​It’s human nature to be hoarders. Thousands of years of human evolution has taken place without a row of shops in the high street or an out of town retail park to cater to our every need at most hours of the day. So humans have developed into hoarders, even if our modern day caves are overflowing with stuff. Witness the growth in ‘Self Storage’ facilities, a service that I am certain didn’t exist twenty years ago. How much ‘stuff’ do people have, that their homes are no longer enough and they need a portakabin sized extension, with lift access and on site security to keep their belongings? And for every organised, sensible person that realises that ‘extra storage space’ would come in handy, are there another dozen whose garage and sheds are rammed to the gunwales? Er…wait…yep that’d be me!
Across the winter months is a fine time for dive kit fettling. Just because the weather is less amenable to actual diving, doesn’t mean you have to spend your weekends doing something more useful. Non-diving partners will fail to see the logic in this argument. From their perspective you aren’t actually driving 2 hours to the dive boat to spend the day diving, therefore you must have time for a variety of other tasks, DIY, family visits, cinema trips, more DIY etc. The list of aspirations held by non-diving partners for days when you aren’t actually diving can be a long one. The length of their list is directly proportional to their lack of understanding about your love of all things scuba. The longer the list, the less they ‘get it’. Having established your weekly dive routine of disappearing from the household radar first thing on a Sunday morning and returning 12 hours later with an offering of fresh lobster, you must be very careful not to relinquish this time during the winter months.
So, what’s a diver to do when the weather is roaring in and the dive’s been blown out? It must be time to sort the dive kit. And this is a task that will take several blown out weekends. The longer you have been diving for, the more equipment you will have hoarded. If you are lucky enough to be the Equipment Officer in your branch then congratulations! You have an almost endless to-do list on behalf of your club. The act of ‘kit fettling’ on such a huge scale will ensure that your ‘dive time’ is protected as you justify needing to go to the clubhouse/pool/mate’s large shed where the club kit is stored by calling out “We need to have it ready for next season” as you head out the door.
I too have been sorting through kit. Dive centre equipment stores act like the extreme version of domestic garages and sheds. Who’d have thought we’d have not one but three Fenzi’s? Who knew that the kit box on the top shelf contained five two-piece wetsuits? And I think I need a bigger box for straps, clips and strange little bits of plastic that I can’t quite place, because I’m sure they’ll come in handy one day and I don’t want to throw them out yet. And there’s the rub, “it will come in handy one day.” I think I could make an absolute fortune if only I could learn to predict when that ‘one day’ moment will occur.
Our kit store should have a bench for kit preparation and rows of neatly stacked boxes.  In reality the amount of equipment in there means that the frequently used items are in on the floor in front of the storage boxes and the bench hasn’t seen daylight on its surface for months. Entering the kit store is like an archaeological project, everything is in layers relating to the time since its last use. The very act of tidying up is like a reverse trip down memory lane. But to combat the hoarding tendency requires more than tidying up. This requires a CLEAR OUT (cue dramatic music)!
There are three things required for a successful Clear Out. Firstly, you need to be in the right mood for it, ruthless, heartless, unsympathetic and a little cavalier. Who cares when ‘one day’ is likely to pop up? You need the space, you haven’t used this in 10 years and if you ever wanted to dive a horse collar again your mate has one you could borrow anyway. Secondly, you will make enormous progress in your decluttering if you think of a suitable recipient for the items that you want out of your way. Donating your old kit to the club means that it hasn’t actually gone, never to be used again. It still exists and you can get the philanthropic pleasure of knowing you donated it to a cause (and it will be the Equipment Officer’s problem now!). Thirdly, you need a reason to even start the clear out and what better reason than some new kit that needs pride of place in your dive emporium? Of course new kit won’t mean that you throw out the old stuff, not just yet, just in case… But perhaps you could clear out the kit you were wearing before the last set?

