CreatureCast – Diving for Jellies

posted by Sophia Tintori / on March 3rd, 2010 / in History, Jellies, Podcast, Siphonophores

Here in the Dunn lab, siphonophores are our favorite animal and the focus of much of our research.

Dr. Phil Pugh is a good friend of the lab, and he also happens to have described more new species of siphonophores than anyone who has ever lived. In the video below, he describes what it’s like to come across a siphonophore in the deep sea with a submarine. What looks like one long body in this video is actually a free-swimming colony of clones — many genetically identical bodies that are all attached. But each body in the group isn’t just like its neighbor. They each do a specific job for the colony. Some individuals will swim, some will catch food, and some will reproduce.

More on siphonophore biology can be found in papers here and here. But we’ll talk about all that later — for now, just take a look.

Footage courtesy of the Bioluminescence lab at the Monterey Bay Aquarium Research Institute. Music graciously provided by Raf Spielman of The Golden Hours. Edited by Sophia Tintori. This podcast is published under a Creative Commons Attribution Non-Commercial No Derivatives 3.0 license.

Royal jellies

posted by Sophia Tintori / on February 17th, 2010 / in History, Jellies

Emperor Hirohito was a man who wore many hats. Most famously, he was Japan’s head of state during World War Two. As emperor, he was the stoic and elegant embodiment of Japan. But he was also a family man, a poet, and a marine biologist.

Hirohito had the Imperial Biological Laboratory built for him when he was 24, which was substantially upgraded three years later when he became the emperor. It contrasted the rest of the Imperial Household in the plainness and usefulness of its furniture. Plain furniture, such as a trash bin made out of a trophy elephant leg.

He would steal away every Saturday afternoon and most Thursdays when he could, to his lab where he would meet with other biologists to identify and describe the species that they had dredged up from the surrounding waters. He had a gentle touch when working in the field. If collecting from a colony of polyps, he would take only a small bit of each colony and would put the rock carefully back in place, so as to let the rest thrive.

After the war he published 32 books of plates, describing some 23 new species of ascidians, 7 new species of crabs, 8 new species of starfish, and 6 new species of pycnogonids. He conducted the first comprehensive survey of the biodiversity of Sagami Bay, but he was particularly well versed in the tiny tentacled polyps that grew on the sea floor, called hydrozoans. All of his work was published under the name ‘Hirohito Emperor of Japan.’

At the top is a photo of Emperor Hirohito with his wife, whose hat is making her look a bit like a hydrozoan herself. Next down is Emperor Hirohito in the Imperial Laboratory, from E. J. H. Corner’s article about Hirohito’s scientific career. Below that is an illustration of a nudibranch (left) from Opisthobranchia of Sagami Bay (1949), and an illustration of a coral (right) from The Hydrocorals and Scleractinian Corals of Sagami Bay (1968), by Hirohito Emperor of Japan. Below is a photo of Emperor Hirohito in Kurume, also in 1949.

Stack of plates in action

posted by Sophia Tintori / on December 17th, 2009 / in Development, Jellies, lab, lifecycles

Look what we caught happening in our refrigerator.

While doing a fridge clean-out in the Dunn Lab, graduate student Rebecca Helm took a look at a forgotten bowl of Chrysaora colorata polyps from our friends Chad Widmer and Wyatt Patry at the Monterey Bay Aquarium. These creatures were left over from an RNA extraction we had done earlier for the Cnidarian Tree of Life Project, and were hidden in the back of the fridge, despite the labs strict ‘no pets’ rule.

Upon inspection, Rebecca noticed that the polyps were strobilating! This is a spectacular type of asexual reproduction, which is explained in more depth in Perrin Ireland’s post on the scyphozoan life cycle.

In this video, a polyp has pinched off into a stack of plate-like discs, called ephyrae. When they pop off of the end of the polyp, they each become a free swimming individual, and a direct clone of the parent polyp. Each ephyra will mature into adult bell-shaped jellyfish. Even before they break away from the poly, they are strongly pulsating as they flex their newly developed swimming muscles before birth.

Video by R. Helm and S. Siebert.

Making babies like a stack of plates

posted by Perrin Ireland / on December 10th, 2009 / in Jellies, lifecycles

aurelia500

Our own lifecycles are pretty simple. Making babies requires sex. Sex creates offspring with new unique combinations of genes. Many organisms are also capable of asexual reproduction, which doesn’t involve sex (as the name implies) and involves only one parent. In most types of asexual reproduction, genes aren’t reshuffled and the offspring are genetic clones of their parent.

Unlike ourselves, many species have lifecycles that combine both  sexual and asexual reproduction. Take the moon jelly, for example. Moon jellies, also known as Aurelia aurita, are perhaps the quintessential jellyfish, with a typical umbrella-like medusa that travels on ocean currents. There is more to their lifecyle, though, than this swimming organism. The swimming medusa does use sex to make babies—but the babies don’t grow directly into swimming medusae. Medusae release their eggs and sperm into the water and these combine to form a zygote (the fertilized egg). The zygote then develops into a planula larva. The planula eventually sinks to the ocean floor and develops into a polyp, an organism that looks nothing like a medusa. Polyps are attached to the ocean floor, usually on a rock or other hard surface, and stay in one place their whole life. They have a mouth surounded by tentacles, just like the more familiar polyps of sea anemones and Hydra. These polyps, however, are incapable of having sex—they cannot make eggs and sperm. Instead, they reproduce asexually. They can asexually produce other polyps, but they can also asexually produce miniature medusae called ephyra. These are pinched off from the polyp’s mouth as if they were a stack of plates, with the most mature medusa on top. The ephyra then swim away, grow into mature medusae, and complete the lifecycle.

