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A Microbenthic Assemblage Response to Ocean Acidification

Paper Reviewed
Amaro, T., Bertocci, I., Queiros, A.M., Rastelli, E., Borgersen, G., Brkljacic, M., Nunes, J., Sorensen, K., Danovaro, R. and Widdicombe, S. 2018. Effects of sub-seabed CO2 leakage: Short- and medium-term responses of benthic macrofaunal assemblages. Marine Pollution Bulletin 128: 519-526.

In addition to concerns about potential negative impacts of predicted ocean acidification (OA) on marine life, there is an alternative uneasiness that carbon capture and storage pipelines and reservoirs designed to sequester CO2 may leak or burst, releasing large quantities of CO2 into the immediate surrounding waters in the oceans where such facilities exist. If that were to occur, the pCO2 in such regions could rise to several times that predicted to occur under even the most pessimistic OA scenarios, resulting in a potentially disastrous situation for marine organisms subjected to such an event.

Attempting to get a handle on just how devastating such a leak or break could be, Amaro et al. (2018) set out to investigate "the potential effects of CO2 leakage on microbenthic assemblages by exposing infaunal sediment communities to different levels of CO2 concentration (400, 1000, 2000, 5,000 and 20,000 ppm CO2), simulating a gradient of distance from a hypothetic leakage, over short-term (a few weeks) and medium-term (several months)" periods of time. Results of their analysis are summarized in the figure below.

In discussing their findings, Amaro et al. report that two weeks after the start of the experiment, macrofaunal species richness and abundance were reduced in all treatments, relative to the control (400 ppm CO2). However, by twenty weeks, they found that "all significant differences disappeared" among the treatments, with the exception of the 20,000 ppm treatment for species richness and the 5000 ppm treatment for species abundance, which were significantly lower and higher than the control, respectively (see Figure 1).

Consequently, given the above observations, the researchers conclude that "the communities in all the CO2 enriched treatments, except 20,000 ppm, converged as the hardiest and most resistant species persisted." And if they could persist up to 5000 ppm for both species richness and abundance (and up to 20,000 ppm for abundance!), then there may be little reason to be concerned about projected future impacts of OA in the open ocean, where pCO2 levels are not expected to rise above 1000 ppm over the next century or more.

Figure 1. The effects of ocean acidification on mean macrofaunal species richness and abundance after 20 weeks of exposure to each CO2 treatment. Adapted from Amaro et al. (2018).

Posted 3 September 2018