Shells? Who needs shells?

Posted on January 23, 2013 by skepticalsquirrel

Exams all done now, so back to the fun of blogging about awesome animals!

So far, the molluscs we have looked at have had some sort of shell, but not all molluscs have taken the shelled path.

Today, and in the next post, we are going to meet some which prefer to be without shells, and are, in my opinion, some of the most beautiful molluscs around: So, without further ado, let me introduce you to todays topic: the nudibranch (from the Latin nudus meaning naked, and the Greek brankhia meaning gills, so literally, “naked gills”)

Berghia coerulescens, a species of nudibranch. Image from wikipedia

This group of animals has a whole lot of awesomeness going on, some of which we will cover today, and then it will spill over into the next post too!

For today, lets take a look at the one in the video, it is called Glaucus atlanticusm and the reason it is awesome for me, is that, despite being a squishy little sea-slug like thing, around 3cm long, it eats these:

Physalia physalis (Better known as the Portuguese Man O’ War) Image from wikipedia

Now, if there is one thing we know about Portuguese Man O’ War, it is that it has a very nasty sting, due to the trailing tentacles being full of cells which can fire toxic darts into its prey (or into an unsuspecting persons leg) (See link HERE for post about Man O’ War)

So how does Glaucus cope with these stings? There is a hypothesis that it releases mucus while eating the tentacles (Yes, because it is small, and the PMOW is much larger, it nibbles its way up the tentacles), which protects its insides from the stings, which can remain active for a period of time after the Man O’ War is dead.

To make it even cooler, it takes some of these stings, and uses them in its own defense. It goes a little something like this:

Glaucus eats the tentacle with the stinging nematocysts within it. Some of these pass through digestion, and end up in growths on the outside of the animal, called cerata. These then become part of the animals defense systems, meaning it can fire them at any attackers.

It has primitive teeth (denticles) which it uses to chomp through its prey, but also to hang onto them

So, this is a fairly cool animal so far, but, it gets even more amazing when you find out some other details about it.

This lovely little animal floats upside down, so its top side is in the water, and its underside is at the surface. It floats because it has a bubble of air in its stomach, but this means it has no way of steering, so it floats around as the winds or currents take it

In common with many fish which are found near the surface (Sharks for example), it uses a form of camouflage which is known as countershading

Its “top” (Which is in the water) is light silvery grey, so it is difficult to spot from below, whilst its “bottom” is a deeper blue, or blue and white, which helps it blend in with the water when seen from above.

I will leave this last image of Glaucus atlanticus for you, and next post we will look at some of the other animals in this family.

Glaucus Atlanticus. Image from EOL (Encylopedia of Life)

Sunday Documentary

Posted on January 13, 2013 by skepticalsquirrel

Yes, yes, I know it is usually the Friday documentary, but, with everything getting back into a rhythm after New Year, I thought a nice Sunday relaxing one would be ideal.

This is a BBC one from late last year, about the life cycle of stars. I started watching it last night, aiming to fall asleep to it, but had to stay awake to the end!

Astronomy is not usually something I post about, as it is not a subject I know much about, but, this one was fascinating!

Enjoy!

Antho-what-now?

Posted on December 20, 2012 by skepticalsquirrel

So, after an extended break, normal service is resuming, although the post today will be slightly off the usual topic of the evolutionary journey.

As I mentioned yesterday, I have been writing my bachelor project, and I thought I would share with you a little of the topic I have written it on.

I could write a post which would keep my good e-friend Argyle Sock very happy, with lots of statistical stuff in it, but, honestly, if I see the terms “not normally distributed” one more time, my head may go pop!

Also, the actual topic is much cooler than the stats (even though they are very cool too of course!).

I would like to introduce to a group of pigments called anthocyanins. These are the reason for the colour of blueberries, blackberries, some grape species, olives and many other fruits, and purple or red colourings in flowers, like these pansies:

Violet pansies: The purple colour is caused by anthocyanins in the petals. Image from Wikipedia

The amazing bright red colours you see in autumn leaves is also down to anthocyanins.

