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What is this bright green string of eggs? – Part 2

This is part two in a three-part series about photos of bright green eggs first submitted to AskaNaturalist.com in the summer of 2014. The photos came from a reader in Nova Scotia and another in Maine. To read part 1, click here. Part 3 will be coming soon.

string of green eggs and tape measure

Nova Scotia “string of bright green eggs”

egg string - maine - 800

Maine “jelly blob”

Previously on “bright green string of eggs”: Two independently submitted strings of bright green eggs or something like eggs, from Nova Scotia and Maine, July-Aug 2014. First thought was amphibians symbiotic with algae. Amphib expert says emphatically, “No!” He suggests algae. Algae expert says “No. Maybe snail eggs?” Rob Dillon, snail expert, says he received a similar photo several years ago, and the person who sent it hatched the eggs and got tiny baby Lymnaea (Bulimnea) megasoma, a freshwater snail of the northern United States and southern Canada.

So the answer to who laid these eggs: snails … but wait ….

Snails with legs?: Shortly after I sent the bright green string photos to professor Dillon, I was doing an image search for various combinations of green, string, eggs, etc. I came across this page: http://www.fishpondinfo.com/egg.htm, where Robyn Rhudy, who describes herself as “Specializing in Nature, Animals, Fish, and Ponds,” has some good information on how to identify various egg masses to be found in freshwater. When I emailed Robyn and asked if she knew what the egg masses from Nova Scotia and Maine were, she said she didn’t, but that she had seen something like this before. She directed me to the bottom of her page about the aquatic insects you can find in a backyard pond, where she describes how a reader sent her a photo and this message:

“I found some eggs in a neighbor’s pond today (July 25) here in central Vermont. The clear 3/8″ diameter strand is configured in a ring about the size of a hair elastic, with hundreds of tiny (salt grain size) green dots in a very orderly spiral pattern along the strand. The ring was attached to a submerged rock and is very elastic….”

“The diameter of the elastic band (which does not break up when handled and will stretch to fit over my hand) is about 1/4″ – 3/8″ when un-stretched. It is about the size of a hair elastic but thicker. It is hard to tell how big the actual egg white part is because they are arranged in a ring and not separate. And the coil of green dots is very uniform and regular. As you can see, I’ve scraped the strand off the rock and have it in a jar to see what hatches….”

This description matches the two bright green strings I previously described in Part 1, including the key fact of coming from the northeastern US/Southeastern Canada region. The only difference is that in the photo submitted to FishPondInfo, the string is less green and more brownish. And the key thing is that when Robyn’s reader hatched the eggs, she drew a picture of what hatched. The creature she drew has six legs and a long abdomen. Definitely not a snail. The only creatures on this earth with six legs are insects, and the drawing looks like many aquatic insect larvae.

chironomus midge

Chironomid midge

With this new information, I renewed my search, but in an insect direction. I soon latched onto the chironomids as a possible source for the gelatinous, spirally organized egg mass . The family Chironomidae includes at least 20,000 species of small flies found worldwide. Chironomids are in the suborder Nematocera, which also includes our all-too-familiar mosquitoes and blackflies as well as midges. Unlike many other midges, however, chironomids don’t bite. In fact, they are often descriptively called “non-biting midges” and many chironomids probably don’t feed at all as adults. That doesn’t mean they don’t annoy people, however. Chrironomids are famous for hatching simultaneously in plague-like numbers from some bodies of water, to the extent that they cover surfaces and ruin summer lakefront parties, and when they die simultaneously, they can form smelly piles of tiny rotting corpses.

Before we wish these tiny creatures off our lovely planet, however, we should acknowledge that the enormous numbers of chironomid larvae, feeding on detritus and microscopic organisms, form a key link in the food chains of nearly every body of freshwater on the globe. They can survive in clean water and they help to clean dirty water. Many species that live in low oxygen conditions in mud have a kind of hemoglobin in their body fluid that helps them pull oxygen from the water. Because hemoglobin makes their transparent bodies look pink or red, these larvae are often called “bloodworms” when they are sold as food for aquarium fish.

