Mommy, Where do Baby Sharks Come from?

Let's start this week off with a little quiz, shall we? What's in the picture below?

"Sand." Alright smart-ass, what else? "Shells."

Courtesy: Patrick Feller via Flickr

If you said mermaid's purse, or shark/skate egg then you're right. All of those animals are part of the chondrichthyes (pronounced: con-drick-thees) class of fish.These fish have skeletons made of cartilage rather than bone. We talked a lot about chondrichthyes diversity in the very first blog post if you'd like to get a refresher. The name mermaid's purse applies to the egg cases of all cartilaginous fish because they're leathery, and most are rounded squares like a purse. The leathery-ness is important too because it's tough but flexible. This means the case is tough enough to protect the embryo, but is flexible enough not to shatter. Instead of nesting; skates and egg-laying sharks just kind of drop their kids off somewhere sheltered on the bottom and get on with their lives. That might sound mean, but mom's body produces a yolk that's so rich and full of nutrients that the babies come out of the case fully formed and ready to survive. (Editor's Note: Depth and Taxa does not condone abandoning one's children with 18 year's worth of food and calling it good.) Laying eggs is a method of reproduction called oviparity, and it's only one of several different ways of developing your babies, all of which cartilaginous fish are capable of.

Oviparity is pretty familiar stuff, but let's go over it anyway because it's the root of the other types of reproduction in sharks and their relatives. Unlike many of their bony relatives, chondrichthyans all fertilize their eggs internally. You can actually distinguish males and females of these fish because males have what are called claspers on their pelvic fins (the fins closest to where hips would be.) Claspers are used to hold onto females during mating and deliver sperm into her vent. (the multi-purpose opening of many marine animals.)

The claspers are the little finger-like nubs on the inside of the fins.

Courtesy: eustatic via Flickr

Once the eggs are fertilized they develop the familiar embryo and yolk combination you might have seen shining a flashlight through a chicken egg. Then, like we talked about before, mom drops the eggs off and they develop until they hatch. While inside the mermaid's purse the embryo has only the yolk for nutrients, so when it runs out the baby starts to get hungry and that helps prompt hatching.

Plus the WiFi in the ocean is terrible, so there's no Netflix to

 keep you perfectly still for weeks at a time.

Courtesy: Marian Gonzales via Flickr

 Of the four types of chondrichthyes; sharks are less likely to lay eggs than some of their relatives. All skates lay eggs, as do all of the chimeras. None of the rays lay eggs, and only about a third of what we commonly call sharks don't give live birth.

The next type of fetal development is a weird combination of eggs and live birth. For a long time this was referred to as ovoviviparity (pronounced: oh-vo-viv-i-pair-itty), but this term is falling out of favor because it implies the fetuses aren't getting any nutrients from mom. Recent research suggests that many, but not all, sharks and rays with this means of development contribute at least some nutrients to their babies. This can be through secretions from the uterus that the unattached babies absorb through their skin or consume, or in the form of unfertilized eggs which the developing young eat after their yolks run out. In at least one species the first fetus to use up its yolk will actually eat its brothers and sisters before being born!

"Don't mess with me man, I have seen some s**t "

Courtesy: Justin Morgan via Flickr

 What's consistent across these means of development is that the embryos are never physically attached to their mom. Most of the sharks that give live birth exhibit these strategies for developing their young. All of that is pretty weird and cool, but buckle up, 'cause we're about to take everything we just talked about and add another layer of bizarre.

The last means of fetal development is called placental viviparity. You read that right, placenta like in mammals. Placental development in sharks is a perfect example of one of my favorite concepts in biology: convergent evolution. Convergent evolution is when two very distantly related organisms develop similar traits or strategies completely independent of one another's genes. So even though some sharks have a similar fetal development strategy to mammals it doesn't mean we're related or that we got that trait from sharks.

Amazingly, in placental sharks, the embryos still start out with a yolk. Like other fish the baby shark starts off using up the yolk's nutrients, but late in this process mom's body supplies some of those nutritious secretions we talked about earlier. While her body does this, the lining of the yolk sac actually stretches out and fills with blood vessels. It reaches from the belly of the developing shark to the mom's uterine lining where it attaches and acts as the link between the two for gas exchange (getting oxygen in and CO2 out) and metabolism (getting nutrients in and waste out). This incredible strategy has developed in only a few species of sharks.