Summer is a busy time for any dive centre, and it’s almost with a sigh of relief that we watch autumn unfold so that things will quieten down a bit.  However, some summers are unremittingly autumnal as a misplaced jet stream can bring repeated low pressure systems rolling across the British Isles causing havoc and mayhem.  Many of our summer dive plans changed at the last minute as gale force winds and torrential rain made sea conditions treacherous and reduced visibility even in the sheltered bays. 
When I lived in west London, all my diving trips necessitated organising towing vehicles, booking accommodation and stupidly early starts.  I just don’t want to see 5am on a Saturday morning unless I have partied through the night to get there – and I suspect those days are behind me now.  Back then my dive trips were organised with almost military precision and planned weeks in advance.  Things are a little different now. 
When I first arrived on the Isle of Man two things struck me; firstly, how everything I’d been taught about dive planning, tidal flows and tides was completely trumped by local knowledge and secondly, how dives could be organised at 5 o’clock in the afternoon with the minimum of fuss and we’d all be in the water for 6.30.  My gung-ho “It’s not too rough really. I’ve planned to go diving so we are” attitude didn’t cut it here.  If you live with such fantastic diving on the doorstep, why have a slightly rough dive?  Wait 24 hours, let the wind drop away and have a really good dive instead.
The Isle of Man is close enough to the North West coast of England to be visible on a good day.  In fact it’s a local story that you can go to the top of Snaefell (our one and only mountain) and see 7 kingdoms in one go.  I’ll leave you guessing to name them all, but the location of the Isle of Man at the geographic centre of the British Isles means that every summer we have clubs setting out in their RIBs to travel across to dive in our waters.  And we offer visitors copious amounts of help to locate sites, plan around tides, transport cylinders, locate parts for their broken boats etc.  One of the visitors this year declared himself both very grateful and surprised that we should help him out so comprehensively and mentioned that other dive centres in the UK had been less than helpful.  Although, it’s true that we are pretty nice folks who want the best for our visitors, there are darker reasons at work. 
The Isle of Man is a limited community of around 80,000 and pretty much any diving story will end up with some link to our centre, whether it’s commenting about closing areas to dredging, helping out a fishing boat towed into harbour with their own nets around their prop or getting involved with videoing the local swimming club in training.  All diving links lead in our direction…..so it’s in our own selfish interests that we help out our visitors.  A lifeboat shout for lost divers swept away on an unexpected current or the hyperbaric chamber being mobilised for a recompression all reflects on us.  Some timely advice and guidance keeps the visitors out of the incident pit for a bit longer and keeps diving out of the news until we have a good news story to impart.
Of course, managing the exposure of diving in the local press plays a role in how we manage our diving activities too.  It’s been suggested that there are only 6 degrees of separation between any two people in the world, but on the Isle of Man that’s around 2 degrees.  Word of mouth is incredibly important.  We have to be safe and be seen to be safe, or our reputation would disappear overnight.  Doing my Advanced Driving test a few years back introduced me to the idea that ‘accidents don’t just happen’.  The same applies to diving, accidents are a culmination of a series of steps.  The advice that we freely give to visitors is the first point we can intervene to stop that series of events unfolding.  If you’re planning a trip across please feel free to get in touch.  If you run a dive centre that begrudgingly hands out dive planning information please have a think about how this reflects on the industry as a whole.  I promise you that it won’t undermine your charter service….the clubs that brought their own boats this year are booked to come and dive off our boat next year…..and looking forward to a less stressful trip. 
And in case you are wondering on a clear day you can see the kingdoms of Mann, England, Scotland, Ireland, Wales, Mann, Heaven and Neptune.