In fact, as I looked for confirmation that these egg masses were laid by chironomids of some kind, I came across this photo on the website of someone who raises goldfish as a hobby: http://goldfishgarage.blogspot.com/2014/05/chironomid-bloodworm-egg-mass.html

chironomid egg mass

Chironomid egg mass

As you can see, this egg mass looks similar, in that it has spirally arranged eggs in a gelatinous string. It’s not exactly the same, but it seemed close enough to offer support for the chironomid idea. And when I asked David, who runs GoldfishGarage.com, he confirmed that he raises chironomids in his garage, as “bloodworm” food for his goldfish.

On his site, David also has a great video that shows the egg mass developing and tiny “bloodworm” chironomid larvae hatching. https://www.youtube.com/watch?v=VtNB6wYzas4#t=115.

Score one for chironomids as the layers of the Nova Scotia and Maine egg masses.

For confirmation, I sent the photos of the Nova Scotia and Maine egg masses to a handful of chironomid experts and asked for their opinions. The answers ranged from “probably” to “definitely!” with the consensus leaning toward the genus Chironomus. And an image search for “Chironomus egg mass” shows several photos of egg masses that look like David’s Goldfish Garage photo and very similar to the egg masses from Nova Scotia and Maine and from Robyn’s Pond Page.

Maine egg mass with hatchlings

Maine egg mass hatching

Ali Arshad, one of the chironomid experts I contacted, suggested that I write back to the AskaNaturalist readers who submitted the egg mass photos and ask them to put them in a bucket and see what hatches. I didn’t hear back from Emily in Nova Scotia, but Nancy from Maine was cheerfully willing to create a nursery for hundreds of mystery insects. She said the original egg mass had been put back in the lake, but she collected another one from her dock. And when it began to hatch a few days later, Nancy sent me this photo:

And that’s when the chironomid train went off the rails.

closeup of hatchling

hatchling

If you zoom in on one of the dozens of hatchlings coming from Nancy’s egg mass, you’ll see this:

The resolution is not great, but what is clear is that this tiny creature has six legs! But if you watch David’s video of chironomids hatching and look very closely, you’ll see that the larvae that hatch from his eggs – like all chironomid larvae – don’t have legs. They are shaped like skinny caterpillars (remember that they are related to moths) and they have stumpy fake legs called parapods.

When I zoomed in and saw six legs on Nancy’s hatchlings, I knew these were definitely not chironomid larvae. And then I realized I should have paid more attention to the drawing that had been submitted to Robyn’s Pond Page, because it too has six legs. In fact, that’s what led me to think the egg masses belonged to insects in the first place. And the drawing is a reasonable representation of Nancy’s tiny hatchling.

I presented the six-legged evidence to chironomid experts who had expressed confidence that the eggs were chironomid, but while they agreed that the six-legged hatchlings were not chironomid larvae, they suggested that maybe the six-leggers were “hitchhikers” that didn’t really belong to the egg mass.

I wasn’t comfortable with that explanation because there were so many “hitchhikers” on Nancy’s egg mass, and for a while, I toyed with the idea that the six-legged hitchhikers were actually feeding on the egg mass. In fact, it occurred to me that maybe that could explain both the six-legged larvae coming from a chironomid egg mass and also explain how someone got baby snails from a similar egg mass (Remember the snails? If not, see Part 1). Maybe the snails were also feeding on the egg mass. None of the chironomid experts I contacted seemed to think much of that idea, however, so I dropped it and reluctantly accepted that these had to be chironomid egg masses.

I put aside the distracting detail of six-legged hatchlings, and prepared to make my determination: Chironomids it is …

But Wait, There is Another Possibility: In the third and final installment of this story, we find out that there is yet another possibility for who laid these egg masses, and it explains the six-legged larvae.

Sources: Sources and thank yous are at the end of Part III, coming soon …

Cite this article as: Pelletier, TC. (December 17, 2014). What is this bright green string of eggs? – Part 2 Retrieved from http://askanaturalist.com/what-is-this-bright-green-string-of-eggs-part-2/ on December 17, 2014.

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What is this bright green string of eggs? – Part 1

Because the sequence of events in the search for an answer to this question took some interesting turns, I’m departing from my usual format to write this answer as more of a diary. If you don’t find this format interesting, don’t worry, I’ll soon return to my regular format.

This is part one in a three-part series.  To read part 2, click here.  Part 3 will be coming soon.

