Just a FAD

Courtesy: Pedasi consultant via Wikimedia Commons

Hi there. My name is Titus. I'm a yellowfin tuna. You're probably guessing this post is going to be all about me and my family, and you're justified in thinking that. But the truth is, this is all about you.

You see your species really, really loves to eat us. Well not so much yellowfin specifically, but my cousins bluefin and skipjack tunas. Bluefin are the most expensive food fish in the world. Someone bought a relative of mine for $1.8 million in 2013! That crazy price tag means most of you have probably never eaten a bluefin. If tuna's ever crossed your lips though, you've almost definitely eaten a skipjack. Skipjack gets sold in cans that say "chunk light" on them and that's about 70% of the tuna in the US. The problem comes when you go to catch skipjack, the way you catch them means you also catch my siblings, and a bunch of other animals in the process.

Now I want to be clear; I have no moral authority to say you shouldn't eat fish. From one apex predator to another; I totally get it. Many of you have probably seen a documentary where we tear through a bait ball like it was nothing. In fact my mom was there when the BBC filmed the original Blue Planet. The difference between the way we catch our fish, and the way you catch yours comes down to effort. We really earn it, you often make it too easy. To what see I mean I'll have to show you a little bit more about where I come from.

"Follow me."

Courtesy: Elias Levy via Flickr

My relatives and I live a pelagic (pronounced pel-aj-ick) lifestyle. That means that we're always swimming closer to the surface than to the bottom. Don't get me wrong though; we've been seen diving over 2,000m down. It's just that we live in the big part of the ocean, the part that makes your stomach drop when you look down and there's nothing but blue fading to black over the miles beneath your feet.

It still doesn't do it justice, but for scale, those aircraft carriers are 1,000 feet long.
Courtesy: US Pacific Fleet via Flickr

It takes some really special adaptations to find food in this great azure emptiness. There's little phytoplankton to feed the ecosystem out here so prey are spread very far apart. That means we have to cross hundreds of miles of what's essentially desert to have opportunities to hunt. And we're not talking about pretty, cactus rich desert like the American Southwest here. The open ocean is more like the Dune Sea on Tatooine from Star Wars.

Even the way we're born is designed to help us get by in the vastness. My mom, carrying about 2 million of the eggs that would become me and my siblings, swam from the open Atlantic into the Gulf of Guinea off the West coast of Africa. Why there? Upwelling and river runoff. Nutrients from the bottom of the ocean and far inland travel into the surface waters of the Gulf and fertilize massive blooms of planktonic algae. Those plant-like plankton feed animal plankton, which are pretty much Gerber baby food for larval tuna.

Way cuter than that weird larval human on the jar
Courtesy: K. Dale via NOAA

I hatched from my floating egg into this rich soup of life where I fed on all kinds of tiny and delicious animals. Seriously, you guys haven't lived til you've tried copepods. Anyway, chowing down on these energetically rich little buggers meant that it only took about a month for me to develop the muscles I needed for adulthood. High stamina "red muscle" in my sides allows me to continuously swim for hundreds of miles with no breaks. In fact, I can't actually breathe if I'm not always swimming so taking a break would be a terrible idea. Those stoic red muscles are the tissue that you eat as poke, or sashimi, or in sushi rolls, or seared, or on salads. You really like to eat our red muscle is my point. And like I said before, I totally understand wanting to eat delicious fish. That's basically my entire diet.

So my parents set us up in a great feeding ground and we grew quickly, but the ocean is a fickle place. Pretty soon the plankton blooms started to die back and the anchovies, herring, and other small fish my relatives and I were eating began to disappear. Luckily one part of the ocean's end of the bloom is another's beginning and I felt something deep inside me stir. This instinct drove me to join up with other tunas and pushed us all out into the formless wilds of the open sea.

And here's where we start to get to the larger point. I didn't school up with just yellowfin tuna. I joined with albacore, skipjack, bigeye, you name it. As long as we were about the same size none of us cared if we were the same species or not. My school doesn't even care if we're all fish; sometimes we work with dolphins. We even hang out with whale sharks every fall in the Gulf of Mexico, those dudes are super chill. While this embracing of diversity is awesome it poses a problem when you scoop up our whole school in nets. If you're fishing for skipjack, which are a stable fishery, but you use a big net you almost always catch a bunch of the rest of us. There are fewer of us yellowfin, and waaaay fewer bluefin than some of the other species. You could theoretically sort through and pick out the species you're not targeting, but remember we don't last long if we're not continually swimming, and to be honest we all look a lot alike when we're young.