So..why have I spent this last semester writing about pretty red colours?

Well..here is where it gets a little more interesting (not that pretty purple flowers are not interesting of course!)

Anthocyanins are also found in leaves which are not about to fall off the tree. Some plants have red leaves when they are young, and some plants can turn on and off the red colouring under certain conditions

Sciencey term for the day: This is called phenotypic plasticity….a phenotype is the appearance something has due to certain genes being expressed. If a phenotype is plastic, it means it can change under certain environmental conditions.

So, I have been looking at a particular plant, which is usually green and grows in shallow lakes. These lakes dry out a bit in the summer (Yes, we have summer in Denmark, sometimes!), and so some of these plants may end up out of the water. If this happens, 90% of these plants turn red, until the water covers them again.

The reason I have been looking at this plant (with a bunch of other people who are much better at scary maths than me!) is because it is not entirely clear exactly what the red stuff in the leaves does. In some plants it seems to act a bit like a sunscreen, in others it seems to stop the plant being eaten by insects.

The amazingly awesome Leaf-cutter ants (Several posts on them will come along a bit later in our evolution journey) will not harvest leaves which are red. This may be because insects do not see red the way we do, they do not have the parts in their eyes which can collect red light.

Leaf Cutter Ants carrying leaves off to their underground farm Image from wikipedia

It has also been suggested that anthocyanins can help plants survive during cold or drought conditions, so, there seems to be a whole lot of stuff that this pigment helps with.

The health food industry has even been getting in on it, and you can buy anthocyanin supplements…this is because in plants, they work as anti-oxidants, and we are always hearing about how having free radicals is bad for us, and so we should eat blueberries, or whatever the cool food to eat this week is (its usually the most expensive one!). I am not entirely sold on this idea, as, last time I checked, I am not a plant.

So anyway, I have been working with an awesome group of my fellow students, and we have been trying to make these poor plants very stressed to see what happens. We grew them under some very bright lights, and then did some tests where we zapped them with..well…an even brighter light, to see what they did.

Personally, I find the plant we have been studying more interesting than the actual pigment we have been looking at, although, that has been fascinating to learn about. The plant itself has no stomata, which are the holes which plants use for taking in carbon dioxide and giving out oxygen and look like this in extreme close-up:

Stomata on a tomato leaf Image from wikipedia

Because this plant has no stomata, it has to breathe through its roots, which is extremely cool! This means that it can only live in lakes which do not have a lot of nutrients in them, because, if you increase the amount of nutrients which end up at the bottom of a lake, you decrease the amount of carbon dioxide which is produced by the bacteria eating all the dead stuff at the bottom.

As more dead stuff ends up at the bottom of the lake, the bacteria down there start using up more oxygen than is available, and so the only ones that can live there produce methane (CH4) instead of carbon dioxide (CO2). This is what is found in my favourite land-types, the wetlands, bogs and moors.

Oh, yes, I forgot to show you a picture of the plant! This is the little thing I have spent 6 weeks growing, and then several weeks cutting up and zapping with bright lights!

Lobelia Dortmanna. Image from wikimedia

So, I hope I did not bore you too much with the slightly off-topic post, and next time we will pick up on the evolutionary trail again, with some weird and wonderful creatures. If you prefer plants, hang in there, we will get to them in a few million years or so!

Collated information on Ash dieback

Posted on October 27, 2012 by skepticalsquirrel

I have been asked by a few people what they can do about the Ash dieback problem in the UK, and whilst I said yesterday that there was no official guidance for the general public yet, there are some informative documents prepared by the forestry commission.

Most of these are in the original post I made (HERE), but as they are at the end of a long post, I will put them up on here again, with the new information.

