Sea hares (Aplysia punctata) are a common find on dives around the south, west and northern British Isle. They are usually around 7cm long but can grow up to 20cm in length. The colour of Sea hares varies from olive, brown, red and purplish black depending on the algal diet. At the head end, two slender rhinophores stand up like the ears of a hare, hence their common name.
At first sight, Sea hares would appear to be an easy target as a meal, there’s no shell, no spines like an urchin, no claws and they move at a fairly slow pace. Sea hares have a mucous coating containing acid and other nasty compounds which might deter some predators, but their party piece is to release a cloud of sticky, purple ink when attacked by hungry predators.
The cloud of purple ink is in fact a mixture of two secretions. On the back of the Sea hare the central structure is called the mantle with an opening called the foramen. Just under the surface there’s the last remnants of what was probably a shell in the Sea hare’s evolutionary history, a protein disc which acts as an internal shell. On the roof of the mantle is the Purple Gland above the gills. The Purple Gland is responsible for storing and secreting the ink. The building blocks for noxious chemicals are obtained from their algal food, particularly from red algae, metabolised and stored here. This strategy is quite common in marine gastropods and a number of these substances are being actively tested for pain killing, antibacterial, antiviral and anticancer activity. It’s powerful stuff.
Beneath the gill on the floor of the mantle cavity is the Opaline Gland. This gland secretes a white liquid that becomes viscous upon contact with water. If you’ve ever seen the videos of Hagfish (Myxini sp.) producing copious volumes of slime as a way of evading predators, then you will already have seen opaline in action.
The ink and the opaline are secreted into the cavity in the mantle where they mix and are expelled towards the predator. The ink has an intriguing role in that it has been shown to be a phagomimetic decoy (phago = eat, mimetic = to mimic). Some species of lobster will drop the sea hare and try to manipulate and eat the ink cloud, thinking that it is food. Whilst testing this idea scientists found another ink effect. The lobsters tried to rub the ink off their antennules. The opaline in the ink blocks the receptors and response to food odours, thereby preventing the predator from recognising that Sea hares are food. It’s the lobster equivalent of a stuffy nose. Whilst the lobster is busy removing the sticky ink, the Sea hare can make its escape. So, in this aspect the ink is rather more than just a cloud to hide the escape of the Sea hare, it is an active cloud which has the effect of blinding the predator.
It can take quite a bit of stimulation to persuade a Sea hare to produce ink. The threshold depends on factors such as the environment (living in a turbulent environment makes inking less likely), how full the gland is and what the stimulus is (inking occurs more rapidly near anemone tentacles that it does in response to an electric shock). If a Sea hare has full ink glands then it will release nearly half of its ink at the first stimulation. Each subsequent stimulation will release 30-50% of the contents. It will take at least 2 days to replenish the gland.
Whilst aquarium owners like the grazing tendencies of Sea hares, they panic about the effect that any inking has on the fish and other residents inside their tank. The jury is out on how much effect the Sea hare ink can have. Sea anemones retract their tentacles, but the evidence for the toxic effect of the ink inside an aquarium is limited, perhaps because the Sea hares aren’t feeding on red algae that are the source of the most potent toxins.
It’s a popular misconception that lobsters are red in colour. That’s because most people have never seen a live lobster, and what gets served up in their lobster thermidor is distinctly red in colour. It’s one of my pet hates when media shows lobsters as red, right up their with the reporter talking about the oxygen tanks worn by the scuba divers. Grrr! As divers we are well positioned to know that lobsters are a dark shade of blue-green, but it’s not just the shell that’s blue, so is the lobster’s blood.
Technically the lobster doesn’t have blood in the way that we would understand it. They have haemolymph, a fluid equivalent to blood that circulates inside arthrpods. Haemolymph is mostly watery with some salts and nutrients dissolved in. There are some cells known as haemocytes, but in arthropods these play a role in the immune system of the organism. There aren’t any red blood cells containing haemoglobin to carry oxygen like we have. Instead invertebrates have some special proteins in their haemolymph called haemocyanins that transport oxygen for them.