"Hey mammals, who's 'highly evolved' now huh!?"
Courtesy: Serena Epstein via Flickr

All of these strategies are spectacular means for getting chondrichthyan babies out into the world ready to survive from the second they emerge. By fully developing inside an egg or their mother; sharks, skates, rays, and chimeras have set themselves up as some of the most successful animals on the planet.

References:

Hamlett, William C., "Evolution and Morphogensis of the Placenta in Sharks", Journal of Experimental Zoology, 1989, vol. 252(S2), pp. 35-52

Musick, J.A. and J.K. Ellis, "Reproductive Evolution of Chondrichtyes", pp. 45-79, In: "Reproductive Biology and Phylogeny of Chondricthyes: Sharks, Batoids and Chimeras", William C. Hamlett, ed., Science Publishers Inc., Plymouth U, 2005

Accessed via: http://www.vims.edu/people/musick_ja/pubs/Repro_Evol_of_Chondrichthyans.pdf

Wourms et al., "The Maternal-Embryonic Relationship in Viviparous Fishes", pp. 5-10, In: "Fish Physiology: Volume XI: The Physiology of Developing Fish Part B: Viviparity and Posthatching Juveniles", W.S. Hoar and D.J. Randall, Academic Press Inc., 1988 

Stubby, Bobtail, Dumplings

Mollusks. Generally they're not a particularly cuddly bunch. For example, most people wouldn't call the inside of an oyster cute.

"D'aaaww who's a good boy?"

Courtesy: Larry Hoffman via Flickr

But there is one group among the mollusks that stands apart. The sepiolidae (pronounced seep-ee-oli-day) are an order of mollusks related to squid, octopus, and cuttlefish. More commonly these animals are called stubby, bobtail, or dumpling squid. None of the stubby squids get much bigger than around ten centimeters (about half the length of an unsharpened pencil), so they're round and small, which makes all of their common names very appropriate. The squid part of the name is a little misleading however because these animals show characteristics consistent with all of their cousins. They spend most of their lives on the bottom, like octopus; they have eight arms and two tentacles, like squid; and they have short rounded mantles, like cuttlefish. 

Who do you think you are? No, seriously I can't figure it out.

A Hummingbird bobtail (Euprymna berryi)

Courtesy: rtonyr via Flickr

Sepiolids are most closely related to cuttlefish which many people guess by the brilliant colors they can produce. Don't let the flashy get up fool you though; stubby squid are some of the best hiders out there. Not only can they change those colors to better match their surroundings, they're also master excavators.

Sepiolids are so cute that they even snuggle up in a blanket to sleep. They dig down by using their siphon (a tube coming from their body that they use to swim and breathe out.) to force water into the bottom and create a little depression. Then they settle down into it and use their arms to wrap themselves in a nice blanket of mud, leaving only their head sticking out.

Makes sense, you've got to wrap a dumpling 

to steam it properly

Courtesy: Nick Hobgood via Flikr

They spend most of the daylight hours tucked in deep water in their sandy beds and come out at night to hunt. Once they're on the prowl they'll often move to shallower water where they're sometimes encountered by lucky divers. 

So if they're this adorable as adults what do their babies look like? Well pretty much exactly like their parents. Dumpling squid have smaller egg clutches than many of their relatives. They lay up to about 50 eggs, which compared to a giant Pacific octopus' max of 100,000 is practically nothing. And unlike many of their relatives' babies, stubby squid don't spend time as a part of the plankton. The young sepiolids break out of their egg cases ready to roll, and walk away to find some food.

The eggs of the Pacific stubby squid (Rossia Pacifica) 

Courtesy: Chris Wilson via Flickr

You'd think that because these animals are so cute and charismatic that we'd know a lot about them. But because they live at the low end of recreational dive limits, are nocturnal, bury themselves, and tend to live on sandy bottoms which divers often ignore, we actually know very little about the lives of these cool little animals.