The Forestry Commission has published a visual guide to symptoms: Ash Dieback Disease

The Forestry Commission has also updated its guidance, with information that this is now a quarantine pest, and gives contact details if you think you have come across a site of infection. It also outlines how it is thought that the ancient woodlands have become infected. HERE

I used this Forestry Commission PDF in my original post, it is fairly easy to read and gives an overview: Chalara Fraxinea

The Woodland Trust has updated their guidance since I last read it, with the advice that any suspected infections should be reported at once: HERE

The Government has said that 50,000 trees have already been destroyed: (BBC source HERE)

EDIT for update: There is a website which will be launching Monday at ASHTAG and there will be a smartphone app launching Monday too. I will post details of that when it arrives.

I mentioned on my fellow blogger Argylesocks post (HERE) that my concern is that with the onset of autumn, we will not know until next year what the extent of the infection is, as the fungus is now in the leaf litter over the winter.

I hope that these are isolated cases in woodlands, but I do not understand why it took from February til late September for this to get attention, or be publicised.

For my non-UK readers, I apologise for the UK-centric posting the last few days. I am currently writing a post relating to a US issue, so will put that up over the soon. I will be returning to my evolution based posting next week, but will keep putting up posts of interest to current environmental issues, to go a little more in depth into those. If you have a story from anywhere relating to environmental or ecological issues which you would like to read a bit more in depth on, you can chuck me an email at squirrellyskeptic at gmail dot com.

Why mature forests matter..more trouble for the Ash tree.

Posted on October 26, 2012 by skepticalsquirrel

I wrote a few weeks back about the fungus which is infecting Ash trees in Europe (HERE)

At the time I wrote that “So far, it seems that the fungus has not managed to infect “wild” trees in the UK, and the government has begun a consultation, which will end on the 26th of October, which could lead to a ban on imports of Ash (and given the severity of the threat, I would hope that a ban is imposed).”

Well, this week it has been announced that the disease has been discovered in mature forests in the UK, as this Guardian article discusses (HERE).

My last post about this was a bit technical and clunky, so I will try to keep this easier to read. I want to try to explain as much of the specifics as I can though, because, when I am finding anything out, I like knowing all the details if possible, rather than just understanding the gist of something.

We are going to take a little detour, as I could just tell you that “Mature forests are important” and let you just take that as read, but I would rather run through the reasons behind my claim.

So, firstly, what is a mature forest?

To most of us, a forest is a forest is a forest, but to biologists, and specifically botanists, there is a difference in the type of forest, and it has to do with a term called succession.

Succession can be thought of as the stages of life of an area, whether that is to do with a wetland, a forest, a field etc.

My ecology textbooks define succession as “Replacement of one community by another, often progressing to a stable terminal community called the climax”

To illustrate this I will use the example of how a natural forest progresses, as it is one of the simpler ones to picture, but this also applies to planted forests, although the starting point is different there, as we actually initiate tree growth.

Diagram showing forest succession. Image from the encyclopedia of New Zealand

So, we start out with our bare ground on the left of the diagram, which usually consists of some soil, maybe some grass species (those little guys get everywhere). This bare ground may be the result of a big event like a glacier retreating, or it could be from the drying up of a lake, or the spread of grasses along a sand dune area. It can also be derelict land which was previously used as an urban area, things are a little more complex in that case, but the basic order still follows.

If we imagine that we have some rocks on the bare ground, and a few tough grasses to start with. The rocks provide a nice cosy place for some lichen to start living, whilst the grass roots prevent what little soil or sand there is from blowing away.

The lichen cause damage to the rocks, and small particles of rocks fall off and get trapped on the ground by the grasses, and other particles flying around in the wind also become trapped. As the lichens and grasses die, or get damaged, they fall to the ground, and begin to form a layer. Eventually, there is enough of this layer (known as humus) to allow mosses to take hold in the area, and as these die off, they too add to the growing layer of dead stuff on the surface, which allows for bacteria to come in and decompose them, adding nutrients to the new soil.

