In May 2017, a female Orca (known as Lulu) was found washed up dead on the shoreline on the Isle of Tiree in Scotland. Lulu was one of the last remaining members of Britain’s only resident Orca population, which now only comprises 8 individuals, 4 males and 4 females. This west coast community had been monitored by researchers for over 25 years.
Orcas are very social animals with the Orca mother at the centre of the pod. Her children, including adult sons, stay together throughout their lives. Female Orcas start reproducing around 13 years of age and during her lifetime a female will have 4 to 6 calves and stop reproducing around 40 years of age. Pregnancy lasts about 17 months and is followed by a period of mothering in which other members of the pod will assist with babysitting duties.
Different organisms have evolved to have different reproductive strategies. At one end of the spectrum there are organisms which produce a huge number of offspring, in some cases the parent then dies or never reproduces again. This Big Bang reproduction is a good strategy if the organism has a high probability of dying early. If the chances of surviving are low, then it makes sense to invest your energy into a Big Bang reproduction when conditions are right and thus ensure your genes carry on into the next generation. Many fish and some insects employ this strategy including salmon.
At the other end of the spectrum are the organisms that have a single or only a few offspring but at multiple times in their lives. Humans along with other large mammals use this strategy, known as iteparous reproduction. These organisms have a low probability of dying early, so it is expected that the offspring will have a good chance of survival to maturity. Any species that takes years to reach breeding maturity and has a limited number of offspring is vulnerable to any factor that impacts on breeding success.
In between these two extremes are organisms like coral, who breed en masse at limited times, generating lots of offspring but only when the moon is in the right phase. These organisms have a constant risk of dying throughout their lives and so a constant reproduction strategy is a good idea, balanced against the resources needed for reproduction to happen.
Researchers are certain that there have been no new calves born into Lulu’s pod in the last 25 years. The entire pod is ageing and it is likely that during our lifetimes there will be no resident Orcas in British waters. A post mortem on Lulu has provided the clues that man-made polychlorinated biphenyls (PCBs) are likely to be the culprit. There has been concern over the persistence and biological effects of PCBs for many years. Scientists have established that physiological effects can be measured with around 30 milligrammes of PCBs per kg of body tissue. Lulu’s level was 975mg per kg. Furthermore there was not evidence that Lulu had ever been reproductively active or ever had a calf.
PCBs are a group of chemicals that were originally made from 1929 until they were banned in 1979, by which time it is estimated around 700,000 tonnes had been produced. They are chemically stable, non flammable, have high melting points and are poor electrical conductors. For many years PCBs were used as insulators in transformers and capacitors and cable insulation, plasticizers in paints and plastic, and pigments and dyes. Does anyone remember the carbonless copy paper? For the younger readers, you’ll need to look up carbon copy (and then you can understand why we cc people on a email) and understand what a revolution it was when carbonless copy paper arrived.
PCBs aren’t very soluble in water, but they are easily soluble in organic solvents and in body fat. They accumulate through food chains and long lived species will end up with high levels. PCBs are still being released into the environment today from poorly maintained waste sites, leaks from electrical transformers and incinerators using a temperature too low. By the 1960s PCBs could be found at trace levels in people and animals around the world, not just in heavily populated areas, but in the Arctic too. The health effects are widespread; PCBs cause cancer, reduce the function of the thyroid and the immune system and cause neurological deficits. Importantly for survival of Orca, PCBs reduce conception rates in females and sperm count in males and reduce the birth weight of calves.
Lulu’s death was caused by becoming entangled in fishing ropes not by PCBs. However, you don’t often hear about Orcas becoming entangled. They are very intelligent, nimble and aware creatures. It’s highly likely that the PCBs in Lulu’s body impaired her ability to navigate a common hazard, but to be brutally honest the PCBs had killed her chances of reproducing years ago. Her body may have washed up in 2017 but her pod have been dying for years. Humans changed the chances of survival and sadly there is no hope of saving them now.