The First String of Green: In July, I received an email and photo from Emily from Nova Scotia:

string of green eggs and tape measure

Nova Scotia “string of bright green eggs”

“We are finding these slimy strings of bright green eggs (?) in the lake. They can be found on the wharf poles, but the ones in the picture were on the cord for the underwater thermometer. Any idea what they are from?”

Emily cleverly included a tape measure in the photograph, which is in inches, so it looks like the uncoiled length of this would be about 2 inches, or 5 cm. The picture is of fairly high resolution (also clever on Emily’s part), and when I zoom it in, you can see that it consists of individual green dots held in a matrix of gel about 3 mm wide. I was able to make a rough measurement of the individual green dots at about 0.4 mm or 400 microns. And although it’s a little hard to count them because they are three dimensional, I came up with about 140 eggs in a 1 cm section of the string.

The string seemed egg-like, and I know some amphibians lay strings of eggs, and some amphibian eggs have a symbiotic relationship with green algae, so my first thought was some kind of amphibian eggs. The individual dots seem too small to be amphibian eggs, but I wasn’t sure about that, so I sent the photo to an amphibian egg expert, who quickly assured me that it was not an amphibian egg mass. He speculated that it might be an alga.

spirogyra algae

Spirogyra algae

That seemed like a reasonable guess, given that the string in the photo looks superficially like the strings of colonial green algae in the genus Spirogyra, as shown in this photo. Spirogyra is much smaller, however, with strands more on the order of 0.1 mm or 100 microns wide. Still, it seemed worth a shot, so my next email was to John Wehr, a professor of aquatic ecology at Fordham University’s Louis Calder Center, and an expert in freshwater algae.

The Second String of Green: Before I heard back from Dr. Wehr, however, I received another email, this time from Nancy in western Maine. She sent me this photo, and said:

egg string - maine - 800

Maine “jelly blob”

“I found this jelly blob or loop in the water on the ladder to my boat in a fresh water lake. I thought it was a round blob but it was more of a loop. These dots were bright green in clear jelly. It was about the size of a quarter. I thought it was a solid round blob but when I moved it, it was actually a line about 2-3 inches (5-7 cm) long. What is it?”

As you can see from Nancy’s photo, what she found was very similar to what Emily found in Nova Scotia. Going on Nancy’s suggestion that the looped mass was about the size of a U.S. quarter (about 2.5 cm or 1 inch), the string seems to be about 4 mm wide, and the individual dots seem to be about 0.5 mm or 500 microns – certainly in the same ballpark as in the string from Nova Scotia. Again, I counted dots in a 1 cm length, and got 125 – pretty close to the 140 of the Nova Scotia string.

Since these two egg masses were so similar, were found under such similar circumstances, and at the same time of year in freshwater from the same part of the world, from that point on, I began to include both masses in my emails to experts, under the assumption that these were two examples of eggs laid by the same creature, or at least similar creatures.

A day or two later, I heard from Dr. Wehr, the algae expert. He said:

“It is hard to tell from this magnification, but they look to me like an egg mass of some animal, which has symbiotic algae in association with them. I am algae person, not a zoologist, but while they may not be amphibian eggs, perhaps they could be snail eggs. Hard to say. But the green color is very likely the algae associated with the eggs,. This is phenomenon very common with salamander eggs and the association is apparently beneficial to both the alga and the eggs.”

The First Answer – Snails:  The snail possibility seemed reasonable to me, and I happen to know a freshwater snail expert, Dr. Rob Dillon at the College of Charleston. Dr. Dillon had been extremely helpful to me in a previous article on the egg masses of Physa snails. So I sent him the photos from Nova Scotia and Maine. Here’s what he said:

“Yes, the gelatinous strings of bright green bodies depicted do indeed appear to be the egg masses of a large pulmonate freshwater snail, Lymnaea (Bulimnea) megasoma (click here for photo, middle of the page). Very little is known about this critter. Its range seems to be restricted to WAY up north – Manitoba, Ontario, Quebec, Minnesota, Wisconsin, Northern Michigan, Maine. As far as I know, the egg mass of L. megasoma has never been described. The only way that I myself am able to identify your photos is that I received an inquiry nearly identical to yours from Quebec back in the late summer of 2011, and was clueless at the time, and my 2011 correspondent hatched the doggone thing out, and sent me a follow-up photo of the juvenile snails.

