Updated: Sep 24, 2019
August. Thirty-seven degrees Celsius. The heat is unbearable. One week of a hot summer on the beautiful Croatian coast is a great idea to live this through! Despite densely populated camp in a sort of a pine tree forest right on the seaside, I was still able to find a spot for myself on the rocky beach and enjoy the days with a refreshing wind and the sea cooling me down with splashes. I love the feeling of the salt on my skin as much as I love to inhale the smell of the sea or fall asleep at midday on a warm stone with gentle music of waves in my ears. Cozy, quiet, perfect.
On the last day, as I was super comfortable in my laziness trying to live the last hours to its best, we were surprised by some big medusas that appeared to be everywhere. What a summer hit! I remember people on the beach pointing into the water, some frantically looking around being unsure whether the water was safe or not. I knew what this Medusa was and I knew the water was safe. More than that, I wanted to meet the visitor and confront him "face to face". With eagerness, I grabbed my camera already packed in the underwater equipment and rushed into the water. As soon as I dunked myself in, I stumbled at some jelly-like »aliens« that could fit into my palm, glittering and drifting around all over. I felt like I was standing in a slowly dissolving gelatine. While I tried to swim away from the shore I needed to fight my way through these jellied, almost transparent floaters. Gently, I would shift them to the side and be astonished by the impulsing little creatures. But I was in a rush to see the big Medusa.
Gliding through the water toward a foggy appearance in the distance, suddenly a dancing beauty greets my curiosity. A jellyfish the size of a basketball with a funny egg-like umbrella and bushy tentacles that resemble a leaf cabbage is a strange marine cnidarian that gives one unforgettably beautiful memories. Right under the surface, being penetrated by the soft sun rays, it is elegantly tilting from one side to another seemingly enjoying the sunbath. A Fried-egg jellyfish (Cotilorhyza tuberculata) is a common inhabitant in the Mediterranian sea and can appear in masses. I was witnessing a "jellyfish bloom".
Cotilorhyza is a true jellyfish (Class: Scyphozoa), belonging to a phylum Cnidaria. In this taxa, it shares its place with box jellyfish (Cubazoa), hydrozoans (Hydrozoa), stalked jellyfish (Staurozoa) and sea anemones with corals (Anthozoa). It conquers the Mediterranean sea and paddles around with eight brittle, short and fused oral arms, also called moutharms, each of them branching several times.
What all cnidarians have in common are cnidocytes. The animals use these so-called "nettle cells" like a harpoon to catch prey. Cotilorhyza is equipped with a subversion called nematocytes to inject her planktonic prey with venom, before ingesting it, however, it is harmless to humans.
Her sting on us has very little or no effect at all.
Like some cnidarians, the Fried-egg jellyfish is in a life long relationship with another organism, called zooxanthellae. While the medusa gives this symbiotic, photosynthetic algae carbon dioxide and shelter with access to sunlight, they provide the animal with energy, like fatty acids for their growth, metabolism, and reproduction. The role of zooxanthellae is so crucial for Cotilorhyza's life that without it the process of strobilation, where the end of a young polyp metamorphoses into a disc-like ephyra (medusa larvae), would not be triggered and therefore, no medusas would be born.
Summer is their mating season when male medusas release sperm packages, called spermatozeugmata from their consequently completely white moutharms into the water and the females, with brood-caring filaments then suck them up through their moutharms. The sperm travels up to the gonads and fertilizes the eggs inside of the female right under her dome. When the swimming, mature planulae develop they are released into the water to find a suitable place where they settle and grow into a polyp. Each polyp will go through a process of budding and strobilation, building a single bud and releasing only one larva (ephyrae) that will grow into a medusa. This yearly life cycle, therefore, includes a pelagic sexually dimorphic phase, because the males and females can be distinguished, and a benthic asexual phase, where attached polyps reside.
