S.O.S. Save Our Shells (and Skeletons)

We are the shelled creatures of the ocean, the oysters, mussels, clams, urchins and starfish. We require calcium carbonate in the form of aragonite and calcite to build our shells and skeletons, as do some species of zooplankton and phytoplankton, coralline algae and the coral reef building organisms. We have survived and thrived in a marine environment that has maintained its stable pH balance for millions of years, but within the last two hundred years, since human beings have become the dominant species on Earth, with the Industrial Revolution, rapidly burning through the available reserves of coal, oil and gas, the ocean has absorbed most of the carbon dioxide emissions generated by human activity, with potentially disastrous results for us.

While you grow your populations to unsustainable levels, we are losing the required materials to build our shells and skeletons. Carbon dioxide dissolves in seawater, and since the industrial age the blue-green waters of our home have become more acidic, and will continue to acidify at a rate faster than we will be able to adapt. Scientists are discovering our shells are already dissolving in increasingly acidic seawater. We are the shelled creatures of the ocean, we are dying and we need your help.

Carbon dioxide influences the global climate. The greenhouse effect is a naturally occurring phenomenon, where greenhouse gases including carbon dioxide, methane and nitrous oxide trap heat and keep the Earth’s temperature warm enough to sustain life. Since the onset of the Industrial Revolution, the human population has expanded rapidly, with increasing demand for energy to fuel civilization. Increased greenhouse gas emissions have added to the greenhouse effect, warming the planet and raising the Earth’s temperature. Atmospheric carbon dioxide levels are currently at their highest levels in fifteen million years. The ocean plays a key role in regulating the global climate.

The ocean holds more than fifty times the carbon dioxide of the atmosphere. Excess atmospheric carbon dioxide is absorbed by the ocean, so most of the carbon dioxide emissions from human activity have entered the ocean. Carbon dioxide is dissolved in seawater, and the excess carbon dioxide has altered ocean chemistry, making the ocean more acidic. Scientists know the current changes in Earth’s climate are caused by human activity through studying historical atmospheric conditions recorded in ice cores, marine sediments and fossilized micro-organisms. The evidence shows atmospheric carbon dioxide concentrations have increased from 280ppm to 376ppm since the Industrial Revolution.

Acidification chemistry

The following explanation on ocean acidification and the effects of calcification on shelled marine invertebrates is taken from ‘Marine Biology, Function, Biodiversity, Ecology’ by Jeffrey S. Levinton, published in 2009 by Oxford University Press, New York (p271).

When carbon dioxide is added to water, the following chemical reactions occur:

CO2 (carbon dioxide) + H2O (water) > H2CO3 (carbonic acid)

H2CO3 (carbonic acid) + H2O (water) > HCO3 (bicarbonate) + H3O+ (hydronium ion)

Seawater contains other forms of carbon besides water and carbon dioxide, and the above chemical reactions include the precipitation and dissolution of CaCO3 (calcium carbonate).

Seawater contains three major forms of dissolved inorganic carbon – carbon dioxide, bicarbonate and carbonate ion – which acts as a stabilizing effect called ‘buffering’, so that additional carbon dioxide resulting in production of hydronium ion acid formation reacts with other components and seawater acidity doesn’t change much. Increases in hydronium ions cause some carbonate ions to react with hydronium ions to become bicarbonate. The reduction in carbonate ion reduces the reaction, resulting in calcium carbonate precipitation.

< Precipitation

CaCO3 (calcium carbonate) <> Ca2 (calcium ion) + CO3-2 (carbonate) 

Solution >

For marine organisms to make calcium carbonate to build their shells and skeletons, a calcium ion must be combined with carbonate from seawater, a reaction that releases carbon dioxide and water in the process. The important issue here is whether increases in carbon dioxide from global warming, climate change and emissions caused by human activity will affect this calcification process. Increasing dissolved carbon dioxide increases acidity of seawater, which would drive chemical reactions toward under-saturation of seawater with calcium carbonate. It is expected that increases in atmospheric carbon dioxide levels should increase dissolved carbon dioxide and reduce pH (increase acidity).

This is a simplified explanation of acidification chemistry – for a more detailed analysis refer to the Smithsonian Institute’s Ocean Portal.

There are two forms of calcium carbonate – aragonite and calcite. They have the same chemical formula, but different crystalline structures. Aragonite is not as stable as calcite, is more difficult to precipitate and is 1.5 times as soluble in seawater. Marine organisms composed of aragonite include reef corals and mollusks. Marine organisms composed of calcite include coccolithophores, coralline algae and planktonic foraminiferans (although the pteropods and holoplanktonic snails have aragonite shells).

The evidence

There have been many studies already done to measure the effects of ocean acidification on the calcification process through both controlled experiments in the lab and via observations in the field. These studies have been conducted on a diverse range of marine species, including oysters, pteropods and coralline algae. There is evidence some species including coccolithophores, crustaceans and purple sea urchins may be able to adapt to rapidly acidifying conditions by growing harder shells. Other marine organisms may proliferate in highly acidic waters and these changes in species and biodiversity will affect trophic structure and marine food webs.

The solution

Safe levels of atmospheric carbon dioxide are approximately 350ppm, but current levels are nearly 400ppm, and would be higher (475ppm) if not for ocean absorption of carbon dioxide. To reduce or prevent an increase in these levels, carbon emissions must be reduced, by burning less fossil fuels and creating more carbon sinks (mangroves, seagrass beds and marshes). Yet these blue carbon sinks are being destroyed. The ocean is being over-fished, so fish farms are constructed, but mangrove forests are being removed to accommodate aquaculture. Seagrass beds are declining at a rate of 7% every year due to human activity.

But even if solutions to reduce levels of atmospheric carbon dioxide are implemented, it is too late to prevent climate change from occurring. This doesn’t mean that you, humanity, shouldn’t do what you need to do – change your behaviour and rethink what it means to be human. You were not put on this Earth to endlessly consume and destroy the beauty of the world and the foundations of life, health and wellbeing, yours and ours. We ask that you live by the principles of simplicity, awareness, sustainability and compassion, with respect for the other forms of life that share the Earth.

We are the shelled creatures of the ocean and we are dying. We ask you, humanity, to understand that you are not the only form of life on Earth, and that your way of life is destroying ours. Your use of fossil fuels is heating up the ocean and causing our watery medium to acidify. We want to continue to survive and thrive in the ocean, as we have for millions of years. Your need to grow your population beyond manageable and sustainable levels will cause many of our species to become extinct. We are the shelled creatures of the ocean and we need your help to save our shells and skeletons before it’s too late.

© 2016 Environmental Warrior
Photo by Wynand van Poortvliet on Unsplash

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