Featured Invertebrate Data
Mastigias papua is considered to be uncommon in the waters off Okinawa's main island, but at certain times of the year (notably mid-Summer) and locations it's commonly seen in great numbers.
The following information of Mastigias papua is taken from Wikipedia.
Mastigias papua, commonly called the spotted jelly or the lagoon jelly, is a jellyfish species living in the Indian and Pacific oceans. Like corals, sea anemones, and other sea jellies, it belongs to the phylum Cnidaria. Mastigias papua is one of the numerous marine animals living in symbiosis with zooxanthellae, a photosynthetic alga.
They have a lifespan of approximately 4 months and are active primarily in mid-summer to early autumn
General description The spotted jelly is so named because of the little dots that garnish its jelly. It usually measures between 3 and 10 cm in length and between 2 and 7 cm in diameter but some individuals can reach 30 cm long. Contrary to most medusozoans, Mastigias papua does not have stinging tentacles. However, some individuals may contain some rare cnidocytes spread on the arms of the animal but they are inoffensive because they have lost their stinging power.
Like all medusozoans, Mastigias papua is 95% composed of water. This water similar density enables it to easily float.
Alimentation Jellyfishes with stinging tentacles are usually hunters. Cnidocyte cells enable them to catch their preys before eating them. The spotted jelly has developed another way to feed itself; it lives in symbiosis with a unicellular photosynthetic organism called zooxanthellae. This unicellular organism settles in the tissue of jellyfishes. It provides products of photosynthesis to the jellyfish, and in return, the jellyfish provides it minerals and nutrients from the soil and the sea water.
In addition to this symbiosis, the spotted jelly has several small mouths used to grab animal plankton. These mouths are disposed all along its oral arms.
Habitat Spotted jellies have been recorded many times in the Indo-Pacific Ocean, between Japan and Australia. They live in shallow waters, and for this reason they are usually found in coastal and lagoonal waters, but also in marine lakes.
This species of jellyfish is well known for living in huge groups, forming aggregates. This atypical behaviour becomes a tourist attraction. The most famous spot to admire these organisms is the Ongeim’l Tketau Lake in Palau. This lake has been formed 15,000 years ago. Like many other lakes of this region, it was initially joined to the Pacific Ocean, and because of geological movements, the lake has progressively become separated from the rest of the ocean. Mastigias papua has therefore been isolated in this closed lake, with other species of medusa. Out of reach of predators, it has progressively lost its cnidocyte cells, and is therefore now totally harmless to scuba divers. The lake of Palau now counts around 10 million individuals of this species.
In general, medusozoans can adapt quickly to their environment, sometimes being the only living organisms colonizing particularly inhospitable places. Jellyfishes have poor needs in terms of chemical, physical and biological environmental factors. They can live in large ranges of temperature, pH, salt concentration, contamination level and therefore, they rapidly proliferate and invade their living environment creating jelly aggregates.
Many other jellyfishes have this aggregation behaviour. In fall 2013, because of a jellyfish proliferation, as much unexpected as impressive, a reactor of 1,450 MW of a nuclear central has been turned off for three complete days. This Swedish central of Oskarshamn was one of the numerous victims of jellyfish proliferation, which blocked the water pumps designed at cooling down the reactor.
Symbiosis with zooxanthellae The spotted jelly lives in trophic mutualism with a unicellular organism capable of photosynthesis: zooxanthella. This mutualism is based on a life cycle which permits an exchange of energy between the two species.
Mastigias papua has two different ways of life through 24 hours. During the day, it stays at the surface of the water, in the photic zone. The photic zone is located between the surface of the sea and approximately 100 meters deep. It corresponds to the zone where photosynthetic organisms can use sunlight as an energy source. The jellyfish swims almost 2 kilometres a day, following the sun, therefore allowing zooxanthellae living in its tissue to optimize their photosynthetic activity. Organic matter produced from this biochemical process is shared between the algae and its host. When the sun goes down, Mastigias papua gains deeper areas and zooxanthellae stop their photosynthetic activity. The jellyfish takes over the role of energy provider. It absorbs nutrients in the soil and stores them in its tissues. When the sun rises again, the jellyfish returns to the photic zone of and makes the absorbed nutrients available to the zooxanthellae.
There are numerous photographs and videos of Mastigias papua found on-line. The Monterey Bay Aquarium has a terrific still photo as well as a video (Jelly Cam), both on the same page.
In addition here are links to two YouTube videos:
I've added a second page w/ a series of images of the species.
In addition, I've added a link to the current and past featured invertebrates via a list and thumbnails.