A salp a.k.a. “sea grape” or salpa, is a barrel-shaped, planktonic tunicate in the family Salpidae. It moves by contracting, thereby pumping water through its gelatinous body. The salp strains the pumped water through its internal feeding filters, feeding on phytoplankton. They can be seen at the surface, singly or in long, stringy colonies. Sometimes they form enormous swarms, often in deep water, and are sometimes even more abundant than krill. Salp populations appear to be increasing. A reason for the success of salps is how they respond to phytoplankton blooms. When food is plentiful, salps can quickly bud off clones, which graze on the phytoplankton and can grow at a rate which is probably faster than that of any other multicellular animal. When the phytoplankton is too dense, the salps can clog and sink to the bottom. During these blooms, beaches can become slimy with mats of salp bodies, and other planktonic species can experience fluctuations in their numbers due to competition with the salps. Sinking fecal pellets and bodies of salps carry carbon to the seafloor, and salps are abundant enough to have an effect on the ocean's biological pump. Consequently, large changes in their abundance or distribution may alter the ocean's carbon cycle, and potentially play a role in climate change. Although salps appear similar to jellyfish because of their simple body form and planktonic behavior, they are chordates, animals with dorsal nerve cords. They are harmless to humans even if there is a direct contact as you can see on this video.
Salps have a complex life cycle, with an obligatory alternation of generations. The solitary life history phase, also known as an oozooid, is a single, barrel-shaped animal that reproduces asexually by producing a chain of tens to hundreds of individuals, which are released from the parent at a small size. The chain of salps is the "aggregate" portion of the life cycle. The aggregate individuals are also known as blastozooids, remain attached together while swimming and feeding, and each individual grows in size. Each blastozooid in the chain reproduces sexually with a growing embryo oozooid attached to the body wall of the parent. The growing oozooids are eventually released from the parent blastozooids, and then continue to feed and grow as the solitary asexual phase, closing the life cycle of salps. The alternation of generations allows for a fast generation time, with both solitary individuals and aggregate chains living and feeding together in the sea. When phytoplankton is abundant, this rapid reproduction leads to fairly short-lived blooms of salps, which eventually filter out most of the phytoplankton. The bloom ends when enough food is no longer available to sustain the enormous population of salps. Occasionally, mushroom corals and those of the genus Heteropsammia are known to feed on salps during blooms. N:joy...