Case in point: Both these pictures are labelled as yellowfin on Flickr. 
The two on the left are skipjacks.
Courtesy: Stephanie Rogers and NOAA via Flickr


To make it worse, people catching tuna often use something called a FAD to lure us in. FAD stands for Fish Aggregating Device. That's a fancy sounding name, but it could be literally anything anchored to the bottom that provides something to hide on, under, or around. Old plywood, clumps of rope and sail, seaweed and branches, literal trash; all are shockingly useful to us pelagic creatures.

 For animals that spend their lives travelling, floating debris is like a cute diner you stop at to pee and buy a slice of pie while on a road trip. Small fish are drawn to the piles because they think it will give them somewhere to hide from predators. Larger fish are attracted to the piles because we aren't dumb. There's literally nowhere else for you to hide anchovy! Anyway this is normal and good when it's natural debris, but when humans place the material on purpose....

Once every fish from miles around has come to your FAD you can efficiently dent the population with a single net haul.

Truthfully, I can't really get mad at you for such cleverness. Humans have used the adaptations they were given to survive challenging environments the same way we have. But the difference is that you have a choice. Your species is so smart that most of you have access to more calories than any of us in the ocean could dream of. So if you want to make sure me and my cousins don't disappear there are a couple things you can do.

Eating lower on the food chain is a great choice. Be like me and eat mackerel! Mackerel have nice, soft white meat like albacore, with none of that fishy taste that scares a lot of people off. Also if you're going to eat tuna make sure it comes from someone who's committed to ensuring we stick around on this planet. Since canned represents the vast majority of the tuna you eat, it's especially important to consider the health of our stocks when you're buying it. Thankfully some nice humans have produced this chart:

Courtesy: Greenpeace via Greenpeace.org

It's awesome! Open Nature, American Tuna, Whole Foods and Ocean Naturals all employ fishing boats that don't use FADs. They also catch us with individual hooks and lines so that it's nearly impossible to catch the entire school! I chase down prey at 30 miles per hour or more so I can understand the thrill of the hunt that comes with bringing a fish in on a single line too. Just know that if it's ever me you catch; I'm gonna fight hard. We're all just trying to live as best we can.

Editor's Note: The text of this post was dictated to a tuna researcher by Titus from his autumn home in the Gulf of Mexico and emailed to the Depth and Taxa team. It would be absurd to think that a fish could type. However tuna do in fact have a broad knowledge of human culture particularly: Star Wars, memes, and Star Wars memes.

References:

Allain et al., "Interaction Between Coastal and Oceanic Ecosystems of Western and Central Pacific Ocean through Predator-Prey Relationship Studies", PLOS One, Vol 7 Issue 5, May 2012 

Via: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0036701

Arocha et al., "Update on the Spawning of Yellowfin Tuna, Thunnus albacares, in the Western Central Atlantic", Collective Volume of Scientific Papers, 52(1): 167-176, 2001

Via: https://www.iccat.int/Documents/CVSP/CV052_2001/no_1/CV052010167.pdf

Gonzales-Andres et al., "Abundance and Distribution Patterns of Thunnus albacares in Isla de Coco National Park Through Predictive Habitat Suitability Models", PLOS One, December 14th 2016

Via: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168212

Scutt Phillips et al., "Revisiting the Vulnerability of Juvenile Bigeye (Thunnus obesus) and Yellowfin (T. albacares) Tuna Caught by Purse-seine Fisheries While Associating with Surface Waters and Floating Objects", PLOS One, June 29th 2017

Via: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0179045 

Precious Argo

How's the old saying go? "If it looks like a duck, swims like a duck, and quacks like a duck, then it's probably a duck."

"Quack?"

Courtesy: Derek Bruff via Flickr

By extension I can imagine this test applies to any animal. Let's pick a random one and try it, shall we? If it looks like a..... Nautilus, swims like a nautilus, and has a shell like a nautilus it must be a nautilus. 

"Oh my God! What did you just call me!?"

Courtesy: Michael Vecchione via TOLWeb.org

Oh yeah I'm sorry, paper nauti..... I mean greater argonaut (Argonauta argo). I totally forgot about you. How about I make the rest of this post about how awesome you, and the other three species in your family, are to make up for it?

