Jellyfish regularly wash up on the beaches of the Netherlands. Sometimes we see the tide line filled with the drill-like remains of compass jellyfish, ear jellyfish or cauliflower jellyfish and every now and then we are startled by giant specimens. The fishermen also regularly have their nets heavy with jellyfish. The animals are beautiful to see in the water, but they are troublesome in the nets. But what’s the matter in our waters that the jellyfish are getting so big? Are they dangerous, those big, slippery giant jellyfish?
A jellyfish that grows into giant jellyfish
- Jellyfish
- Giant jellyfish in the Netherlands
- Sea mushroom
- Types and stitches
- Fishermen suffer from giant jellyfish
- Plankton
- Soft winter
- Special features of the soap mushroom
- Reproduction
- Washing up of jellyfish
Jellyfish
A jellyfish on the beach looks flat, dirty and slippery. With a little luck, the colors and drawings of the animal can still be seen and that is part of its beauty. A swimming jellyfish is a joy to watch. He are creatures that move gracefully. They can be admired in aquariums: Ecomare on Texel, for example, has a jellyfish aquarium.
Giant jellyfish in the Netherlands
In mid-May 2014, Ecomare will publish a report about various finds of giant jellyfish. It sounds disturbing, as if the end of time is approaching and all the terrible things we have done to the earth are being repaid by the growth of monsters that haunt us. However, the explanation of the giant jellyfish is simple. The winter of 2013/2014 was mild (it was the second mildest winter in three hundred years), so many jellyfish survived the winter. They have grown nicely in the meantime, making them larger than usual in the spring of 2014.
Passed common jellyfish
The large jellyfish are called giant jellyfish, but they are not as gigantic as that name suggests. Most of the specimens we find on the beach are 12 inches, but the oversized specimens can reach 50 to 60 centimeters in diameter. The giants that were found in May 2014, on the Wadden Islands but also along the Dutch and Zeeland coasts, measured about 50 centimeters and weighed more than ten kilos.
Winter
It occasionally happens that jellyfish continue to grow. Jellyfish do not survive a cold winter, they all die and only the polyps survive. It only produces young jellyfish at the end of spring, which you see in the sea and on the beach in summer and which are not yet that big. The giants found in the spring of 2014 were sea mushrooms, also known as cauliflower jellyfish. The largest specimens found weighed 11 kilos.
A giant cauliflower jellyfish swims off the British coast in July 2019. It was 1.5 meters long. A diver saw him at Falmouth, South England. Like the other giant jellyfish, this is an animal that did not die in winter; it is one of 2018 that has continued to grow. This species also has weak stinging cells, which are harmless to humans.
Sea mushroom
The sea mushroom is the largest jellyfish that occurs in Dutch waters. This jellyfish species does not pose a danger to humans, because it has such weak stinging cells that they cannot penetrate human skin. The sea mushroom or cauliflower jellyfish is the light blue jellyfish with the dark blue brim on the cap and cauliflower-shaped catch arms, which are not tentacles. He doesn’t have one. They occur in the Mediterranean, Black Sea, Atlantic Ocean and the North Sea.
It feeds on plankton, which is filtered out of the water by the jellyfish with the thick lobed catch arms at the bottom. The genitals can be seen through the transparent hat. In male jellyfish they are blue-white and in females the sexual organs are brown-white. The jellyfish often suffers from parasites, such as jellyfish shrimp, that nibble on the jellyfish.
Types and stitches
Various jellyfish species occur in the North Sea and Wadden Sea: compass jellyfish, ear jellyfish, blue hair jellyfish, comb jellyfish, sea mushroom. A compass jellyfish is a nasty plug, but an ear jellyfish or sea mushroom are harmless to humans. The rib wall does not sting either, but the blue hair jellyfish does have long tentacles with nettle cells. So stay away and watch from a distance.
Fishermen suffer from giant jellyfish
Fishermen can also suffer from jellyfish. An abundance of jellyfish makes it just so heavy that it is sometimes difficult to bring in. In May 2014 the shrimp fishermen suffered from ear jellyfish. The cause of this massive presence of jellyfish is also sought in the mild weather of early spring.
Plankton
Jellyfish are counted as plankton, animals that have to let themselves be carried by the current. Swimming against the current is not beneficial for plankton and therefore for jellyfish. Jellyfish live on planktonic animals that in turn live on plankton plants, such as diatom.
Plankton peak
Plankton starts to grow as soon as the days get longer. Diatom is leading the way. As the days grow longer diatom grows. At one point, growth is so explosive that there is a lack of silica in the water. That is the moment when the diatoms die and that is also the moment of the first plankton peak. Animal plankton likes this and benefits from it and in turn grows explosively. That is bacon to the face of plankton-eating fish, such as herrings and sprats.
Soft winter
Normally, the jellyfish season starts after the first plankton peak. That means no abundance for the jellyfish. The winter of 2013/2014 was extremely mild, causing the jellyfish to develop earlier and fall with their noses in the plankton butter. The jellyfish could benefit from the plankton peak that spring. The sea is therefore full of well-fed ear jellyfish and overgrown sea mushrooms. Such a jellyfish peak never lasts long; within a few weeks it will be over. A second jellyfish peak in summer only occurs when there are unusual conditions, such as high water temperature, absence of natural enemies and living in closed systems such as the Veerse Meer. Then the jellyfish sometimes want to grow en masse in August.
Special features of the soap mushroom
The large jellyfish found on the beaches are of the sea mushroom or cauliflower jellyfish or Rhizostoma octopus. The jellyfish has a number of characteristics:
- It’s a disc jellyfish;
- it is a cnidarian;
- he has no real organs, no lungs, blood, or circulation;
- he has specialized tissue in epidermis, stomach and primitive nervous system;
- he has an incomplete digestive system, the mouth is also anus;
- it is eaten by tunas, sharks and sea turtles;
- they are passive floats that can move with swimming strokes;
- he has no eyes, but he perceives light and dark;
- he has a vestibular organ;
- there is jelly between two cell layers;
- he has eight arms, which are not tentacles, they do not sting;
- young fish can hide between the catch arms, young horse mackerel for example.
Reproduction
Jellyfish reproduction is very special. He is both sexual and asexual:
- There are male and female jellyfish. They release reproductive cells into the water;
- these cells meet in the water and fertilization takes place;
- this produces a polyp that attaches itself to a plant or shell;
- the polyp grows and forms saucers or caps that come off one after the other. These are young jellyfish;
- the jellyfish floats in the water and grows into a large jellyfish in a few months.
Washing up of jellyfish
On the beach you can often see jellyfish on the tide mark. They were washed up with the help of wind and current in the water. Jellyfish cannot swim, they float and carry on the current. With offshore wind, an undercurrent is created in an onshore direction. With this current, ailments floating near the coast can be carried to land and washed up on the beach.