218-01 copyThe Life and Death of Algae (2007) Jonathan Crinion

INTRODUCTION

After the Second World War the idea of continuing with the frugality that had been a necessity seemed perverse in what appeared to be a world of plenty. By the early 60’s cars were big status symbols with big engines and filling them with gasoline was just something that you did. Plastic, another petrochemical based product, became the material of the future. You could almost make anything out of this new material and when you were done with it, you just threw it away. All the while the global population was increasing and cars went from being a luxury to a basic need. Every day millions of people wake up and turn on these carbon dioxide producing machines. By 2007 the world population had grown to 6,636,788,085 (1) and with them the concentration of carbon dioxide (CO2) in the atmosphere has increased dramatically. While cars were not the only producer of CO2 they were indicative of an seaice07 copyunconscious societal attitude in which nature existed to be exploited.  Natural carbon sinks such as peat bogs and the oceans have begun to exceed their traditional capacity to sequester carbon from the atmosphere. Green house gases in the atmosphere are causing the planet to heat up and the polar ice caps have begun to melt far faster than anyone could have imagined. James Lovelock believes that between 2012 and 2017, all of the polar ice will have melted. (2). As the oceans rise, the currents will change, water temperatures will fluctuate and all marine life will be affected.

This is a brief story about the life of the marine algae and the role they play in removing tons of carbon from the atmosphere and even affecting the weather. As the planet heats up and CO2 levels increase, can these organisms adapt and continue to remove carbon from the atmosphere or will the changing environmental conditions simply drive them to extinction? Image 1

 

THE EUTROPHIC ZONE 

di8752enz copyImage 2

About 70% of the Earth is covered with water and of that, 97% is salt water. (3) The warmer upper layer of oceans is called the Eutrophic layer because it defines the boundary for how deep the suns rays can penetrate into the water. The plant portion living in the Eutrophic zone, where there is enough sunlight to support photosynthesis, are called phytoplankton. Phytoplankton is a large group of organisms that is mostly composed of single-celled algae and bacteria. The word Phytoplankton comes from the Greek phyton, or plant. Plankton is also a word derived from the Greek, meaning wandering and as we shall see, this is quite an apt description. The term plankton is simply a description of a life-style rather than a genetic classification. (4)

There are over five thousand different types of Phytoplankton with a biomass that outweighs all other the marine life put together. This is a remarkable statistic given the extremely small size of these organisms, which ranges from 0.2 to about 60.0 microns. (A micron is 1/1000 of a millimetre.) It’s not hard to imagine that if the Phytoplankton’s environment is affected in any way there will be repercussions elsewhere in the web of life. One of the photosynthesising phytoplankton living in the sunny Eutophic zone is an algae called the coccolithophore. ‘Phytoplankton are the foundation of the marine food chain and they can influence Earth’s climate’ (5) What makes the coccolithophore so important to our story is that they remove a massive amount of carbon dioxide from the atmosphere. Coccolithophores use the carbon dioxide dissolved in the ocean to make a calcium carbonate shell like structure. For millions of years these calcium carbonate structures have been precipitating to the ocean floor, which under pressure, turn into chalk and limestone. Over millions of years the chalk and limestone finds its way back to the surface through plate tectonics or by volcanic action that draws it up from the softer ocean floor that has moved under the more solid continents. This cyclical process over millions of years helps to maintain a healthy environment by constantly replenishing the nutrients necessary to continue the complex interactions that make up Gaia.

