The blue sea creatures washing up on Southern California beaches are blue button jellyfish, also known as Porpita porpita. These jellyfish are native to the Pacific Ocean and are found in warm, tropical waters. They are a type of hydrozoan, which are a group of animals that includes jellyfish, corals, and sea anemones.

Blue button jellyfish have a small, round body that is about the size of a grape. Their body is blue and they have a long, trailing tail. They do not have tentacles, but they do have stinging cells that they use to capture prey. Blue button jellyfish are predators and they feed on small plankton.

Blue button jellyfish are not typically dangerous to humans, but they can cause a mild sting if they come into contact with skin. The sting is usually not serious and will go away on its own.

Blue button jellyfish are often found in large numbers, and they can sometimes form blooms. Blooms occur when there is a sudden increase in the population of jellyfish. Blooms of blue button jellyfish can be caused by a variety of factors, such as changes in water temperature or the availability of food.

Blue button jellyfish are not a new species, but they have become more common in Southern California in recent years. This is likely due to a combination of factors, such as climate change, pollution, and the overfishing of their predators.