Slowly, I approach the animal until I find myself very close to it but do not want to disturb it by touching. I admire its beauty and study every detail that my eyes can reach. Its subtle, thick, white arms strike in a rhythm like a heartbeat and dense blue and purple tips just color the sea like a bouquet of violets and daisies. As I walk my eyes over its jelly structure discovering all the fascinating features and trying to make sense of the egg-like appearance, something very curious catches my attention. Something unexpected and mysterious. I am being watched! Hiding inside of the jellyfish, being exposed and covered again by the rhythmical swinging of the umbrella, now you see them now you don’t! Their big, dark eyes and silver bodies fill out the windows between the adjacent arms and it is almost impossible to count the many viewers that are looking at me. It’s a lovely surprise being noticed by the juvenile fish who live in this jellyfish housing. I can hardly resist my enthusiasm and feel my eyes widening in this pleasant wonderment as they may as well. We are all in awe of each other, staring.
This kind of symbiosis is well known. Many different kinds of fish can find a temporary home with Cotilorhyza but commonly one would find mackerel juveniles. The Jellyfish is their refuge until they are big enough to leave and find a safe place somewhere between rocks on the benthos. Basically, they spend their early life traveling around seas inside of a jellyfish. What an adventure this must be!
Cotilorhyza is a well-known inhabitant in this sea of my vacation spot but this time it comes in the company of another. The almost invisible creatures and that strange obstacles on my way into the water are floating us by in a milky density. Along with their small, sparkling bodies my view turns into a gallery of beautiful colors, glitter, and gentle movements enveloped into the warmth of the sunlight.
Mnemiopsis leidyi, also known as a sea walnut or a comb jelly is a Ctenophore, native to the Atlantic ocean. Decades ago, it was smuggled into the Mediterranean sea by ballast water from ships where it doesn't have any natural predators for which reason it reproduces fast and easy. It feeds on zooplankton including fish eggs and a feast like that can threaten the fish populations, which makes fishermen very unhappy.
The small comb jelly is an intruder here, as we call him and recently it gained another human title, "a pest" for giving us economical troubles and "an invasive species" for being a challenge to its suddenly new environment that we threw him into. In Italy, this small creature was blamed for almost exterminating the sardines.
So, what are jellyfish, actually? When I ask the internet it gives me a few definitions that are quite similar: "A free-swimming, transparent, gelatinous marine animals.... umbrella-shaped body... tentacles... stings...". In science, the term Jellyfish normally stands for any member of Cnidaria with a medusa-phase. However, to some, any gelatinous creature that is found in the water is a "jellyfish". To keep things simple I will use the term "jellyfish" referring to plankton of Cnidarians, Ctenophores, and Chordata (including salps). And, before I continue, "plankton" stands for any organism in water that cannot swim against the current.
"Jellyfish blooms" are a natural pattern in the life of jellyfish
Jellyfish are players in many different shapes with several different traits. They are diverse. Hundreds of millions of years ago they went separate ways and developed a high growth rate and some complexities, like asexual reproduction allowing them to rapidly increase populations. The result of this process, therefore, is sudden "blooms" which is a natural pattern of their reproduction.
In the Mediterranean sea, they have been a frequent subject for over two decades now. Mostly they occur in the summer months strongly disturbing human activities and giving us financial troubles.
All over the world, these "blooms" have been reported causing a lot of damage to our economy. Threatening fishes, destroying fishing nets, and causing loss of harvest. Another critical issue that gives us headaches are clogged desalination plants as well as nuclear- and coal-fired power plants.
Due to the fact that availability of freshwater is the most critical issue for human health, industrial development, and national security worldwide, one incident where jellyfish clogged the desalination plant which led to a water reduction by 50% for several days is a serious issue.
For many countries, tourism is the main income and for many tourists, jellyfish are unattractive. They can sting and in rare cases even cause death. Box jellyfish are responsible for most deaths and injuries in the seas and are considered more dangerous than any other marine animal. Ironically, human activity in the seas is increasing and due to climate change, the seas are getting warmer toward the poles. Consequently, people will cross their paths with these animals more often and incidents will increase.