We’ve had a rather enjoyable club trip away during the winter. A chance to escape the grey, wet and cold and get a bit of sunshine. It helped that the trip was planned as part of an Advanced Diver exped, as that meant I didn’t actually have to do much to smooth the whole trip along. Our AD candidate had picked a BSAC centre to go diving with, assuming this would mean that our reasonable levels of experience (including First Class Divers and instructors) would be recognised and we would be treated accordingly. The dive plan was submitted by email and when we arrived the owner of the dive centre went to quite some lengths to tell us he was going to follow our plan exactly.
Day 1 wasn’t so bad, apart from a really strange conversation about compasses, and how if you look at your compass and it says 90 degrees then you are in fact swimming West. We tried to explore this assertion, after all it would mean rethinking the entire way we brief for dive sites, skipper boats and well, just generally everything. How could we have all got this far and been 180 degrees out? We asked if this was caused by having a compass with a sighting window, maybe looking at it from the top, but nope. We were assured that 90 degrees was West. End of discussion, let’s go diving. We took our own compass bearings on the shore (safe bearing was North). Our check out dive took a strange turn when instead of the 15 metre bimble we’d been briefed for we ended up at a 32 metre wreck. During the surface interval, we were assured that this dive had been in the plan, but even the AD candidate looked puzzled and it was her plan! Whilst on the surface we asked about the time for the second dive. It was a mandatory hour away, but who knows why it’s an hour. A couple of us tried to look at our plan functions to gauge when we’d have enough dive time for the next dive but we were stopped because “decompression is only a theory anyway”. We were doing an hour on the surface and then we’d be going back in.
By the next day, things took another turn for the bizarre. The first dive brief of the day explained that the dive 1 would be out from the harbour and turn right, and the second dive at the same site would be out and turn left. The first dive was pretty good, shoals of fish and a couple of angel sharks. We came back to the shore, had a bite to eat and swapped cylinders. Whilst we were standing in the sun to warm up a bit, someone asked about the topography for the second dive. At this point the story changed, we were told that there was nothing to the left apart from barren rocks, our dive guide couldn’t imagine why anyone would want to turn left, or who had suggested we should and we would be going right again. The second dive to exactly the same site was disappointing. The tide had changed, the shoals of fish had moved on and we resorted to a little bit of wombling to clean up the reef.
By now we had established that we were becoming the victims of gaslighting. Gaslighting is a form of persistent manipulation and brainwashing that causes the victim to doubt her or himself, and ultimately lose her or his own sense of perception, identity, and self-worth. The term is derived from the 1938 stage play Gas Light, in which a husband tries to convince his wife that she’s insane by causing her to question herself and her reality, flickering the gas lights as he does. Despite having been around for over 75 years, the term has recently resurfaced with Trump’s presidency in the USA.
We had the classic signs; blatant lies, denial of what had been previously agreed and attempts to manipulate and divide opinion the group. Once we’d identified that this sort of behaviour was in play, everyone’s guard was up. Fortunately, we’ve all know each other for a long time and dived together for many years. Each night our dinner and beer debrief covered very little about the dives and much more about the bizarre antics. The carefully written up dive plan that was the point of the trip had disappeared and was never mentioned again. Next time we’re all going to put our basic qualification and not mention any further diving experience. We think it will be easier all round.
Ever since the footage from Blue Planet II hit our screens, there has been a growing awareness of the devastating impact of plastic on the marine environment. Anyone who has taken part in any of the Great British Beach Cleans organised by Marine Conservation Society volunteers will have already know much of the debris collected every year is plastic, from fish crates to drinks bottles, rope to the cotton bud sticks with cigarette butts thrown in for good measure. Whilst the MCS encourage volunteers to collect every item in a 100 metre stretch for their survey work, its certain that there are some plastic particles that are just too small to be picked up. These are the microplastics.
Microplastics are particles less than 5mm in size, ranging down to 5μm. That’s the Greek letter mu which represents micrometers, one million times smaller than a metre, a thousand times smaller than a millimetre. This size range is why these particles are called microplastics. Microplastics are not as easy to count. A collaboration between the University of Portsmouth and a charity called Just One Ocean is running a scheme to encourage people to survey their beaches for microplastics. There’s a carefully designed citizen science method to allow data from around the UK shores to be submitted and collated. We don’t fully understand the scale of the problem yet, but scientists from a number of disciplines are expressing concerns that it’s much larger than anyone suspected.