Haemocyanins are metalloproteins that have two copper atoms which can reversibly bind to a single oxygen molecule. Oxygenation causes a colour change from the colourless deoxygenated form to the blue oxygenated form. Haemocyanins are only found in molluscs and arthropods but aren’t limited to marine animals and can be found in tarantulas, scorpions and centipedes too. Haemocyanins turn out to be rather more efficient than haemoglobin at binding to oxygen in cold environments and when the oxygen pressure is low. Sounds ideal for the average marine crustacean.
Lobster haemolymph has been shown to have antiviral properties, but only in the uncooked state. In research it was shown to be effective against the viruses that cause shingles and warts. In fact, there is an American based company that has developed a blood-based cream for treating cold sores and skin lesions, although it’s yet to get approval from the regulatory authorities.
So, we’ve established that copper coloured proteins give lobsters their blue blood, but that’s not the explanation for the shell changing colour when the lobster is cooked. For this we have to look at another protein called crustacyanin, and its best buddy astaxanthin. Astaxanthin is a carotenoid pigment so it absorbs blue light and gives off red/orange colour. Astaxanthins are mostly synthesised by microalgae and enters the marine food chain. In shellfish the astaxanthin becomes concentrated in the shell. Its likely that astaxanthins have a string antioxidant and anti-inflammatory effect and may protect against age-related degeneration. Astaxanthins are also found in some sponges, starfish and in species of octopush and cuttlefish. They give the muscle tissue of the salmon its characteristic colour.
Crustacyanin is a very interesting chromoprotein, that changes colour depending on whether it is in water or dehydrated. When it’s bound to the lipid like astaxanthin it has a distinctly blue colour. While a lobster is alive, crustacyanin stays bound tightly to astaxanthin, so tightly that the astanxanthin’s light-absorption properties are quashed and the complex appears to be blue-green in colour. That all stops when the lobster hits the boiling water.
Crustacyanin is not heat stable, so the boiling temperatures cause it to unravel and lose its grip on astaxanthin. The true colours of the astaxanthin then shine through in the red lobster shell. In fact, they were there all the time, you just couldn’t see them. It’s the same mechanisms for cooking shrimp too. Flamingos rather cleverly digest the crustacyanin protein to release the astaxanthins that colour their feathers soft pink.
In 1973, four hostages were seized in a bank robbery in Stockholm, Sweden. A convict on parole attempted to rob the bank but as the siege situation developed he negotiated the release of his friend from prison to help him. The hostages were held for 6 days in the vault. When the siege was finally over none of them would testify against their captors and they even started raising money for the defence’s legal team. Baffled by the responses of the hostages, further assessment was sought.
A Swedish psychiatrist examined the hostages and described ‘Stockholm Syndrome’. In cases where Stockholm syndrome is present, victims start out as powerless, but go on to develop positive feelings towards their captors. Sympathy for the cause and goals an often follow hostages back into their real life. This can cause cognitive and social problems, and a feeling of dependence on the captor.
Stockholm syndrome probably arises as a coping mechanism. The victim wants to survive, and that is a stronger instinct than hating the person who has created the hostage situation. A positive emotional bond will help survival, but there’s a danger of being spotted as a fraud. So the victim ends up believing that they really do like their captor.
You’re by now, probably wondering why I’m writing about this topic…and whether you’ve accidentally picked up a copy of Psychiatrist Monthly. But actually, Stockholm syndrome is an extreme example of how an imbalance of power in any relationship can have a massive influence on how the parties behave. For this reason, educational establishments (from schools to universities) have very strict guidelines about appropriate relationships between teaching staff and students. Teaching staff (or instructors) occupy a position of power over the student. Instructors grade work, give personal feedback, ensure standards for the course are met. And students will hold the instructors in high esteem because of their position and experience. Most educational establishments would require a member of teaching staff to remove themselves from teaching any student who they were having a relationship with. In this case the student may be so overwhelmed by the instructor’s attention that they may feel unable to say no, concerned about the impact on their progress. And the student will normalise this behaviour in their future life.