COCCOLITHOPHORES

Scientific classification:cocco7 copy

Domain:                      Eukaryota

Kingdom:                   Chromalveolata

Phylum:                      Haptophyta

Class:                          Prymnesiophyceae

Order:                          Isochrysidales

Family:                       Noelaerhabdaceae

Genus:                         Emiliania

Species:                       E. huxleyi                         (6)                                                                     Image 3: Coccolithophore, Emiliania Huxleyi

Coccolithophores are in the Eukaryotes Domain, which includes organisms with a nucleus, and a defining trait is that they have flagella, a tail like appendage that they can wiggle to create movement towards food sources. Coccolithophores have two flagella. One 2a_csphterms copyof the characteristics of the Prymnesiophyceae Class is that they have a Haptonema between the two flagella when the cell is in its motile stage. (6) The haptonema is thought to be a sensory organelle used to capture particulate matter from algae or bacterial cells. The particulate matter is gathered on the haptonemal tip and when a certain amount has been captured the Haptonema bends and deposits the material close to the end of the cell where it is taken in by phagocytosis, which is the process of surrounding particles by the cell membrane for digestion. (7) One particular type of Coccolithophore shown in the images above (Image 5; Coccolith) is called Emiliania Huxleyi (Ehux). Ehux produces coccoliths, which are small individual platelets that form a protective layer around the cell. The coccoliths are made by removing carbon dioxide from the surrounding water. Image 4; Section of Coccolithophore showing flagella and Haptonema

SEQUESTERING CARBON

Coccolithophores are single celled photosynthisisers and are thus able to use sunlight to convert carbon dioxide and water into sugars and oxygen. The coccolith molecules are made out of one part carbon, one part calcium lithsd1 copyand three parts oxygen. Together that makes calcium carbonate (CaCO3). The coccoliths are formed by a bio mineralization process inside the cell in which calcium and carbonate ions come together to form Calcite (CaCO3s) which is extruded to the exterior, similar to the way humans produce nails. While the coccoliths can be quite ornate they are dead mineral structures. (8)

Coccolithophores are responsible for producing more than 1.5 million tons (1.4 billion kilograms) of calcite a year. (9)

Each time a molecule of a Coccolith is made it removes one carbon atom from the ocean. The coccoliths of Ehux are approx. 2.5 x 10-6 metres in diameter, and weigh approx. 1.8 x 10-12 g each. Of this weight, the average contents of carbon, oxygen and calcium (CaCO3) atoms in the Coccolith have been measured to be 0.28, 0.87 and 0.67 x 10-12 g per Coccolith respectively. That doesn’t sound like very much but it amounts to about three hundred and twenty pounds of carbon sequestered for every ton of coccoliths produced. It’s estimated that the Coccolithophores are responsible for producing more than 1.5 million tons (1.4 billion kilograms) of calcite a year. (9) All this calcite will eventually fall and build up on the ocean bottom to become chalk or lime stone. The ability of Coccolithophores to remove carbon atoms from the atmosphere plays an important role in preventing the build up of CO2 in the atmosphere and in turn keeping the planet at a habitable temperature. (10) But now that the Coccolithophore’s environment is changing we need to consider their options for survival.

BLOOMING AND CLOUDS

When nutrient rich water is brought to the surface by currents and up-welling coccolithophores and other algae feast on the nutrients. As the algae gather on the surface to feed, they produce an amazing spectacle visible from space as their light coloured CaCO3 coccoliths, with a high albedo, reflect the sun light and turn the water a turquoise colour. This dense mass of algae coming together is called a bloom. The amount of CaCO3 in the top 60m at one of these bloom sites has been conservatively calculated at 7.2x 10 to the 4th tonnes.’ (11) As the algae collect to feed on the nutrients, zooplanktons swarm in to feed on the algae. As the algae are digested by the zooplankton dimethylsulfoniopropinate (DMSP) is released and converted into dimethylsulfide. (12) Dimethylsulfoniopropinate is produced within the algae cell and is thought to have various functions. Firstly it is thought to protect the cell from drying out as the osmotic pressure of the salty sea water tries to get in and secondly it acts like a form of antifreeze to protect the cell from freezing. Other researchers believe that the DMSP acts as an antioxidant, which might help the algae in water with low iron content. (13) The literature seems to indicate that DMS can be produced by some forms of algae on their own, such as Ehux, but that the DMS is other wise produced when the cells are damaged by water turbulence or from being digested by the zooplankton. Others believe that the DMS is released as a defence mechanism against the zooplankton.