Over time, the nutrients and soil layer builds up, and small, tough plants can begin to grow there. These are often other grasses, ferns and very small bushes (Box 2 in the diagram). Microbes, insects, worms etc begin to colonize the young soil.

As the soil quality improves (because the plants there die, and are broken down, and nutrients build up in the soil), and the stability of the soil increases due to the growing number of plants, seeds which are blown in the wind, deposited by animals etc begin to be able to grow, and some of these will be from trees.

Initially, only small, hardy trees can grow, but new species come in and as the conditions continue to improve for plants, taller trees begin to take hold. These do not grow in the earlier stages as tall trees usually require higher levels of nutrients than bushes, or dwarf trees.

Now we have a young forest, and species of animals and birds begin to colonize the area. Trees begin to grow taller, and form a canopy, this leads to a change in the communities of plants which are on the forest floor, and the ones which die off further improve the soil quality.

Finally, we reach the mature forest stage, where the animal and plant communities are stable, and as a tree dies, a sapling takes its place. In some ecosystems, trees can stay short, like a new tree, for years until a gap opens up in the canopy, then they all race to be the one to take the place in the sun at the top. Whilst individual trees may change, the overall structure of the forest stays the same at this point, which provides stability for the animal, bird and insect populations, and leads to the forests which we love to walk in.

Whilst the exact age at which a forest is defined as mature varies (depending on the types of trees which are present), a mature forest is several decades old. If these forests are able to continue developing, they eventually are classified as Ancient Woodlands, which in the UK means forests which have been there for 400 years or so (the current definition of an ancient forest in the UK is forests which have existed since 1600).

EDIT FOR UPDATE: I have found out that one of the woodlands affected is actually an Ancient Woodland, which is believed to have been in place for around 1000 years. Info about Ashwellthorpe HERE

Ok, so now you know why I feel that mature forests are important. They provide a stable habitat for wildlife and other plants, and due to the length of time which it takes for them to develop, they are not something which is easily replaced. They also play a role in preventing soil loss from rain or wind erosion.

Now, you are probably wondering why Ash trees are so important, and why the media have been giving this so much attention.

Ash is the fourth commonest tree in the UK, and many forest areas have it as the dominant species. (source: Woodland Trust). Birds such as woodpeckers and owls live in Ash trees, as they are easy for them to hollow out, and they provide food and a habitat for a diverse range of animals, insects, mosses and lichens (For more info, see the Royal Forestry Society link HERE)

Ash woodlands are part of the UK Biodiversity Action Plan, and are listed as a priority habitat in the plan. (See page 60 in this PDF), and they say:

“Mixed ashwoods are amongst the richest habitats forwildlife in the uplands, notable for bright displays of flowers such as bluebell.. primrose..wood cranesbill and wild garlic . Many rare woodland flowers occur mainly in upland ashwoods, such as dark red helleborine.., Jacob’s ladder.., autumn crocus.., and whorled solomon’s seal … Some rare native trees are found in these woods, notably largeleaved lime… and various whitebeams…. Upland mixed ashwoods also harbour arich invertebrate fauna, which may include uncommonor declining species. The dense and varied shrub layer found in many examples can in the southern part of the types range provide suitable habitat conditions fordormice… The alkaline bark of old ash (and elm where it still survives) supports an important lichen flora…. ” (Latin names have been removed, hence the dots)

Aside from the ecological importance, it has a long history in the UK and Northern Europe, it is suggested as the “world tree” from Norse Mythology (Yggdrasil) and Ash has been used in the UK since early history, as everything from spears to walking sticks, furniture etc.

So, seeing as these woodlands are on the Priority habitat list, you are probably thinking that the government has taken immediate action on this, and had in fact begun to assess this threat as soon as they heard of it. Well….not quite. George Monbiot over at the Guardian has pointed out that the government were made aware of the threat to the Ash tree in the UK some time ago, before the imported infected trees were discovered, and that even importers of Ash trees were recommending that action be taken (link HERE)

So, what is the government in the UK doing? They have announced that a ban is being implemented starting Monday (link HERE). Bear in mind this fungus was first found in the UK 8 months ago (February)…. Would it have taken so long for action to be taken if we were talking about infected livestock?