"We can live with that. I'll just sit here and make sure you

 don't mess up again"

Courtesy: NOAA Photo Library via Flickr

Okay where to start? Well, how about at the very beginning like my nanny used to say. Disclaimer: My nanny may have just been Julie Andrews movies. Anyway, we've known about argonauts for an incredibly long time. Their delicate, paper-thin, shells have been found painted on artifacts from 4000 years ago! Of course, back then we barely knew anything about these animals because we were mostly finding their old shells washed up on the beach. 

However many of the ancient Greeks were talented naturalists, and they started looking closer at these coiled beauties. Aristotle noticed that the argonauts could climb out of their shells because they aren't attached to them like a true nautilus or any other shelled mollusk. So how did Aristotle think argonauts got their shell? Well he assumed they stole it. For the longest time scientists thought that argonauts couldn't be making their own shells, so they were taking them from an unknown animal and using them as boats. Now this seems a little crazy, but add in the fact that female argonauts have sail-like webs on two of their arms, and you have the perfect animal to send after the golden fleece. 

Hahaha...What is it even...? Hahaha...There's a boat to compare it to..Hahahaha!

Bless you for this: Gerard Van der Leun, via Flickr

Although the theory that argonauts combined Grand Theft Auto and that pirate Assassin's Creed (Hold on I have to go pitch an idea to Microsoft) persisted well into the 1800's, eventually science started to sober up. We later discovered that female argonauts make the shells using glands in their webs that secret calcite. They spread these webs out over the shell and lay down material bit-by-bit like nature's 3D printer. 

 On the left you can see the webs with chromatophores, extended over the shell.

On the right this female has pulled the webs back, exposing her construction.

Courtesy: Michael Vecchione via TOLWeb.org

 If you're an astute reader, you've probably noticed that I've only mentioned female argonauts so far. This follows the history of these animals because for the longest time we had no idea what the males looked like. Why? You might ask, well they're tiny, like really tiny, only 1% the size of a female, and the biggest species' female only gets to 30cm across. Plus the males don't build shells, oh and sometimes they only have seven arms.

See argonauts are octopuses, and they normally have eight arms like any of their relatives. However one of a male octopuses arms is very different from the others. The third arm on his right side is called a hectocotylus (pronounced: heck-toe-cot-oh-luss) and it's used for reproduction. The males of most bottom-dwelling octopuses insert their hectocotylus into the female's gill opening; and sit there for a bit while a packet of sperm passes from inside his body, down the arm, and into the female's oviduct. Argonauts don't have the luxury of that kind of time though. They differ from their cousins by living up in the water column, instead of down on the sand. Living in the open ocean is great way of avoiding competition with your cousins down below, but it also means you have to travel far and quick to find food, mates, and shelter. 

Because the ocean is so big, and argonauts so small, males may not have many chances to find a female. To make sure they mate effectively the male argonaut's hectocotylus actually breaks off inside the female's body cavity, and he swims away. By embedding his sperm delivery system in the female, the male has insured that it's his DNA that fertilizes the eggs. Plus it's a great way to screw with naturalists. This is not a joke, the scientist who first found a hectocotylus buried in a female argonaut thought it was a parasitic worm!

 Plus what the hell do we call this thing, a septopus?

The eighth arm is kept inside that pouch.

Courtesy: Edwald Rubsamen via Wikimedia Commons and Public Domain

Now here's where the functional beauty of the female's shell can accompany its aesthetic beauty. Since she lives up in the water there's very little to attach her eggs to, and good material could be floating hundreds of miles from the female argonaut, so she lays her eggs right inside the shell. Female argonauts handcraft baby strollers to push their kids around in until they hatch. Not only that, but the shape of the shell allows the female to trap air in its top which helps counter-act the weight of her body and the eggs; and keeps her from rising or sinking too fast. 

You can see the eggs hanging out of the lower part of this female's shell.

She's new to this whole arts and crafts thing.

Courtesy: Bernd Hoffman via Wikimedia Commons

So how'd I do argonaut? Did we cover everything that makes you so cool? Be fair, we don't know much about you since you're all so small and you live in oceans around the entire world.

Whoooo! Nice work! Go team Argo! High eights all around!