James Lovelock proposed a negative feed back cycle in which algae play a part in regulating the climate and he suggested that the Coccolithophores were releasing the DMS for a purpose. As the algae produce DMS, it reacts with oxygen in the air to form solid sulphur particles. These particles then provide a surface for water vapour to condense on which in turn become clouds. As clouds form750px-Cwall99_lg copy there will be an updraft as the water surface cools. As more air moves in to replace the rising air the surface of the water will be churned up. Smaller Coccolithophores near the surface can be lifted out of the water and taken to lofty heights before falling back to earth some distance from where they started. The churned up water would bring more nutrients back to the surface and the wind has helped to disperse the Cocolithophores. The clouds will blow away and the water will then warm up again thus stimulating algae growth, which in turn will stimulate the DMS release and the cycle starts again. An additional advantage of this process is the dispersal of the sulphur molecule onto land. Stephan Harding points out that ‘Sulphur is essential for life – without it the amino acids that build up proteins cannot be made’ (14) Image 8; Coccolithophore bloom

In an Article entitled ‘Send in the clouds’ two scientists from the University of East Anglia, Peter Liss and Andrew Watson, believe that cooling the surface of the water is good for algae because as the surface water heats up it becomes cut off from the up welling of nutrients from below. These scientists also believe that the Coccolithophores may benefit from the nitrogen in the rain from the clouds that they have helped to create by releasing DMS in the first place. (15) It was later that Bill Hamilton of Oxford University speculated that the reasons the Coccolithophores were releasing DMS was to get themselves moved to a different location. In other words a form of dispersal similar to the way plant seeds ride the wind to a new location. It is also known that algae blooms can produce surface foam, which the wind can easily pick up and then lift the organisms high into the atmosphere to be deposited in a new location. Hamilton said “dispersal is the third priority for an organism, after survival and reproduction” (16)

So we see from the various pieces of the puzzle there are many different ideas on offer. If DMS is released when algae are being attacked by zooplankton during a bloom the purpose of the DMS might be a defensive one. Additionally the weather produced as a result of the water condensing on the sulphate aerosol that in turn relocates the algae may be the key to ensuring that some of the algae will survive to propagate again. Regardless of the reasons that DMS is produced we do know that the effect is to help relocate the algae and provide a valuable source of sulphur. 

PRECIPITATION OF CALCIUM CARBONATE

When considering the effects of climate change, one variable is the transition from making CaCO3 from the CO2 near the surface and putting it into storage on the ocean floor. Coccolithophores are extremely light in comparison to the surrounding water. In fact they are almost at the point of neutral buoyancy and typically fall at10002 copy a rate of about 1 metre per day in very still water. As the size of the Coccolithophore increases through the production of more coccoliths, so does the weight and thus the rate at which it falls. Coccolithophores require either turbulent water or their own motility to stay in the euphotic zone. (17) So how is it that they end up at the bottom of the ocean in the areas they inhabit rather than being carried thousands of kilometres away by the strong ocean currents circling Earth? The answer is that they are an important part of the food chain. During a bloom zooplankton digest them and then excrete the coccoliths in fecal pellets. These fecal pellets are much heavier than individual Coccolithophores and therefore descend to the bottom at an average of 200 metres per day. As can be seen in the photograph the concentration of coccoliths can be quite significant and a single fecal pellet containing thousands of coccoliths can be as large as 500 microns (0.5 of a mm), which is visible to the human eye. The bar in the photo represents 100223545_b4391cd9 copymicrons. Surprisingly it’s not these clumps of Coccolithophores in fecal pellets that make up the majority of the matter that falls to the ocean floor but rather it is the constant marine snow made up of smaller organic and inorganic particles that pervades the entire ocean and is constantly falling very slowly to the ocean floor. (18) As the layer builds up on the ocean floor over millions of years the organic matter disintegrates and the calcite matter becomes compressed, forming chalk and eventually line stone under the extreme pressure of the water and layers above. One final note is that it is important to remember that the Zooplankton are also in that food chain that leads all the way from small fish up to birds. If something was to impede the growth of algae, which are the foundation of this food chain, there will be a ripple effect through the entire food chain. Image 6: Fecal pellets, Image 7:  The Seven Sisters, chalk cliffs UK.