I apologise for the very long post, but I feel it is important that I explain exactly why we need to make sure that we do not lose our Ash trees the way we lost our Elms, and I am very angry at the government response.

Bivalves…Sucking and Sieving

Posted on October 23, 2012 by skepticalsquirrel

Today we pick back up with our journey through evolution and natural history.

Last time we met the Spider Conch and today, we meet some of its relatives, the bivalves. As the name suggests, these animals have two shells, and the ones you probably know best are oysters and clams. Today I will write about the various feeding methods of these animals, and then the next post will be on movement and vision.

There are bivalves which resemble a 2-shelled animal we met earlier, the brachiopod (HERE), and so can be easily confused.

The first bivalve I would like you to meet today is Pedum spondyloideum, or the blue-lipped coral oyster. I am mostly showing you this one because I think it is spectacularly beautiful

Blue lipped coral oyster. Image from wikipedia

This is a teeny tiny scallop (or Pectinidae to give it the proper family name), which lives between corals. These are in the same order as oysters (Ostreoida), so are related to them, but are in a different family to what me and you know as oysters.

There is an important differences between these, and the other molluscs we have met so far;

General anatomy of a bivalve. Image from Merriam-Webster

I mentioned before (HERE) that molluscs have a rather cool tongue called a radula, which is essentially lots of rows of tiny teeth that they use for scraping food off of surfaces.

If you look at the diagram above, there is no label saying “radula”. This is because bivalves do not have one! (They also do not have a head!) The image below shows the internal structure of a clam, and will help me explain what they do instead of scraping food:

Internal anatomy of a clam, image from Encyclopedia Britannica

In the image above, you can see something labelled the “incurrent siphon” and the “excurrent siphon”. As these animals breathe (by extracting oxygen from the water), they cause small currents around their gills. These currents contain not just water, but yummy particles of food, which get moved towards the gills. There are cilia (those small hair-like wavey things we have bumped into a lot) on the gills, which move these currents towards tiny pores.

If you take a peek at the top diagram, there is something labelled as the “labial palps”. These, and the gills produce mucus (like you do when you have a cold), and this covers the food particles and they fall down towards the mouth where they are eaten. So yes, they do eat food covered in snot! Large particles like sand fall down into the mantle, and are carried out by cilia again (those little hairs just get everywhere don’t they?). Sometimes these particles get stuck in the mantle, and become irritating, at which point they become pearls (although not the sort we use for decoration, they are formed differently).

This method of feeding is known as filter feeding, and is how most bivalves eat. There are some species however, who obtain their food using a method known as deposit feeding.

This is thought to be the original form of feeding for bivalves. Instead of the gills assisting in filtering food, they are used purely for breathing, whilst the labial palp has tubes attached to it which stick out to grab food from the sand or mud. Food which is caught in currents moving towards the gills is also grabbed and eaten.

Still other species use symbiosis with small organisms (a lot like the corals do) whereby these organisms carry out photosynthesis and the bivalve gets most of its nutrition that way, while doing a small amount of filter feeding. The most well known example of this is the giant clam, which is a huge animal, up to 1.2m or so long.

Giant clam, image from wikipedia

These animals are so huge that they are not able to move, so they sit on the sea floor, often in places like the Great Barrier Reef:

Giant clam on the Great Barrier Reef. Image from National Geographic

The bacteria, and dinoflagellates which I wrote about HERE obtain food by photosynthesis, like plants do, and then the Giant Clam feeds on the by-products produced, as shown in this video:

One final point about bivalve feeding. Because they filter feed, they also perform a role in cleaning water, which benefits other organisms in their ecosystem, and mussels can be used as an indicator of how polluted a body of water is. This is because as they feed, heavy metals and other pollutants are filtered, and build up within their bodies as they are unable to process them (like us with mercury etc). So, if you measure the levels of these pollutants in mussels and other bivalves, it gives you an idea of how polluted the area is.