​I’m something of a diving evangelist; I’m happy to help new divers, old divers and lapsed divers, from whatever brand of training they subscribed to.  There are a myriad of reasons why divers fall out of the habit, though I suspect that families and finance are the big ones.  Young families are an enormous drain on time and resources and I’m sure I’m not the only diving parent just ticking the time away until junior can undertake diver training and we can set out on a diving adventure together.  My diving will be massively improved with my guilty conscience at leaving my offspring finally expunged.
But when is it time to hang up your fins?  At what point does diving just not make sense anymore even if you love the sport and have spent years involved in it?  None of us like to admit we are growing older, less capable and more vulnerable….but time keeps moving on and our bodies are programmed to decay.  Accumulated injuries and life’s wear and tear start to take their toll. 
I laughingly joke after a full day of diving and training that this is a young man’s game – it’s not a joke but a heartfelt cry of anguish.  I’m learning to pace myself, something I would never have thought about in my 20’s.  Nitrox is my very best friend even for shallow training sessions.  It takes the edge off the sub-clinical DCI that we all experience, leaving me less tired and capable of keeping going.  But I know that in reality I am just compensating for the effects of getting older.
But at what point does is the compensation not enough?  I’ve had the honour of trying to assist a once excellent and accomplished diver back into the water after a break of over 15 years.  It has been a challenge for both me and the diver.  The equipment and skills have changed and we have worked in the safety of the pool.  But the real changes are the personal ones, physical strength and mental processing.  I’ve changed my approach entirely from one of assisting a fellow instructor to one of just trying to keep this diver and any potential buddies safe. 
I think one of the key factors with someone I have trained from scratch is that they are aware of the dangers and aware of their own limitations.  By contrast, taking someone who, in their day, was one of the foremost divers and instructors in their club is a scary proposition.  Without trying to be harsh, I find myself as Diving Officer mentally registering a huge number of limitations including possible buddies, depths and conditions.  This is taking all my people skills and has reawakened branch politics and disagreement from years before I even started diving!
So what have I learned?  In future I will try not to be over-awed by any diver’s past glories, but instead rely on my own observations regarding ability.  Returning divers rarely take up the offer to attend Ocean or Sports diver lectures, but refreshing theory knowledge is essential especially if the subject matter has moved on.  Mainstream diving has changed.  My offer of Nitrox was met with incredulity. The Devil’s gas?  And you give it to Ocean Divers?! But my motives were entirely about trying to keep my elderly friend safe.  .
And the really big lesson is trying to judge when to give up on diving altogether.  Will I notice when the time has come for me?  Will I be able to look at my physical state and work out that my diving days are behind me? Or will I be the one looking for a sympathetic Diving Officer willing to work out how to achieve my one last dive?  Do I set the limits now?  I will give up diving when I can no longer carry my own cylinder?  (But then we have disabled divers now for whom we carry kit around.)  I will give up diving when the instructors are 40 years younger than me?  I will give up diving when it seems like too much hard work?
The incident reports in the last few years have highlighted a possible increased risk to elderly divers.  Maybe it’s time to bring back a diving medical for specific sections of the diving community, perhaps the over 60’s?  And maybe that defines the end point of my diving too.  When I can no longer pass the rigorous HSE diving medical I will give up diving altogether.  Instead of waiting until I start to endanger myself and others, if I can’t make the medical I need for professional instructing, it will be time to hang up the fins and watch my children continue in the sport I love.  For now I will make the most of the time that our diving overlaps.

​The issue of children being able to dive is an emotive subject.  During my years in diving I have seen the debates rage back and forth about what age limit should be set.  When I became involved in the Clubmark scheme several years ago I was motivated not necessarily by the idea of attracting children into sport, as by the concepts of fair access and freedom from discrimination.  If you read the fine-print of many Branch constitutions many of them still include the ability to black-ball new membership usually couched in the phrase “membership applications will be subject to approval by the branch committee.”  The grounds and procedures for accepting or refusing a membership application and the mechanisms for appealing the assessment never seem to be included.  Even if you asked, I suspect no-one in the branch would be able to explain.  I have no idea how often, if ever, this clause is invoked – but wouldn’t you hate the thought that, after an evening’s visit to the club you are considering joining and a quick chat in the bar, committee members could decide that you just ‘don’t fit’ and refuse your application? Perhaps when joining a branch we should modify Groucho Marx’s oft quoted put down?  Please accept my resignation.  I don’t want to belong to a club that won’t accept anyone as a member.
Of course, the really successful BSAC branches are those who welcome everyone as a member.  These are the branches for whom getting a Clubmark award is just a case of putting the paperwork into a file and getting it sent off.  The biggest barrier to this happening is that they are probably having so much fun snorkelling, diving, doing outreach work and recruiting new members that there just isn’t time to get the evidence together. 
The politics involved in the management of a dive club can frequently overwhelm the members involved.  As the equipment and techniques involved in diving evolve, the long-serving members find that they are suddenly not the ‘expert’ voice that they were in previous years and feel deep resentment.  Young enthusiastic members feel frustrated as they argue their case in committee meetings. 
Dive clubs tend to elicit deeper bonds than other sporting clubs.  We rely on our diving buddies not only to share the safe diving we are all seeking, but to provide the support to take on more challenging dives and the back-up when things go wrong.  Members of other sports clubs don’t have to rely on each other in anything like the same way.  Poor teamwork on a football pitch means you lose the match, but no-one’s life would be endangered by it.  Poor teamwork on a dive trip means oxygen cylinders don’t get checked, dive briefs get skipped and the outcomes can be deadly serious. With strong links to the people in our dive club come strong emotions.  Longstanding members of a club will know each other’s families, children will spend their summer holidays on dive trips and learn to snorkel or dive within the branch.  Non-diving partners can frequently be found supervising a game of beach cricket for a coach load of divers’ children.  So woe-betide any Johnny-come-lately who suggests that, instead of the annual pilgrimage to Weymouth, they would like to head to the Farne Islands this year.  You are not suggesting that diving with seals might be a fun trip.  Oh no! You are (inadvertently) criticising years of family summer holiday tradition! How very dare you?
Diving attracts people from a wide range of day jobs and with that diverse background comes a wide range of skills.  The key thing for all of us is the ability to work within the team, to respect each other’s perspective, to negotiate change and to keep an open mind.  The job of the Diving Officer maybe delegated from the National Diving Officer but really good DOs will have a skill set that would make a recruitment agency go weak at the knees.  Some time ago a study tried to calculate the value of a mother, checking all her many roles and pricing the commercial equivalent.  The final figure was somewhere over £100,000 a year.  Putting a value on your DO will reveal a similar scary figure.  Can you imagine employing someone to check the training, observe instructors, meet and greet, strategically plan, keep tabs on the kit and manage the members within the branch?  For those frustrated members within clubs please note I specifically said putting a value on your DO, not a price! Dive branches can be the most frustrating places in the world at times – but they can also be the most rewarding and supportive environments for your dive adventures. Choose yours wisely.