EXTINCTION OR ADAPTATION ? 

With the excessive amounts of carbon dioxide being pumped into the atmosphere each day the question is what will become of coccolithophores and other algae that sequester carbon? A large part of the CO2 continues to be dissolved into the ocean as wind and wave action mix the air with the water. The effect of constantly adding CO2 to water is that it becomes acidic and thus lowers the pH value of the water. If we look back at how Coccolithophores make their calcium carbonate coccoliths we remember that calcium and carbonate ions must come together to form CaCO3s but only if they occur in the right concentrations and if there is a balance of inhibiting compounds that the Coccolithophore can deal with. Inorganic carbon can occur in the oceans in three forms: As dissolved CO2 gas, as bicarbonate (HCO3) and as carbonate (CO3) ions and it is the pH balance of the water that determines how these compounds will form. As the ocean becomes more acidic from the build up of CO2 the acidification is causing Carbonate concentrations to fall. As the concentration of Carbonate falls it becomes more and more difficult for the Coccolithophores to make CaCO3 and even when they are able to make

nine copyImage 9: Ocean chemistry graph:  ‘As carbon dioxide builds up in the atmosphere, a large fraction has dissolved into the ocean, increasing the total amount of dissolved inorganic carbon and shifting seawater chemistry toward more acidic conditions. Since the end of the last century, the amount dissolved CO2 gas ([CO2 (aq)], has increased because of both the rise in inorganic carbon levels and acidification. Simultaneously there is a decrease in the water’s pH, indicating rising acidity, and a decrease in the carbonate ion ([CO3 2- ], the substance that many marine animals use to build their shells.’

coccoliths the acidic water tends to dissolve them or they are deformed. Without the coccoliths the coccolithophores will become vulnerable to other phytoplankton predators, which could wipe them out completely, thus destroying one of the planets most prolific CO2 sequesters and possibly further exacerbating the climate situation. A possible positive note is that, during the Cretaceous period, about 145 million years ago, we know that the concentration of CO2 was actually higher than those of today and that there is evidence in core samples that Coccolithophores existed during that time. (19) Unfortunately past performance is not always indicative of future performance and the conditions that allowed the algae to survive in the past might be quite different from the conditions that we face today.

 What is clear from this short essay is that marine algae are part of a much larger web of life. They are the foundation of the marine food chain and if their population collapses from acidification of the oceans, so will others that depend on them. Without the algae to give off DMS we will loose the role that DMS plays in seeding clouds but more importantly a vital method of sulphur dispersal.

The discovery of Coccolithophores. A brief history.

 Since the early 1800’s scientists have been intrigued by Coccolithophores. The quest to collect, classify and analyse them, continues around the planet to this day, not only because they are intriguing organisms but because of their carbon sequestering ability. The first recorded observation of Coccolithophores was in 1836 by a Micro paleontologist named Christian Gottfried Ehrenberg while examining chalk from the island of Rugen in the Baltic Sea. He was later to hand draw, over a period of fourteen years, five thousand of the forms he found in chalk. The drawings were published in 1854 in his book Mikrogeologie. Observations continued and years later the laying of transatlantic telegraph cables required that various soundings were made to determine the condition of the seabed. A process of taking sea floor core samples was developed and the cores were examined. In 1868 while examining a core sample, a biologist named Thomas H Huxley, from which the latter name of Emiliania Huxleyi was later derived, identified coccoliths and coccospheres in the sample. As microscopes evolved so did the understanding of Coccolithophores and by 1900 H. H. Dixon, A. Weber van Bosse and H. Lohmann had documented the various growth stages and understood that the coccoliths were made inside the cell and extruded to the surface where they locked together to form the coccosphere. By 1902 they had identified the flagella and proposed the name ‘nannoplankton’ due to the 1 to 60 angstrom size. In the 1950’s the scanning electron microscope allowed for detailed analysis of the calcareous nanoplankton and highly refined biostratigraphic zonations had been mapped out.  (H1)

REFERENCES

1) Source: U.S. Census Bureau, Population Division http://www.census.gov/main/www/popclock.htmland

2) Lovelock, James, Unpublished Schumacher lecture, 9 Nov 07.

