SOLVING A BIOMECHANICAL MYSTERY: HOW JELLYFISH SWIM AND FEED IN THE PAST, BIOLOGISTS BELIEVED THAT ALL JELLYFISH PROPEL THEMSELVES FORWARD BY RAPIDLY SQUIRTING WATER OUT FROM THEIR PULSATING BELLS. HOWEVER, THIS THEORY DID NOT ENTIRELY MATCH UP WITH THEIR , OF THE ROGER WILLIAMS OBSERVATIONS. MARINE BIOLOGIST, DR SEAN COLIN UNIVERSITY IN THE US, USES A VARIETY OF TECHNIQUES TO SHOW THAT LARGER JELLYFISH USE COMPLETELY DIFFERENT MOTIONS TO SWIM AND FEED. HIS TEAM’S DISCOVERIES TELL US A LOT ABOUT THE LIVES OF THESE FASCINATING ANIMALS TALK LIKE A MARINE BIOLOGIST JELLYFISH – a group of primitive invertebrate animals from the PHYLUM – in biology, the level of classification that ranks above class phylum Cnidaria, which use pulsating, umbrella-shaped bells to move, and below kingdom and trailing tentacles armed with stinging cells to capture prey and evade predators SCUBA DIVING – an acronym that stands for ‘Self-Contained Underwater Breathing Apparatus’, which many biologists use to study CTENOPHORE – similarly primitive gelatinous invertebrates, which ocean ecosystems use fused cilia (called ctenes) to move and to draw prey to where they can be sensed and captured JET PROPULSION – when an object rapidly ejects a fluid in one direction, propelling itself in the opposite direction BIOMECHANICS – the study of the physical motions and structures used by living organisms ROWING PROPULSION – an alternative propulsion mechanism discovered by Sean and his team, where pulsating bells manipulate ECOLOGY – the study of the interactions of living organisms with pressure in the surrounding water each other and their surrounding habitat Among all of the creatures in our oceans, few propulsion. Previously, biologists thought that all as well as their wider roles in natural ecosystems. are more ancient or mysterious than jellyfish and jellyfish swam in this way. However, for animals However, because oceans are such complex and ctenophores. First appearing over 500 million with bells larger than 5 centimetres in diameter, intricate environments, the researchers could years ago, ctenophores swim through water by the water volumes they hold become far too not be sure that even their most well-designed waving tiny, hair-like protrusions on their cells, heavy for weak jellyfish muscles to expel them experiments were entirely realistic. named ‘cilia.’ Jellyfish, also called ‘jellies,’ evolved quickly. Dr Sean Colin at the Roger Williams at around the same time, but use completely University in Bristol, Rhode Island, US, was first Since then, Sean’s team has explored a variety different strategies to move around; in fact, they faced with this biomechanical mystery early on of different ways to improve observations. were the first animals to move using muscle- in his career and he has studied it extensively These have included cutting-edge techniques powered swimming. Incredibly, the muscle layer ever since. in SCUBA diving, and the use of remotely- they use to swim is just one cell thick, making operated submarines in deeper water – both them extremely weak. Because of this, jellies WHAT TECHNIQUES HAS SEAN’S of which have allowed the researchers to needed to evolve highly efficient ways to propel TEAM USED TO STUDY JELLIES AND accurately capture the behaviours of wild jellies themselves through water. CTENOPHORES? and ctenophores. They have even worked In their earliest studies, Sean and his colleagues with a team of engineers to design a robotic Today, all jellyfish do this by contracting their used video recordings to study how jellies and jellyfish. By tweaking the design of its bell to umbrella-shaped bells. In small jellies, this causes ctenophores in captivity interacted with water efficiently propel itself forwards, they could water to rapidly squirt out of the bell, generating and prey. Their aim was to study what types and learn a lot about the real biomechanics used by enough force for them to dart around using jet how much food these animals tend to consume, real jellyfish. © Irina K. - stock.adobe.com DR SEAN COLIN The Roger Williams University, Bristol, Rhode Island, USA FIELD OF RESEARCH Marine Biology RESEARCH PROJECT Sean’s research centres around the swimming and feeding habits of jellyfish and ctenophores. Through these different techniques, Sean’s have shown it to be one of the most efficient team has now made several ground- swimming mechanisms in the animal kingdom. breaking discoveries about the differences in FUNDER biomechanics between large and small jellies. WHAT DOES THIS TELL US ABOUT THE National Science Foundation DIFFERENCES IN FEEDING HABITS WHAT HAVE THE RESEARCHERS BETWEEN CTENOPHORES, AND LARGE DISCOVERED ABOUT JELLIES’ AND SMALL JELLIES? SWIMMING HABITS? Sean’s work has revealed that jellies use jetting Ctenophores may have evolved at around the The shapes of jellyfish bells can vary widely, and rowing for completely different processes. same time as jellyfish, but they use completely depending on their sizes. Small jellies have more For smaller animals with