Introduction: A Surprising Sight in Cornish Waters
If you’ve been out on the water in Cornwall during the warmer months, you might have spotted something magical floating just beneath the surface. Salps are rare, flowing sea creatures that were frequently seen in large numbers in Cornwall last year.
These shimmering, translucent chains are often described as “gelatinous sea creatures” or, more appealingly, “fairy lights of the sea”! In this blog, we dive into the fascinating world of sea salps and what makes these bizarre jelly-like strings so extraordinary.
What Are Sea Salps?
Salps are marine invertebrates, meaning they lack a backbone, but have an outer exoskeleton made of cellulose. Along with other sea squirts, salps are classified under the subphylum of Tunicata and all possess dorsal nerve cords and notochords.
According to the World Register of Marine Species, salps are common with 42 described species of salp found worldwide. The most frequently type seen around Cornwall is the common salp (Salpa fusiformis). Salps can form chains that drift in the sea. They mostly feed on phytoplankton, but also anything small enough to be caught in their feeding net.
Appearance: Nature’s Oceanic Fairy Lights
Salps have transparent, barrel-shaped bodies made of cellulose and circular muscles. These muscles contract, pumping water rapidly through their tube-shaped bodies. This allows them to move through the water by jet propulsion.
Salps are elongated, with a rounded front, and a flat rear. Salps can occur in dense swarms, as solitary zooids, or as colonies. Solitary zooids usually measure between 22 and 52 millimetres in length.
Unique Characteristics of Salps
Salps are considered among the fastest growing multicellular animals on Earth., They are capable of increasing their body length by up to 10% per hour, and reach full maturity in just 48 hours.
Salps are members of a group known as “sea squirts”. As water is pumped through their bodies and out of their rear as sinking fecal pellets, food is collected and they are propelled forwards.
Adult salps undergo two distinct phases: an asexual oozoid phase and a sexual blastozooid phase. When the asexual oozoid is ready to reproduce, it generates long chains of salps, each a clone of itself.
These salps then further develop into sexually reproducing blastozooids. The initial chain will consist only of females producing eggs that are fertilised by nearby male blastozooids. These eggs develop internally, before being born as young. Eventually, the entire chain transitions into males that release sperm to fertilise the eggs of nearby female blastozooids.
Why Are Salps Appearing in Cornish Waters?
Salps are rarely seen around Cornwall, but when the conditions are right, salps can be seen in huge numbers. The right conditions will allow populations to reproduce and grow rapidly, causing huge blooms.
In 2024, there were reports of sightings across the west and south coasts of Cornwall. These sightings were likely driven by onshore winds, bringing salps into bays where they accumulate in large numbers.
Sightings could also be driven by ocean currents, water temperatures and environmental factors such as the number of predators. Salps are herbivores, so feed on vast quantities of phytoplankton, but this also makes salps easy prey for marine species such as jellyfish, turtles, seabirds, and fish.
Warming Waters
Salps can be found from 0 to 800 metres depth in the water column. They exhibit a vertical migration pattern, moving closer to the water’s surface at night, before returning to depth in the day. Research has suggested that water temperature influences this vertical migration, with an increase in water temperature causing an increase in metabolic rate (total energy turnover).
Salp distribution will be affected by climate change, and we expect large changes in their abundance as warmer waters create conditions where nutrients are abundant. That said, it is important to note that an excessive temperature increase could also disrupt salp lifecycles, or lead to conditions that cause local die-offs.
Changes in Currents
Salps are sensitive to changes in ocean currents as this can impact their behaviour, distribution, and survival.
Salps may be carried to different regions on drifting currents, away from specific feeding grounds. Salps’ feeding efficiency can also be altered by water movement. If there are changes in ocean currents, the availability and concentration of phytoplankton could shift, impacting their energy intake.
Alternatively, in areas of strong upwelling currents, where nutrient rich waters from the deep are brought to the surface, salp blooms may occur. This increase in salp production could adversely lower phytoplankton abundance, reducing the food available for salps.
Are Salps a Sign of Healthy Oceans?
While salps are not necessarily an indicator of ocean health, salp presence and behaviour can provide insights into the state of an ecosystem and the impact of climate change.
Salps carry carbon dioxide as they filter large volumes of water, and this plays a key role in fighting climate change. A swarm of salps contribute to the oceans’ carbon cycle and, spread over 38,000 square miles, can capture up to 4,000 tons of carbon dioxide in a single night!
By filter feeding, salps package waste into dense fecal pellets that rapidly sink into the depths. This process is known as carbon sequestration. On the other hand, salps can compete with other marine organisms for food, which can potentially play a role in disrupting the marine food web.
Sea Salps vs. Jellyfish: How to Tell Them Apart
Despite both salps and jellyfish being gelatinous creatures, there are some key differences to tell them apart.
- Feeding Unlike jellyfish, salps do not have stinging cells (nematocysts) that they use to capture prey and feed. Instead, salps feed by filtering everything they can catch in their feeding web, (internal nets of sticky mucus).
- Appearance Instead of the barrel-like body of the salp, jellyfish have a bell-shaped, umbrella-like body, with tentacles hanging from their rim. Jellyfish are often more colourful in comparison to salps.
- Size The size of salps and jellyfish also varies, with individual salps often only a few centimetres long, compared to jellyfish which can reach several metres in diameter.
Why You Should be Excited About Salp Sightings in Cornwall
Salp sightings in Cornwall are rare, often limited to a few each summer, making each encounter special. The unique appearance of salps makes them one of the more unusual marine creatures to see.
Salps can act as environmental indicators, providing information on any changes in ocean currents, water temperature, and plankton availability to help inform conservation management. Photographic opportunities for underwater photographers offer a unique subject to create stunning images.
Salp sightings also provide educational value in an opportunity to discuss the lesser-seen, smaller, marine species, highlighting the incredible diversity of life in the ocean, and the importance of protecting it.
What are Salps? Here Are Some FAQs
Q: Do salps sting or bite?
A: No, salps do not sting or bite, but mainly go about their business of filtering water to obtain food.
Q: Are salps a type of jellyfish?
A: Salps are not a type of jellyfish but in fact have a more similar evolutionary history to humans than jellyfish.
Q: Where are salps found?
A: Salps are widespread throughout the Pacific and Atlantic oceans.
Q: What species feed on salps?
A: At least 200 different species feed on salps, including fish, turtles, and seabirds.
Q: What to do if you spot salps?
A: If you encounter salps around Cornwall, share your sightings with ORKS