In all this "Jellyfish-blame" though, scientists speculate that the reason for current blooms could be human-made actions like overharvesting the seas, eutrophication (a process where too many nutrients are added into water), bringing non-native species into new environments, and climate change. Seemingly, we are the ones causing all these troubles and we are in need of a solution.
In order to find the best solutions to our problems with nature, we need to understand it first.
Ecosystem services describe an interaction of ecological, social and economic processes and are involved in fulfilling our needs and at the same time preserving a well functioning ecosystem. According to MA (Millenium Ecosystem Assessment, 2005), Jellyfish provide several ecosystem services in four different categories.
To our most critical problem of climate change, they contribute the most with regulating services in a process of carbon sequestration, where they convert dissolved CO2 into organic carbon and sink it to the ocean bottom. Salps feed on plankton and pack it into dense fecal pellets that rapidly sink to the seabed. Along with jellyfish-falls (carcasses), they play an important role in carbon transfer from the surface.
Provisioning services stand for the resources in the ecosystem that provide us food, fiber, and fuel. Jellyfish have been harvested and consumed by China, Japan, and other countries for over 1700 years. In science, they are popular for the green fluorescence protein (GFP) which has revolutionized studies in cell- and molecular biology and venoms have been heavily studied in the hope of finding a way to treat different diseases in human medicine.
In supporting services jellyfish contribute to the primary production by sloppy feeding where the leftovers (like inorganic nutrients C, N, and P) of their meals become available to phytoplankton. By swimming between different layers in the water column, a process called biogenic mixing, they vertically transport nutrients to other organisms. As hosts, they provide different resources for many other animals, like shelter, food, transport, and a substrate. They are prey for hundreds of different species and also important predators for many others.
Marbled rock crabs (Pachygrapsus marmoratus) dining on the dead Cotilorhyza
Cultural services involve citizen science programmes that encourage the public to get involved. Whenever jellyfish are washed to the shore in masses the public is invited to count and identify the stranded animals on beaches. In aquaria jellyfish are an enormous attraction and more than that, they fascinate children which opens the window to education.
So, how do we handle jellyfish crowds? Adaptation management has been suggested that may help us out, however, it comes with higher costs.
To a minimal change in a region (low density), like destroyed nets and affected beach tourists, we would respond with "coping" by repairing nets, using educational programmes, monitoring jellyfish and providing the first-aid kit. To a moderate change in a region (moderate density), like clogged power plants, we would respond with "adaptation" strategy by using barriers for jellyfish removal. To a high density, we might need to respond with "transformation" by moving away from the traditional fishing ground, which would be the most expensive way out and the least favorite one.
Obviously, jellyfish contribute a lot to biodiversity and play an important role in the ecosystem. Their existence is closely connected to other organisms which are again connected to us. Can a world be without jellyfish? Clearly not. We definitely must find a way to coexist.
As the future will bring us more encounters with these animals it is very important for society to learn about them. Sadly, the media puts them into a very negative perspective which ends up to be the only information in our minds about these animals and consequently, fear is the only thing we have for them. It is crucial for us to understand the value of jellyfish in the ecosystem as well as to be aware of their contribution to human well-being.
The human perception of Jellyfish as a "pest" has built a strong lack of awareness in the value of these animals in nature.
They are extremely beneficial to us as to all inhabitants around us. We may have forgotten, but we completely depend on the natural world and its resources. We must learn to respect that and treat nature with care.
I am overwhelmed by the paddling creatures around me and just want to drift along. The current is our guide. They take me along the shore, so I follow in the rhythm of their strikes. It feels good to be with them and I feel we all belong there. After all, we are all Nature. With strong hope in me for a better Human, I let them be, waltzing on.
Further articles worth reading:
Hakai Magazine; In the Future, Jellyfish Slime Might Be the Solution to Microplastic Pollution
Hakai Magazine; How To Fix a Jellyfish Sting
Hakai Magazine; The Secret Social Life of Jellyfish