We have seen quite a lot of mysterious, gelatinous, jellyfish-look-a-like small, almost translucent blobs wash up on beaches along the Kwa-Zulu Natal coastline and Mozambique this past week with some people speculating that these are mermaids tears. However, these little animals are quite incredible and known as salps.
Despite looking like a jellyfish, salps are taxonomically closer to humans than jellyfish. As larvae they have a thin flexible notochord similar to a backbone making them our closest living invertebrate relative. Salps also have internal organs and structures that jellyfish don’t have, such as a vascular system, a heart and a pharynx. There are more than 70 species of salps and they can be found in the ocean worldwide but are most abundant in the Southern Ocean which offers a lot of food to these fast growing animals.
They range in size from less than 1 cm to over 30 cm and are typically shaped like a barrel. Some refer to them as a bag of water with a stomach, but they are a lot more than that. They have contracting muscle bands around their bodies and when they contract these muscles water is pushed through their bodies which also pushes them through the water. This is one of the most efficient examples of jet propulsion in the animal kingdom. They use this technique not just to move around, but also to feed. They are non-selective filter feeders eating everything that gets trapped in their feeding filter through which they push water when they contract those muscles, said SAAMBR Executive Manager, Maryke Musson.
Salps thus can only eat when swimming around and generally eats mostly phytoplankton.
They have a very complex life cycle known as alteration of generations and have a solitary asexual stage and a colonial sexual stage. They start of as female, but eventually end up as male. They can mature within 48 hours and is thought to be the fastest growing multicellular animal on Earth, increasing their body length by 10% every hour when food is in abundance.
They can live between 2 weeks and a few months. They are also referred to as the ocean’s vacuum cleaner and are very important for cycling nutrients though the different depth zones of the ocean. As they move up and down through the ocean, often in very large colonies especially near algal blooms, they spread nutrients downwards to other ocean communities. They produce rather large faecal pellets (poops) that sink rapidly transporting carbon from the surface to the bottom of the ocean and thus leading to substantial net carbon sequestration impacting positively on the global carbon cycle.
Salps are an important food item to more than 200 marine species, including various species of fish, such as the sunfish and also sea turtles. Sea salps are edible! Apparently, they are more nutritious than jellyfish but still tastes mostly salty to us humans. They do not sting or hurt anything and are known as gentle plankton eaters. They are usually driven towards the beach by winds and ocean currents, usually corresponding to big phytoplankton blooms in the ocean. When there is an abundance of phytoplankton there is usually an abundance of sea salps.
These little creatures will reproduce to match the availability of their food source.
So, those little blobs in the ocean and sometimes on the beach are actually complex relatives positively impacting on the ocean’s biological pump playing a potentially important role in climate change, while having one of the strangest life cycles. The best thing of all is that many salps produce a beautiful blue glow visible in the dark from many meters away as they are among the most brightly bioluminescent pelagic organisms.