Dr. Dillon admitted he was unable to explain the green color of the embryos. He agreed that it looked like an algal association, but he pointed out that as far as he knew, that kind of egg/algae association had never been documented in a freshwater snail. Still, it seemed like maybe we had an answer to the question of who laid these beautiful egg masses.

Or did we?

Wait, There is Another Possibility: In the second installment of this story, we find out that there is another possibility for who laid these egg masses, and the experts who give me that possibility are just as certain about it as Dr. Dillon. The plot thickens … to read Part 2, click here.

 

Sources: Sources and thank yous are at the end of Part 3, coming soon …

Cite this article as: Pelletier, TC. (November 19, 2014). What is this bright green string of eggs? – Part 1 Retrieved from http://askanaturalist.com/what-is-this-bright-green-string-of-eggs-part-1/ on December 17, 2014.

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Is this a dragon paw?

shredded turtle foot

found by the dog

The Question: Look what my dog dragged into our home! Can you help us identify who/what/where this claw came from?? It was about the size of my palm. My son says it looks like a dragon paw!

Submitted by: Susan, Wisconsin, USA

(click on photos and graphics to expand)

The Short Answer: The only wild animal in Wisconsin that this could possibly come from is a large snapping turtle. Three very similar species of snapping turtles are found only in the Americas, with a Central American version (Chelydra rossignonii) and a South American version (Chelydra acutirostrisI) joining our North American species (Chelydra serpentina). The larger alligator snapping turtle (Macrochelys temminckii), is in the same family, the Chelydridae, but its range doesn’t extend into Wisconsin.

The common snapping turtle is a large turtle, with a maximum length of about 45 cm (18 inches) and weight of about 20 kg (45 pounds) in the wild. Snapping turtles, like most turtles and reptiles, have generally been considered to exhibit “indeterminate growth.” In a species with indeterminate growth, individuals develop at a rate that is usually dependent on the amount of food available, and they typically continue to grow throughout their lifetimes, although at a much slower rate as adults. Most fish, for example, continue to grow as long as they live. Animals with “determinate” growth, on the other hand, include mammals and birds, which, if given enough food, grow at a fairly predictable rate until reaching a certain age, at which point they stop growing at all (except for gaining weight).

baby snapping turtle

baby snapping turtle

The generalization that all reptile species, including turtles, exhibit indeterminate growth is definitely not true, and as we’ve learned more about growth patterns, the picture has become more complicated, even for species that do exhibit indeterminate growth (more on that later). But it is mostly true that most snapping turtles grow throughout their lives. They grow much faster as juveniles, with a growth rate of about 1.5-3 cm per year (1/2-1 inch) for the first decade of life, but only about .2 cm per year (less than a 1/16 of an inch) after the age of about 20. This rate can vary quite a bit, depending on the amount of food and the length of the active season. The growth rate of snapping turtles in Algonquin Provincial Park in Ontario, for example, is about half that of more southern turtles in the first few years of life. And the farther north you go, the longer it takes for turtles to reach reproductive maturity.

If you search online, you can find estimates of the maximum age of snapping turtles that range from 30 years to 150. The 30 year estimate is undoubtedly wrong, and the 150 years may be extreme also. But turtles in general can be very long-lived. A recent study (Congdon et al., 2013) estimated that in some populations it would take 75 years after reaching maturity at the average growth rate of adult snapping turtles to reach the size of the largest turtles in the study. Adding that to the typical age of about 15 years at reproductive maturity gives an age of about 90 years for some of the largest turtles. This is a very rough estimate, but it suggests that some big snapping turtles have lived a long time – especially in the northern parts of the snapping turtle’s range, like Wisconsin, where turtles are likely to grow slowly.

Your “dragon paw” may have come from a turtle that hatched before the Great Depression.

It’s not surprising that snapping turtles live a long time if you look at their adult survival rate. By the time a snapping turtle reaches reproductive maturity, it is big enough and formidable enough to have very few natural predators. In fact, in many parts of North America, the biggest cause of mortality for snapping turtles is people:  boat propeller strikes, cars, and trapping by people for food.