Courtesy A.E Verrill via Wikimedia Commons and Public Domain

References:

Finn, Julian K., "Taxonomy and Biology of the Argonauts (Cephalopoda: Argonautidae) with Particular Reference to Australian Material", Molluscan Research, 2013, Vol. 33, No. 3, 143-222.

Heeger, T., Piatowski U., & Moller, H., "Predation on Jellyfish by the Cephalopod Argonauta argo", Marine ecology Progress Series, Vol. 88, 293-296, 1992.

Orenstein, Marcie, "Marine Invertebrates of Bermuda: Paper Nautilus (Argonauta argo)", The Cephalopod Page, 

Accessed via: http://www.thecephalopodpage.org/MarineInvertebrateZoology/Argonautaargo.html 

Mangold, K., Vecchione, M., & Young, R., "Argonautidae", Tree of Life Project, 

Accessed via: http://tolweb.org/Argonauta

Over the Moon...fish

If you're at all curious about the ocean, and let's face it you're reading this blog so you probably are, you're most like likely aware of the mola mola. Molas are also called sunfish thanks to their penchant for lounging at the surface like beach goers looking for a tan. 

That's fair, this is about what my thighs look like the first 

time I go out in shorts every year.

Courtesy: Sandip Bhattacharya via Flickr

So if there are sunfish out there, are there moonfish? That may sound like the kind of lame joke your uncle might make at a family dinner, but it's actually a valid question. And yes there are a couple of species commonly called moonfish. My favorite of these, and an animal I only discovered recently, is the opah (Lampris spp.). Opah look a little like mola, but they're completely unrelated.

Oooo, shouldn't have gone with the spray-on tan.

This fish is incredible. Believe it or not they're related to oarfish. If you've never seen them before, oarfish are anything but round and squat. In fact the giant oarfish (Regalecus glesne) is the longest of any bony fish, usually growing to 8 meters. It's believed that giant oarfish originated the legends of giant sea serpents. While they're generally pretty different; if you look at opah and the oarfish (dibs on the band name) side by side you can see a bit of a resemblance.

Talk about awkward family photos.

From Field Book of Giant Fishes 1949 courtesy: Biodiversity Heritage Library 

Both fish have those large dorsal (on their back) fins with a large crest in the front. They've also got long pelvic fins extending down from their bodies. It's going to sound incredibly unscientific to describe it this way but they're also both very shiny. The scales of these fishes are so reflective that their group name (Lampriformes) means the shapes of light. That reflectivity is really useful in both fishes' habitat, the open ocean.

Okay, so why are we not talking the sea serpent one? The opah just looks like someone took a belt sander to the edges of a tuna. Its tail is so small compared to the rest of its body it doesn't even look like it would help the opah swim. Ah, you're right imaginary snarky reader! Opah don't use their tail fin to propel themselves through the water. Instead they use their pectoral fins, flapping them up and down like a penguin! They're also massive, the biggest opah ever caught weighed over 300lbs. Yet despite their size and stubby looking fins opah have been recorded speeding away from predators at four meters per second. That's about twice as fast as most people jog.

In order to move all that mass around opah have powerful muscles behind their pectoral fins. The muscles are so burly that they look, and apparently taste, more like beef than fish; even though the rest of the opah's muscles are similar to those of tuna.

"Moo?"
Courtesy: Io [Public domain], via Wikimedia Commons

It's kind of incredible that we have a lot of information about what Opah taste like, and you can find plenty of recipes online, because we hardly know anything about their biology and life history. Opah live in deep water, rarely coming to anything shallower than 50 meters and they don't live in schools. Both those things make them especially hard to study. It doesn't help that during the day when we humans like to be awake, opah spend time at the deepest parts of their range foraging mostly for squid.

Most encounters with opah come from fisher people long-lining for tuna. Long-lining is a fishing technique where several-hundred meter lengths of line are dropped down covered in hundreds of baited hooks. Inevitably something other than the target species gets caught; thinking they're snagging a free meal. This is referred to as bycatch, and many bycatch species aren't commercially valuable, so they're thrown back dead. Fortunately for fishers opahs' tasty meat makes them very valuable and they're able to keep and sell them. You can watch some guys in Hawaii filleting an opah in the video below. Skip ahead to the 2:50 mark to get past the local TV shenanigans, or enjoy the dorky jokes and watch the whole thing.