Deadly bands

posted by Stefan Siebert / on October 28th, 2009 / in Jellies, Siphonophores

091028Tentillum3bright

Cnidaria is a group of animals that includes – among other things – jellyfish, corals and sea anemones. They take their name from the greek word for nettles (knide) because of to the sting and rash that a close encounter with them can cause. They elicit this response with a particular type of stinging cell that only they possess, the cnidocyte, which is arguably the most complex cell possessed by any animal. When triggered, a cnidocyte releases a hollow harpoon that penetrates prey organisms – or a swimmer’s skin- and injects toxins. These harpoons are microscopic, and there are many types of cnidocytes each with a different type of harpoon. Some create a painless sticky sensation, others are so powerful that a sting from just one cell can cause considerable burning.

The siphonophores, a group of colonial cnidarians, have multiple polyps and medusae that are specialized for tasks such as locomotion, feeding or reproduction. The picture on the left shows a feeding polyp (the prominent white structure in the center) of the siphonophore Nanomia bijuga. This feeding polyp is attached to the stem of the colony, which stretches across the top of this photo. Each feeding polyp has a single tentacle, and this tentacle has side branches with dense batteries of cnidocytes. Most of the cnidocytes are densely packed into a fascinating complex structure – the cnidoband. These are the orange spirals in the photos. The cnidoband ends in a filament (lower part of the picture) which contains sticky cnidocytes. The terminal filament makes first contact to the prey and sticks to it, which then tugs the cnidoband as the prey struggles. The cnidoband then stretches out and its cnidocytes fire as a unit, deploying their deadly power. These Nanomia bijuga were collected using the ROV Ventana with the friendly support of MBARI. Photos by Stefan Siebert.

Hiding submarines beneath jellyfish

posted by Casey Dunn / on September 9th, 2009 / in Jellies, Siphonophores

Nanomia

With the advent of submarine warfare, the ability to locate large underwater objects with SONAR became of prime strategic importance. Active SONAR detects objects by listening for echos from pulses of sound. As SONAR became more widely used, though, some very strange things were seen in the open ocean. At times, the SONAR suggested that the ocean floor was much shallower than maps and direct depth measurements indicated. Ships sitting in one place would also find that the depth of the ocean would appear to change through the course of the day, as if the sea floor were heaving beneath them.

Something was creating a false bottom that the SONAR couldn’t see through. Submarines found that they could dive right through this layer, hiding beneath it and rendering the SONAR above useless. Details about these false bottoms in the open ocean were closely guarded military secrets during World War II.

It had been suspected that the false bottom was made of large groups of animals, but nets sent to this region usually came up empty. Then, in 1963, Eric Barham, a scientist at the US Navy Electronics Laboratory, reported his first-hand observations form aboard the research submarine Trieste. His dives were coordinated with ships above that monitored the position of the false bottom with SONAR. When Trieste arrived at the false bottom it did find animals, and lots of them. They were siphonophores, extremely fragile colonial jellyfish that are notoriously difficult to collect. They are so fragile that they usually turn to slime in nets and pass right through the mesh.

How could something so delicate and gelatinous have such a strong signature on the SONAR, powerful enough to hide entire submarines? Many species of siphonophores have a gas filled float that serves to regulate buoyancy, and possibly to sense which way is up. The siphonophore that was found in the false bottom, Nanomia bijuga (see photo above), has a float that is about a milimeter in diamater, which is predicted to resonate at a frequency very close to the sound pulse used by SONAR. This resonance scatters the sound, and when there are lots of siphonophores the scattering is so thorough that the SONAR can’t penetrate through the swimming jellyfish.

Besides revealing the important impacts of a poorly-known colonial jellyfish on military technology, these findings also indicate how difficult it can be to measure the abundance of jellyfish. They weren’t detected in nets sent to the false bottom, but there were enough of them to hide entire warships. This measurement problem is compounded when we try to establish whether jellyfish are rising or falling in abundance through time. Because they are so difficult to observe, their abundance has likely been dramatically underestimated in the historical record. As we see more jellyfish with improved sampling methods, it is hard to know if they are more numerous than they used to be.

The Nanomia bijuga photo above was taken by Claude Carré at Villefranche. The float is at the upper right of the image. More information on siphonophores can be found at siphonophores.org.

kahikai

posted by Casey Dunn / on August 16th, 2009 / in Jellies, Science & Art

scypho

Eric Roettinger and Mattias Ormestad have launched kahikai.org to showcase some of their beautiful animal photographs. Both are postdocs in Mark Martindale’s lab at the University of Hawaii, where I also spent a couple years. In addition to presenting their photos, kahikai (which means “one ocean” in Hawaiian) will be serving as a repository for primary developmental biology data, such as in situ hybridization images. Eric also curates a set of photos he has taken of other subjects at livingonabeach.org.

Siphonophore video

posted by Casey Dunn / on July 26th, 2009 / in Jellies, Siphonophores

These siphonophore clips were put together from a series of dives by remotely operated underwater vehicles at the Monterey Bay Aquarium Research Institute, with thanks to Steve Haddock. For more information on siphonophores, a group of deep-sea colonial animals, see siphonophores.org. I originally made the segment for the home page of the journal Current Biology when they published a Quick Guide on siphonophores.

This video shows three different species of siphonophore, filmed at depths of hundreds of meters off the coast of California. The first is Apolemia, which can reach more than 40 meters in length (yes, meters), making it one of the longest animals in the world. It is sitting motionless in the water with its tentacles retracted. The second is Erenna, which uses glowing lures to attract prey. The third is Chuniphyes moserae, a fast-swimming calycophoran siphonophore.