Mangrove jelly fish (Cassiopea xamachana) is so called because it is mostly found in the roots of mangroves in the southern Gulf of Mexico, Caribbean, and other tropical waters. They are also called the Upside Down jellyfish because they tend to settle upside down in muddy and shallow waters. On first sight, they do not really resemble a jellyfish, instead looking more like a sea anemone, or a bluish green flower on the waterbed. However, this appearance also provides the jellyfish with very effective camouflage and protects it from likely predators.
The interesting aspect of the mangrove jellyfish is its symbiotic relationship with unicellular algae, known as zooxanthellae. This alga is photosynthetic in nature and uses sunlight to produce nutrition. This nutrition is then also absorbed by the jellyfish. The reason a mangrove jellyfish is always upside down and lives in shallow waters which are saturated with sunlight, is to allow give these algae, which reside in its body, access to ample sunlight, so that photosynthesis of food becomes possible.
However, the product of this process of photosynthesis is mainly carbon and does not fulfill all the nutritional requirements of the mangrove jellyfish. So, on the other hand, the mangrove jellyfish also excretes stinging cells in columns of mucus that rise above its body into the water column. The jellyfish catches it food, mostly plankton and zooplankton, when it gets paralyzed by these stinging cells. The mangrove jellyfish also have venom filled nematocysts on its tentacles for the same purpose of stinging its prey and then transporting it near the mouth for ingestion. You may be surprised to know that unlike other jellyfish, the mangrove jellyfish does not have only a single mouth. In fact, it has mutated to form a number of secondary mouths. The primary mouth reduces the food into tiny fragments, which are then ingested by these numerous secondary mouths.
Mangrove jellyfish are usually found in large swarms. Sightings of individual jellyfish are very rare. The entire swarm of mangrove jellyfish is usually settled at the bottom of the water, near the muddy surface of the waterbed. They only rise to the surface if there have been great disturbances in the water. When such disturbances do occur, they rise up to the surface, all together as one, stay afloat for a few moments, and then settle down back at the surface of the waterbed.
Another interesting aspect about the mangrove jellyfish is that they are crabs, who crawl on the surface of the waterbed; sometimes carry the mangrove jelly on their backs. They do this to essentially avoid being preyed upon by larger animals and use the sting of the jellyfish as their defense.
As far as humans are concerned, they are most likely to be caught up in the mucus columns in the water that contain stinging cells of the mangrove jellyfish. The stinging cells are slightly toxic in nature and can cause severe itching. However, if a human disturbs an entire swarm of mangrove jellyfish, they will all launch upwards towards the surface of the water together and release more stinging cells into the water. This situation can be vary dangerous to humans.