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Corals and Shellfish

June 1, 2011

In this post Catlin Arctic Survey Science Programmes Manager Dr. Tim Cullingford rounds-up the latest in ocean acidification research.

Visit our science resources web page for more links to full academic papers on the themes of previous Catlin Arctic Surveys – sea ice loss, ocean acidification and thermohaline circulation.


If you bubbled some CO2 into your bath water, you’d make it fizzy like soda water.  However, you wouldn’t be too bothered about the effect of that little change in acidity when you took a bath.  But a small organism (let’s say an adult plankton) in the bath might feel more of an effect.  That’s because, compared to us, the plankton has a higher surface area to volume ratio, so its environment (the bath-water) is far closer to all the cells in its body, than for us.  That means even a slight change in bath chemistry is likely to affect it more significantly.  So you can imagine then, that this change is likely to be even more significant for the tinier larvae of the adult plankton.

Ocean acidification is a process a bit like adding CO2 to water.  It is caused by increases in CO2 in the air, itself a result of humans burning fossil fuels.  It is well understood to threaten small marine organisms with a shell, because more acid waters make it harder to form, and harder to keep a calcium-based shell.  But it can have other effects on viability and behavior, especially early in the organisms life history.  This area of the effect of ocean acidification is only beginning to be understood.  Two recent papers in ‘Proceedings of the National Academy of Sciences’ illustrate the difficulties likely to be encountered by the larvae of key marine organisms.  To do this the researchers performed acidification experiments sending the organisms ‘into the future’ and ‘into the past’.

Paper 1: ‘Sending coral larvae into the future’

Coral reefs are not only important from the perspective of tourism, but they provide key habitats for marine life and are drivers of biodiversity.  The first paper devises an experiment on fertilization and growth of coral larvae, essential to forming the foundations of the extensive architecture of a coral reef. To do this the researchers set up test incubations comparing current ocean CO2 levels with the higher levels (and hence lower pH and increased acidity) predicted for oceans by the end of this century.  This type of experiment has been described as ‘sending the organism into the future’, because the experiment attempts to reproduce predicted future ocean conditions, to see what effect this has on the organism.  Coral can reproduce sexually, and they show that acidification inhibits fertilization of coral eggs by sperm to form larvae.  Moreover, the ability of the resulting larvae to settle and establish themselves on a hard surface to form the foundation of a new colony, and the rate at which the new colony starts to grow are also inhibited by acidification. acidification compromises recruitment success of the threatened Caribbean coral Acropora palmata
Rebecca Albright, Benjamin Mason, Margaret Miller, and Chris Langdon

Paper 2: Sending shellfish larvae back to the past

The second paper describes an experiment that goes a step further by examining not only predicted future ocean CO2 on adults, but also that of pre-industrial (before 1750) concentrations on larvae, ‘sending the organism into the past’.  It looks at the larvae of two commercially important shellfish: clams and scallops.  Compared to current conditions, they show that under the lower pre-industrial ocean CO2 levels (and hence higher pH and reduced acidity), the rate of larval growth and the ability to change into the mature polyp form is faster.   Similarly the survival rate and the ability to accumulate fats, crucial to the structure, growth and energy supply of the larvae is higher under pre-industrial conditions.  Finally, they confirm that, as might be predicted, the shells of the adult clams and scallops are more robust under pre-industrial conditions, and are malformed and eroded under conditions predicted later this century. - Effects of past, present, and future ocean carbon dioxide concentrations on the growth and survival of larval shellfish
Stephanie C. Talmage and Christopher J. Gobler


Both papers are examining the further potential range of effects of ocean acidification on marine organism larval health and behavior.  As these effects are separate to the better-known effects on shell formation in adults, it remains to be determined how ocean acidification interferes at the larval level. It remains to be established whether this is through changes in environmental cues known to be affected by acidification (e.g. ocean pH, sound transmission, nutrients) that the larvae rely upon as signals for their normal developmental pathways.

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