The most recent episode the M-Net's The Wild Ones: Aquarium: An Aquatic Life featured one of the Two Oceans Aquarium's most beloved animals - the arrival of several Japanese spider crabs, and the introduction of the team that cares for them.
We chatted to Operations Manager Tinus Beukes, Senior Aquarist Kevin Spiby, Aquarist Kaye Williams and Animal Health Coordinator Tersia Greenstone about their work with the Japanese giant spider crabs, and tried to answer some of your questions.
How are the spider crabs able to survive so long out of water during transport?
Tinus: The crab is packed in wet sphagnum moss, which is kept damp with sea water and ice packs. The oke goes in the bag with moss and 100% oxygen gas is pumped into the bag.
The crab's book gills are in chambers that are in direct contact with the oxygen, so they don't need to pump water through them. As long as they stay damp, the humidity is 100% and the oxygen is 100%, they're A-for-away - the gas just diffuses straight through the membrane.
Think of a car aspirating air: If you look at an F1 car with a flipping amazing air intake - that's like those two chambers next to the spider crab's eyes. Having said that, smaller crabs do better - there's a relation between the gills' surface area and the crab's body surface area - so bigger crabs actually need water to support their joints, but that ratio between gill and body size gets smaller as they get bigger meaning they have to be transported in water.
Want to know more about the crabs' 14 722km journey? Here's the original article on their arrival at the Aquarium.
What do you find most fascinating about these spider crabs?
Tersia: For me, the most interesting thing is how they moult. I've been in a tank with them when they've moulted and it's interesting to see how they actually climb out of their old carapace because you would think, "What happens to the legs?" But, they actually pull themselves out beautifully in one motion once they reach a certain point.
Tinus: It's their sheer size; very few people who walk into the Aquarium, if any, expect to see a crab that size. From the time you are young, you already know what a crab looks like, but nothing approximates the sizes of these ones. Few people know that spider crabs exist.
Kevin: Their leg span is obviously their most striking feature - that they can get so big. But apart from that, if you sit and watch them clean themselves, they are very dexterous with their pincers and their arms, so they can reach all around and bend. It's quite entertaining to watch!
Kaye: Their spunk! Just the attitude of a spider crab, they aren't really as afraid as other crabs. They don't run off when they see a human, they stand their ground.
Want even more reasons to be fascinated by spider crabs? We did a Kreature Feature about them!
Nothing in SA compares to them in size, but what comes closest?
Tinus: There are two animals actually. The first one, which you don't really see anymore because of overfishing, is the West Coast rock lobster which can actually grow to about 80cm. In terms of an actual crab, you can look at both the Cape rock crab and the Cape stone crab and a type of Namibian ghost crab, which can grow to have a carapace size of about a small side plate - which you might look at and think, that's very close to a spider crab, but their legs are much shorter. Not more than 40cm across.
Why don't spider crabs get decompression sickness from being brought up?
Kevin: Spider crabs have no air holes or air pockets inside their bodies, all their cavities are filled with liquid. So when a fish that has a swim bladder comes up from a depth, it expands, but with invertebrates that doesn't happen.
Tinus: If you look at an animal like a fish, somewhere in the fish is a gas space which can expand and contract. These crabs don't have any of those spaces, it's all hydrostatic pressure. A good way to picture it is, take a normal syringe, suck some air into it, put your thumbs over the end and push the plunger - you'll see how compressible that air is. Draw that same syringe full of water, have a go and you'll see it is difficult to compress. Because the crab is also contained in a shell, there is very little internal pressure differential when it is brought up, so it survives. If you learn how to scuba dive, or know Boyle's law, you see how a small air bubble expands as it rises - the same thing happens in animals. A fish would explode, but because the crab doesn't have these gas pockets it is fine.
What are the most challenging animals you've ever been involved in shipping?