When would-be instructors first attend a BSAC Instructor Foundation Course, we run a session on what the ideal instructor would look like. Usual (and valid) responses include knowledgeable, patient, approachable, organised and skilful. Rarely does anyone mention ethical. In PADI’s instructor manuals, there’s a small section on ethics, although it seems to deal more with the ethics of business than the relationship between an instructor and a student. And yet, instructors are in a position of extreme power. On smaller courses, especially technical ones, there may only be one instructor for 2 students. That instructor will play a variety of roles during the course, mentoring and assessing the student.
Diving at all levels in built on trust. Instructors that build a positive relationship with a student will achieve more as they work to develop the student’s skills. But whilst this relationship can be hugely beneficial, they are in a situation where a massive imbalance of power in possible. The risks for student infatuation with the instructor are real. Ask any experienced instructor and they will be able to tell you of the students who came a little too close. In the stress of the course with the worry of whether you’ll pass, those evolutionary survival mechanisms kick in. The need to survive outweighs the desire to fight back against the demands of the course (and the instructor delivering it). Scuba instructors get idolised, and that’s not always a healthy situation. Stockholm syndrome may be at the extreme end of the scale, but the potential imbalance of power exists. Treat carefully my fellow instructors.
No ship yard ever built a ship with the intention that it should end up on the seabed. By design ships are intended to keep the water on the outside (or in controlled areas like ballast tanks). From the earliest hollowed logs and coracles to the ocean going supertankers, the aim is to find materials that create a good airspace and allow the vessel, cargo and crew to stay on the surface. As construction methods have evolved, so have the materials that are used. For any vessel owner, the necessary maintenance to keep the water out is an ongoing and relentless battle.
Once a ship sinks, the process of decay inevitably starts. There are a number of parameters that affect how quickly a wreck will break up. A shallow wreck is exposed to the mechanical shearing forces of wave action and the remarkably destructive scouring of sand. Many wrecks become wrecks because the end up punctured on shorelines. In the battle between the rock and the metal hull, rocks often come out the winner. However, deeper wrecks evade the action of the weather and therefore will remain intact for longer.
Any biological material on a wreck which will decay very quickly. Body flesh is quickly scavenged by crustacea and fish. The hard matrix of the bones that are left behind is mostly hydroxyapatite (a mixture of calcium and phosphate) which is soluble in the sea and becomes more soluble at depth. This is why the deep ocean isn’t several metres deep in fish and whale bones, they dissolve.
The next most fragile structure on any ship wreck is the wooden components. Modern ships with chipboard partitions fare particularly badly once submerged, and can fall apart within a very short space of years. Wood is made up of cellulose and lignin molecules. Cellulose is the main part of the cell wall from the tree that the wood came from. Cellulose isn’t water soluble but the chains of cellulose are held together by hydrogen bonds which water helps to promote. Surrounding the cellulose chains are lignins. These are complex polymers that give wood rigidity and resist rotting. The levels and type of lignin vary between different species of tree. Teak, the beloved material for decks of many vessels, has a high lignin content, which helps it to resist degradation.
For the metal components of a wreck to decay there are several factors that will affect the rate of decay. Salt minerals dissolved in the ocean, particularly sodium chloride (the same stuff you sprinkle on your chips) is a major player. In salt water metals will corrode about 5 times faster than in fresh water. Salts break into charged ions which allow the conduction of electricity and metal ions from the ship will enter the water, gradually thinning the metal plates of the hull. Salinity levels can vary massively depending on the location. A nearby source of freshwater can reduce decay. Salinity is maximum at the surface and decreases down to 500 metres, although it rises again around 2500 metres down.
Oxygen levels in the water will also affect the rate of decay. Oxygen reacts with metals to produce metal oxides eg iron reacts to produce iron oxide ie rust. Metal oxides are weaker than the metal they derive from. So gradually the layer of metal turns to rust, which will thin the metal hull even further. Oxygen levels are at a maximum near the surface and decrease down to about 1000m, and then they increase with depth.
Finally, let’s consider temperature. A higher water temperature means all the water molecule are moving faster and at a molecular level, all these reactions occur more quickly. Deeper wrecks in colder waters have a slower decay pathway.