Microplastics have many sources. Large plastic pieces tumbling around in the marine environment will gradually break down into smaller and smaller pieces. Washing synthetic clothes in a washing machine releases microfibres into the waste water. If you run a tumble dryer you will know that you have to clear out the lint from it. That is just the larger fibres that get trapped. Smaller particles will enter the air blown out from the dryer. Microplastics have been found in the air, soil and water across the world. Since the 1960s, plastic particles were deliberately put into toothpastes and body care products as microbeads. They helped scrub the plaque off your teeth or acted as an abrasive layer to remove dead skin in facial scrubs. Those plastic beads were useful for about 2 minutes (because we all brush for the recommended time don’t we?) and when you rinsed and spat, those plastic beads were set free on the world. And the chances are they will exist long after you have gone.
We also find microplastics in food and bottled drinks. Filter feeding marine life picks up the particles from the environment. Mussels tested from 8 locations round the UK and samples bought from 8 UK supermarkets were all found to contain 70 microplastic particles per 100g of meat. Beer, honey and sea salt have also been shown to be good sources. Some studies have shown that over 80% of tap water samples contained microplastic and bottled water was even worse. One sample of bottled water had over 10,000 plastic particles in a litre. Science has a funny way of examining such issues, they’ve even looked at human faeces to gauge the levels that we are consuming. They found 20 microplastic particles for every 10g of stool sample.
So, what’s the big issue? Indestructible little bits of plastic that are so small you can’t see them with the naked eye? And they obviously pass through your intestine because they are too big to be absorbed. Why should anyone care? And to a certain extent we don’t fully know yet – and that may be the scariest aspect of this story.
When plastics are made, they aren’t a pure substance. Thousands of different chemical additives can be thrown into the recipe to manipulate the properties of the plastic. As large plastics breakdown, these additives are released. The other concern is that microplastics are very good at adsorbing (not absorbing) certain chemicals onto their surface. You might have heard of a few of these; PCBs, PAHs and DDT are on the detected list. We’re reasonably certain that probably 90% or more of the plastic microparticles that you’ve ingested have passed through your intestinal tract. But what scientists cannot quantify yet is whether they transferred damaging levels of toxins to you on the way. The data so far suggests possible disruption of your gut microbiome and inflammation. The consequences of long term repeated exposure to the toxic chemicals carried by the microplastics is still being assessed. It doesn’t bode well. We know from other species how devastating persistent organic pollutants can be.
There are estimated to have been 8.3 billion metric tonnes of plastic made since the 1960s, of which over 4.9 billion metric tonnes has been discarded into the environment. This is a problem that will not be easily solved and we are all at risk.
Before 1920, having tanned skin was associated with working outdoors and indicated that you carried out manual labour. The societal ideal was pale skin which showed that you were rich enough to stay indoors, although the pursuit of pale skin often involved powders containing lead and mercury, which weren’t exactly great choices from a health perspective. The Western Europe attitudes started to change in the 1920s when Coco Chanel started to popularise the idea of a tanned skin, and this trend accelerated through the explosion in cheap air travel from the 1960s, so that having a tan showed you could afford to take the time off work and lounge around catching some sun’s rays.
The concept of desirable skin colour varies around the world. Whites try to tan, whilst across Asia the sale of skin lightening creams and lotions is at an all time high. Your natural skin tone is determined by genetics and that is directly correlated to how much UV radiation you are exposed to. The higher the level of UV radiation, the darker the tone of indigenous skin. As some populations of humans moved to more northern latitudes there was a shift in genetics. With less UV radiation causing damage, there was a positive selection of individuals with lighter skin, who could synthesise more vitamin D. As societies changed from hunting to agriculture, there was a need to maximise the vitamin D synthesis to make up for the loss from the diet. About 40,000 years ago the mutations for pale skin emerged in both the East Asian and Western European populations.
