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.
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.
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?
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.
Sellafield is located across the Irish Sea on the Cumbrian coast and is approximately 32 miles from the Isle of Man, on a clear day you can just about see it. The main activities at the plant include reprocessing of spent fuel from nuclear power reactors and storage of nuclear waste. There are no longer any nuclear power plants in operation at the Sellafield site. It was built in the late 1940s to manufacture plutonium for atomic bombs and Sellafield is one of the most radioactive places on earth. In its prime the plant was releasing eight million litres of contaminated waste into the sea every day. In 1957 the plant became the site of the worst nuclear accident in Great Britain's history, The Windscale Fire. This was a blaze that raged for three days, releasing radioactive gases into the air. The discharge of low level liquid wastes from the Sellafield site in the north west of England is the most significant source of artificial radioactivity in the Irish marine environment.
Now the site is mainly used for nuclear fuel reprocessing, and this and other activities gives rise to the discharge of low level radioactive materials in the form of liquids and gases into the environment. These discharges are regulated by the UK authorities and limits for releases are set by the Environment Agency of England and Wales (EA). Liquid radioactive waste is discharged from the plant into the Irish Sea via a pipeline, about 3 km from land. Gases are released from the plant via a number of chimneys (referred to as ‘stacks’). Discharges into the Irish Sea peaked in the mid-1970s and have dropped significantly in recent years. This is as a result of improved waste treatment facilities at Sellafield, which convert much of this radioactive waste into a solid for long-term storage.
As a result of the discharges from Sellafield, low levels of artificial radioactivity can be detected in sediments, seawater, seaweeds, fish and shellfish taken from the Irish Sea. A wide range of marine samples are collected and analysed on a regular basis by both the EA and the Manx Government. This monitoring can show where the radioactive particles become concentrated. As expected many particles end up in sea bed sediment, so there are sometimes slight increases when the winter storms have been especially ferocious and stirred up the seabed. Generally, levels are falling from their peak in 1998.
There are several radioactive isotopes that are monitored, Technetium-99, Caesium-137 and 134 and Cobalt-60. Of these, Tc-99 is regularly tested for by catching lobsters. Tc-99 concentrations in our local lobsters have declined from a peak of around 400Bqkg-1 in February 1998 to average 10 Bqkg-1 during 2015. These Tc-99 concentrations are lower than the levels found in lobsters caught off the Cumbrian coast. The EC recommended maximum permitted level for Tc-99 in seafood which is 1250 Bqkg-1, so these lobsters are safe to eat and regularly eating seafish will only make a minor contribution to your overall radiation exposure.
Now it’s not true to say that lobsters are immortal, but once they reach adulthood they don’t have many predators except humans. Good lobster fishery management sets minimum landing sizes for lobsters, ensuring that they are at least able to breed once before being caught. Small lobsters can get out of pots through the escape hatch or they are returned to the sea anyway.
Just as lobster pots discriminate against small lobsters, they also prevent very large lobsters from getting in. Consequently, larger lobsters do tend to live a very long time. The lifespan of European lobsters has been estimated at between 30 and 50 years. Large lobsters have lived through the peak discharges from Sellafield, unlike their smaller 3-4 year old counterparts who got caught in lobster pots and tested. Lobsters have a fairly high affinity for Tc99 and they accumulate the radioactive particles in their bodies. But the only real predator for the large lobsters is, you’ve guessed it, divers.
Something to think about the next time you wrestle a monster lobbie from under a rock
Some years ago I craved having a tropical fish tank. I’d had coldwater fish starting with the short-lived goldfish I won at the carnival hoopla stand, but tropical fish seemed like they were more interesting. The big problem is that a fish tank is a bugger of a thing to move and at that time in my life it became a chore and a burden. I relocated 6 times with the fish in bags inside a coolbox, hence it was with some relief that when the last fish died I emptied out the last of the water and put the tank away, promising that when life was a little less hectic I’d get it back out and set it up again. About 6 months later disaster struck when I cracked the glass at one end, but I didn’t get rid of the tank, just planned on repairing it. One of those tasks on my endless to-do list.
And then my goals changed. Stuff the guppies and their frilly tails, why not set up a coldwater marine tank? After all I spend a large amount of my life underwater, why not bring some of the great critters back? Several times a year I visit schools on the Isle of Man and bring a variety of sea creatures in to meet the children and explaining something about their lifecycles. I’ve developed a habit of going and collecting little stuff anyway.
A chance conversation with one of our club members who wanted to rehome one of his tanks, ended up in him loaning me a pump and a chiller unit as well as a fish tank without a crack in the end. At 10am we were having a brew in the dive centre and by 2pm I was stood ankle deep on the slipway filling a cleaned out sofnolime container with seawater. Our marine tank was installed and populated within 24 hours. And if I thought the tropical freshwater tank was hard work, I had another shock coming. Weekly 50 litre seawater changes are just hard work.
I now spend my time thinking about the ecological balance of the tank much more than I ever bothered with guppies. When you keep tropical fish there is loads of info about how many fish per litre of water etc, for British marine life tanks there isn’t the same guidance. A small edible crab was a disaster and massacred poor Kevin the Masked Crab within 24 hours. Kevin had a dodgy past himself, and was often seen amputating limbs from small brittle stars, so he was called Kevin the Killer Crab, but we had grown fond of him and it was sad to see parts of his exoskeleton scattered around the tank.