References:

Rodrigues et al., "Burying Behavior in the Bobtail Squid Sepiola atlantica (Cephalopda: Sepiolidae)", Italian Journal of Zoology, Apr 06, 2010

Anderson, Roland C.,  "Rossia Pacifica, Stubby Squid", The Cephalopod Page,

www.thecephalopodpage.org/Rpacifica.php

The Great Pacific Garbage Chowder

The Great Pacific Garbage Patch: it's flashy, disturbing, simple, a great band name, and... is completely misleading. That name was given to an area in the Pacific ocean by Curtis Ebbesmeyer when a colleague reported on the amount of floating plastic in the area. Because the name is so catchy it stuck, and has been used extensively in popular media reports ever since. So what's it look like? Well prepare yourself, below you're going to see a picture from the very heart of this trash zone that's been described as having a surface area twice the size of Texas.

Where's all the garbage?
Courtesy:  ---=XEON=--- via Panoramio

The problem with the term patch is that it suggests a covering, like in a patch of grass; or a lot of big pieces, like in a cabbage patch. Neither of these is what you see in these areas. Really what's happening is that giant ocean currents, called gyres, are concentrating tiny bits of plastic (called microplastic) in their middles. The gyres are more like plastic chowder than a plastic patch. And just like in a chowder the chunks aren't evenly distributed. Different types of plastic have different densities, so they float at different heights in the water column or even sink to the bottom.

This is the North Pacific Gyre. There are two major gyres in the Atlantic and Pacfic,
 and one in the Indian Ocean
Courtesy: NOAA Ocean Service's Making Waves podcast

So why isn't the plastic more evenly distributed, or at the very least why isn't it close to land? Well it has to do with the fact that the gyres are circular currents. When particles sit in water they are partly held up by how fast the water is moving. In swirling water, like the gyres or a cup of tea being stirred, the water at the center is moving slower than the water at the edge. Particles catch on the slow water and are pulled into the center where they stay more or less still.

 Red sprinkles in water before, during, and after stirring: Some sprinkles float, others sink; all concentrate into the center; just like pieces of plastic caught in the ocean gyres.

There are a number of issues associated with plastic in the ocean, and all originate with the fact that plastic doesn't biodegrade. Plastics are designed to last forever; they're stable, cheap, and sturdy. When we throw out plastic it never turns back into the minerals that it came from. Plastics just continually degrade into smaller and smaller pieces, but they stay plastic for functionally forever.
The first problem is that plastic takes up space. Several studies over many years have led to calculations of about 35,000 tons of microplastic and 250,000 tons of larger plastics in the oceans. All of those bits can easily lead to entangled marine animals.

The other big issue is that act of breaking down. As plastics break into smaller and smaller shards they're inadvertently gobbled up by smaller and smaller organisms, entering the food chain at more levels. While they're breaking apart and mixing around in the ocean, the chemically raggedy edges of the plastic grab onto many of the toxins commonly found in sea water. This takes those chemicals from their spread out, and therefore less dangerous, state to concentrated on one of these bits. Some of these toxins are hormone disruptors and there's a growing body of evidence that they can and will affect fish by changing their reproductive organs to those of the opposite sex.

Lastly, when plastic breaks down it becomes much harder to clean up. Imagine trying to separate all the parts out of real chowder, including the spices. Some of it can be picked out pretty easily, but others not so much. The microplastics are so small that we can't go out and grab it all because we'd have to screen the water with nets with really tiny holes. Nets with tiny holes are also how you catch plankton, so to catch the estimated 5 trillion bits of plastic out there we would probably decimate plankton populations.

"A few billion more of these and we can save and destroy the ocean at the same time"
Courtesy: NOAA Photo Library via Flickr

There's also the problem of some plastic sinking. For years surveys of ocean plastics weren't finding as much as researchers expected, but we knew that our waste was making into the ocean, so where was it all going? Well it turns out, straight to the bottom. A three ocean study of deep sea sediments has found significant amounts of microplastic fibers in the depths. A lot of these fibers were rayon and acrylic, materials found in synthetic clothing that probably got into the water from particles coming off as the clothes were washed.

Alright if we can't clean up everything then what do we do? Well the beautiful thing about this issue is that it's entirely in our hands. There isn't a single company or government that has caused all this pollution, so there's no one to fight with to make it stop. We are so powerful in this situation it's unprecedented. The most important thing is to stop using plastic like it has a short life. That tupperware you or your parents bought in the 70's and is still in your kitchen; that's how plastic should be used. Keep that sucker around forever and hand it down to your kids too. Those Legos that have been dropped, washed, stepped on, pummeled, and still haven't broken. Hell yeah that's my kind of plastic. Where you can, eliminate single-use products, and when you're out walking pick up a piece of litter each time. If we do these things we can make a dent in the 30% of all plastic that gets thrown away within a year.

