Salps do it two ways.

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Posted by Merry on March 04, 2013 at 15:21:33:

In 2012, we were absolutely inundated with salps. Caught in current lines, individual salps littered the surface. Dense swarms of salps at depth appeared either as wheeled bouquets, elegant coils, or slithering chains. In fact, a 2012 survey by the NOAA Southwest Fisheries Science Center in Santa Cruz, performed from the ship Bell M. Shimada, yielded trawl nets that contained as many as 500,000 salps. Contrast this with 235 salps per trawl in 1999!

There are about 50 described species of salp. What can be confusing in their identification is that the solitary animal is physically different from a member of the aggregate. Not only are the solitary and aggregate forms morphologically different, but each reproduces differently as well.

The solitary form is the asexual phase of the reproductive cycle. It simply clones itself, producing hundreds of babies that are joined together in chains or coils. The aggregate form, the sexual phase, uses the old-fashioned egg and sperm approach, and produces a single embryo per salp. The two forms alternate each generation, allowing salps to proliferate rapidly and in huge numbers when food is abundant.

Alternation of generations was discovered in salps in 1818 by the German poet, zoologist, and botanist, Adelbert von Chamisso. Chamisso was traveling on a voyage around the world on board the Russian brig Rurik, as part of the expedition to find the Northeast Passage. In recognizing and describing this phenomenon, Chamisso demonstrated remarkable insight. Considering how little was known about marine animals in the early 1800ís, itís not surprising that his contemporaries didnít buy the idea. Consequently, it took more than 20 years to confirm alternation of generations in salps.

A portrait of Chamisso with one of his drawings.

 photo Chamissocomposite_zps3b8f0ae4.jpg

I thought you might be interested to see representatives of 4 species of salp in their reproductive stages. These species are commonly found around the Palos Verdes Peninsula in Southern California.

I chose Cyclosalpa bakeri to illustrate the reproductive cycle with its alternation of generations.

 photo Cbakerireprocycle900_zps34782d2b.jpg

A close look at solitary phase Cyclosalpa bakeri embryos. The parent salps appear to be deteriorating, as a hoard of feasting hyperiid amphipods contribute to their demise.

 photo CyclosalpamatureembryosDSC_5025_zpse4550a7f.jpg

Here are both forms of Cyclosalpa affinis.

 photo CyclosalpaaffinisopaqueclusterDSC_7341_zpsa99b15d8.jpg

 photo CyclosalpaaffinissolitarystolonchainDSC_7364_zpsef299ede.jpg

In Pegea confoederata, contrast the aggregate shape with the blimp-like solitary form. This odd salp doesn't look svelte enough to be pelagic!

 photo PegeaconfoederatacompositemainDSC_5572_zps9bc9701e.jpg

Here are individuals in the Pegea confoederata aggregate, producing one embryo each. The embryos are attached to the dorsal wall. Theyíll develop into a single, globe-shaped animal.

 photo Pegeaconfoederataaggregateembryos2_zpscc8d93a8.jpg

This solitary Pegea confoederata is cloning babies from its reproductive stolon.

 photo PegeaimprovedDSC_5615_zps988c4dbe.jpg

Hereís another view of the salp chain emerging from the stolon, plus a hitchhiker.

 photo PegeaformingspiralDSC_5614_zps65315471.jpg

After detaching from the stolon, the small buds of Pegea confoederata rapidly grow into a chain of 5-inch long individuals.

 photo Pegeaconfoederatasemi-circleDSC_5624_zpsdf245e43.jpg

The last species here is Salpa maxima. It dominated our dives last year with a spectacular bloom.

 photo SalpamaximasoitarystolonDSC_5023_zps29239499.jpg

A section of a Salpa maxima chain in the aggregate phase of the life cycle.

 photo SalpamaximadevelopingembryosDSC_4907_zpsbcf06f4a.jpg

 photo SalpamaximalargerembryoDSC_5124_zps7df3e4d7.jpg

This beautiful photo was taken in situ by Larry Madin of Woods Hole Oceanographic Institution. It shows well-developed embryos in a salp chain.

 photo LarryMadinsalpembryos_zps812fb513.jpg

Check out salps carefully during the next bloom. You may find that baby salps are easier to see in a live animal than in a photograph!

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