in corals and sponges

Authors: Kathleen Morrow, David Bourne, Craig Humphrey, Emmanuelle Botté, Patrick Laffy, Jesse Zaneveld, Sven Uthicke, Katharina Fabricius and Nicole Webster.