prolate bells, an different strategies to capture prey. By waving elongated, torpedo-shaped ‘prolate’ bells, which effective hunting strategy is to sit still inside the fused cilia on their bodies, they move water help them to jet quickly and efficiently through a nutritious water current, with their stinging slowly past their sensory structures. This allows water. In contrast, larger jellies have flatter, tentacles extended. When a predator comes them to scan the surrounding water and divert plate-shaped ‘oblate’ bells. As Sean’s team along, or if the current becomes depleted of any nutrients towards their tentacles. has discovered, these animals have evolved a food options, the jellyfish can then rapidly completely different way of moving around than dart away and reposition itself, allowing it to WHERE COULD THIS RESEARCH LEAD their smaller cousins. maximise the time spent feeding. This behaviour IN THE FUTURE? has had a big impact on the evolution of their Sean and his colleagues will now continue An oblate jellyfish will start this motion by tentacles: with the size and type of their to study the biomechanics of jellyfish and slowly contracting its bell. This causes the highly prey depending on the spacing between their ctenophores. They will focus on areas including flexible circular margin at the bottom of the bell tentacles, and the number and type of stinging how their shapes relate to their swimming and to suddenly bend and flair out, like the skirt of a cells they contain. feeding habits; their roles in ocean ecosystems; twirling dancer. This means that the margin acts and how SCUBA techniques can be used to like a flappy oar: pushing water away from the In contrast, oblate-shaped rowing jellies better study natural environments. outer edge of the bell, creating a large region are moving constantly. They use their own of negative pressure in front of the jellyfish. swimming motions to generate nutritious water Many areas of research could benefit from these Finally, the bell will move to compensate for currents, which they pull and circulate through discoveries. Since oblate jellyfish usually have far this pressure deficit, and the entire jellyfish is their tentacles. This means that the capture larger guts than their smaller cousins, they can propelled forwards. surfaces have a significant impact on how these consume far larger amounts of prey at a time. A jellies interact with the surrounding water. In better knowledge of their feeding habits could Sean and his colleagues have now dubbed this Semaeostomes (an order including Lion’s Mane help biologists to better assess their impacts on behaviour ‘rowing propulsion.’ As well as clearly and Sea Nettle jellyfish), long, frilly arms are fragile marine ecosystems, particularly when observing the process in wild jellies, they have used to capture large plankton and fish larvae. species are introduced to new areas. Elsewhere, also shown it to work in a robotic jellyfish – On the other hand, the order Rhizostomes, jellyfish and ctenophores could have a lot to which could only move forwards when a flexible, which include Cannonball and Barrel jellyfish, teach us about how swimming and flying first circular flap was added to its margin. The speed do not have tentacles at all. Instead, they use evolved in other, more complex animals, and it provides may be slow, but since the motion oral feeding disks featuring large clusters of cilia, how they manipulate the fluid surrounding them requires such little muscle power, the researchers allowing them to filter for far smaller prey. to move. © Josef Krcil. - stock.adobe.com ABOUT MARINE BIOLOGY As with other strands of environmental science, their work, each of these steps can be fun expertise. This increases their ability to answer what motivates those who work in the field of and rewarding. A job like Sean’s, for example, questions, ultimately making their work more marine biology is a passion for the natural world allows him to develop a diverse variety of productive and enjoyable. and the mysteries it holds, a desire to uncover skillsets, including teaching, SCUBA diving, its secrets and an unflinching commitment videography, computer analysis, and writing. WHAT ARE THE KEY ISSUES FACING to protect it. As Sean’s research shows, years THE NEXT GENERATION OF of meticulous research provide invaluable HOW IMPORTANT IS IT FOR MARINE MARINE BIOLOGISTS? insights into the oceans, their ecosystems and BIOLOGISTS TO COLLABORATE WITH We all know that, due to climate change, the fascinating creatures who inhabit them. EACH OTHER? Earth’s ecosystems are now transforming Perhaps most importantly, marine biologists – Since every researcher has their own unique rapidly – with every organism responding in and other environmental scientists – are at the way of seeing the world, collaborating with a different way. This can have far-reaching front line of effort to solve the many problems others as part of a team is an essential consequences for natural environments, now facing the natural world.