If I had to take a wild guess on this turtle, given that your dog presumably found it in a suburban neighborhood, on land, it was probably hit by a car.  It may have later been torn apart by a coyote, a fox or your dog, but that’s probably not what killed it.  Dr. Justin Congdon, at the Savannah River Ecology Laboratory, has studied snapping turtles for more than 30 years. He gave me a different theory. “When people catch and butcher snappers, they typically cut off the head and feet first because reflex movements of the turtle make both a risk to the person doing the butchering. I suspect that’s what happened here and the dog found one of the discarded feet.”

common snapping turtle

common snapping turtle

More on Growth of Snapping Turtles: The Congdon et al. study looked at tagging and recapture data for nine species of North American turtles and found that all had indeterminate growth, in that about 80% of the individuals in the population continued to grow as adults. Interestingly, however, about one out of five adult turtles didn’t grow at all, even across time periods of a decade or more. So it appears that in these turtles, at least, the determinate/indeterminate dichotomy may not be so clear cut.

There is an evolutionary trade-off for animals with indeterminate growth that pits growth as a juvenile versus growth as an adult. The larger a female turtle, the more eggs she can lay. And generally, the larger a male turtle, the more battles he wins against other males in the competition to mate with females. It’s better to be bigger.

The trade-off occurs because once turtles begin mating, the energy expended by males competing and the energy expended by females to form and lay eggs slows their growth rate to a crawl (pun intended). Turtles that postpone mating so they can grow larger before they begin reproducing are at risk of being eaten or otherwise killed without ever producing any offspring. If they survive to that larger reproductive size, however, they may enjoy a long adulthood of prolific reproduction.

Turtles that begin mating at a smaller size, and then continue to grow slowly after that, may take a very long time to reach the size needed to produce large clutches of eggs or win their battles against other males. They are, however, more likely to have at least some offspring before something drastic happens to them.

Let’s hope your turtle had a long and successful reproductive life. Snapping turtles are still common across their range, but their numbers have decreased sharply in some places, as people overharvest them for consumption in the U.S. and shipment to other countries as well. Because few hatchlings make it all the way to adulthood, it will take a long time for snapping turtle numbers to recover to the levels prior to human harvesting.

Sources:  Special thanks to Dr. Ronald J. Brooks and Dr. Congdon for their help in reviewing this article.

Congdon, J D, Gibbons, J W, Brooks, R J, et al. (2013). Indeterminate growth in long-lived freshwater turtles as a component of individual fitness. Evolutionary ecology, 27(2), 445-459.

Galbraith, D A, Brooks R J, & Obbard M E. (1989). The influence of growth-rate on age and body size at maturity in female snapping turtles (chelydra-serpentina). Copeia, (4), 896-904.

Congdon, J D, Dunham A E, & Sels R. (1994). Demographics of common snapping turtles (chelydra-serpentina) – Implications for conservation and management of long-lived organisms. American zoologist, 34(3), 397-408.

Armstrong, D P, and Brooks, R J. “Estimating Ages of Turtles from Growth Data.” Chelonian conservation and biology 13.1 (2014):9-15.

Bennett, A M, & Litzgus, J D. (2014). Injury rates of freshwater turtles on a recreational waterway in Ontario, Canada. Journal of Herpetology, 48(2), 262-266.

Cite this article as: Pelletier, TC. (October 10, 2014). Is this a dragon paw? Retrieved from http://askanaturalist.com/is-this-a-dragon-paw-2/ on December 17, 2014.

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What is chasing these birds?

Mourning Dove

mourning dove

The Question: It’s VERY hot and humid here in Milwaukee – the cicadas and other insects seem to be the only ones enjoying it. Last night while walking my dog about dusk, I saw two different mourning doves being “chased” by something about 1.5 inches (4 cm) or so. The bird was flying quickly – in one case it had tried to land in a maple tree and then seems to have been sent off as this shape followed it. Could the tormenter be a cicada?

Submitted by: Lezlie, Wisconsin, USA

(click on photos and graphics to expand)

 

cicada killer

cicada killer

The Short Answer: Lezlie, it doesn’t seem very likely to me that it would be a cicada. I would rather expect the bird to be chasing the cicada than the other way around. But in trying to think of a 1.5 inch flying creature that a bird might wish to avoid and that might also be associated with a noisy population of cicadas, I first wondered whether it could it be a cicada killer, of which there are several species in the U.S. These large wasps (as large as 5 cm, 2 in) specialize in preying on cicadas. The female cicada killer stings a cicada to paralyze it and then stuffs the cicada down a hole dug in the ground. The cicada killer lays an egg on the cicada and when the egg hatches, the larva consumers the cicada. Female cicada killers tend to dig their holes in the same area, so in sandy, dry soil, you can sometimes see dozens or hundreds of these holes, especially when cicadas have a big year. During the summer, the males, which cannot sting, form “leks.” A lek is when males congregate to struggle for dominance and females arrive to mate – usually with the winners.

