Advanced detection equipment has no effect on jellyfish, so the investigation process of jellyfish by Chinese researchers is also difficult and tortuous.
Researchers can only take boats and go out to sea once every two months to study jellyfish using primitive methods such as naked eye observation and fishing with fishing nets.
It was in 2011 that Chinese researchers achieved significant results in their study of jellyfish.
On July 21, 2011, researchers set sail to investigate Jiaozhou Bay.
Jiaozhou Bay is located in the southern part of Shandong Peninsula. It is a fan-shaped bay with an area of 390 square kilometers. During that expedition, the researchers placed fishing nets at three points in Jiaozhou Bay.
After dropping the fishing net, the research ship moved forward. Every minute, four or five jellyfish appeared silently beside the ship, including the giant jellyfish and the huge sand jellyfish.
But whenever people use simple scoop nets to catch them, the jellyfish often slip away before the net gets close.
Although jellyfish do not have brains, their most sensitive sensory organs are distributed on the edges of the fans of each jellyfish. These sensory organs have the functions of both ears and eyes. Whenever there is a storm outside, they can sense the approaching threat through the infrasound in the sea water and escape early.
After three hours of hard work, the researchers pulled up two fishing nets, but the results were not satisfactory, as the nets only caught a few jellyfish.
The researchers were all very curious.
It was the fishing moratorium period, which is when the ocean should be most populated with fish, but not a single live fish was caught.
After investigation, researchers found that there were too many jellyfish in that sea area, which ate up all the eggs of local fish, causing a shortage of marine fish.
As for why there are so many jellyfish in that sea area, researchers explained that one reason is that humans overfished fish, causing the jellyfish larvae that were originally eaten by fish to escape the disaster, survive in large numbers and grow into adults.
Secondly, as the number of fish in Jiaozhou Bay decreases, there are fewer natural enemies competing with jellyfish for food, which provides an opportunity for jellyfish outbreaks.
When the third fishing net was caught, researchers found that the net was still filled with jellyfish and six large jelly-like objects.
Local fishermen said that they had not seen such a large jellyfish in the coastal waters for decades, which was shocking.
Ten years ago, large-scale fishing survey ships operated in the Yellow Sea and the East China Sea, and all they caught were marine fish, with jellyfish rarely seen.
That survey found that the three most common jellyfish species in my country's jellyfish outbreak were the moon jellyfish, the sand jellyfish and the cyan jellyfish.
"Brother Yang, are you sure these jellyfish are edible? I heard that they are very dangerous." Fang Youqun was lying on the side of the boat. He said the word "dangerous" but there was actually no fear in his eyes. He had no fear of jellyfish, which looked weak but were actually extremely terrifying.
"The danger is real. Jellyfish are one of the most ferocious carnivores in the world and one of the most toxic creatures in nature. But it is also true that they can be eaten. Now in many restaurants around the world, there are chefs who specialize in cooking jellyfish or sea cucumbers." Xiang Yang said with a smile.
"The outbreak of jellyfish is caused by overfishing which has reduced the number of jellyfish's natural enemies. But globally, some areas are not overfished. For example, in Antarctica where we are located, the climate is extremely cold and it is not a region with developed fishery resources. Yet there are signs of jellyfish outbreaks. This is really strange," thought Xia Pengjie on the side.
"I don't know about that. You have to ask the scientists who specialize in jellyfish." Xiang Yang said with a smile.
In fact, it is difficult for scientists to solve this problem.
With the continuous outbreak of jellyfish in recent years, many scientific research institutions and maritime universities have begun to pay attention to this creature.
Xiang Yang’s alma mater has a special major related to jellyfish.
In order to find out what other factors besides overfishing may cause jellyfish outbreaks, scientists have set up a laboratory that can control and simulate the marine environment, and selected the moon jellyfish, the most widely distributed jellyfish in the world's oceans, as the first batch of samples for breeding and observation.
The moon jellyfish has four ring-shaped stomachs. The reproductive glands are located below the umbrella and corresponding to the stomachs.
Usually, a pair of male and female jellyfish can produce 100,000 sperm and eggs. After fertilization in the water, the fertilized eggs sink to the bottom of the sea, find something hard to attach to, and develop into polyps.
The polyp is only two millimeters in size and is the larva of the moon jellyfish.
But scientists discovered under a microscope that the polyp has a strong predatory ability and can even catch a brine shrimp directly into its mouth.
According to relevant surveys, as long as polyps appear in a sea area, more than half of the zooplankton in the entire water area will be consumed by the polyps.
The appearance of polyps greatly reduces the food for fish and has a great impact on the overall ecological balance of the ocean.
"The most annoying thing about jellyfish is that they have no brains, do not know when they are hungry or full, and spend their entire lives eating. The food they eat is usually mainly plankton, supplemented by small fish and shrimps. Sometimes they even prey on their own kind. If jellyfish are allowed to become a disaster, the blow to the fishing industry will be absolutely devastating," said Xia Pengjie.
Xiang Yang nodded, "That's right. So now that we have encountered these stinging jellyfish, we have to find a way to salvage some of them even if it is thankless. Not to mention that these stinging jellyfish are edible and are quite expensive."
Xiang Yang once saw stinging jellyfish preying on moon jellyfish in the laboratory.
The usually beautiful and gentle stinging jellyfish is like a white-haired witch when eating. Its most powerful weapon is its tentacles. When it catches its prey, the hundreds of stinging cells in each tentacle will quickly penetrate the opponent's flesh and then immediately release venom, paralyzing the prey in a short moment, making the prey completely unconscious and helpless at the mercy of the stinging jellyfish.
Xiang Yang had witnessed with his own eyes the ferocious side of the seemingly gentle jellyfish, so Xiang Yang did not dare to underestimate these jellyfish at all.
Xiang Yang looked at the crew members who were already wearing protective clothing and said, "When jellyfish are feeding, they will first use their stinging cells to sting their prey to death, eat some of it, and more will sink to the bottom of the sea and be wasted. When you are fishing for jellyfish, you must not take off your protective clothing, understand?"
"Don't worry, Brother Yang, we promise not to let the jellyfish touch our skin." Fang Youqun said nonchalantly.
Xiang Yang frowned and said, "I'm not saying that you shouldn't encounter stinging jellyfish. I'm saying that you are not allowed to take off your protective clothing during the entire salvage process. The tentacles of stinging jellyfish can be up to 50 meters long, so its lethality is still strong at a distance of 50 meters. As long as you don't wear protective clothing, you will definitely get caught no matter how careful you are."