I have to give credit to Edward Humes, author of Garbology for the term "plastic chowder" it really is a perfect metaphor.

References:

Cozar et al., "Plastic Debris in the Open Ocean", Proceedings of the National Academy of Sciences, Vol. 11 No. 28, 2013, DOI 10.1073/pnas1314705111

Accessed via: http://www.pnas.org/content/111/28/10239.full

Ericksen et al. "Plastic Pollution in the World's Oceans: 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea", PLOS ONE, 2014, DOI 10.1371/journal.pone.0111913

Accessed via: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0111913

Woodall et al, 2014, "The Deep Sea is a Major Sink for Microplastic Debris", Royal Society Open Science, 1:140317, http://dx.doi.org/10.1098/rsos.140317

Rochman, Chelsea, "A Story About Fish, Plastic Debris, and Sex", Deep Sea News, 2014,

Accesses via: http://deepseanews.com/2014/10/a-story-about-fish-plastic-debris-and-sex/

Humes, Edward, "Garbology", Ch. 5-6, Penguin Books, 2013

Over 1000!

Imagine my surprise when I logged onto the blog this morning and saw that Depth and Taxa has surpassed 1000 page views! I'm pretty sure my face looked something like this.

I appreciate you all sharing in the exploration of the marine environment with me. This blog has only been active for four months, and I never expected it to get to this point so fast. To everyone in the states, and the folks around the world who have been learning along with us,

Thank you, Dziekuje, Merci, Danke, Tesekkur ederim, Gracias, Dankjewel, Diakuju, and Spasibo.

The Notorious B.I.G.

"Where does everyone keep getting that number!" I shouted irritably one day while doing some research for the Seattle Aquarium. I was profiling the giant Pacific octopus (Enteroctopus dofleini) and the number that kept coming up was 272Kg/600Lbs. Don't get me wrong, giant Pacific's are well named. They're the largest octopus species in the world, and they can be massive. The largest animal I ever encountered was an octopus named Roland who weighed over 90 pounds and he had an arm span above ten feet.

Giant Pacific octopus also grow incredibly fast. They're short lived, only lasting 3-5 years in the wild, and they go from the size of a grain of rice to broader than a man's height in that time. It's been estimated that they average a gain of 1-2% of their body weight every day. They literally grow exponentially. A well-fed octopus gets bigger today than it got yesterday, and will get bigger tomorrow than it got today.

What had me so flustered about that 600 pound claim is that most giant Pacific octopus never get any bigger than 70 pounds, and the reliable accounts of extremely large animals only weighed around 120 pounds. I found article after article that referenced that size, in both the popular press and the peer-reviewed literature. Six hundred pounds is so far off from what's normally their maximum that I began thinking fish stories might not always be about fish. Many articles even acknowledged that any account above 120ish pounds was probably unreliable.

"I swear it was like two people across!" (Person in this example is defined 
as one elementary aged child) 

Courtesy LAZLO ILYES via Flickr

     Of course it's not not unheard of for a population of animals to shrink over time due to human influence. For example, the dusky grouper (Epinephalus marginatus) from the Mediterranean, is thought to be much smaller than before modern fishing pressure. In ancient Roman murals dusky grouper are portrayed as almost as large as a man, now they rarely get bigger than around 50cm (about 19 inches). Giant Pacific octopus on the other hand haven't really been a targeted catch thanks in part to their chewy texture. It could be that pollution has affected the health of these species, but the reports of truly giant octopus were claimed to be from Alaska where human impact is less significant.

Alright, so where did this number come from? Well lucky for our quest to discover the origins of the "super giant Pacific octopus, TM" , science has a spectacular convention of citation. At the end of every peer reviewed article the authors are expected to cite previous research that informs their experiment and is the basis of their prior knowledge. You can think of it as a built-in BS alarm.