So for a shipwreck to survive, we require a well-constructed, high quality metal in thick sheets, sunk in fairly cold water, deep enough to avoid wave action and sand scouring, so somewhere sheltered would be ideal……welcome to the wrecks of Scapa Flow!
Stefano Lorenzini was an Italian physician born in Florence in 1652. One of his teachers at the medical school in Pisa was Francesco Redi who as well as being a physician spent time experimenting to prove that spontaneous generation (life just appears) was a myth, mostly with maggots and flies. As part of his work Redi, like all scientists of a time without cameras, made incredibly detailed anatomical drawings. Redi inspired Lorenzini, who in 1678 published the work that he is best remembered for, an in-depth study on the anatomy and physiology of sharks. This work contained the discovery of the Ampullae of Lorenzini, the special electromagnetic sense organs found in sharks and rays. But although Lorenzini described and drew the Ampullae, it would take nearly 300 years before modern science could explain how sharks had an additional sensory organ not seen in most other animals.
The Ampullae of Lorenzini form a network of jelly filled canals that open in small pores through the surface of the skin which can be seen as dark spots on the skin. At the back end of the canal is a collection of receptor cells that have a unique structure and allow the shark to sense electric and magnetic fields. The gel in the canals is keratan sulfate which has one of the highest known conductivity of any known biological material (about 1.8 milliSiemens/cm). The ampullae are clustered and each cluster connects to a different part of the skin, so the shark can get detailed directional information from this network.
The cells that actually detect the electrical field have a very special structure. There is a single layer of excitable cells closely packed together. The membrane of these cells facing into the canal is packed with voltage dependent calcium channel proteins. The rest of the canal lining has a very high resistance, which means that any voltage difference is effectively concentrated on the electroreceptor cells. A change in the electric field in the jelly allows these proteins to open and calcium floods into the cells. This causes the other side of the cell (away from the canal) to release neurotransmitter signalling to the shark.
Sharks have been shown to be more sensitive to electric fields than any other animal, possibly as low as 5 nanoVolts/cm – that’s 5/1,000,000,000 of a volt detected in a 1cm long ampulla. All living creatures produce an electric field by muscle contractions and as a result of the internal body chemistry. So being able to detect weak electrical stimuli probably allows sharks to hunt prey animals, including those buried in sand. Basking sharks have been observed swerving around jellyfish whilst feeding, after all the last thing you’d want clogging up your gill rakers would be lots of jellyfish and their stinging nematocysts.
It’s likely that the Ampullae of Lorenzini also allow sharks to sense magnetic fields. Any moving conductor will induce an electric field, so seawater moving on ocean currents, with the Earth’s magnetic field will produce electric fields well within the range that sharks can detect. Behavioural studies have shown that magnetic fields can change the behaviour of sharks. The ability to sense and orientate along magnetic field lines may help explain some of the large distance migrations that have been found using shark tagging experiments. Great white sharks have been shown to migrate over 2000 miles in open ocean to feeding grounds in the Pacific Ocean. Whale sharks have been tracked on journeys over 4800 miles. That is an astonishing figure considering that they don’t have sat nav guiding the way! So next time you’re up close and personal with any shark or ray, have a look for the black dots around their snout and remember that 340 years ago an Italian doctor and fish fanatic spotted the same thing.
In Japan it takes 3 or more years or rigorous training to become a Fugu chef and the pass rate for the exam is less than 40%. Fugu is a dish prepared from pufferfish, which is potentially lethal due to the presence of Tetrodotoxin (TTX). Budding chefs learn how to carefully remove the most toxic parts of the fish without contaminating the meat. Even though the liver of the fish is considered by some to be the tastiest part, its also the most poisonous organ. With such high stakes, restaurants serving Fugu are controlled by law, but there are around 20-40 incidents a year in Japan, with a fatality rate of around 7%. Most of the fatalities aren’t associated with restaurants, but with home preparations. Never has the phrase “I’m dying to eat” been more apt.
The symptoms of ingesting a lethal dose of TTX include dizziness, exhaustion, headache, nausea and difficulty breathing. The victim remains conscious but cannot speak or move. Breathing stops and asphyxiation follows. There is no known antidote. Treatment consists of emptying the stomach, giving the victim activated charcoal to absorb the TTX and putting them on life support until the poison has worn off. You can add in whatever prayers you feel like at that point. If the patient survives the first 24 hours then recovery over a few days is common.
