WHOA! JELLYFISH – EVERYWHERE! I was back in Lanzarote in the Canary Islands, in part to shoot design images for a creative lighting course.
My brief was to obtain images of a diver using natural light at regular intervals from the surface to 20m.
Cruz Yago Gonzalez of Native Diving had agreed to be my model. She and I chose Puerto del Carmen as the location of the dive, purely for the calm waters and easy shore entry.
We decided to surface-swim out to the entrance of the bay, then descend in stages to the sandy bottom at 20m, where a friendly grouper called Felix usually waited – a different kind of model, we hoped, for another exercise on the course.
As we swam out, I remarked to Cruz that the water seemed much colder than my previous visit in November.
The sea temperature then had been 20°C, but my computer was now showing the surface temperature at only 18°, and it seemed much colder than that because of the wind from the north.
As we sank just below the surface, I took a photo of Cruz, then we descended to 5m to take another. Moving down again to 10m, I became aware of what I at first thought were thousands of jellyfish pulsating around me.
Not only were there lots of individual translucent giant condom-looking creatures with eyes, there were also many chains of them strung together, some with only three or four, others with over 50.
I signalled haphazardly to Cruz, enquiring whether they would sting, but she just shrugged her shoulders.
OK, I thought, do we abandon the dive and get out of the water as quickly as possible, or continue with the risk of getting stung
I looked below to see several divers swimming towards the shore. I figured that they were at 20m and probably just finishing their dive.
They all seemed to be OK, so I decided that we should continue. Clicking off a few images for identification purposes, I got back on track with Cruz and the course.
ONCE WE GOT DOWN TO 20M, I could see many hundreds of individual jelly-like creatures lying on the sand, some still pulsating, others deflated and full of sand.
I had never, in all my 20 years of diving, seen anything like this spectacle!
Dodging and weaving around them, I managed to take the images needed, then we headed back to shore.
I considered myself lucky to be covered head to toe in neoprene, with only a small area of my face left unprotected. I was absolutely sure that we had encountered some deadly swarm of jellyfish.
As soon as we surfaced, I asked Cruz what they were and whether they stung. She said she didn’t know and had seen them only once or twice before, many years ago, when the water temperatures were colder than normal, as they were now.
She told me that when she had first seen them they had appeared suddenly, but not in such numbers as now, and they had disappeared again after only a couple of days, as quickly and mysteriously as they had appeared.
When we returned to the dive centre, we asked other staff whether they knew what the creatures were.
Petra Van Borm told me that they were not jellyfish, but free-floating tunicates called salps. She had seen them the previous day, and had tried to do some research on them. She believed that they were Salpas thomsoni tunicates.
Jose, the owner of Native Diving, told me that he had not seen this particular type before, but had seen giant pyrosomes, cylindrical or conical colonial tunicates made up of hundreds of thousands of individuals, most years in Lanzarote around this time of year
When the water was cooler, however, he had never seen these particular tunicates we had seen today.
THE SALPAS THOMSONI is regarded as one of the most efficient re-packagers of small particles, thereby playing a major role in the biogenic carbon cycle of the ocean.
Very little is known about its general ecology. It belongs to the tunicate family and lives for less than one year. It is an indiscriminate filter-feeder and collects food particles of varying sizes, ranging from the tiniest plankton to small fish.
The ability to eat different-sized organisms makes this filter-feeder particularly hardy and able to survive where other filter-feeders cannot. It is the human equivalent of being able to consume anything from a sausage to a cow in one go.
Salps capture food particles with an internal mucous filter net. It was previously thought that the smaller particles would escape, but studies have found that around 80% of the food is captured and filtered, down to the tiniest organisms. This explains how salps can survive in open ocean environments where other creatures cannot.
Most significantly, however, this attribute affects the salp’s ability to perform carbon cycling on a great scale.
The process of filtering starts with a mesh made of fine fibres inside the salp’s translucent and hollow body.
As it pulses rhythmically, it draws sea water containing organisms in through an opening at the front end.
The food is captured by the mesh and rolled into a strand that proceeds to the salp’s gut. Large faecal pellets are then formed and discarded.
Salps remove vast amounts of fixed carbon from the surface waters and bury them into the deep ocean via these fast -sinking pellets. Because of the differing sizes of food, salps are able to produce much larger pellets that are heavier and sink more quickly, thereby taking more carbon from the surface and sinking it to the bottom of the ocean more quickly.
The more carbon that sinks to the bottom of the ocean, the more space there is for the upper ocean to accumulate carbon, so limiting the amount that rises into the atmosphere as carbon dioxide.
Although thought to be very rare because they are hardly even seen, it is now thought that salps are becoming more abundant. They are known to have a circumpolar distribution, but are more typically found in the Southern Ocean around the Antarctic.
They have been recorded increasingly in higher latitudes, usually associated with warm water intrusions and following winters with relatively low sea-ice development, because they are unable to use ice algae as a food source.
The huge, long chains I had seen were the salps mating. They have a complex life-cycle with alternating sexual and asexual phases.
The sexual phase consists of forming a chain a colonies, whereas in the asexual phase the salps are solitary.
If conditions are favourable, which they obviously were in Lanzarote, salps can generate dense swarms in a very short period of time. In solitary form, they can grow to around 10cm. The chains can consist of up to 150 members.
Salps are unable to regulate their filtration rate. If there is too much to filter in the water, their mucous nets become clogged. This is why they are mostly seen in colder, Antarctic waters, which are less productive in terms of food.
In Lanzarote, though the temperature and conditions were suitable for the large aggregation, when the wind direction changed to the south the ocean whipped up the normally calm bay, causing fine sand particles to enter the water column.
I saw many salps lying on the sandy bottom, seemingly weighted down by ingested sand.
MARINE BIOLOGIST JAMIE WATTS, regularly in the Antarctic as an expedition leader, told me that he had never seen these tunicates in such long chains as I had seen.
Over the next six days we dived in several locations in Lanzarote. We saw the tunicates again on day four, when we dived Puerto Del Carmen again, but didn’t spot them at other dive-sites around the island.
When we dived Puerto Del Carmen on the sixth day, it was as if they had magically disappeared. There wasn’t a sign of the tunicates even having been in the ocean!
They had appeared in their thousands quite unexpectedly and suddenly, and disappeared just as unexpectedly and suddenly.
Cooler sea and air temperatures than normal, with a cold wind and unusual rain, could explain why the salps turned up in Lanzarote. So, while I was complaining that my sun-tan wouldn’t be topped up, I found a hidden treasure in the form of an eco tunicate.