Statistical analypus thinks you should have used an eight tailed test.
Courtesy canopic via Flickr

So I took the opportunity to put on my detective cap and dig around some scholarly research! I have friends I swear, they're humans and everything. Anyway after a little leg work (keyboard work?) I managed to track down the source of the 600 pound octopus in the room. It turns out that in 1975 William High wrote a summary of knowledge about giant Pacific octopus for the National Marine Fisheries Service's annual report. This article was cited by almost every paper I had been looking through, so I suspected it was what I needed. Thankfully the good folks at NOAA keep an online archive of these reports.

In High's summary he discusses how large these animals can get and even he doesn't totally buy the hype at first. He states: "Much larger ones (octopus bigger than 100 pounds) have been reported, but like the Loch Ness Monster, these usually elude the careful photographer or scientist." which is basically the scientific paper equivalent of "cool story bro." But then just a few lines later he goes on to say: "In the late 1950's I interviewed a Canadian commercial diver Jock MacLean... He reported capturing an immense creature weighing 600 pounds and measuring 32 feet from arm tip to top. MacLeans photographs, unfortunately, were of poor quality. Smaller animals, to 400 pounds, were occasionally taken..." Seriously!? Poor quality photos and the testimony of a guy whose job it was to go and get narc'd all the time are all we're going on. You'll have to forgive me if I remain skeptical.

"No you can't be real! The scientific literature doesn't substantiate 
your existence!" -The ship's naturalist
 "Denys de Montfort Poulpe Colossal" by Pierre Denys de Montfort († 1820)
 - Ellis, R. 1994. Monsters of the Sea. Robert Hale Ltd. Licensed under Public domain via Wikimedia Commons  

Sadly it looks like the reports of "super giant Pacific octopus ™" have been exaggerated, even among those who try hardest to avoid hyperbole. Although I can't help but wonder; why is a giant octopus such a universal story? From the legends of the kraken to the creature that supposedly lives under the narrows bridge in Tacoma, Washington; monstrous octopus just capture our imagination. Maybe long ago there were octopus large enough to destroy a ship, or maybe having no frame of reference in the vastness of the ocean led to exaggeration. Either way the real giant Pacific octopus is a huge, magnificent creature that deserves our respect.

References:

Cosgrove, James, & McDaniel, Neil, "Super Suckers: The Giant Pacific Octopus and Other Cephalopods of the Pacfic Coast.", Harbour Publishing, March 2009

High, William, "The Giant Pacific Octopus", Marine Fisheries Review, Vol. 38 No. 9, Sept. 1976
Accessed via: http://spo.nmfs.noaa.gov/mfr389/mfr3893.pdf

Guidetti, Paolo, & Fiorenza, Micheli, "Ancient Art Serving Marine Conservation", Frontiers in Ecology and the Enironment, 9: 374-375, DOI 10.1890/11.WB.020

Life, uh, Finds a Way

A few hundred years ago we believed that nothing could live in the deep sea. Even as our understanding of the world grew, in some ways we lost our imagination. We began to understand that the deep was incredibly cold, very low in oxygen, and subject to astonishing pressures. So we assumed that this environment was just too inhospitable . Boy were we ever wrong.

A mile and a half down (2560m), on the vent field of an active volcano.
Courtesy NOAA Ocean Explorer via Flickr

More and more, we're seeing that life not only exists in the darkness, but thrives. A few weeks ago we talked about animals up in the water that survive with little light, but now we're headed to the bottom. The above image comes from a deep sea hydrothermal vent community, which in the last few years has become relatively well known. Thanks to programs like Blue Planet and Planet Earth, there is beautiful footage of these ecosystems readily available to the public.

But hydrothermal vents are a small part of the ocean bottom. Other incredibly diverse ecosystems exist, and with the prevalence of the internet, researchers are starting to show them as they're discovered. Some of the coolest environments being found are cold seeps.

There are several types of cold seep ecosystems, but what defines them all, is gasses escaping from underground into the water. Seeps have been found all over the world, from as shallow as 15m (easily diveable) to over 7000m (not easily anything), and even in inland bodies of water. Generally seeps are found on the edges of continental slopes where the earth's crust is bending and folding. Unlike hydrothermal vents cold seeps are not due to magma heating seawater and expelling it back out of the ground. Seeps form in places where a lot of plant and animal matter has settled to the bottom, become buried, and decayed. As that material breaks down it makes a lot of methane gas. Then as the ground bends it squeezes the gas, pushing it closer to the surface through the soft sediments on top. My apologies for being crass, but yes, the earth does fart.