So, what on earth is the pufferfish doing with this potent neurotoxin? It turns out that in the marine environment pufferfish aren’t alone. TTX is also found in blue ringed octopus, Astropecten star fish, Xanthid crabs and some newts and toads too. But despite its widespread appearance in the animal kingdom, none of these creatures are actually synthesising the TTX. The toxin is produced by bacteria that infect or live in the animal, and the animal concerned uses the TTX as a defensive biotoxin, and sometimes also as a venom eg octopus and arrow worms (Chaetognaths).
TTX acts by blocking sodium ion channels. Nerve cells have to pump sodium ions outside of the cell in order to be ready to transmit a signal. Sodium ions can’t cross cell membranes, so a special protein gateway exists in the nerve cell membrane that helps move the sodium out. Block this protein and the nerve cells will lose their ability to send a signal. This prevents the nerve from being able to send messages to muscles, resulting in reduced muscle movement. There are slightly different sodium ion channel proteins in the nerves controlling skeletal muscle and those controlling cardiac muscle. Victims of TTX poisoning will experience progressive paralysis throughout their body, whilst remaining conscious until shortly before death. A truly awful way to go.
TTX turns out to be remarkably toxic. The lethal dose of cyanide is 8.5mg per kg of bodyweight, but it would take only 4% of that amount of TTX to be lethal. TTX can be absorbed orally, by ingestion, by injection or through abraded skin. As the TTX levels are due to bacteria, there is a seasonal, geographical and species variation. It’s no wonder that the Fugu chefs need years of training. Poisonings from TTX are almost exclusively associated with the consumption of pufferfish from Indo-Pacific regions, but this is mainly because pufferfish just aren’t eaten as commonly elsewhere. In New Zealand in 2009 several dogs died after eating grey side gilled seaslugs (Pleurobranchus maculate) found washed up on beaches. The slugs were found to have ingested high levels of TTX.
Naturally occurring TTX has been used in traditional Chinese medicine for over 4000 years to treat convulsive disease. In 1774 Captain James Cook recorded that his crew ate locally caught tropical fish and fed the left overs to the pigs kept on board. The crew had mild symptoms (numbness and shortness of breath) but by the morning all the pigs were dead. The crew had a very lucky escape, although its not known if they had pork for lunch the next day!
One of the hardest skills for some divers as their diving career progresses is learning to use a compass. Once you’ve mastered the technical aspects of making sure it’s moving freely and not locked off inside the casing, the biggest hurdle is trust. You need to gain a Jedi like perspective as you accept Obi-Wan’s guidance to “Use the Force”. And generally, that’s fine, until there’s a nearby wreck and your compass stops being attracted to the earth’s magnetic field and starts interacting with the ship’s magnetic field instead.
When iron hulled ships were introduced, the effect of the metal hull on steering compasses was first observed. During construction the metal in the ship adopts the magnetic field of the dockyard used for construction. In modern construction methods, the high currents used for welding the steel plates together create magnetic dipoles in the steel, thus magnetising the ship…
During the American Civil War, mines were developed that were activated by contact. The target ship hits the horn on the mine. The soft metal of the horn buckled under impact, smashing a glass ampoule with battery acid inside. The acid electrolyte dropped into the waiting battery, energizing it and heating a platinum wire inside the mercury fulminate detonator. Boom.
At the start of WW2, the Germans developed a new magnetic trigger for mines. For a while the British were stumped as to how these mines worked. But in November 1939 a German mine was dropped from an aircraft and landed on mudflats in the Thames estuary at low tide. The mine was disarmed and taken to Portsmouth, where the mechanism was examined. A magnetic needle which was pulled by the target ship’s magnetic field completed the circuit and fired the mine. Later sophisticated versions would use a counter that didn’t fire for the first few ships to pass.
Establishing how the mine worked held the secret to protecting vessels, you just need to wipe out the magnetic signal. Magnetic field strength is measured in units named after Carl Guass, so the process of removing the magnetic signature is known as degaussing. Remove the magnetic field from the ship and it can safely pass over the mines without triggering an explosion.