This video shows oysters and how they can function as filterers of water:

As mentioned in the video, populations of bivalves are decreasing in some areas, and this means they are less able to filter the water, which in turn has an impact on the other animals and plants in the ecosystem.

Friday Documentary

Posted on October 12, 2012 by skepticalsquirrel

This weeks documentary is following up on a post I made earlier, where I showed some Bathymetry images HERE

This one is from Discovery Channel, and is called “Drain the Ocean”, and shows some very nice images of what the seafloor looks like, and some of the amazing creatures down there. It also helps illustrate why I think we should investigate the ocean before we go into space.

Stalks, eyes and feet

Posted on October 10, 2012 by skepticalsquirrel

Last time I wrote about life on Earth, we covered Cowries, and how they were used as currency. We are staying within the molluscs still, as there are a couple more organisms I want to show you, to illustrate the different solutions that have been found to the same problems, namely feeding, and getting around.

Today, we are going to meet the cutely named Lambis lambis, or one of the Spider Conch molluscs, we may also meet some of its relatives.

Everyone knows what a conch shell looks like, it is the famous “Listen to the ocean in this” shell, and the ones you may have seen probably look like this:

A shell of Lobatas gigas, the Queen Conch. Image from wikipedia

This is the shell of Lambis lambis:

Lambis lambis shell. Image from gastropods.com

I have already covered how shells are formed, by secretions from the mantle, the fleshy part of the mollusc, so that is not what I am writing about today, although I am sure I will write a post about how the different shell shapes arise at some point!

The shell above has spikes all around it, and one long spike at the bottom. The long spike at the bottom is where we will start today, because it is actually functional, it is called the Anterior siphon canal, and it provides support for an appendage called a siphon, which is an extension of the mantle. This structure draws water into the cavity within the animal, and passes water over the gills, assisting in getting oxygen from the water, but also acting as a “nose” (Otherwise known as a chemoreceptor) to help the animal find food.

Lambis lambis is a herbivore, but this does not mean it is not guided towards food by what we would know as smells.

Here is what the external (outside the mantle cavity) body parts of Lambis lambis looks like:

Morphology of Lambis lambis. Image from University of Queensland

There are several features of this mollusc (and all conchs), which I want to elaborate a bit on, as I think they are fairly cool.

Firstly, the radula (the toothy tongue thing we met HERE), which is usually contained within the cavity, is actually on the end of the part labelled “proboscis”, so it has a stalk with its mouth on the end, and the radula too.

Here is a video of one chomping away happily on some algae, note the eyes which are also out on stalks, these are checking out the area for predators while it is eating, and if one is spotted, it pulls itself back inside its shell. I personally like the eye stalks, as they look a little bit like cartoon alien eyes.

All true conchs are herbivores, (that is, ones which are members of the Strombidae family). Other animals are known as conchs too, and not all these are herbivores, for example the crown conch (Melongena corona) feeds on oysters and clams by using its proboscis to pry open a bit of their shell and eat them from inside their shell.

The other very obvious structure in the morphology picture is the foot, and the part labelled “operculum”. This is used to dig into the sediment to..well..propel the animal, or turn it over if it gets upside down. I think this is easier to see than to explain, so here are two videos showing this in action:

Finally, here is a video showing this funky creature moving along a flat surface:

It is not just us humans who like these shells…hermit crabs also use them as mobile homes, as these two videos show:

I hope I have shown you some things so next time you see one of these pretty shells, you also think about the very cool animal which lives inside it.

Shells and cash

Posted on October 5, 2012 by skepticalsquirrel

The last post about Life on Earth was about Cowries, and I said that this time I would write about some of the ways they have been part of human society for a very long time.

