Jellyfish are marine animals widespread in every sea and coast. Floating in the currents, they feed on small fish and crustaceans, which they catch thanks to their tentacles and mouth, armed with stinging cells. In turn, they are a source of food for many other species, including turtles and tuna, which are very fond of them.
Swimming among groups of iridescent jellyfish of IllusiOcean, you too can be enchanted by the extraordinary sight of this underwater world. A game of reflections, lights and shadows, where your gaze is lost in the endless abyss.
But all that glitters is not gold: among the bright umbrella-shaped bells, will you be able to identify the traces of the human threat?
Jellyfish belong to the Cnidarian phylum, which also includes corals. They are composed of 95-96% water and the main part of their body is the mesoglea, a gelatinous structure consisting of water and fibrous proteins, that supports them and allows them to move. In the upper part of their body we can find the umbrella, and below it the mouth, from which the oral arms branch off to capture and ingest prey. The tentacles start from the margin of the umbrella and come into action as an offensive or defensive mechanism, through an impulse which is sent by a receptor that communicates with a discharge system to release stinging organelles, called nematocysts. This process takes place with a pressure of about 140 atmospheres: 70 times that of a car tire!
Jellyfish also have a simple nervous system that includes rhopalia, which are sensory structures that can contain structures that are sensitive to chemical stimuli (chemoreceptors), light (ocelli) or that allow spatial orientation (statocyst).
Furthermore, the various species of jellyfish have different life cycles. In some species, after sexual reproduction there is an intermediate stage in which they are anchored to the substrate and generate larvae (ephyrae) asexually through the segmentation (strobilation) of a particular polyp, called scyphistoma, which presents a similar structure to that of the jellyfish, but upside down.
58 out of 370 million tons of plastic come from Europe. A massive production, determined by the characteristics of the plastic itself: a cheap, resistant and lightweight raw material, which is also very easy to produce.
However, once introduced in nature, plastic stays around for several decades, causing damage and breaking into tiny pieces, called microplastics.
Plankton, that include organisms over a wide range of sizes, provide a crucial source of food to many aquatic species. So for the marine fauna one of the main threats comes from the toxicity of plastic, which is a vehicle of harmful substances that accumulate in the organisms that ingest it.
It is quite common for predators to mistake plastic for the species they eat, such as jellyfish: a problem that concerns many turtles, natural predators of jellyfish. In fact, many of them were found with pieces of plastics in their organisms.
In recent years, researchers have conducted many studies on the pollution of the seas and the effects of this material on marine species. One of the latest problems has to do with the Covid-19 pandemic: if single-use face masks are not disposed of properly, they can have direct harmful effects on the environment, or release pollutants into it.
Venice and the Maldives: two geographically distant places with similar fragilities.
What do they have in common? They’re both places where life depends on the sea, historic docks and important centers of trade. Both are just a few meters above sea level, 80 cm for Venice and 1 m for the Maldives, and they’re also listed among the UNESCO protected sites. Moreover, they share a common threat: climate change.
Venice fights against sea level rise with MOSE and the restoration of the Venetian Lagoon environments, such as velme (lagoon beds uncovered at exceptional low tides) and barene (tabular terrain covered only at exceptional high tides), which deposit sediments, ensure water change and reduce swell.
Being prepared to face this challenge is crucial: just think that in the last 25 years there have occurred more high tides (greater than 110 cm) than in the previous 120 years.
If Venice is protected by an artificial structure, in the Maldives coral plays a similar role. Here the coral reefs form a natural barrier for the islands, reducing swells and mitigating exceptional high tide effects.
Moreover, there is a fragile balance between the growth of corals and the natural bioerosion of their skeletons, which form the local islands. Due to global warming, many corals have disappeared as natural reefs have been reduced. Today the government of the Maldives is developing climate change adaptation programs and is studying coral reef restoration methods, concerning on the one hand the artificial reinforcement of the coastline and, on the other, the creation of restoring coral reef programs, the protection of which is crucial in order to safeguard the country.