There were two ways of cancelling out the ship’s magnetic field. The permanent one was to put thick bands of electrical wire around the length of the vessel, known as coiling. Passing an electrical current through these cables generated an electromagnetic field that cancelled out the ship’s own field, thus rendering the ship invisible to the mine mechanism. Royal Navy Commander Charles Goodeve oversaw this system, and it even allowed for the polarity to be reversed when ships were in the southern hemisphere so that the ship appeared to have the same magnetic field as the natural background. But this equipment was expensive and difficult to install.
Measuring a ships natural magnetic field was a complex business. A series of magnetometers are anchored to the seabed about 5 metres apart for a 150 metre run. Each magnetometer wa connected to a fluxmeter on the shore. The ship passed over the magnetometers and the readings from the fluxmeter were used to create the ship’s signature. From this starting point the number of turns of the degaussing cable could be increased or decreased, or the current altered until the signature was minimised.
A second quicker method was to wipe the hull of the ship, with a current carrying cable running a pulse at about 2000 amps. The large cable was dragged down the sides of the ship in a process known as deperming. This wasn’t a permanent solution though, as the ship travelled through the Earth’s magnetic field it slowly became magnetised again. This started in late 1939 and helped protect many of the vessels that carried out the evacuation from Dunkirk. In a 4 day marathon session prior to the evacuation over 400 ships were ‘wiped’ in this way, though there are concerns that some of the ‘wiping’ may have not been as effective as hoped. The Isle of Man vessel Mona’s Queen was lost to a magnetic mine on 29th May 1940 just outside Dunkirk harbour, and stories persist to this day among the relatives of the crew that the ship wasn’t properly protected.
Comb jellies are a common sight around British waters, particularly the sea gooseberry (Pleurobrachia bachei). With a clear body and measuring only a couple of centimetres long, it’s easy to overlook these beautiful little animals apart from one thing, stunning rows of rainbow coloured hairs running along their body. With no skeleton and composed of 99% water, you’d be forgiven for thinking that these were very simple creatures, but actually they have some pretty neat stuff going on.
Firstly, let’s start with where the comb jellies fit in, they are not the same phylum as jellyfish. Jellyfish (Cnidaria) have complex lifecycles and stinging cells. Comb jellies (Ctenophora) have a simple life cycle and make glue to catch prey. The problem for scientists trying to study the evolution of the Ctenophores is that they don’t make very good fossils so the records are patchy at best. Genetic studies indicate that Ctenophores are much older in origin than other animals, and predate the bilaterian animals (those with bilateral symmetry) by millions of years.
There are 2 major cell layers, the external epidermis and the internal gastrodermis. Between these layers is the mesoglea, a jelly like layer. The Ctneophores have muscles running through them and the outer epidermis contains a basic nervous system known as the nerve net. Comb jellies are named for their unique feature, plates of giant fused cilia (small hair-like cells) which run in eight rows up and down their bodies. These cilia are used to propel the comb jelly through the water.
Many comb jellies have a single pair of tentacles and often these tentacles are branches and give the illusion of many tentacles. The branched tentacles are used to catch prey, but unlike the toxins from jellyfish, comb jellies use glue. Special cells called colloblasts respond to touch by firing a spiral filament and releasing sticky glue. Once the prey is stuck the comb jelly reels in the tentacles and brings the food to its mouth. Most comb jellies are carnivorous and will eat anything. Until recently it was believed that comb jellies spat out the indigestible waste particles, but it now seems like they release them through pores in the rear end – which is probably part of the evolutionary puzzle in explaining when animals developed anuses.
What about the beautiful rainbow coloured pulses of light? Whilst some comb jellies can produce light by a special chemical reaction to give photoluminescence, our sea gooseberry can’t. The rainbow colouring is caused by refraction of light through the hair like cilia cells. Light travels at a constant speed in a vacuum, but when light encounters a material that is more dense, it slows and its pathway bends. The different wavelengths in visible light bend at slightly different angles. This means that the cilia act like the glass prism you played with in physics classes as a schoolchild, splitting the light into separate wavelengths. The refractive index (how much the light will bend is almost the same for the comb jelly tissue as it is for the salty sea water. The hair like cilia amplify the refractive effect creating an iridescent pulse that is mesmerising to watch. The effect works across the visible and UV light wavelengths, meaning a fluorescent torch will also give a great image.