Cowries as we saw, have very shiny, smooth shells, and this has led to them being used a currency throughout both ancient history, and modern times:

This is a species called Monetaria moneta, which looks like this:

Monetaria moneta (also called Cyprea moneta). Image from Gastropods.com

As you may have noticed, the name of this animal sounds a lot like the word “money”, and in fact, this particular Cowry, and one or two other species, have been used historically as currency.

In China, they were used as currency from at least 1200 BC, and the Chinese Han character for money is the same character as for sea shell.

Cowrie shells from ca 900 BC, image from University of Maine

They were also used in Bengal in India as currency, and widely used throughout the Asia-Pacific region.

They were extensively used in the Maldives

Many African nations also used shells as currency, and during the slave trade era, Europeans would use cowrie shells in exchange for slaves, and there was a trade in cowrie shells between Asia and Europe for use in Africa. Excavations of sites in the USA have uncovered cowrie shells in both the slave houses, and the houses of people who were involved in the slave trade (See further reading).

The use of shells as currency within Africa continued until the early 20th century, and in Ghana, some of their coins display cowrie shells as the image on one side.

20 Cedis coin from Ghana, image from the British Museum

Mondays post will be staying within Molluscs, but moving on to another amazing animal!

Corals and Starfish

Posted on October 2, 2012 by skepticalsquirrel

I thought I would write this post today as it is about some organisms we have already covered (quite extensively, as I got a bit carried away!): in these posts: Here, Here and Here as well as Here.

Browsing the news sites while munching breakfast this morning, I came across this story in the Guardian about the Great Barrier Reef and also this one about Caribbean reefs (Full report link in further reading), and I thought it would be a good idea to write the post I forgot to before, about the threats facing coral reefs today.

The articles mention 3 things which are affecting reefs,storms, predation and bleaching.

Storms are perhaps the most obvious cause of damage, the waves during a storm hit the coral reefs (which are in shallow waters, and so take the full force of the waves as they near land), and this breaks the coral. This video shows the aftermath of a hurricane on a Mexican reef:

Bleaching occurs when the organisms which live inside the corals are expelled by the corals, leaving the reef looking white:

Bleached coral, image from NOAA Coral Reef Watch

This bleaching has a number of causes, changes in the level of incoming solar radiation can affect particularly sensitive photosynthetic organisms, as too high light levels can be damaging to the cells which they use for photosynthesis,prolonged exposure at low tides and bacterial infections can also impact the organisms.

A number of the causes can be linked to human activity, some of which you will have heard of, and others which are less familiar, so I will briefly cover the main ones here:

Ocean acidification is the result of increasing carbon dioxide levels in the ocean, as shown by this equation:

CO₂ _(aq) + H₂O $\leftrightarrow$ H₂CO₃ $\leftrightarrow$ HCO₃^– + H⁺ $\leftrightarrow$ CO₃^2- + 2 H⁺

What this says is that carbon dioxide and water react to form a product known called carbonic acid (which you may know from sparkling water drinks). This compound forms ions (a molecule or atom which has a charge) of bicarbonate (HCO_3^–) which you may know from bicarbonate of soda used in cooking,and hydrogen ( H⁺). These then react further to form carbonate (CO₃^2-) and two hydrogen (2 H⁺). The + or – indicates whether there is a positive or negative charge, so carbonate has a negative charge of 2.

Now, the reason this makes the ocean more acid is that, as you know, the scale used for measuring acidity is the pH scale. This scale is basically about how many hydrogen ions there are in a solution (in this case, sea water). More hydrogen ions in a solution mean that the solution is more acidic.

This is balanced usually by calcification, which is the reaction of calcium with carbonate to form calcium carbonate (chalk or limestone are the best known forms of this), which is used in the shells of many organisms, and is used in coral reef building. The problem comes when more CO2 is entering the oceans than can be taken out by natural processes, which leads to the oceans increasing in acidity. One of the problems with this is that, as you probably know, acid and chalk or limestone do not go so well together, and increasing acidity affects the organisms with shells, or corals. This puts them under stress, and they can expel the microorganisms which live inside the coral tubes.