The most important pigment in the skin is called Melanin. Specialised cells call Melanocytes make the pigment and pack it into the Keratinoctyes that make up a layer in the skin. Melanin is an important molecule as it controls the amount of UV radiation that can penetrate the skin. Some UV radiation is needed for vitamin D synthesis, but too much is harmful. UV light is divided into 3 different wavelengths of light, UV-A, UV-B and UV-C. UV-C and some UV-B are absorbed by the ozone layer in the atmosphere, which is a very good thing as without this absorption UV levels would be dangerously high (and quite possibly life on earth wouldn’t exist!). Some UV-B is absorbed by the epidermis (the upper layer of the skin but UV-A can penetrate further into the skin and interacts with the cells in the dermis. UV-B causes an increase in melanin production and UV-A causes the melanin molecules to change and become darker.
However, tanning is not the only consequence of UV exposure. Although no-one knew it during the 1960s, too much exposure to sunlight is the cause of 90% of all skin cancers, eye damage, immune system suppression and all the signs of ageing associated skin damage. As this message started to become understood, the tide has turned against tanning salons, and anyone out in the sun was urged to wear a hat, cover up exposed skin and slap on the sun cream….and then we hit another snag. In March 2018, Hawaii announced that it was bringing in laws to ban sun creams containing oxybenzone, which is the most widely used UV absorbing molecule in all sun creams in use today.
Once upon a time, Para-amino benzoic acid (PABA) was widely used in suncreams. Patented in the 1940s PABA was the first molecule to be used absorb UV-B in sun creams, but it fell out of favour as it stained clothes and caused allergic reactions. Then came Oxybenzone as the next generation molecule with the ability to absorb UV-A and UV-B. Oxybenzone isn’t just used in sun cream, but as a UV protection for a wide range of plastics too. Hawaii have recognised a study that showed that tiny amounts (microgrammes per litre) of oxybenzone cause coral larvae to stop moving around and prevented them from developing a hard skeleton. To understand the concept of just how toxic this is, that’s lethal levels at half a teaspoon in an Olympic sized swimming pool.
It’s time for a switch away from the UV absorbing molecules like PABA (still in use as the derivative padimate O) and oxybenzone. Perhaps we need to return to the mineral reflective suncreams with their chalky finish. Have a look at the label on your suncream. There are several alternatives hitting the market now, although for some of them the claims can be hard to verify. Perhaps the safest option for us and the environment would be to take the lesson from Victorian society and just cover up? Stop putting any plastic solutions into the sea including the lotions you slather on.
In the depths of winter, there are two major factors that reduce diving time, low pressure weather systems and snot. As the air becomes colder and drier, the cells lining the nasal cavity have to work quite hard to warm and moisten the air that we breathe in. The cells producing the mucus are called goblet cells (which is a reference to their shape, not an instruction for what to do with the mucus). The mucus itself is a mix of proteins which contribute to the protective role in a number of ways; enzymes that can attack bacterial cell walls, antibodies to bind to pathogens and lactoferrin to mop up any free iron.
But the real star of the snot show is Mucin, a group of large proteins with lots of sugar molecules bound to the central regions of the molecule. These sugars are important as they allow the Mucins to have gel-like properties with an amazing water holding capacity. Aggregations of Mucin molecules are secreted by the cells lining the airways (and digestive tract too) and the sugar coating helps them to resist digestion. Over 20 human Mucin genes have been identified and the proteins that they produce help bind pathogens together, and are one of the reasons why you will make more snot when combatting a nasal infection.
It’s not just humans and other mammals that can make Mucin, a similar group of proteins is found in the most humble gastropods. We are all familiar with snail trails. (I’m sure that was my Nan’s phrase for a small child with streams of nasal mucus running down their top lip!) Snails move using a combination of their muscular foot and a lubricating slime. Now here’s where it starts to get strange, mollusc slime is a non-Newtonian fluid. It doesn’t follow the normal rules that govern viscosity in fluids, but rather changes as stress is applied to it. This explains why the same mucus can be used to allow snails to move and to bind to a surface. As the wave of contraction from the muscular foot of the snail acts on the sticky slime, the slime changes to become a free-flowing liquid. When the pressure is removed, the slime becomes gel-like again, allowing snails to lodge in overhangs and defy gravity.