Lastly, there’s a few things you should know about comb jelly reproduction. Comb jellies are hermaphrodites (both sexes in one individual) and can spawn eggs and sperm freely into the sea, through their mouths. They do this on a continuous basis unless they are starved of food, when they will shrink down and stop breeding. But feed them up again and they will start spawning again. Rainbow coloured hair, sticky glue fishing nets and continual reproduction – what’s not to admire?
Any diver who has been to Scapa Flow to visit the remains of the World War I German naval fleet will know the story of the 21st June 1919 when 74 ships were scuttled. Due to some heroic efforts only 52 ships actually hit the seabed. Initially, the British Admiralty were determined to leave the German fleet on the seabed and let them rust. But the wrecks were a considerable hazard to local vessels, with several being grounded on up-turned hulls. By 1922 the demand for scrap metal had increased and the Admiralty started selling off the wrecks for salvage, £250 for a destroyer and a mere £1000 for a whole battleship (of course 100 years ago that was the equivalent of £54,000 but that still seems cheap).
Over the next 8 years Ernest Cox developed some incredible techniques to lift huge battleships from the seabed within Scapa Flow. The wrecks were salvaged for fixtures and fittings with artefacts being recovered in good condition including bottles of wine, musical instruments, and the metal ships were broken up for scrap sales. By 1930, the price of scrap metal had crashed leaving the whole operation in danger of financial ruin and by 1933 Cox sold out to Metal Industries Group and they lifted the last of the battleships in 1939 as World War II loomed. Just 3 battleships and 4 cruisers remained. These are the wrecks that divers now visit, but they all bear the scars of the salvage work carried out by Nundy Ltd and then from 1970 by Dougall Campbell as Scapa Flow Salvage Company. Explosives were used to blow holes into engine rooms to get the non-ferrous metals and to open up the hulls to recover the valuable torpedo tubes. Campbell also realised that the armour belts of 14 inch thick steel with a high content of nickel and chrome were easy to recover and valuable enough to be worth the effort. [Dougall freely shared his amazing knowledge to a number of Scapa Flow projects in advance of the centenary, and sadly passed away on July 26th 2018].
Sensibilities have changed regarding wrecks and their salvage. HMS Vanguard is now considered a war grave after she was lost with 845 men following an explosion in her magazine in July 1917, but by the 1950s and then again in 1970s, she was salvaged for her propellers, condensers, torpedo tubes, armour plating and Weir pumps. It wasn’t until 2002 that the wreck became a Controlled Site and diving was restricted, but for 85 years she was stripped of any useful metals ie the ones that would command a good price on the scrap market.
Early salvage operations were driven by the demand for scrap metal. In post WWI industrial development was being held back by lack of metal. But post WWII there was a new driver for recovering steel produced before WWI, lack of background radiation in the metal itself. As the nuclear and space races took hold on the 1950s and medical advancements in 1960s, there was a growing demand for steel that had very low levels of background radiation. Atomic testing in the 1950s released Cobalt-60 into the atmosphere. Steel production involves pumping air (or oxygen) through molten pig iron, which reacts with impurities creating oxides that can be removed as slag. Atmospheric atomic tests released atmospheric radiation which peaked in 1963, so any air or oxygen used to produce steel since that time introduced low levels of background radiation into the metal.