The thing is we don't know how this catch affects the opah population. Some people think they're safe because there isn't a targeted fishery, and others think we don't know enough to say whether they're being seriously harmed or not. The Monterey Bay Aquarium's seafood watch program, which is well researched, recommends avoiding eating opah from international sources, and only occasionally enjoying those caught in US waters. This is because the US has some of the best fisheries management in the world, and lots is being done to cut down on bycatch.

References:

Lee, Jane, "Rarely Seen Moonfish, Size of Manhole Cover, Caught on Camera." National Geographic: Weird and Wild, February 5th, 2015

McClain et al., "Sizing Ocean Giants: Patterns of Intraspecific Size Variation in Marine Megafauna", PeerJ, 2015, DOI: 10.7717/peerj.715, Accessed via: https://peerj.com/articles/715/

Polovina, Hawn, & Abecassis, "Vertical Movement and Habitat of Opah (Lampris Guttatus) in the Central North Pacific Recorded with Pop-up Archival Tags.", Marine Biology, 2007 DOI: 10.1007/s00227-007-0801-2

"Order Summary for Lampriformes", Fishbase, 

Accessed via: http://www.fishbase.org/Summary/OrdersSummary.php?order=Lampriformes

Sympathy for the Devil Fish

In case you've never heard the Rolling Stones song Sympathy for the Devil; go ahead and watch this video. Not only will having the song in your head make this post make a lot more sense, but it's also one of my favorite songs of all time.

Below you'll find the Depth and Taxa version of the lyrics. There's some ambiguity as to which animal I'm talking about, so see if you can figure it out before the end.

Please allow me to introduce myself
I’m a fish with planktonic taste
I’ve been around the whole wide world
Swum many a mile ‘cross the wastes

And I went  down to Africa
From the Azores, out at sea
Made the trip on currents

WOO! WOO!
Courtesy Grant Bishop via Flickr

that pushed me ‘long, and let me feed

Pleased to meet you
Hope you guess my name
But what’s puzzling you
Is the fact that I’m so tame

We’re all ovo-vi-vipar-ous
When we know that it’s time, to give birth
Got a real long gestation

Often times, it’s two years

My bat like wings
Are the perfect things
For the heaving seas
That I slowly swim

WOO! WOO!
Courtesy Kevin Bryant via Flickr

Pleased to meet you
Hope you’ll guess my name, oh yeah
Ah what’s puzzling you
Is the fact that I’m so tame, oh yeah

I made the list
When your scientists
Noticed the decline
Of this group of mine
Men shouted out,
“Look at those devil horns!”
When really they
Are ce-pha-lic fins

Let me please introduce myself
I’m a fish of planktonic taste
And I’ve been trapped in big drift nets
Who just write me off as their bycatch

WOO! WOO!
Courtesy William Warby via Flickr

Pleased to meet you
Hope you guessed my name
But what’s puzzling you
Is the fact that I’m so tame

Pleased to meet you
Hope you guessed my name, oh yeah
But what’s confusing you
Is the fact that I’m so tame

Just as all true seals are the phocidae
And all the squalids, sharks        
We're devil rays
just call me Mobula
Cause I’m in need of some defense

So if you catch me
Have some courtesy
Have some sympathy, and instinct
Use all your well-learned fishing tricks
Or I’ll end up, gone extinct, oh yeah

WOO! WOO!
Courtesy Patrick Neckman via Flickr

Pleased to meet you
Hope you guessed my name, oh yeah
But what’s puzzling you
Is the fact that I’m so tame

So did you figure it out before the end? The animal is, of course, the last image: the giant devil ray (Mobula mobular). I hope you enjoyed the different format this week. If you have questions, or you'd like a little bit more traditional post about these beautiful fish, let me know in the comments!

References:

"Skates and Rays" The Shark Trust

http://www.sharktrust.org/en/skates_and_rays

"Mobula moblar: Devil Ray" Encyclopedia of Life

http://eol.org/pages/213344/overview

The Age of Sail

Oh boy are we going into the woods this week. For those who know me it's no secret that I love jellies (The squishy animals. I don't care much either way about the fruit spread.) So when IFLScience posted this article about by-the-wind-sailors, Velella velella  (dibs on the band na...oh) washing up in their thousands in Monterey bay I couldn't help but get excited. Not only because velella are incredibly cool, but because just explaining what they are is an odyssey of learning on its own. Incidentally this is one of the cases where using the scientific name is actually easier than the common one, so from here on I'll be referring to these animals as velella.