For marine snails, it’s slightly harder to see the need for a lubricant, but it turns out that the slime trail for some species has even more functions. It’s a big commitment for some species to make a slime trail, estimated at up to 60% of their total energy use. Periwinkles will sniff out and follow fresh trails made by other molluscs to reduce this energy requirement. Mucus trails bind microalgae from the water when they are fresh and so they can be an excellent food source. Yep, that’s right, eating the algae from someone else’s snot trail is a good thing for Periwinkles, but please don’t try this at home!
Limpets are grazing feeders who return to their ‘home-scar’ on the rock every time the tide goes out. For them, the mucus trail is their route to find the carefully etched out rock into which their shell can clamp down to protect them from predators, sealed with a mucus layer to prevent them drying out. Not so much “Follow the yellow brick road” as “Follow the limpet snot trail” to get home. With the right conditions, you can see limpet snot trails on rocks as the tide falls.
For some molluscs, their slime trail is also important for mating. Chemical signals indicate the sex of the snail, allowing prospective mates to find and copulate. Male periwinkles can track down a female by following chemical markers in the slime. But the females of one species of periwinkle (Littorina saxatilis) turns off this signal to avoid mating. L.saxatilis live in dense colonies and like other periwinkles will mate up to 20 times a day throughout the year. This seems like a strange strategy for any species to survive, the general rule being that males mate as often as possible, whereas females try to be selective about mates.
Why would female L.saxatilis try to avoid mating? Males mount onto their mate and crawl around to the lip of the shell. This means that the female is then bearing the load of adhering both parties to the rock, and remember that our slime is non-Newtonian, more stress makes it flow. Having a male periwinkle on your back will double the stress and can result in both parties being swept off the safety of the rockline. For females, mating will increase their chances of being predated upon. So the female L.saxatilis turns off the sex signal in her slime. Males will still follow the slime trails, but it’s a 50:50 chance that they could be trying to mate with another male at the end of the journey.
Since Ancient Greece snail slime has been used in cosmetics. It contains high levels of hyaluronan which is a major component of the proteins that support our cells. It is freely available as a cosmetic claimed to promote the formation of collagen and help to improve skin structure. More seriously, hyaluronan is gaining popularity as a biomaterial scaffold which is helping the next generation of bioengineers to promote the formation of blood vessels in tissue engineering. Something to ponder when you are relegated to shore cover as you are too snotty to dive…
July 1969 is best remembered in popular culture for the Apollo 11 moon landings and Neil Armstrong’s declaration of “..a giant leap for mankind.” But at the same moments as the world was transfixed by NASA’s reports, another equally challenging expedition was underway off the North American coastline. Six men on board the Ben Franklin drifted for 30 days in the currents of the Gulf Stream, using very little power apart from their floodlights.
The Gulf Stream project grew out of earlier bathyscaph explorations. Bathys means deep and skaphe means light boat. Bathyscaph expeditions were designed to explore the depths, to plummet to the sea bed, make observations and then return to the surface. During the 1950s successful dives were made into the Marianas Trench at a depth of over 10,000 metres.
The Ben Franklin was different, she was a mesoscaph, meso meaning middle, and her design reflected that idea. The Ben Franklin was designed to be a light vessel using modern steel and Plexiglas to ensure that in the event of any problem, she could always return to the surface. Whereas launching bathyscaph required considerable winch power and large support vessels, mesoscaphs were expected to operate in shallower waters, with minimal surface support.
It took Jacques Piccard, a Swiss oceanologist (and no relation to Jean-Luc) nearly a decade to design and build the Ben Franklin. Jacques father, Dr Auguste Piccard was himself an ocean explorer who designed bathyscaphs and it was his discussions with Jacques that initiated the mesoscaph project. The design was a cylindrical cabin capable of holding the crew, with 400kg of Lithium hydroxide in panels to absorb the carbon dioxide, over 1100 kg of silica gel to absorb the water and reduce humidity, 250 kg of liquid oxygen and enough dehydrated food to last for 30 days. Piccard orginally envisaged the interior being lined with mahogany, to emulate a fine yacht, but was overridden and the internal structure was clinical and white.