A stream of bubbles escapes from the ground at a cold seep
Courtesy Deepwater Canyons 2013 - Pathways to the Abyss NOAA-OER/BOEM/USGS

The gas alone is not enough to establish an ecosystem; some organism needs to harvest the gaseous bounty to start a food chain. On land and in the surface waters, plants convert the sun's energy into chemical energy using CO2. At cold seeps bacteria and archaea convert the energy in the methane (CH4) coming from underground, and sulfate in seawater, to a type they can use. In a spectacular bit of symbiosis the archaea manipulate the methane and the bacteria manipulate the sulfate, then they use one another's products to complete their energy conversion. The exact nature of this back and forth isn't well understood, but scientists do know it produces hydrogen sulfide.

The hydrogen sulfide is then used by bacteria living inside animals to produce even more energy. These animals (some types of mussels, clams, and tube worms) have little to no digestive system. They get their energy straight from their symbiotic bacteria. At many cold seep sites large mats of bacteria and archaea are surrounded by these animals. Sometimes they even form a bulls-eye of different colors radiating out from the center.


Bacterial mats (white) and mussels (brown/orange) thriving at a cold seep
Courtesy NOAA Photo Library via Flickr

These large sedentary animals draw in small animals that take shelter in the jumbled chaos of their shells. Predators of those small organisms then come hunting. Many animals also feed directly on the bacterial mats, so there don't even have to be larger organisms around them. Entire ecosystems develop from the toots of the planet. Some of the animals that take advantage of cold seep environments are even ones that we eat, like sablefish and crabs. King crabs have even been observed feeding on bacterial mats, leaving, and coming back only after enough time has passed for the mats to regrow!

All of this biological activity helps contain methane (a potent heat trapping molecule) in the sea, keeping the temperature of the earth from rising even more. Also many seeps found in very deep water have low enough temperatures and high enough pressures for solid ice crystals to encase methane molecules. These "methane hydrates" also help keep carbon out of the atmosphere. You can see the biological and geological carbon traps interacting in this adorable video below.



Cold seeps are a good number of deep sea ecosystems, but there's more talk about, and even more to discover. Clearly the ocean bottom isn't quite so lifeless as we once believed. And probably it's even more full of life than we currently understand. Jurassic Park's Ian Malcom knew what he was talking about.

References:

Levin, Lisa, "Ecology of Cold Seep Sediments: Interactions of Fauna with Flow, Chemistry and Microbes", Oceanography and Marine Biology: An Annual Review, 2005, 43, 1-46, Taylor & Francis

Accessed via: http://levin.ucsd.edu/publications/Levin%20OMBAR%2005.pdf

Niemann et al., "Methane-Carbon Flow into the Benthic Food Web at Cold Seeps- A Case Study From the Costa Rica Subduction Zone", PLOS ONE, Oct. 2013, DOI: 10.1371/journal.pone.0074894

Accessed via: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0074894#pone.0074894-Niemann1

"Discovery of a New Chemosynthetic Community" NOAA Ocean Explorer

http://oceanexplorer.noaa.gov/explorations/13midatlantic/logs/may8/may8.html

A Ray of Hope

Courtesy kathleenreed via Flickr

It's a story that lends itself to hyperbole. An unknown disease causing the literal disintegration of a large group of animals across a wide geographic area. Sea star wasting disease has been on the minds of every marine science professional for the last two years. And amazingly...wonderfully, this issue has captured the attention of the general public as well. Through traditional media, the internet, and personal experience, sea star wasting has become, I think, the most visible issue facing the oceans today.

In case you haven't heard, throughout the North East Pacific, from Alaska to California sea stars have been dying off in large numbers. The animals begin to show signs of distress by curling their rays in unusual ways. Then white lesions (any kind of damage to tissue) appear on the outer skin. These lesions then disintegrate further until holes appear. Eventually the holes grow so large that limbs separate from their bodies, and the animals crumble into piles of skeletal plates. Some reports have stated that the disease causes the arms to walk away from the body, but that is a blatant exaggeration. Partly because stars don't have brains, their limbs can survive for a surprisingly long time after they've been separated from the central disk. So while the disease does cause the arms to come off, it's not what's causing them to keep moving. Sea stars can even deliberately drop off limbs in an attempt to protect the rest of their body from disease and predators. Then they grow a new ray in it's place.

