Friday, February 18, 2011

Red Sea Expedition: A remarkable chain of events

After a brief trip to freezing-cold Boston (brrrr), I'm now in Saudi Arabia, once again examining fish-coral interactions and continuing the work we started last year. I am once again grateful to be hosted by my colleague Dr. Michael Berumen, an Assistant Professor of Marine Science at KAUST, the King Abdullah University of Science and Technology.

A photo from today's dive in the Red Sea (Photo: R. Rotjan)

On my way here, I flew over Egypt, of course all-the-while wishing my friends and colleagues in Egypt a smooth and safe transition in this tumultuous time, following the recent chain of events. You'd never know from the air that anything had changed, though. I flew over Luxor (the ancient city of Thebes) at sunset, and then over the Nile, and then Valley of the Kings. Looking down at the desert with the setting sun was stunning (sorry no photos - couldn't get my camera fast enough), and I was struck at the beauty of desert mountain chains.

Now, 2 days, 5 dives, and less than 10 hours of sleep later, I am once again struck by the beauty of chains - but not mountains this time. Today's dives were full of research-related activity, but we all spent a moment or two admiring the chains of salps that were visiting the reef.

(L) A long chain of salps, curling as it gets caught in the reef; (R) Many salp chains floating above (Photos: R. Rotjan)

Salps are pretty interesting creatures. They look like jellyfish, but guess again! They are actually more closely related to vertebrates (they are in the Phylum: Chordata). They are relatively rare on reefs; the only other time I've seen them is blue water diving with Dr. Larry Madin (Woods Hole Oceanographic Institution) in the Phoenix Islands. The reason salps are so rare is because they are typically open ocean, pelagic animals. They slowly swim through open water, all-the-while filtering the water for food. Every once in a while, they get swept onto the reef from offshore. We were diving on very dramatic reefs with slopes that literally rise from the depths without much by way of ledges or shelves--just a steep wall of coral, and then an open vista of blue.

Reef wall to the left; open water to the right; salp chain getting blown in from the blue to the reef. (Photo: R. Rotjan)

Salps don't always form chains; they can also live as solitary individuals. But an individual can reproduce asexually by making clones, which form a chain. The chains start out small, both in size and number, but 10's-100's of clones can form, all tiny at first. The chains can stay together for a long time, swimming and feeding on plankton together until they eventually break apart from each other.

Chains can curl, bend, or be straight, but are always beautiful. (Photos: R. Rotjan)

They are important organisms that filter phytoplankton in open oceans. They are difficult to study, but Dr. Larry Madin is an expert (see his posts from the Phoenix Islands Expedition here).

A salp chain close up from bellow, looking up. Clouds are visible above. (Photo: R. Rotjan)

For me, salps are an important reminder that reefs are connected to the sea around them. It's tempting to think of a coral reef as an oasis in the middle of an open-ocean desert (especially in Saudi Arabia!), but the open ocean is full of life which interacts with reefs. For example, when salps get swept onto a reef, they also become food for many fishes. We observed tons of feeding behavior as tons of reef fish ventured out of their comfort zones to nibble on a small salp-snack. Nutrients in the open ocean also arrive on reefs from offshore and from deeper currents. Pelagic filter-feeders like salps also help to keep waters clean and clear (which is critically important for tropical reefs).

Red sea reef with crystal-clear water (Photo: R. Rotjan)

Typically, when I'm on a reef wall, my attention is wholly focused on the corals and my back is to the blue. But today, I had a great reason to turn around and admire the salps and remember the critically important role of the organisms in the surrounding sea.

More soon,



  1. I remember seeing these salps while diving the reefs in Subic Bay, Philippines back in about 1983. I dove there regularly during 1982 and 1983. One season there were none of these, the next season they were numerous.

    Dave Wheeler

  2. Hi Dave,

    You were lucky to see them! They are somewhat seasonal I think, given that salp chain abundance can track major phytoplankton blooms. Thanks so much for reading; the reefs must have been amazing in 1983.


  3. These photos will come in handy this summer when Aquarium visitors ask about the "strange chains of globs" washed up on beaches.
    Thanks Randi!