Setting out from Florida, there was no big fanfare or press launch. The initial plan was to see if they could last 3 days and then make a decision over whether to continue. So on 14th July 1969 the Ben Franklin was towed into position and at 20.34 the hatch was closed. The crew descended initially to the bottom of the sea and then rose slightly controlling their descent by ditching ballast weight or adding air to ballast tanks. Over the next 30 days they would drift for 2800 km at speeds between 0.2 and 3 knots. They experienced internal waves within the Gulf Stream that would cause their depth to oscillate by over 100 metres, although the rate of rise didn’t concern the crew. They established that there was perceptible daylight at 600 metres and conducted a series of acoustic measurements using explosions set off from two surface support vessels.
On board for the trip was an observer from NASA, whose primary function was to look at the interaction between the crew. 50 years ago NASA was already considering the International Space Station and longer voyages to Mars. The Gulf Stream project provided an ideal test bed to study sleep patterns which deteriorated after the first 3 weeks and eating arrangements, as crew members chose to eat alone rather than together. Bacterial contamination, firstly of the cold water supply and then of the walls and floors would have posed a serious threat to the crew had the experiment continued beyond 30 days. Even an increase in the cleaning regime failed to stem the growth of bacteria.
Communications between the Ben Franklin and the surface support vessel the Privateer take place using an acoustic telephone, and the recordings made by the NASA observer show that the stress levels of the crew rose enormously at times when communications were restricted by weather or surface vessels deviating their course due to other ships. On 24th July 1969 as the crew of Apollo 11 splashdown into the ocean, the crew of the Ben Franklin are experiencing a temperature of 14 degrees and tumultuous seas as the internal waves catch the vessel. It wasn’t until 14th August that they surfaced and at 8.09 the hatch was opened. They were due east of Baltimore and the US Coastguard vessel Cook Inlet was there to rendezvous with them. A week later the Ben Franklin had been towed into New York for a hero’s welcome. A remarkable tale of human endeavour had come to an end, but in a world transfixed by the moon it was barely noticed.
Normally the ferries coming to the Isle of Man run at sensible times, but there is one particular scheduled service that leaves the port of Heysham at 02.15. In the winter, when the only other crossing is 14.15, I seem to find myself on the ‘overnight’ boat far more often than I would like. The boat doesn’t load until at least 01.30, so for a couple of hours I usually try to sleep in the carpark. Cold, rainy and situated next to the nuclear power station, it’s not exactly conducive to any restful sleep. Even if I do doze off I still have that dreadful anticipation of being woken by the port staff to drive onto the car deck.
I’ve learned now to book one of the cabins on the ferry. Head to the customer services desk, collect the key and find the cabin with the beds made up ready. If I’m quick I can kick my shoes off and be asleep before the safety announcement. The journey is just under 4 hours and the arrival in the Isle of Man is accompanied by an announcement and the lights in the cabin coming on. It doesn’t feel like I’ve actually slept at all. After a short drive home, I usually try for more sleep, but it’s not always easy during the day. I usually need a good night’s sleep to recover from my acute sleep deprivation.
As divers we often travel some distance by road, ferry or plane to get to our dive destinations. Travel arrangements can involve early check-ins and sleeping in unfamiliar places. There is considerable research into the effect of sleep deprivation and its effect on behaviour, particularly for in relation to driving. Sleep deprivation has the same hazardous effect as being drunk. Research has shown that being awake for 17-19 hours impairs performance to an extent that is comparable to having a blood alcohol level over the drink driving limit for the UK. As drink-driving has now become socially unacceptable, how many of us are aware that our driving could be as impaired by lack of sleep?
I think back to my days living in London, getting up at 4am to tow the club boat to the South coast, two waves of two dives and some food followed by the drive home. The boat would be stowed away by about 10pm, so the last few hours of towing a rib would have had me well into the fatigue zone. The evidence suggests that performance decline sets in after 16 hours awake, add this to sub-clinical decompression related post-dive tiredness and I think I was in dangerous territory.