Increasing temperatures in the oceans also places corals under stress. We all have a temperature range which we can survive within, and some organisms have smaller ranges than others, especially those which live in zones with fairly constant temperatures.

Apart from concern about coral reefs and other marine organisms, one of the problems with a warming ocean is that warmer liquids can hold less gas (Like when a beer goes flat as it gets warm, this is because the carbon dioxide in the beer is released as it warms up). The image below shows the solubility of carbon dioxide in water as temperature increases. One of the implications of a warming ocean is that it will be less able to store carbon dioxide, and so will release more to the atmosphere.

Solubility of CO2 in water. Image from Wikipedia

At present, there is both increasing acidity in the oceans, and increasing temperatures, because the temperature increase is not enough to reduce the carbon dioxide entering the ocean, because it is not saturated, which means it is still able to take dissolve gases.

This movement of carbon dioxide into the oceans is a very important part of the carbon cycle. The diagram below illustrates this cycle, and as you can see, the largest store of carbon is within the oceans. The numbers represent gigatons of carbon (A gigaton is 1 followed by 9 zeros tons, or 1000000000 tons)

Carbon Cycle, the bold black text is the amount of carbon stored in each place, and the purple text is the flux, or amount moving between each area. Image from Nasa.

Finally, and apologies for boring you with the chemistry above, the most abstract of the relationships for today: Crown of Thorns starfish.

Very brightly coloured Crown of Thorns starfish. Image from Wikipedia

More usual colouring for a Crown of Thorns: Image from Wikipedia

This is definitely a very pretty starfish, but it is bad news for our friends the corals.

It preys on corals, and does so by climbing on top of the coral and turning its stomach inside out (extruding) to dissolve the corals tissue with digestive acids. Whilst predation in itself is not a problem, and is part of a normal ecosystem, there are occasionally explosions in the population of these starfish, and there is a discussion about the causes of this. At present, the likely cause appears to be an increase in nutrients in the ocean.

This can be a bit abstract, so I will try to explain it. I wrote in THIS POST about how the high levels of phytoplankton in the Antarctic are due to the nutrients from the continents being carried to Antarctica by ocean currents. This ties in to today’s post because there has been observed to be a link to periods of increased rainfall or floods, and an increase in the population of this starfish a few years later. (Link to article in Further Reading)

The mechanism appears to be as follows: During periods of heavy rainfall on land, a lot of nutrients are washed off with the rainwater (runoff). These nutrients primarily come from fertilizers used for agricultural purposes.

These are carried downstream to the oceans, where they accumulate, and are carried on currents. These added nutrients allow for an increase in the population of phytoplankton, and these are food for starfish larvae. This increase in food allows for more of the larvae to survive to mature into starfish, which then feed on the reef.

This video shows a survey being done of the Crown of Thorns population on the Great Barrier Reef

Finally, overfishing, both for food, and for aquarium fish can affect the balance of the ecosystem, as this video briefly discusses.

What can we do about this?

Well, reduction in the amount of fertilizers used in agriculture would reduce the run-off, but this has an impact on agricultural yield for the communities in the regions affected by the monsoon flooding. In Australia and other places, population control measures for the starfish have been implemented with varying levels of success.

The one thing we can do something about is the overfishing of reefs and other areas, by buying sustainable fish, and not having exotic fish in home aquariums.

The good news is that reefs do recover from bleaching effects, given enough time, and provided that the surrounding ecosystem is not too damaged, and that the effect is a “pulse”, that is, a one off event which causes for example a sudden surge in ocean temperature (like El Nino). Sustained increases in temperature, predation or acidity may be harder to recover from.

Skeptical Squirrel

Science and nature for all

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