At the Two Oceans Aquarium, we care for some of the ocean's weirdest and most wonderful creatures - jellyfish. We chatted to Two Oceans Aquarium Aquarist Krish Lewis, our resident "jelly guy" about these incredible animals, answering your questions and revealing what it is like to work with these enigmatic animals every day. Let's find out what it takes to care for jellies:
Hi Krish, where did you get your passion for jellies?
Krish: I like things that are "limited edition". Not a lot of people work with jellies, especially in South Africa, so I'm one of the only people working hands-on with actual jellyfish rather than the genetics. I enjoy the fact that I get to figure things out, it racks my brain. Jellies are a challenge, and I enjoy finding a challenge, and that's probably why I love them.
Do you have a favourite jellyfish?
Krish: My favourite jellyfish is the Benguela compass jelly, Chrysaora fulgida, because since 1997 scientists have been trying to close the lifecycle (figuring out all its life stages and how to grow it into an adult jellyfish in the lab). I got to join that research team and in 2014 I got to be the one to close the lifecycle. I was over the moon!
A jellyfish I would love to see, which is found off our east coast, called Cephea cephea, or the crown jellyfish. It's this beautiful pink, ornate, weird-looking creature - it's gorgeous. And another one I would like to see is Labonema, which looks similar to the crown jellyfish, but looks like a mass of pulsing ribbons as it swims.
What's the best part of your Aquarium workday?
Krish: Seeing the jellies develop and grow. I need to check on them and feed them three or four times a day. That may sound boring, but sometimes when I come in the next day they've grown so much they look like a completely different animal from what I was working with the day before. Physically seeing those changes is so rewarding.
What do you feed the jellies?
Krish: They get Artemia at least thrice daily and rotifers twice a day. At least three times a week they get a smoothie to fill in any gaps in their diet. This is a mixture of seafood: hake roe, pilchards, prawns and white mussel. They are all deboned and shelled before blending because the jellies can't digest calcium carbonate. In addition to this, the jellyvorous species (the ones which eat other jellies), get fed one or two other jellies a day.
If they can't digest calcium carbonate, what happens to the bones if they eat a fish?
Krish: A jellyfish has gastric filaments that sit in its head next to its gonads. After it has digested the parts of the fish that it can absorb, it ejects the bones out of its mouth again. Its mouth is also its anus - you can refer to it as a "manus" if you are in a joking mood.
How long can a jelly survive without food?
Krish: If a jellyfish doesn't eat, it goes into degrowth. If you feed it enough it will grow until it reaches its optimal size, but if it doesn't eat it will use up its reserves and start to shrink. So to have the biggest, healthiest and prettiest jellyfish, we try to feed them constantly, as in the wild they would constantly be swimming around in the zooplankton.
What eats jellyfish?
Krish: Sunfish, sea turtles, some fish... The bearded goby (Sufflogobius bibarbatus) actually eats jellyfish that die and sink to the ocean floor beneath the Benguela Current, and of course, some jellyfish eat jellyfish.
There are also some European scientists and companies making jellyfish crisps by using ethanol to dehydrate jellies and turning them crispy. According to them, different alcohols give the jellyfish a different flavour. Lastly, in the East, they eat blue blubber jellies because of their smooth crunchy texture - they add them to ramen noodles and stuff.
What's your strangest jellyfish story?
Krish: That's definitely the pink meanie story. We collected Cape compass jellyfish (Chrysaora agulhensis) in False Bay, which needed to be fed live jellies for a while as they were wild caught and needed to heal the holes caused by parasites. I was on study leave one Friday, and Aquarist Bamanye Mpetsheni caught some wild jellies to feed to them and, unbeknown to him, he introduced a very rare species of jelly, which only occurs in very cold water on our coast.
So, when I came in on Monday, expecting to see six Cape compass jellies, there were only two left. I was like "Hrm, something is weird here", and when I looked closer I saw it was the pink meanie. I got super excited and I literally screamed "It's the unicorn of jellies!" People thought I was crazy. So by total fluke, we caught one of the world's rarest jellies.
How long do jellies live?