3) University Corporation for Atmospheric Research 1995-1999, The Regents of the University of Michigan

4) Stout, Prentice K., Phytoplankton: Plants of the sea, Rhode Island Sea Grant, http://seagrant.gso.uri.edu/factsheets/phytoplankton.html

5) Young, Jeremy, Palaeontology Dept. The Natural History Museum, London, UK http://www.noc.soton.ac.uk/soes/staff/tt/eh/coccoliths.html)

6) Herring, David, What are Phytoplankton, NASA, Earth Observatory, http://earthobservatory.nasa.gov/Library/Phytoplankton/

7) Pienaar, Richard N., Coccolithophores, Ultrastructure and calcification of coccolithophores, Cambridge University Press, 1994, pg.27

8) Emiliania Huxleyi home page, http://www.soes.soton.ac.uk/staff/tt/,2007)

9) Pienaar, Richard N., Coccolithophores, Ultrastructure and calcification of coccolithophores, Cambridge University Press, 1994, pgs13-17

10) Harding, Stephan, Animate Earth, Green Books, UK, 2006, pg. 107

11) Hunt, Lynn, Send in the Clouds, New Scientist Print Edition, Issue 2136, May 1998, pg 21

12) Norris, Katina Bucher, Dimethylsulfide Emission: Climate Control by Marine Algae, Food and Agriculture Organization of the United Nations, http://www.fao.org

13) Sunda, W. Kieber, D J Kiene, R P Hunts man, 2002, An antioxidant  function for DMSP and DMS in Marine Algae. Nature Issue 418, Pgs, 317-320

14) Harding, Stephan, Animate Earth, Green Books, UK, 2006, pg. 131

15) 14) Hunt, Lynn, Send in the Clouds, New Scientist Print Edition, Issue 2136, May 1998

16) Holligan et al., Coccolithithophores Cambridge University Press, USA, 1994, Biogeography of living coccolithophores in ocean waters, pg 161

17) Young, Jeremy R., Coccolithiophores, Cambridge University Press, USA, 1994 Functions of Coccoliths, Turbulent Mixing, pg. 71

18) IBID, Variable Accelerated sinking, pg 71)

19) Tyrrell, Toby, National Oceanography Centre, Southampton, University of Southampton, emiliania huxleyi. http://www.noc.soton.ac.uk/

IMAGES

Cover)  Emiliania Huxleyi home page: http://www.soes.soton.ac.uk/staff/tt/,2007)

1) Arctic ice loss:

http://www.carbonequity.info/aboutus.html

2) Eutophic zone: Apologies source unknown

3) Ehux: Picture courtesy of Jess Gorick http://www.soes.soton.ac.uk/staff/tt/

4) Images and terminology: Jeremy Young

 Palaeontology Dept. The Natural History Museum,http://www.noc.soton.ac.uk/soes/staff/tt/eh/coccoliths.html

5) The International Nannoplankton Association http://www.nhm.ac.uk/hosted_sites/ina/terminology/2coccosphere.htm

7) The Seven Sisters, chalk cliffs UK.

http://www.geograph.org.uk/photo/2235457)

8) Ocean chemistry graph, Figure courtesy of Scott Doney, Woods Hole Oceanographic Institution

http://www.whoi.edu/oceanus/index.do

HISTORY

H1) Siesser, William G, Coccolthiophores, studies, Cambridge University Press,1994, pgs1-2

 Historical background of coccolithophore 

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