Our current population includes about 10 hermit crabs, who mainly seem to fight over shells and ignore the rest of the inhabitants. We have two small shore crabs, although one of them is getting a little larger and consequently even hungrier. I’ve a feeling he’ll be heading back to the shore next weekend. We’ve ended up with about 30 North Atlantic Prawns who pounce any food in the tank, and will come to your hand if you put it in. Small Purple Henry starfish, a juvenile scallop, a small common sea urchin, some limpets, Top Shells and Periwinkles complete the scene. We’ve had small fish (they get eaten).
The current star of the show is our Leach’s Spider Crab (Inachis phalangium). Leachy has a small triangular carapace which will reach a maximum of 3cm. I picked him as he ran across a sandy patch between rocks. I’ve seen small spider crabs before, but never really bothered too much about them. Leachy’s small size made him a target for the tank. After a short trip in an old ice-cream container, he was released in the tank. On the same day, another diver brought in 3 small Snakelocks Anemones.
It turns out that Leach’s Crabs have a commensal relationship with Snakelocks Anemones, the crab benefits but not to the detriment of the anemone. Females stay with their anemone and males will rove around looking for a mate and then return home. They are beautifully camouflaged, with legs covered in sponges and algae. This isn’t by chance, Leach’s Spider Crab actively collects sponges and algae and attaches them to specially shaped spines on their legs and carapace. The sponges are unpalatable and stop predators from attacking the spider crab. The algae form a part of the diet, which also includes food debris from the anemone and the mucus from the tentacles. Our intrepid little Leachy has beautifully evolved to fit into his ecological niche. Admittedly, that’s not meant to be in a dive centre tank, but on the plus side, none of his natural predators are there. We’ve so far avoided large fish or octopus. Periwinkles occasionally find their way out past the pipe work so we’d have no chance of keeping a cephalopod and Leachy is safe for now and I’ve learned a lot more about him.
Once upon a time my Editor and I went diving together. It was a few weeks after he had penned an opinion that back entry dry suits were an integral part of the buddy relationship. It was, he opined, important to trust your dive buddy to close the ridiculously expensive brass zip without trapping your undersuit or that annoying flappy bit of neoprene stuck in the back of several suits. Relying on your buddy to ensure the zip was closed all the way, contributed to the mutual support aim of buddy diving. As we stood kitting up for our dive, I happily fastened my front-entry plastic zip with the minimum of fuss and decided to tackle Simon about his ill thought-out piece.
I have a front entry suit because I like being responsible for myself…or more precisely I don’t always trust my buddies, especially if my buddy is a trainee or new to dry suit diving. I lack the ability to rotate my neck like a barn owl to check that everything is OK behind me. It only takes one trainee, who earnestly assures you that the zip is closed when in fact it’s half an inch open, to make you reconsider. When that cold rush of sea water starts running down your shoulder, you know that this is one mistake you won’t be making again!
But how do you get the dive manager or boat crew to double check your zip without offending your buddy? Surreptitiously sidle over to the crew as you leave harbour, keep your voice low so it can barely be heard above the engines (and definitely not by your buddy) and assume some wistful position that doesn’t look like you’re hugging a large imaginary tree? And of course all the while you must try not to offend your buddy and generate “trust issues” because at the very first time you are supposed to rely on their assistance you bailed and found another source of help.
So for me a front entry suit solves all of these problems. If my zip isn’t closed properly, then that’s my fault and my soggy right leg. For anyone thinking of getting a suit with a plastic dry zip, they are fabulous but never ignore the need for silicon greasing the stop end, even between dives if you’ve peeled out of your suit. But it’s my responsibility and I’m good with that.
Front entry suits frequently have two zips, the dry one and a cover zip, and this can cause endless problems too. I took my eye off the ball one day whilst doing a dry suit introduction in the pool. I will accept some of the blame, but we had just done a session at the dive centre trying on suits, and the concept of a dry zip and a cover zip had been discussed as we established that this particular suit was a good fit. I am to blame for thinking that our discussion would be remembered barely an hour later when we kitted up on poolside. When I turned to look at my two eager divers, they had closed their zips and were ready for the stride entry. Yes, the cover zip was closed. No, the dry zip wasn’t. Yes, the suit filled with water (luckily the warm pool version). No, the diver couldn’t climb up the pool ladder unaided. The phrase “I seem to be getting a little wet” was a total understatement on her part. Once dekitted, we laid the unfortunate lady down and rolled her around on the pool surround to empty the water. To give her credit she laughed nearly as much as we did and gamely carried on the orientation session. Five years on she is still diving, in a front entry suit, which she knows has two zips and one of them is very important.
Sadly she’s not the only one who’s been caught out in this way. Even some quite experienced visiting divers have missed the ‘hard to do up’ brass zip and relied on the ‘easy to do up’ cover zip in one of our rental suits. A cold shot of Irish Sea water down the leg is a salutary lesson in the need to familiarise yourself with hired equipment. So for anyone who read, noticed and remembered Simon’s treatise on the importance of back zipped suits for buddy trust and diving, maybe I was wrong to criticise him and perhaps divers with front entry zips could do with their buddy’s assistance, just sometimes.
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.