Swimmers share sea with Salps

Wainui Beach: New Zealand beaches can turn at times into a bubble tea of salp. Picture by Kevin Weatherley

Some of the region’s beachgoers found themselves swimming in what felt like a sea of gelatinous bubble tea at the weekend. Sarah Curtis investigates . . .

While many feared the weird gelatinous globules bobbing all around them might have been jellyfish, a biologist with the National Institute of Water and Atmosphere Research (NIWA) Dr Svenja Halfter has confirmed the creatures were salps – a totally harmless type of plankton that don’t sting or bite.

“Salps are common around New Zealand, especially in the summer,” Dr Halfter said. “Warm waters and lots of algae to feast on make perfect conditions for a bloom. Because salps can reproduce asexually (basically cloning), they can become abundant very quickly if the conditions are right.”

Dr Halfter said depending on food availability, temperatures, and currents, the salps were expected to be around for another few weeks.

And if they were at one beach in the region, they were often at others.

According to online sources, salps are related to us — more closely so than jellyfish. Salps are in fact the most closely related to us of all plankton. The largest known solitary species of them even has a very human-like name — Thetys Vagina.

Salps — sometimes colloquially called sea grapes or ocean jellybeans — are a member of the Tunicata, a group of animals also known as sea squirts. Their clear, almost invisible bodies are a modification evolved so they can live among other plankton, but avoid predation.

You’ll no doubt feel them in the water before you see them. They’re often only visible by a small clump of food in their see-through stomach.

Shaped like small barrels, they propel themselves through the sea using a band of muscles to pump water through their feeding filter, capturing any particles in it, before ejecting it from a second siphon at the other end of their body.

They have a complex gender-fluid life cycle with some species banding together at times in chains — like a necklace made of transparent glass beads.

They’re 97 percent sea water, so it’s highly unlikely anything bad would happen should a swimmer accidentally swallow some. If it did, it would likely be linked to a harmful algal bloom consumed by the salp, and not the salps themselves.

They’re not strong swimmers and are probably too large to find their way into most human orifices. That said, they’re pretty gross to walk or lie on in wet sand and not the most pleasant thing to share the sea with — unless you like the feeling of swimming in bubble tea or gelatinous soup.

There are 45 species of salps worldwide. They live in every ocean except the Arctic, with the highest density found in the Southern Ocean.

New Zealand has many salps, and they seem to be common on the East Coast of Australia as well.

It takes a combination of oceanographic conditions for them to swarm, but research shows that during a swarm they can cover an area up to 100,000 square kms, with more than 5000 individuals per m3.

Sometimes warm water might bring species down from Australia. Other times phytoplankton blooms lead to salp blooms on the East Coast of New Zealand. They are basically everywhere in our waters, just not all the time.

Although they look simple in structure and don’t have a “brain”, they are still sentient beings — that is, they can still feel things, albeit via a more primitive nervous system than in animals with a brain.

They are fragile and will die quite rapidly if roughly handled or removed from the sea. Often seen in glistening lines as they wash up on the beach along the high tide mark, they lose their transparency and become more opaque as they die. Many also die when they break off a chain.

Their relationship to humans (through virtue of a bony spine-like structure) isn’t the only surprising thing about them. They also play an important role in the ocean, with a pooper-scooper role so important to the marine environment that experts call them the “vacuum cleaners of the sea”.

Salps reproduce asexually and can grow so fast that they reach maturity in 48 hours. They are thought to be the fastest growing multicellular animal on Earth, increasing their body length by up to 10 percent per hour. This quick turnaround time enables salps to take advantage of algal blooms, increasing their population size rapidly when there is a sudden abundance of food. Because of this, salps are very important for cycling nutrients through the different depth zones of the ocean. Many fin fish we love to eat in New Zealand — blue warehou, silver warehou — feed on salps.

Salp poop sinks rapidly — up to 1000 metres deep in a day — therefore transferring carbon faster than most other sea creatures. And when the salp dies, its body also sinks rapidly, sending even more carbon to the ocean depths.

According to a study published last year, salps, jellyfish and other gelatinous creatures such as comb jellies remove up to an estimated 6.8 billion tonnes of carbon each year from seas around the world. Of that, some 2bn tonnes of the carbon is thought to fall to the seafloor where it stays locked up and can’t contribute to global warming.

Salps remain largely unappreciated, but they play an outsized, powerhouse role in curbing climate change.

Since salps and other short-lived but abundant organisms can’t be protected in the way that large megafauna can, it’s important we protect the marine environment they live in.

While the salp concentration is very high, they can clog fisheries nets, but they are more of a nuisance than being really harmful.

Apart from clogging the occasional fishing net, salps don’t pose any risk to any kind of infrastructure in New Zealand. However, overseas they have at times caused nuclear power companies to temporarily shut down their reactors.

Such was the case in April 2012, when a giant swarm of salp clogged intake screens used to keep marine life out of the seawater that cools the Pacific Gas and Electric Co’s nuclear reactor at its Diablo Canyon power plant on the central California coast. There have also been similar reports in South Korea and Sweden.