 "We can rebuild him, we have th...." "No that's okay he'll do it himself"

Courtesy Jill Siegrist via Flickr

So why can't the stars regenerate from the damages of the disease, and what the heck is causing it in the first place? Well for the last two years the answer has been a big, fat, "I dunnuh", but that's because researchers have been furiously looking into it, and good experimentation takes time. There has been amazing collaboration between aquariums, research labs, and everyday folks to study the spread and cause of wasting. From this collaboration a new study has identified a virus that is associated with sick stars.

Last year a team of researchers discovered the first virus associated with echinoderms. They found the pathogen inside the tissues of sea urchins on Hawaiian coral reefs. This virus was a type of densovirus which are most commonly found infecting arthropods, like crabs, shrimps, and insects. In the urchins the virus wasn't causing any disease, but as the outbreak of sea star wasting became more severe the scientists wondered if something similar might be at fault. 

First they needed to see if there were any viruses in the stars at all, so the scientists separated virus sized particles from the tissues of sick stars and injected healthy ones with this material. They also boiled samples of those particles before injecting other healthy stars; doing so destroys the DNA that viruses could use infect the organisms. Sure enough the stars that received potentially active viruses became sick with wasting and the ones that received the boiled samples did not.

MMMM Nothing like a nice hard-boiled virus to start the day

Courtesy michelle@TNS via Flickr

From there the team ran a viral DNA analysis on the sick animals and found a densovirus that is unique to stars. They named the pathogen Sea Star associated Densovirus or SSaDV for short, and the more copies of the virus the stars were carrying the more likely they were to start wasting. Interestingly the team found that for most stars, the larger the animal, the greater the viral load, but the opposite was true for the sunflower star (Pycnopodia helianthoides). Sunflower stars were one of the first and most heavily impacted by the disease, so I'm curious if this association may have something to do with that. Through this, and some other lines of evidence, these researchers have found a compelling correlation between this virus and sea star wasting.

So is that it? Can we all wash our hands of this and get on with out lives? In short, no. The study confirms the existence of a virus associated with wasting, but it doesn't look at how the virus interacts with the sea stars' cells. It's extremely likely that the virus alone isn't what's causing the stars to die. Especially since the researchers looked at samples of stars collected as far back as 1943 and found the same viral DNA. And when you think about it that makes sense. When you contract a virus you don't get sick purely because the virus is in your body. You get sick because the virus combines with your stress from work, and the bacteria in your environment, and the fact that you stayed up late having drinks, to tax your immune system until it can't suppress the virus anymore and you get symptoms.

There has been extensive coverage of this study, but the problem is that many news outlets are claiming the answer has been found and they have ignored an important takeaway from the paper's conclusion. From the paper itself: "However it remains to be seen how infection with SSaDV kills asteroids, what the role is for other microbial agents associated with dying asteroids, what triggers outbreaks, and how asteroid mass mortalities will alter near-shore communities throughout the North American Pacific Coast." (Hewson et al. 2014). Essentially the author's are saying " this is a good start, but we have a lot to look into."

It's even possible that disease is a normal means for the

environment to handle overpopulation of echinoderms

Courtesy US Fish and Wildlife via Flicker

It all seems a bit bleak, but like I said before there has been an incredible amount of collaboration, and unprecedented visibility to the plight of West coast stars. Knowing the densovirus is associated with the disease won't stop it, but now we have jumping off point to further our understanding. This is a unique opportunity for you, as an interested person, to participate and keep this research alive.

So if I could ask one thing of you all it's this: Keep paying attention. Stay up to date, visit your local aquarium and ask questions, follow researchers on twitter. You can even go out and survey beaches for wasting stars yourself and scientists will use your data. Together we can develop a strong understanding, citizen and scientist alike, of what this disease is and does. So if you make statement about stars, or upload some pictures to social media I encourage you to attach the hashtag #RayOfHope, and we'll see if we can keep the momentum going.

For more information on the study that identified the virus check out this great summary from Ed Yong with National Geographic. Or read the paper yourself for free on the National Academy of Sciences website. 

References:

Hewson et al., "Densovirus associated with sea-star wasting disease and mass mortality", Proceedings of the Natural Academy of Sciences, Oct 2014, DOI 10.1073/pnas.1416625111