I was back in Lanzarote to conduct an underwater photography workshop, but also to shoot design images for the INON UK Level Two creative lighting course. My brief had been to obtain images of a diver using natural light at regular intervals from the surface to 20m. Cruz Yago Gonzalez, of Native Diving, agreed to be my model. We chose Puerto del Carmen as the location of the dive, purely for the calm waters and easy shore entry. We decided we should surface swim out to the entrance of the bay, then descend down in stages to the sandy bottom at 20m, whereby a friendly grouper called Felix, usually waited, being, hopefully, a different kind of model for another exercise for the course.
As we swam out, I remarked to Cruz the water seemed so much colder than my previous visit in November. The sea temperature then had been 20 degrees C, however, my dive computer was showing the surface temperature at only 18 degrees C, although it seemed to me much colder due to the wind from the North. As we descended just below the surface, I took a photo of Cruz, then we sunk down to 5m to take another image. Sinking down again to 10m, I became aware of what I 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 signaled haphazardly to Cruz if 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 on with the risk of getting stung. I looked below me to see several divers swimming towards the shore, but figured, they were at 20m and probably just finishing their dive.
They all seemed to be ok, so I decided we should continue.
Clicking off a few images for identification purposes, I then proceeded to get 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 I was covered head to toe in neoprene, with only a small area of my face left unprotected. I was absolutely sure they were some deadly swarm of jellyfish.
As soon as we surfaced, I asked Cruz what they were and if they stung. She said she didn’t know and had only seen them once or twice before, many years ago, when the water temperatures were colder than normal, as they were now. She told me when she had seen them then they had appeared suddenly, but in not so many numbers as now, and disappeared again after only a couple of days just as quickly and mysteriously as they had appeared. When we returned to the dive centre, we asked the other staff in the dive centre whether they knew what the creatures were. Petra Van Borm told me they were, in fact, 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 thought they were Salpas Thomsoni tunicates. Jose, the owner of Native Diving, told me 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 Salpa Thompsoni 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. They belong to the tunicate family and live for less than one year. The are indiscriminate filter feeders and collect food particles of varying sizes ranging from the tiniest plankton to small fish. Because of this ability to eat different sized organisms, this makes these filter feeders particularly hardy and able to survive where other filter feeders can not. It is like the human equivalent of being able to consume a sausage to a cow in one go. Salps capture food particles with an internal mucus filter net. It was previously thought that the smaller particles would escape, however, in studies it was found around 80% of the food actually captured and filtered were made of the tiniest organisms. This explains how salps can survive in the open ocean environments where others can’t. Most significantly, though, this affects the salps ability to perform carbon cycling to a great scale. The process of filtering starts with the mesh made of fine fibers inside the salp’s translucent and hollow body. As a salp pulses rhythmically, it draws in seawater containing organisms through an opening at the front end. As the food is captured by the mesh, it is then rolled into a strand then proceeds to the salps 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, which are heavier and sink more quickly thereby taking more carbon from the surface and sinking it to the bottom of the ocean quicker. The more carbon that sinks to the bottom of the ocean, the more space there is for the upper ocean to accumulate carbon, hence limiting the amount that rises into the atmosphere as Co2. Although thought to be very rare due to the fact they are hardly even seen, it is now thought they 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, as they are unable to use ice algae as a food source. The huge, long chains I had seen were where the salps were 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 consists 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 seem in colder, Antarctic waters, where the water is less productive in terms of food.
In Lanzarote, although 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 the fine sand particles in Lanzarote to enter the water column. I saw many salps laying on the sandy bottom, seemingly weighted down by ingested sand. Jamie Watts, marine biologist, a regular expedition leader in the Antarctic, told me he had never seen these tunicates in such long chains. Over the next 6 days we dived in several locations in Lanzarote. We saw the tunicates again on day 4 when we dived Puerto Del Carmen again, but didn’t spot them on another other dive sites around the island. When we dived Puerto Del Carmen on the 6th day, it was as if they had magically disappeared. There wasn’t a single 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. Having cooler sea and air temperatures than normal, with a cold wind and unusual rain, this could explain why the salps turned up in Lanzarote. So, whilst I was complaining that my sun tan wouldn’t be topped up, I found a hidden treasure in the form of an eco tunicate.