Tinus: Sho! Garden eels are quite sensitive - years ago we shipped some and that was nuts. They are tiny, you are looking at something that is about 15cm long with the thickness of a really big earthworm. We imported two species, Gorgasia preclara and Heteroconger hassi from Japan that had to go from Japan, via Singapore, have a stopover in Singapore, get reacclimatised and then flown here - little things that size cost US$125 each, without transport fees! They are mega-sensitive, and I worried about those because they were such a high risk and expensive fish to ship. Other challenges are always sharks because they need so much water, you are almost always looking at at least half a million rand just to ship a shark. You can't insure a live freight, which always increases the stress.
How do we stop diseases and parasites from the wild from affecting our animals?
Tersia: So, very importantly, we have a 30-day protocol where everything that comes from the ocean goes into quarantine for 30 days. They get a general treatment because we don't know what is on their gills or on the fish that might harm our healthy animals downstairs. Some animals, like the spider crabs, can't really go into the quarantine because they need a low water temperature - there is no chiller in the quarantine room, so we would treat them in their new exhibit. We've had black spots on our spider crabs before, they usually come out of the wild with them and we treat that with a disinfectant on a weekly basis until the spots heal.
How often do they moult?
Kaye: It depends on what study you read, some say annually, some say it depends on their growth rate. We just had two moulting in the past few weeks, and those were the first moults we saw in about two years. As they moult, they are very soft, so we put up a curtain to protect them from the other spider crabs which may injure them. They become very vulnerable.
Tinus: Because of the lower pressure in an exhibit, compared to the deep ocean, these crabs do experience more difficulty when moulting. I remember years ago when we got our first spider crabs there was a worldwide phenomenon where captive crabs were struggling to moult - they got stuck in their old shells and would die. I got into the tank with a scalpel and scissors to help remove as much of the shell as possible, and we never lost any more that way.
How did Tokyo Sealife Park originally catch them?
Tinus: As far as I know, they are caught as bycatch from lobster pots and demersal trawls. The guys at Tokyo Sealife Park go buy them from the fish market - they let the fishermen know they are looking for them, so when they get brought up, the small ones are kept alive on deck for the aquarium to collect. One thing that is very interesting is how the legs get tied up, apparently, there are people in the market that can truss up a crab in under two minutes, but Sealife's staff had to learn how to do that.
Why did we bring these animals all the way from Japan?
Tinus: If you look at "aliens" in the Aquarium, things that aren't found in South African waters, we do get the odd fish that is brought here purely for welfare purposes. But the two species we chose ourselves are the Amphiprion ocellaris, those western clownfish, because Finding Nemo as a movie did so much good for conservation awareness. The only other species is the spider crab - something so unusual and massive is just awesome, a perfect ocean ambassador. When you ask people a few months after their visit which animals they remember, it is normally the Nemo tank and the spider crabs in their top five.
What are some of the unique challenges of working with spider crabs?
Kevin: They are delicate - surprisingly delicate! They can pull each other's arms and legs off, especially after moulting, so you always need to be on the lookout for that. They look strong and armoured, but they need to be handled with care.
Kaye: Patience! You have to practice patience because everything they do is slow. Daily tasks involve cleaning their tank, dosing their tank with bicarb to help their shells stay strong. And then Monday, Wednesday and Friday it's feeding, making sure each spider crab gets some white mussel or prawn - they usually eat about two each. They might look clumsy trying to open a mussel shell, but they always get it right. Spider crabs are so, so strong.
What did it feel like to hold such a unique animal in your hands?
Kevin: At that stage, I was so cold! But no, obviously that's why we work here, we get to do things with animals that most people would never get to do in their lives. Holding an animal that big in your hands, you've got to remember that they are still small - you can only imagine what it would be like to hold them if they were a fully grown adult - they grow up to 4m or something close. It's something different, it's special.
Have you ever been pinched by a spider crab? How was it?
Kaye: No, no, no I'm too cautious for that. But Tersia has.
Kevin: No never, but Tersia was pinched.
Tersia: Sho, ok, I don't know what I can compare it to. It's definitely a lot more sore than being clipped by a peg! It's quite painful, they hold on and don't let go. They can draw blood, but luckily that didn't happen to me! Tinus also got pinched.
Thank you Tinus, Kaye, Kevin and Tersia for your time and giving us some insight into the thought, passion and care needed to take care of these majestic animals!