The Window of the Universe
Diversity of the Sea
at Yumeshima
The world of small organisms
in the water right in front of the site
Looking closely at the water collected from the sea facing the Expo site,
you can find some tiny things moving inside.
With a microscope, you can see various plankton swimming inside the water,
probably far more than you could imagine.
Exhibition Contents
Characteristic plankton are found in the sea around Yumeshima. Here, let's introduce some zooplankton that move uniquely. In the venue, you can also see the images of phytoplankton like diatoms with various different shapes and colors on a wide screen.
Penilia avirostris
Penilia avirostris belongs to Sididae, the only family including both freshwater and marine species. As the Japanese name suggests, its shell is exceptionally thin among all water fleas, and its body looks transparent in water.
Podon polyphemoides
As the Japanese name suggests, it has a notably large eye, which takes up most of its head. You can clearly see ommatidium that make up the compound eye.
Synchaeta sp.
Most cladocera and rotifera live in freshwater, and there are only a few species that live in the ocean. Synchaeta is a soft rotifer without a shell. The organs on the side of its head are called "ears," but they are not hearing organs.
Brachionus plicatilis
It is a representative species of marine rotifer, and is widely used as a food for fish cultivation. This species includes several species that cannot be identified only by their appearance (cryptic species). Many brachionidae live in freshwater.
Acartiidae
Copepods may be one of the most abundant multicellular organisms on Earth, with more than 10,000 species reported. Its Japanese name "kai" means the oar of a ship. It has legs that look and function like an oar.
Zoea larva of crab
Crabs, the representative organisms found on shores and beaches, also spend their larval stage as plankton. After the zoea stage, which looks like a shrimp, larval crabs develop into the megalopa stage, with a shape closer to an adult crab, developing a horizontally-long carapace and legs spreading out sideways.
Nauplius larva of Balanomorpha
Many aquatic organisms spend their larval stage as plankton even though adults become sessile or nektons. Some of the representative examples are balanomorpha, shellfish, crabs, and ragworms.
Veliger larva of Gastrooda
Shellfish begin to form a shell when developing from the trochophore larva into the veliger larva. It becomes clear at this stage whether the shellfish is the Gastoropoda or Bivalvia. The parts moving in the movie are cilia, which will be lost in the adult. They swim in the water with these cilia.
Ragworm larvae
The hatched larva of ragworms float in the water in a ball-like form called the trochophore larva. Starting with such a form, its rear grows long and forms segments. This image is a stage during development into the nextchaeta larva.
Nectochaeta larva of Phyllodocidae
The ragworm belongs to the Annelida and has a long body as an adult, like the earthworm. However, it spends its larval stage as plankton. Various ragworms living around Yumeshima, and their larva also take a different morphology depending on the species.
Müller's larva of Polycladida
Polycladida belongs to the Turbellaria. Its cilia move in a swirling motion and can be found from this larval stage, which can also be seen in this movie.
Obelia sp.
Obelia, one of the genera of jellyfish, has a flat bell, and its movement can be seen clearly with a microscope. Many jellyfish species spend their entire life as plankton. Nemopilema nomurai is one of the largest plankton.
Oikopleuridae
Oikopleuridae belongs to the Urochordata, meaning in Japanese that it has a notochord, which is a primitive form of spine, in its tail. Urochordata is the invertebrate that is the closest to a vertebrate. In the movie, the structure rotating like a toothed gear inside is a gill.
Ciliate
The ciliate is one of the major plankton living in the ocean. It has long cilia not only on the edge of its body, but also vertically.
Back Story
Natural environment of Yumeshima
Yumeshima, the Expo site, is an artificial island originally used as a final waste disposal site. However, after more than 30 years from its creation, it is now a place with abundant nature, where not only small organisms but also various birds and insects live. In particular, the birds are diverse. There are 13 species of geese/ducks, and 30 species of shorebirds found in spring and 37 species of it in autumn. There are also some endangered species here. For instance, Ruppia maritima, a plant detected as "extinct" on the Red List of Osaka Prefecture, was rediscovered in the marsh on the island. Yumeshima was designated as Rank A in terms of the biodiversity hot spot of in the Red List of Osaka Prefecture in 2014, and it is considered as a particularly important place for the preservation of biodiversity.
Diversity of small organisms
These small organisms that cannot be observed in detail without a microscope actually have an important role in supporting the biosphere of the Earth. For example, the oxygen produced by phytoplankton living in water accounts for about half of the oxygen existing on Earth. Also, bacteria and fungi, which are even smaller, are the key players in maintaining the biogeochemical cycles by decomposing the organic matter in the water.
The food web starting from phytoplankton to zooplankton, and further on to larger fish and animals, has such a large scale that it may also affect the terrestrial ecosystem, including humans. If the activity of phytoplankton were to stop, life activity all over the earth would also stop working. If zooplankton were to disappear, fish and large aquatic animals would lose their access to phytoplankton and their nutrient source, and humans would be unable to utilize aquatic resources. In this way, the diversity of such small organisms support the macro biosphere of the entire planet, including humans.