How many times though do our trip risk assessments include fatigue? I got up at 5am this morning to collect a group coming in from the ferry. During the summer there is an 03.00 crossing from Liverpool arriving in the Isle of Man at 05.45. If I think I felt tired as I arrived at the ferry terminal – you should have seen the divers we collected! Some of them had managed a little sleep in the airline style seats, but not much. We’ve brought them back to the accommodation and sent them all to bed. We expect to be diving this afternoon, and one of the risks I’m now assessing is how much sleep they haven’t had.
I can’t find any specific research into the impact of fatigue on diving, but I am happy to accept that driving is a reasonably good surrogate activity. Drowsy drivers experience difficulty remembering the last bit of road and slower reaction times. Impaired cognitive and motor performance aren’t good for divers either. We learn about the impairment due to narcosis (with that amazing slide that has several pints of beer on!), but being awake for long periods is going to cause those effects without even stepping in the water. Maybe there are hints about this in our training, we do advise to have a good interval between flying and diving, but there’s nothing explicit regarding sleep deprivation. If you aren’t convinced that this is a problem, perhaps you should know that it’s been estimated that sleep deprivation is implicated in 1 in 5 road accidents. Sleep deprived drivers are much more likely to get angry with other road users and deal poorly with stressful situations (like navigating unfamiliar roads).
Caffeine can help, but only in the short term and not with all the aspects. It can improve alertness and reduce reaction time, but fine motor control isn’t improved even with high doses. So, I could send all the divers to the local coffee shop and insist they top up their espresso quota, but I know that won’t last. Instead, I hope they have their heads down and are napping now. Me? I’m too wide awake and writing columns instead!
Scallops (Pecten maximus) are a national concern on the Isle of Man. We have some of the most protected scallop populations in the British Isles. Licensed boats can only fish during daylight hours in certain areas of the sea and not during the summer months when the scallops are breeding. The catch is landed into harbours around the island; creamy, pink shells in 25kg bags loaded onto pallets for the forklift truck to move them into wagons.
If you glance down into the harbour its usually possible to spot the white inside of a few discarded shells shining on the seabed below. These shells eventually wash across the bay and onto the beaches, but they don’t always arrive in the same colour as when they were discarded. Many of the shells are stained dark brown or black, colours we never see during dive surveys of scallops.
Shells are mostly made of calcium carbonate which is white in colour, mixed in with about 2% of protein. As molluscs develop they absorb minerals from their environment and secrete calcium carbonate from their mantle to create their shell. The protein makes the shell very strong, but lightweight and resistant to dissolving in water. Shells are self-repairing, and the mollusc can secrete more shell material as needed for repair or growth. Naturally occurring colour and patterns in shells is as a result of mineral ions incorporated into the shell structure. But that doesn’t explain the post-mortem colouration of the scallop shells.
Shallow burial of shells causes iron oxides to form in the tiny pits on the surface of the shell and causes brown staining. The black colour is usually due to microscopic crystals of iron sulphide. These crystals form in the absence of free oxygen which can occur if shells become buried deeper in mud or sand.
Although my local harbour is sheltered, it doesn’t provide the deep mud conditions required to blacken shells, but there is a much more common cause. Burial under just a few centimetres of seaweed rotting on the beach will provide suitable anoxic conditions for sulphide formation. Hence blackened shells on the beach is a relatively quick process occurring under mounds of kelp and wrack.
There are some mollusc species that live well buried into deeper sediment. The Ocean Quahog (Arctica islandica) is a subtidal species of clam that is renowned for it’s longevity. Some individuals have been recorded at over 500 years old. The shells of Quahogs have dark black colouration, but they have a long time to absorb the necessary pigment. Whilst the shell is buried in the sediment, a siphon to the water provides for food and oxygen to the creature below.
Naturally acquired pigment probably strengthens the shell. Colour patterns often align with spiral or axial sculpture. Instead of producing and transporting a thicker shell, it might be more energy efficient for molluscs to make pigments. Pigments impede propagation of a crack in the shell. The structural explanation also works for colour inside of shells. A good example is Mercenaria mercenaria (the quahog or cherrystone clam). The purple inside the shell, hidden when the animal is alive, lies along the edges of the shell, just where predator whelks are likely to attack. Strangely young Merceneria don’t make the purple pigment. Their shells are too thin to resist attack anyway, so they concentrate their efforts on growing a thicker shell and surviving to when their pigment strengthened shell is going to ensure a long life.