Ordinarily, this isn’t an issue. You wouldn’t notice or be affected by a trace in your cutlery or the spice rack in your kitchen or the panels in your car. But it matters if you are trying to build sensitive instruments to detect radiation. Geiger counters, body scanners and space equipment can all be affected by the low level of radiation introduced during the manufacturing process. That makes the steel armour plating from the pre-atomic era significantly more valuable than would otherwise be the case. Our latter found sensibilities to protect the wrecks as war graves wasn’t apparent decades ago. In Scapa Flow the salvage has stopped, but internationally wrecks are disappearing in their entirety. Happily, the half-life of Co-60 is short, only 5.26 years. Since the moratorium on atmospheric testing in 1963, levels of atmospheric radiation have been rapidly dropping, with only occasional contributions from Chernobyl, Windscale, Three Mile Island. This means that production of low background radiation steel is now possible, combined with computerised correction for background levels. However a drop in the market value of pre-atomic steel is unlikely to save wrecks around the world, particularly in Asia where even the former pride of the British Navy HMS Prince of Wales and HMS Repulse have been targeted by metal scavengers.
Over a year ago when we set up our marine tank, complete with filters and chiller, I envisaged that it would be mainly the rock pool animals that would survive. My inexperience at maintaining a marine tank would be compensated by the relatively hardy nature of rock pool creatures. Any critter that has evolved to tolerate massive variations in temperature and salinity (rainwater run off dilutes the salt in rock pools, but evaporation makes them saltier) was probably going to survive my attempts to keep it alive. As time has passed, we have become more adventurous about the creatures that we have attempted to keep, but the latest inhabitant of our tank is another step up…
We have a shark egg case. With a live lesser spotted catshark. And we can see it growing!
We see catsharks quite often on dives, in fact they’re probably the most common shark. Many non-divers are stunned when you tell them that there are 21 species of shark that are native to British waters, and probably another 19 or so migratory species too. The film Jaws was released in 1975 and over the past 40 years has had a massive negative impact on the general public’s perceptions about sharks. Organisations like the Shark trust have been battling this perception ever since. Even my own children make jokes about Jaws like sharks, when they have never seen the films and have had the privilege of diving and snorkelling with sharks. And now we have a live shark in the dive centre!
We have no idea if the shark in our tank is male or female. It’s currently less than 2cm long and inside it’s 7cm long protective egg case. At this stage there is more yolk than embryo shark. Shining a torch through the egg case allows us to see the embryo wriggling around inside the case. The hunt has been on for a gender-neutral name, and we’ve settled on Charlie the Catshark. We are much more used to seeing mermaids purses wash up on beaches than finding one alive and still growing, and managing to get it into an environment that we can observe its development. We don’t have any dog whelks in our tank. They are voracious predators and you can bet that anything capable of drilling into a Periwinkle shell for a meal would have no trouble getting through the mermaids purse to eat Charlie.
Whilst we watch Charlie grow we will see the yolk sac diminish in size. It’s easy to understand that the yolk must contain ‘nutrients’ to allow this growth; amino acids to make proteins for muscle and cartilage, and fatty acids which are vital to make cell membranes and to metabolise for energy. Shark egg yolk can contain over 50% fat which is roughly similar to chicken egg yolk. Most of the fatty acids are unsaturated fats which is important to keep them mobile in the low temperature of the sea. There are no carbohydrates. It’s hard to get carbs into an efficient storage molecule in such a limited space. There are other substances in the yolk vital to Charlie’s development especially hormones which will drive growth and sexual characteristic development.
We are going to have a long time to wait. It will take 9-10 months before Charlie chews his/her way out of the egg case. At that point, Charlie will be around 15cm long and will be heading back to the sea before he/she has a chance to eat everything else in the tank. My money is on the shrimp being the first casualties. But really a marine tank in a dive centre is no place for a young shark to grow up. For now, Charlie is safe inside the egg sac and the other inhabitants in our tank are safe from Charlie.
We have a rare chance to capture the attention of local children. We often have young visitors into the dive centre to hold a hermit crab, small urchin or starfish, but now we can show them a shark and talk about conservation. We are hoping to catch them before the cultural references to sharks start to become ingrained. The latest viral hit song ‘Baby Shark’ will help too. A combination of an ear-wormy irritating song that kids adore plus the chance to watch Charlie grow. This is a hearts and mind battle we have a good chance of winning. Do do do do do (a quick online search required if you haven’t seen/heard it yet – and my apologies!).
Michelle has been scuba diving for nearly 30 years. Drawing on her science background she tackles some bits of marine science. and sometimes has a sideways glance at the people and events that she encounters in the diving world.