Photo by Georgina Jones/Sharon Albert Photo by Peter Southwood	Salps There are between 20 and 40 species of salps known world-wide, mostly in tropical and subtropical waters. They can have an immense effect on their environment, since they are known to be among the fastest growing of all animals outside of yeasts and bacteria. Some can eat their own weight in 24 hours. Biologists on the east coast of the United States talk of 'salp years' when the salp population increases by 1000 times over normal and the water clears because of the filter feeding action of the salps. The population feeds so voraciously that other species in the plankton can be reduced by two thirds and krill can't even reproduce because the salps eat so much of the available food. Salps are barrel-shaped with two openings to their bodies, oral and atrial. Water is pumped into the body by movement of muscle bands which run round the body perpendicular to the direction of water flow. The animals can move in either direction by regulating the valve action of the front and rear openings in a sort of jet propulsion. Swimming in salps is a remarkably multifunctional activity. As water is pumped through the body, the animal is able to use the water flow for acquiring chemosensory information about its environment, for gas exchange, for excretion, for sperm dispersal and, of course, for feeding. Inside the animal and supported by gill slits is a cone-shaped mucous net. Particles as small as 1mm are non-selectively filtered out of the inhaled water by being trapped in the net. The net is constantly moved to the gut region by the action of small hairs or cilia. It is also continually renewed. Salps produce a steady rain of faecal pellets, which sink rapidly and are known to transfer significant amounts of food to mid-water and deep-sea communities. Reproductively, salps have a pretty complex lifestyle, being both colonial and solitary and in alternating sexual and asexual reproduction. Colonial salps are produced from the asexual reproduction of a solitary individual, called an oozooid. These bud off long chains of individuals at different stages of development, which start off female and are then fertilised by older males in the chain. The embryo of the young is attached to the body wall of the parent and develops inside the parent's body. The juvenile eventually occupies the entire body of the parent before casting it off and going on as an oozooid to bud off yet more chains of new salps. It is easy to see just how their population growth is so rapid. Salps are eaten by a wide range of other animals, which is perhaps fortunate, since they might otherwise have already eaten all the plankton in the sea before suffering their own final population collapse. Jellyfish eat them, as do comb jellies, turtles, marine birds and many fishes, including the sunfish. They also act as travelling homes for several crustacean species and some fishes use them for food, brood space and transport. Salps are rare around the Peninsula since they are mainly open ocean creatures, and the ones we do see are normally damaged or dying. Identification of different species can be difficult even from good photographs, but distinguishing characteristics are usually concerned with the number and width of muscle bands, the connections between bands if any, and if the muscle bands are interrupted. Animals may lack bilateral symmetry or have trailing 'tails'. The photographs show a probable sighting of Salpa maxima which was spotted in False Bay in July. The reddish body inside the animals is the gut. The narrow muscle bands can be clearly seen in one of the photos, as can damage the colony has suffered bumping into rocks in the shallow water.
References: Thanks to Georgina Jones for this article. Invertebrate Zoology 7th edition, EE Ruppert, RS Fox and RD Barnes, 2004 Pacific Coast Pelagic Invertebrates, A guide to the common gelatinous animals, D Wrobel and C Mills, 2003 An Introduction to the Zooplankton of the Benguela Current Region, MJ Gibbons
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