​Christmas is an interesting time for divers, not least because it’s one of the few holidays that we actually take to spend with our families.  During the year, bank holidays are a chance to travel a bit further afield for some diving.  By Christmas, diving activities tend to be reduced by autumnal, windy weather.  Suddenly instead of fondling kit while you wait for your air fill, you’re fondling Hello Kitty plush dolls for your niece in a Toys R Us queue that makes the early morning rush at Stoney Cove look like a rather civilised affair. 
Let’s face it, all divers really want for Christmas is more dive kit.  But there are two things conspiring against you opening your perfect gift on Christmas day.  Firstly, divers are notorious for justifying new pieces of kit throughout the dive season, “my drysuit really won’t last until the end of June” or “I’m going to need a gas switching computer to take full advantage of the AMG course.”  And then the real clincher – no-one else understands what kit you need and that extends to your dive buddies too.  The kit that works for one diver is another person’s worst nightmare.  Just look around your next club dive and you’ll see all the different choices that we make for our dive kit.  So is it any wonder that your nearest and dearest buy you a micro towel, a flask for the post-dive coffee and a novelty bath plug in the form of a bright yellow jellyfish?  Act early!  Find out now if your favourite local dive store does vouchers.  Better still, find out if they will do vouchers over the phone or online. It is far too dangerous to let non-diving partners visit the store and see how much the kit actually costs!
Now I’m not a qualified meteorologist.  Living on an island has the advantage that I only need to know how much and which way the wind is headed over the Irish Sea and I can plan my dives accordingly.  But even during the settled high pressure systems in the summer, planning dives more than 48 hours in advance can be a dangerous game.  But I’m going to stick my neck out.  Christmas Day will be calm, dry and sunny.  Surface air temperatures of 8 degrees will match those in the sea, making for a pleasant diving day.  In fact this may be the most pleasant diving conditions of the winter season, and we’ll all be building Lego Harry Potter, challenging everyone to stay awake after lunch and trying to look like we really were experts with programming Big Track the first time around.
Your only chance is a Boxing Day dive.  Convincing Gran that she needs to babysit for a few hours so that you can go out to collect scallops for dinner is only going to work if Gran is going to eat the scallops too.  Most relatives would welcome a seafood diversion from turkey, and your offer will be accepted.  Suddenly, the pressure is on – now it’s not just a few scallops as you swim along on a gentle branch dive – now you have to prove your worth as a diver scavenger.  Come back with less than three scallops per person and face the scorn of the non-diving relatives.  There’s no point trying to explain the impact of dredging, overfishing or habitat loss.  You will lose the argument.  All that your nearest and dearest will see is the shiny, expensive dive kit that you loaded up in the morning and their empty supper plates in the evening.  It’s just not worth the grief that you will get.  Perhaps it’s safer to leave the kit in the garage until New Year, do the family thing and tell tales of your diving exploits instead? Cold turkey sandwich, anyone?
New Year’s Day usually brings dive clubs and their families together to blast off the excesses of the previous night.  A local dive for many clubs will mean the lake in the local nature reserve.  Ok so it’s only four metres deep and two of those metres are thick black sediment, but it’s water isn’t it?  Rope signals are reviewed, tenders practice their stance on the shore and the bravest/daftest divers slip into the water.  Families will stand around consuming mince pies and holding your new flask and micro towel ready for when you return! Happy New Year!