Chuck Holliday, an emeritus professor of biology at Lafayette College in Pennsylvania, has studied cicada killers extensively. He says that when they are on a lek, male cicada killers will chase anything that in any possible way could be a female cicada killer. Pretty much anything that moves.

“They will chase small birds, people and even small stones thrown in front of them. After all, for them, it’s ‘mate in the next 1-2 weeks or die childless.'”

European hornet

European hornet

My first thought was that maybe it was male cicada killers that chased the doves. But Professor Holliday pointed out that cicada killers in Wisconsin (which would be Sphecius speciosus) would be done mating around the middle of August. So since you made your observations in September, that pretty much rules out cicada killers. He suggested that chaser would be more likely to be European hornets (Vespa crabro), another large wasp (up to 2.4 cm for workers, 3.5 for queens). They look a bit like oversized yellow jackets. European hornets build nests in tree holes, and will sting to defend the nest. If a bird were to inadvertently fly near a European hornet nest, it will probably get chased. There have been reports of European hornets killing small birds such as hummingbirds. And Dr. Holliday suggests a hornet might even be hoping to take a bite out of a dove. “Hornets (including yellow jackets) will land on carcasses and even people and bite out a chunk of skin to take back to the grubs in their nests to feed them.”

So it seems more likely that it was a European hornet than a cicada or a cicada killer, and the connection with cicadas may be nothing more than that cicadas and European hornets are both associated with trees. But if you see it again, look to see if it’s a large hornet. If it’s a cicada killer, from a distance it will look mostly black with some red, whereas the European hornet will show yellow, like a large bee or yellow jacket.

Cite this article as: Pelletier, TC. (September 19, 2014). What is chasing these birds? Retrieved from http://askanaturalist.com/what-is-chasing-these-birds/ on December 17, 2014.

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What are these clear jelly blobs on the beach?

The Question: We found clear jelly like blobs washed up along the ocean beach. They look like they could be jellyfish without tentacles. I stepped on one by mistake and it did not hurt. What are these?

Submitted by: Sheri, Rhode Island, USA

(click on photos and graphics to expand)
Aurelia labiata

Aurelia labiata

The Short Answer: Sheri, what you are describing sounds like the remains of jellyfish, probably moon jellies (this includes several species in the genus Aurelia). People report seeing these jelly discs on beaches all over the world. David Albert, professor emeritus at the University of British Columbia, has studied Aurelia labiata, the moon jelly that is common on the west coast of North America (Aurelia aurita is the east coast version). He says that what you are seeing is the “mesoglea” of the jellyfish.

moon jelly anatomy

(1) stomach (2) tentacles (3) oral arm (4) mesoglea (5) gonads (6) endoderm (7) mouth

The mesoglea is a stiffer layer of jelly that provides structure to the moon jelly. So when you find one on the beach, you are essentially finding the skeletal remains of a dead jellyfish.

Live moon jellies don’t generally cause a sting that you would notice, and once they die, the hundreds of tiny tentacles fall away pretty quickly, so as you discovered, you don’t have much to worry about in picking up a moon jelly disk. That is not true of all dead jellyfish, however, so you should be a little cautious.

I wrote previously about moon jellyfish at http://askanaturalist.com/where-did-all-these-jellyfish-come-from/

Aurelia_aurita_-_003

Stranded moon jelly


How do They Get on the Beach?:
A moon jelly doesn’t want to be on the beach, of course. But although they can swim by pulsing their bell to push themselves through the water, they’re not exactly strong swimmers. By angling in one direction or another, they get some directional control, but for the most part, they can swim up and float down. So it seems like it might be pretty easy for a moon jelly to end up on the sand, doomed to disintegrate and be picked up by beach goers. It turns out, however, that moon jellies have behaviors that almost always keep them off the beach.

Dr. Albert has studied the behavior of moon jellies and has found that while they normally keep themselves a meter or two (about six feet) away from the surface of the water, if they bump into or sense the bottom in shallow water, they swim up and stay near the surface for some period of time. Why would they do that?