There are lots of other reasons for shells to have different colours. A favourite project for marine science students is to send them to look for colour variation in Flat Periwinkles (Littorina obtusata). In this case pigment is used for camouflage, allowing the winkles to hide amongst the bladder wrack on the shore. Pigments may serve as a warning to possible predators, or the pigmentation pattern may provide a template for future growth of the shell. But there doesn’t have to be a reason for pigmentation in all cases. Oxygenated mammalian blood is red, not for any evolutionary reason, but because that’s the chemistry of the situation.
Seals are collectively known as pinnipeds, which means from the Latin pinna (fin) and pes (foot). This classification includes the walruses, eared seals and true seals. The Isle of Man and the rest of the British Isles are home to resident populations of Grey seals (Halichoerus grypus) and Common seals (Phoca vitulina). Common seals (also known as Harbour Seals) are found in both the North Atlantic and North Pacific. About 35% of the European population of common seals lives in UK waters. By contrast Grey seals are only found in the North Atlantic, Baltic and Barents Sea. The entire world population of Grey seals is probably no more than 400,000 individuals, with about 40% of them living in UK waters. Although we tend to take seals for granted, we should perhaps appreciate how lucky we are to have them in the waters around us and see them so often.
There’s been a long understanding that the pinnipeds evolved from land based mammals. This concept in itself is a little strange, as the general gist of evolution is that our ancient ancestors left the watery environment for a life on land. But somewhere millions of years ago, some of the mammals returned to the sea to take advantage of the feeding opportunities that existed there. Whales and dolphins have definitely taken their return to the marine environment to the extreme and evolved to the point that they can no longer safely return to the land. When they do, the amazing guys from the British Divers Marine Life Rescue swoop in and work their hardest to throw them back into the briny again. In the pinnipeds we have a group of species who spend their time mostly in the marine environment, returning to land only when necessary. On land seals are ungainly, slow and clumsy, which made them an easy target for hunting. In the water, they are agile hunters, capable of diving to about 200 metres for up to 15 minutes.
The clues to the pinnipeds evolutionary past are clear in a number of ways. Their forelimb has five webbed fingers, with claws that are used for grooming and fighting. This five fingered (pentadactyl) limb structure is a common evolutionary feature, linking many vertebrates including reptiles, birds, mammals and amphibians. Just let that sink in for a moment. You can see the same bone structure in pretty much every group of animals with bones. The humerus at the top, an elbow where the radius and ulna join, a wrist connecting to fingers. It’s there in the bats wing (with elongated fine boned fingers and skin stretched over them), it’s there in frogs (although the ulna and radius have partly fused), and cats and dogs and tigers and crocodiles and in us..
In seals the flipper bones that would be the equivalent of your arm are shortened, so that what appears to be their armpit is in fact their elbow (front flipper) or ankle (hind flipper). Their metatarsals (fingers) are elongated compared to ours and the skin in between gives them something akin to swimming gloves. Close interaction with a seal will reveal that they can still bend their webbed fingers to grip and hold onto objects or, if you are lucky enough, onto you as you are diving. Their flippers are well adapted to propel them through the water. When swimming quickly, the hind flippers are used in a side to side motion, and the front flippers are held against the body. If you have watched seals turn under water, you’ll know that they stick out a front flipper to perform sudden changes of direction. Cruising speed for seals is about 2 to 3 knots, but when hunting seals can move at an astounding 20 knots (that’s probably faster than most club ribs!).
Seals are part of the Caniformia (dog like) sub order of the Carnivora group of Mammals. In fact, most divers that have had encounters with seals will tend to describe them as being like big puppies. Despite this, there have been many studies suggesting that seals are in fact more closely related to bears than they are to dogs. Perhaps the fact that we are more likely to have encountered and interacted with dogs rather than bears gives rise to our misconception? Remember that Grey seals are the largest living carnivore in Britain, can grow up to 2.3 metres and weigh over 300kg and treat these amazing creatures with the respect they deserve. When you get to shake hands with a seal next time, count his fingers and say hello to a very distant cousin.
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.