Somewhere way back in your training, you were probably introduced to the Incident Pit. It’s a fairly dramatic diagram with the words “fatal” and “death” appearing at the bottom. The concept was meant to inspire you to deal with problems early, keep control and stay safe, with the tag line “Don’t fall in.” This always seemed to be a slightly strange thing to say to divers, who are destined to fall in (to a body of water) quite deliberately. Other than encouraging you to run through your own personal risk assessment for a dive, that’s about all the standard training material has to say about pre-dive thinking.
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In many sports the technique of visualisation is used to help elite athletes achieve their potential, and there’s good evidence that it works at lower levels too. Visualisation is the process of creating a mental image of what you want to happen or feel in reality. An athlete could use this technique to picture crossing the finishing line first. For a diver there is clear potential to visualise a relaxed, in control dive and achieve a state of calm and well-being before a dive. In fact, most people naturally tend to think through and rehearse what’s about to happen to them. So quite possibly you have started to think this way already.

Sometimes these preparatory thoughts can be plagued with recurring images of past mistakes or near misses, and that’s not conducive to ensuring the success of the upcoming dive. It can be more helpful to actively direct your pre-dive thoughts and control those images in your head. And the visualisation probably needs to be more than just a visual experience. To really be successful, you would need to focus on all the senses; the rush of cold water, the smell of the sea, the feeling of pressure on your legs as you enter the water, the sound of your bubbles.

When you visualise the successful dive, you are stimulating the same regions of your brain as you do when you physically perform the same action. So, thinking the dive through, with all it’s stages, is a way of conditioning your brain for a successful outcome. Perhaps the visualisation starts before the dive, right back to the preparing your equipment. And the beauty of this preparation is that you could be doing it anywhere. Picture being on the bus thinking about packing your kit for the weekend.

What if we extend this to thinking through the different situations that may arise underwater? Rather than the scary prospect of the Incident Pit, why not challenge divers to visualise their response to common problems? What would they do if their torch fails on a night dive? It’s too easy to just say “I’d get my back up torch out”. In order to visualise it you would have to work through being able to open your BCD pocket (feel the zipper in your hand, hear the zip and feel as it bumps along the teeth), feel through the gloves for the piston clip, unclip the torch lanyard from the D ring, feel the lanyard in your hand etc. Which pocket? What else in in there to avoid dislodging? How will the torch feel in my hand? This is a far more powerful psychological technique than a glib “Get my back up” response.

For divers just starting out on their diving journey, visualisation can be an excellent way to deal with the nervous trainee. Try to remember the first time you put all your dive kit on. How tight did your neck seal feel? How restricted was your movement? These are things we all take for granted now. We have done it often enough that we barely register the sensation. I think there is a real value in talking through that first dive. This is not part of your SEEDS brief, this is so much more. Find a quiet space, sit down and step your way through the dive, start building the neuronal connections in a positive way and help boost performance.

It doesn’t matter how carefully you monitor your fluid intake before a dive, or how close to dive time you leave the last toilet visit, we have all got out from a dive ready to rugby tackle anyone standing between us and the toilet. It’s well known that going for a dive causes an increased need to urinate. There are some interesting physiological changes that come to play. Immersion and temperature changes cause a narrowing of the blood vessels in the extremities. This results in an increased volume of blood to the central organs which is interpreted by the body as fluid overload. This causes the production of antidiuretic hormone (ADH) to stop, signalling to your kidneys that they need to produce urine to lower the blood volume. So even if your last toilet visit was only minutes ago, you can quickly find yourself feeling the need to go again.
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It’s almost impossible to give an exact measurement for the volume of the human bladder as everyone’s ability to hold urine varies. Normal adult bladders hold between 300 and 400ml but can hold up to 600 or even 1000ml in some cases. The need to urinate is stimulated by the expansion of the bladder which triggers the Micturition reflex centre in the spinal cord. Most adults will feel the need to urinate when their bladder is only around a quarter to a third of its normal capacity. In normal circumstances, adults will feel the need to empty their bladder about every 3 hours, but as divers we know the effect that immersion plays.