When waves break in shallow water and then recede, the overall flow of water is shoreward at the bottom and seaward at the surface. That seaward flow at the surface is called an ebb flow. When moon jellies reverse their normal behavior in shallow water to position themselves near the surface, they place themselves in that ebb flow and get carried out into deeper water.

Aurelia_aurita_02

This doesn’t always work, of course. Dr. Albert says, “Moon jellies have behaviours that help them avoid stranding. However, jellies are primitive animals. Their behaviour has to be looked at statistically. The behaviours don’t always occur at the optimum time . For example, in some jellies, swimming toward the surface doesn’t occur until the water has become quite shallow. In that case, the ebb stream may no longer be very strong and it may be very thin. So, a jelly may be less likely to drift out of a shallow area and less likley to avoid stranding. Also, if there is a wind pushing them toward a shore on an ebb tide, they may become stranded.   The ebb tide will serve to help them drift away from the beaches, but the wind initiated currents may be stronger.”

Still, despite these occasions when the normal behavior doesn’t work, Dr. Albert asserts that the vast majority of moon jellies don’t become stranded. He says the ones that end up as mesoglea disks on the sand were probably dead before they washed ashore.

A Little Jellyfish Anatomy: What looks like a simple blob of jelly is actually a fairly complex blob of jelly. Surrounding the mesoglea disk are layers of tissue that contain channels to move tiny particles of food from the edge of the jellyfish bell to the center, where its mouth and stomach are. When you see a live moon jelly, you’ll also notice four prominent horseshoe-shaped objects. These are the moon jelly’s gonads, where it produces eggs or sperm. When you find a dead moon jelly on the beach, you may see a blob that is 25-40 cm (10-16 in.) wide, and includes the four horseshoe shaped gonads. That would represent a fairly intact adult moon jelly. As it becomes more and more degraded by wave action and decay, all that’s left is the tougher center of the mesoglea disk, which might be as little as 7 cm (2.5 in.).

What Does a Jellyfish Think About: Dr. Albert is a behavioral neuroscientist, so his interest in moon jellies isn’t really in how they end up on beaches. He is fascinated by the fact that a moon jelly can exhibit true behaviors, even though it has a nervous system that doesn’t look anything like what we think of as a brain. There is no central mass of nervous tissue in the head of a moon jelly. A moon jelly doesn’t even have a head. It’s “brain” is spread throughout the organism. Yet it changes its swimming behavior and direction in response to complex sensory information that includes temperature, salinity, touch, and light levels. Somehow, without having what we think of as a brain, it coordinates this information from the various parts of its body and “decides” on a response.

These are not simple reflexes, like when your hand jerks back in response to heat. This is more like you lying in the hot sun and deciding, “I’m getting hot, I should go be in the shade.”

No one is suggesting that a moon jelly “thinks” the way we do. But it seems to take in sensory data and then change its behavior over a period of time, which suggests some kind of processing. Jellyfish have been around for about 500 million years. Far longer than us and even longer than dinosaurs. In fact, if longevity is the measure, then jellyfish are one of nature’s big success. Dr. Albert’s hope is that by studying the simple behaviors of an animal that was “thinking” long before we were, we can gain insight into how all animal brains work.

moon jellies

Aurelia aurita

Jelly and Peanut Butter: If you search online for “moon jellies on a beach,” you’ll find other sites that show pictures and if you look at the comments, you’ll see numerous jokes about jellyfish washing ashore in their desperation to find peanut butter. On one of the sites I came across, someone called OceanDreamer went one step further:

“My intuition tells me that thousands of jelly fish came ashore searching for peanut butter fish. They combine for a tasty treat because of the sand-which-is there.”

I should probably turn off the comments on this article to avoid jelly and peanut butter jokes, but I kind of like them.

Sources: Albert, D J. (2014). Field observations of four aurelia labiata jellyfish behaviours: Swimming down in response to low salinity pre-empted swimming up in response to touch, but animal and plant materials were captured equally. Hydrobiologia, 736(1), 61-72.

Albert, D J. (2011). What. Neuroscience & biobehavioral reviews, 35(3), 474-82.

Cite this article as: Pelletier, TC. (September 1, 2014). What are these clear jelly blobs on the beach? Retrieved from http://askanaturalist.com/what-are-these-clear-jelly-blobs-on-the-beach/ on December 17, 2014.

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