Krish: It depends on the kind of jellyfish. Normally they live between three and nine months, maybe a bit longer. But, there is a jellyfish that is considered immortal. Basically what happens is that if the jelly gets injured or if it "doesn't want to live as a jellyfish anymore", it turns back into a polyp - which is like an adult turning back into a baby.
The longest-lived jellyfish at the Aquarium have been the blue blubbers, which have been alive since their exhibit opened about three years ago. Our compass jellies live for about a year and a half and the moon jellies more than nine months.
Are you secretly trying to learn the jellyfish's secret to immortality?
Krish: No, I'm not, no I'm not. I'll leave that for someone else to do - that's a problem with a lot more sleepless nights!
How do you breed jellies at the Aquarium?
Krish: When a new species comes in we check if we have adult males and females by removing a small piece of their gonads. We look at this piece under the microscope to see if it has sperm or eggs, if it's male or female. We then mix the eggs and sperm together and let that brood for a few hours until we have planulae. When we have planulae, we transfer them to a glass container with filtered seawater and try to get them to settle on plates to form polyps. Once we have the polyps, we technically have that species of jellyfish at the Aquarium forever. When we have these polyps it takes a few months for us to figure out how to get them to strobilate efficiently, producing many ephyrae. And then it takes a few more months to figure out the ideal conditions for that jellyfish to grow.
How did such a weird animal evolve?
Krish: When animals are grouped on the phylogenetic tree, we look at them in terms of evolution. Jellies have muscles, which contract when an electrical current gets sent through them, propelling them through the water. But they do not have a mesoderm, which I mentioned in the show, which is the structure needed to develop a brain. So that means jellies are "pre-mesoderm", and even though they don't have a brain they can move and hunt for food actively, like box jellyfish do, and even sleep, like box and upside-down jellyfish do.
What are the main types of jellyfish?
Krish: Ok, so scyphozoans are "true jellyfish" - ones that look like a typical jellyfish. If you think about an umbrella with a handle, that's a scyphozoan jellyfish. They generally have tentacles around their bell, and they have singular polyps that can clone themselves over and over. Upside-down jellies are also scyphozoans, but they are in a group called rhizostomes which don't have tentacles around their bell, have eight lips and have thousands of tiny mouths on each lip instead of just a one central one.
Hydrozoan jellyfish don't generally follow the typical jellyfish body plan, they are often just a saucer shape, or like a weird blob or very glowy. There are some scyphozoans that can glow, but bioluminescence is usually associated with hydrozoans. Hydrozoan polyps are not singular, they form networks like train stations, where they are all interconnected. The polyps in the network all have different functions - some reproduce asexually to make jellyfish, some just eat and some just build up the network.
Cubomedusae are 'box jellies', they are shaped like little boxes. Even though they have no brain, they have very complex eyes and many of them have 360 vision. They can actually swim against the current, whereas hydro- and scyphozoans usually just drift. They use this ability to actually change direction if they see prey. They will actually chase after schools of fish, they can dodge and swim around obstacles like mangrove roots. Some of them can actually distinguish shapes, it's quite weird. In most cases, a polyp changes directly into a medusa without cloning, so their cultures don't last forever, which is why we don't yet breed them at the Aquarium.
Comb jellies are not jellies at all, they are Ctenophores, whereas actual jellies are all Cnidarians. They actually have a semi-rigid structure, like ribs, which hold their shape. These ribs also have microscopic cilia which help them move and refract light to give them beautiful rainbow colours. The other major difference is that they have a separate mouth and anus, not a combined one like jellyfish. Comb jellies also do not have any stinging cells at all.
Tell us more about their lips?
Krish: In true jellyfish, called scyphozoans, there are usually four lips, but some have eight, like the blue blubber jellyfish. These lips are formally called "oral arms" and they are basically conveyor belts of stinging cells and cilia that rub together to move food that was stung by the tentacles and umbrella up to the jellyfish's mouth.
Why are "jellyfish takeovers" happening?
Krish: Jellyfish are really cool in that they can live in environmental extremes that fish can't. So, jellyfish can live in environments where lots of fish have been removed, or where the environment has been polluted. That's why jellyfish fill environments where the animals are absent, but their food is still present, or serve as indicator species for when things go wrong for other animals in an ecosystem.
Thank you Krish for your time and giving us some insight into the thought, science and passion needed to take care of these weird and wonderful animals!