There’s always a big debate in the wetsuit diving community about whether peeing in a wetsuit is acceptable or not. In a drysuit, the debate becomes somewhat redundant unless you have a P-valve fitted. But is there any danger to ‘holding it in’? When you first feel the need to pee, your bladder probably has quite a way to go before it’s completely full. As your bladder fills up the muscles around it will contract to keep urine from leaking out until you’re ready – just make sure you can get out of your suit fast enough!

The dangers of holding your pee are mostly cumulative, so the occasional episode probably isn’t harmful. However, if you are diving frequently and often find yourself ignoring the need to pee you run the risk of urinary tract infections, urinary retention (the muscles can’t relax even when you want to pee) or bladder atrophy (leading to incontinence). But for most people, you can hold your bladder full for a few hours without serious complications, even though its uncomfortable.

If you dive in a wetsuit, you can of course make the call as to whether you pee in your suit or not. The old saying is that 50% of divers pee in their wetsuits and the other 50% are liars. So whichever camp you fall into, just make sure you flush your suit through before you get out of the water and start to take it off, and please wash your suit thoroughly between dives.  If you’re a drysuit diver, there’s always the option of adult nappies to ensure that you can relieve yourself. If that seems a little retrograde, or as you march middle age a little too prophetic, then perhaps a P-valve is an option.

Not surprisingly there are hazards associated with P-valves too. Ignoring the issues with getting a stick-on condom or the female cup attached successfully, so that the urine does actually enter the tubing to leave suit, there are reported cases of urinary sepsis. The tubing used to connect the urine to the P-valve is the ideal breeding ground for Pseudomonas bacteria, and it only takes a small amount of backward flow to introduce those bacteria into the body. If you think rinsing your wetsuit is a bit of a faff, syringing antiseptic through P-valve tubing should give you some perspective.

​As I child I had a budgerigar called Dinsdale. Dinsdale was a pretty happy bird who would cheerfully run round my desk, leaving special presents on my homework (!) and hop back into his cage on command. He loved hitting the bell that was attached to a little round mirror and pecking hard at his cuttlefish.  Of course, he didn’t really have a whole cuttlefish in the cage with him, just the hard, bony bit.

Cuttlefish bones aren’t actually bones at all, they are a special kind of shell.  And while we are at it, cuttlefish aren’t fish either. Cuttlefish are one of the Cephalopods and they have their own family name Sepiidae. The early ancestors had a shell for protection and existed before the first fish had evolved. Modern cuttlefish don’t have an external shell but rely on camouflage for evading predators. 

The common cuttlefish (Sepia officinalis) also produces a brown ink, which can be harvested from their ink sacs.  Most of us would recognise the colour of the ink from old fashioned brown sepia photos, and that’s how the ink got its name. The chemistry and biosynthesis of ink in cephalopods is fairly complex. It is a form of the common biological pigment melanin which is the same molecule responsible for your skin developing a tan after exposure to sunlight. Who’d have thought you and the cuttlefish would have so much in common? The eumelanin in the ink sacs is also found in fossils from the early Jurassic period around 200 million years ago.

For a soft bodied animal, it seems strange that there should be a good fossil record. The cuttlebone is generally well preserved. When the cuttlefish are alive the cuttlebone is a mix of chitin (a really large structural sugar molecule) and aragonite (one of the three forms of calcium carbonate). After the animal dies, the chitin will break down fairly readily but the aragonite persists. That means that it is possible to find fossilised remains of cuttlefish that are readily identifiable and from modern catches of cuttlefish, your budgie gets a calcium supplement.

The cuttlebone has a very specific function in the cuttlefish. It’s clearly not for defence – what use would an internal bone be? Cuttlefish have a short life span, maybe only 1-2 years and during that time they have a phenomenal growth rate (up to 10 kg) so for a cuttlefish conserving energy is critically important. The cuttlebone structure is full of holes and the cuttlefish can control liquid or gas into those spaces to effortlessly control its buoyancy.

