Ocean acidification: The impact on biofouling communities

Ocean acidification is an emerging global problem and is attributed to the uptake of atmospheric carbon dioxide by our oceans. Over the last decade there has been increasing focus in the scientific community on studying it’s potentially negative impacts on marine organisms.

A study published this week, conducted by British Antarctic Survey, examined how biofouling communities are impacted by and adapt to the ongoing acidification of Earth’s oceans. Biofouling refers to the accumulation of microorganisms, plants, algae, or animals on wetted surfaces. These communities can be categorised into  ‘calcareous‘ (hard shelled) fouling organisms that include barnacles, encrusting bryozoans, mollusks, polychaete and other tube worms, zebra mussels and ‘non-calcareous‘ (soft shelled) fouling organisms including seaweed, hydroids, algae and biofilm. Over 1700 different marine species are estimated to comprise biofouling communities and are responsible for impacting numerous industries including underwater construction, desalination plants and ship hulls. Removing these organisms (a process called antifouling) is estimated to cost around $22 billion a year globally. Reporting in the journal Global Change Biology, the authors, comprised of scientists from British Antarctic Survey, Centro de Ciências do Mar, Instituto Portugues do Mar e da Atmosfera and University of Cambridge, investigated how these communities may respond to future pH decrease.

In the first experiment of its kind, over 10,000 animals from the highly productive Ria Formosa Lagoon system in Algarve, Portugal were allowed to colonise hard surfaces in six aquarium tanks. In half the tanks, the seawater had the normal acidity for the lagoon (PH 7.9) and the other half were set at an increased acidity of PH 7.7. The conditions represented the IPCC’s prediction for ocean acidification over the next 50 years. After 100 days, organisms with hard shells (Spirobid worms — Neodexiospira pseudocorugata) reduced to only one fifth of their original numbers, while sponges and some sea squirts (Ascidian Molgula sp) increased in number by double or even fourfold.

Lead author Professor Lloyd Peck from British Antarctic Survey (BAS) says:

“Our experiment shows the response of one ‘biofouling community’ to a very rapid change in acidity, but nonetheless shows the degree to which these communities could be impacted by ocean acidification, and to which its associated industries may need to respond. What’s interesting is that the increased acidity at the levels we studied destroys not the building blocks in the outer shell of the worms itself, but the binding that holds it together. Many individuals perish, but we also showed their larvae and juveniles are also unable to establish and create their hard exoskeleton.”

The significance of this research is that with the ongoing effects of climate change, there are still many unanswered questions about how this change will affect marine life. The rapid uptake of heat energy and CO2 by the ocean results in a series of changes in seawater carbonate chemistry, including reductions in pH and it’s carbonate saturation state. Currently surface waters are supersaturated with respect to all forms of calcium carbonate, however with increasing ocean acidification the ocean pH falls and reduces the carbonate ion concentration, making the calcium carbonate structures of organisms vulnerable to dissolution¹. For example, mussels and oysters have shown to exhibit a 55% decrease in shell and body growth at pH 7.3 ², with net calcification decreasing by 25% at 2 times the pre-industrial carbon dioxide levels as predicted for the year 2050. Coccolithophores, planktonic algae which produce blooms so large they are visible from space, produce calcitic liths or plates. Experiments indicate that some species (e.g. Emiliania huxleyi and Gephyrocapsa oceanica) may experience decreased rates of calcification by 16% at 2 times current CO2 levels and 30% at 3 times CO2 levels ³.  It has also been suggested that  to compensate for this struggle to maintain calcification, some organisms may be forced to reallocate resources away from productive endpoints such as growth4. Overall, different species and groups of marine animals vary in their ability to cope with, and compensate for, hypercapnia (elevated CO2 levels) and lowered pH with implications for marine trophic interactions.

Over the past 20 years, measurements have shown that surface ocean pH has reduced by 0.1 pH unit relative to pre-industrial levels, which equates to a 26% increase in ocean acidity and by the end of the twenty-first century, reductions of 0.4 – 0.5 pH are predicted to occur 6. With the rate at which ocean acidification is accelerating, scientists, resource managers, and policymakers recognise the urgent need to strengthen the science as a basis for taking action to prevent further damage to our oceans.

Photo credit: Leyre Villota Nieva (BAS)

Article Source: Peck, L. S., Clark, M. S., Power, D., Reis, J., Batista, F. M. and Harper, E. M. (2015), Acidification effects on biofouling communities: winners and losers. Global Change Biology. doi: 10.1111/gcb.12841

Additional Sources:

  1. Orr, James C.; et al. (2005). “Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms”. Nature 437 (7059): 681–686.Bibcode:2005Natur.437..681O. doi:10.1038/nature04095.PMID 16193043. Archived from the original on 2008-06-25.
  2. Michaelidis, B., Ouzounis, C., Paleras, A. and Pörtner, H.O. (2005) Effects of longterm moderate hypercapnia on acid–base balance and growth rate in marine mussels Mytilus galloprovincialis. Marine Ecology Progress Series, 293, 109–
  3. Riebesell, U., Zondervan, I., Rost, B., Tortell, P. D., Zeebe, R. E., Morel, F. M. M. (2000) Reduced calcification of marine plankton in response to increased atmospheric CO2. Nature, 407, 364–367.
  4. Hannah L. Wood, John I. Spicer and Stephen Widdicombe (2008). “Ocean acidification may increase calcification rates, but at a cost”. Proceedings of the Royal Society B 275 (1644): 1767–1773.doi:10.1098/rspb.2008.0343. PMC 2587798.PMID 18460426.
  5. Pörtner H.O, Langenbuch M, Reipschläger A. Biological impact of elevated ocean CO2 concentrations: lessons from animal physiology and earth history. J. Oceanogr. 2004;60:705–718.doi:10.1007/s10872-004-5763-0
  6. Doney SC. 2010 The growing human footprint on coastal and open-ocean biogeochemistry. Science 328, 1512– 1516. (doi:10.1126/science.1185198)

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