If you’ve been taking a chilly dip or walking along our Storm Bay beaches in Tasmania lately, you’d have seen lots of mysterious jelly-like sea creatures washed up or in the water. But what are they and why are they turning up here? Our Institute for Marine and Antarctic Studies (IMAS) zooplankton expert, Associate Professor Kerrie Swadling, explains.
Lots of jelly-like marine life has been washing up on our local beaches lately – from Coningham to Opossum Bay, and along the east coast near the Tasman Peninsula. You might have mistaken them for a type of jellyfish or their eggs, but they’re actually a species of zooplankton called salps. While they’re common visitors to our beaches, they don’t turn up every year.
Salps don’t have stinging cells like jellyfish, and they’re not dangerous. They are semi-transparent barrel-shaped animals made up mostly of seawater, with a brown spot (their guts) inside.
They may look like simple creatures, but they have muscle bands encircling their body which contract to propel them through the water. The seawater pumped through their bodies is strained through mesh filters, capturing algae and particles in the seawater.
After salp blooms like we’re seeing now, the water is often very clear because the salps have filtered out and eaten all the algae – so it’s the perfect time for a dive or a snorkel.
Chain of salps...
Salps have an interesting life cycle, known as an ‘alternation of generations’. The chain of salps is the aggregate phase of the life cycle, when individuals remain attached while swimming and feeding. Salps in chains start out as females and, if unfertilised, will transition into males as they age.
Each salp in the chain can reproduce sexually, with females fertilised by males in older chains. Each one grows an embryo that’s released into the water, which is the solitary, asexual phase.
When marine conditions are good as we’ve seen lately, the solitary salp buds off a new chain of aggregates that grow and complete the life cycle. This alternation of generations allows salps to have a fast generation time, with another local species being able to double its population in just 48 hours.
Salp blooms are usually short-lived. For example, the Salpa fusiformis currently flourishing in Storm Bay lives for up to 22 days. It can survive in temperatures from 14 to 22oC, but seems to peak at around 16.5oC. Under favourable conditions, this species can number up to 400 per cubic metre of water.
We know that, locally, salps are eaten by Blue Warehou (also called snotty trevally) and some seabirds. But because they leave behind no hard parts in the stomachs of predators, it’s difficult to know which animals eat them. DNA is helping us understand more about their predators.
Cover image: Salpa fusiformis
Credit: Katherine Baker