The cuttlebone is a long oval structure made of around 100 chambers, with the chamber lying at the head end being the oldest, other layers are added as the cuttlefish grows. Lying along the cuttlebone is the siphuncle, which is a strand of tissue that connects all the small chambers.  In order to add water to the cuttlebone, the cuttlefish makes the blood in the siphuncle more salty by pumping salt out of the chamber. Water in the chamber is drawn out of the chamber and into the blood by osmosis and oxygen and carbon dioxide come out of solution and make up the volume in the chamber by diffusing from the siphuncle.  So it’s not true to say the siphuncle pumps the water….more that it pumps the salt and that causes the water to be drawn out. Siphuncles rarely get preserved in fossil records but you can usually see the notches in the cuttlebone where the siphuncle used to be.
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Removing water from the chambers of the cuttlebone reduces the overall density and causes the cuttlebone to float. Cuttlefish aim to maintain neutral buoyancy and will swim up or down with the minimum of effort. In addition to this, the cuttlefish can control whether the chambers towards the head or the tail end are water filled or gas filled, making it’s journey from depth towards the surface even easier as it adjusts its trim. Next time you’re diving, be more cuttlefish, perfect buoyancy and perfect trim.
 

​While reviewing some marine survey videos lately I found myself mesmerised by watching an octopus move across my survey area, settling and changing colours before moving again and changing yet again. The colour change was so rapid and the octopus completes three quick changes before scooting off out of the video.  It got me to thinking that colour changing is a pretty cool skill to have. The most us puny humans can manage is to develop a tan, producing melanin in the skin to try and prevent the damage that UV radiation can cause.

Colour in cephalopods (octopus and squid) depends on 4 different types of cells.  The first layer of colour controlling organs in the skin are the chromatophores.  Each chromatophore consists of a small balloon like sac filled with pigment. Each sac is connected to around 20 muscles, and each muscle is controlled by 2-6 nerves linked directly to the brain of the octopus. The octopus can stretch the balloon-like sac and allow the pigment to cover a large surface area, so we get to see the black, brown, orange, red or yellow colour just under the surface of the skin. When the muscles around the sac relax, it shrinks and the colour is hidden.  Chromatophore sacs are individually controlled so the cephalopod can control which colours are displayed and where, hence the patterns seen in cuttlefish.  Deep water cephalopods have very few chromatophores as colour isn’t much use in an environment with little light.

The next layer of colour organs under the chromatophores are the iridophores. Iridescence is the property of luminous colours that change depending on the angle they are viewed from. Iridophores are the key to how cephalopods create the metallic green, blue, silver and gold colours. Iridophores work by reflecting light from stacks of very thin cells.  It’s not certain how iridophores are controlled, but they are slower to respond than chromatophores so it’s unlikely to be controlled by nerves but more possibly by hormones.

Then there’s the leucophores. These are cells that scatter full spectrum light, so they appear white. In fact, they will reflect any light that is shone on them, and the light doesn’t change with the angle that you view at. It’s thought that having leucophores underlying the chromatophores increases the intensity of the colours that we observe. Leucophores also help with the cephalopods ability to colour match because they reflect the surrounding light.

Cephalopods have 3 types of specialised colour creating organs in their skin to mimic their background for camouflage and communicate. The cephalopod eye is remarkably similar to a vertebrate eye consisting of an iris, lens and photoreceptor cells. The similarity is often cited as an example of convergent evolution, both vertebrates and cephalopods need to observe their environment and they have solved how to do this in a similar way. But there is a critical difference, cephalopods are colourblind, so their eyes only see in black and white. How on earth does that make sense? An animal with the ability to make a myriad of colours, metallic sheens and mesmerising patterns can’t actually see in colour?

The explanation for this apparent contradiction is that the cephalopod eyes have wide pupils in a strange variety of shapes, U-shaped, W-shaped or dumbbell shaped. When light passes through the wide pupil, the lens in the eye acts as a prism and splits the light into different colours, a large pupil allows for more splitting, known as chromatic aberration.  Cephalopods use their wide pupils to create the maximum chromatic aberration and focus on these different wavelengths by changing the depth of their eye ball (altering the distance between the lens and the retina). So, cephalopods can detect colour, not by using special proteins embedded in cells in the retina (like we do) but by changing whether the light focusses on the retina at all. They find it easy to focus distinguishing between bright and dark colours, so that probably explains why display patterns are usually colour separated by black bars.
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But if a cephalopod can’t really see so well, how on earth do they mimic their environment? The secret to this lies in the presence of opsin (light detecting protein) in the skin. Its thought that its possible for some cephalopods to sense how much ambient light is present across their periphery and adjust their skin colour and brightness accordingly. To camouflage yourself, you don’t have to be a perfect match for your surroundings, you just have to match it slightly more than your predator can distinguish. 

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.
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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.