Hundreds of velella washed up on a beach. A surprisingly normal occurrence.

Courtesy Bettina Walter via Flickr

Now on the surface jellies seem pretty simple, and in terms of structure they are. They have no brain, their outer layers are usually one to three cells thick, and since they only have one hole in and out of their body; they eat and poop from the same opening. But jellies are one of those groups of animals that are so diverse and confusing they make a game of thrones family tree look like an elementary school ancestry project. In fact what we usually call jellyfish aren't even all the same thing. Let Steve Haddock from the Monterey Bay Aquarium Research Institute (MBARI) explain how there is no such thing as a jellyfish.

Seriously though MBARI has the best youtube channel

If you aren't able to watch that video it basically explains that so many different types of animals have evolved gelatinous forms that there isn't a great case for calling anything a jelly. In the interest of simplicity however when I refer to something as a jelly I'm talking about a tentacled, free-swimming life stage of either a scyphozoan, hydrozoan, or cubozoan. These three groups are classes of cnidarians (pronounced: nye-dairy-annes) which are animals whose tentacles have cells containing venom injecting harpoons. These stinging cells (called cnidocytes) are used partly for defense, but primarily  for prey capture. This is actually why humans can't feel the stings of many jellies; the relative size and sturdiness of their prey compared to the jelly determines how strong the sting needs to be. Jellies that prey upon fish, squid, and larger crustaceans need to make sure their prey is paralyzed or dead almost the instant it comes into contact with their tentacles. If  prey were to struggle hard enough it could do serious damage to the thin skinned, gooey jelly. Even though many jellyfish can't hurt you; I never recommend people touch them. So many types of jellies look similar to one another that it can be hard to tell the painful stingers from the harmless ones.

Especially the way most people find them.
Courtesy Justin Henry via Flickr

So where does the whole "tentacled free-swimming life stage" I mentioned fit into our story of velella? Well jellies have an astonishing life cycle. There are two completely separate phases to these animals. The phase we're most familiar with is usually what's called the medusa. Medusas have distinct sexes and reproduce when males release packets of sperm into the water which the females have to eat. Not only is there only one way into and out of the jellies, but the females' reproductive organs are inside their digestive track. Many species brood their eggs for a while holding them in their tentacles. From those eggs are hatched babies that will never become the free-swimming jellyfish. Instead they leave their mother's embrace and find a spot to settle on the bottom. Once settled they morph into their other major life stage; the polyp. Polyps usually look like very tiny sea anemones. They feed on plankton and detritus (particles of dead stuff) building up energy like a caterpillar. And like a caterpillar they go through a metamorphosis; not into an adult jelly but into a cloning machine. Entirely new organisms grow out of the polyps' bodies. This is the medusa that we know and love. It's like small frogs growing out of the side of tadpoles that never become the adult form! For you visual learners out there, below you'll find the life cycle in a beautiful chart. And in case you've been wondering what the difference is between the hydrozoa and the scyphozoa one big separator comes in the polyp stage. Scyphozoa divide their baby jellies in nice neat stacks whereas hydrozoa bud off all over their bodies.

"Reproductive cycle of jellyfish" by Zina Deretsky, National Science Foundation - http://www.nsf.gov/news/mmg/mmg_disp.cfm?med_id=65102&from=search_list. Licensed under Public domain via Wikimedia Commons

Okay, we've gotten a good understanding of what a jelly is and how their lives work so we can return to our friend velella. Velella is a type of hydrozoan who takes everything we just talked about and flips it the middle tentacle.

Oh my god he's doing right now right now!
Courtesy Andrew via Flickr

 Instead of having a polyp that sticks to the bottom velella has a polyp that sticks to the surface! That's right the beautiful sail-carrying jelly is the stage that does the cloning. For a long time it was assumed that velella was a special multi-polyp, colonial, siphonophore like the Portugese man-o-war Physalia physalis. In fact they look quite a lot alike and behave similarly. But studies now suggest velella is a pretty unique organism being one of only a couple animals in the porptid family. And it's not entirely clear whether the floating polyp is one relatively big individual, or a big shared float with a colony of clones underneath.

Okay, so if what we see is the polyp stage, where are the medusas? Well amazingly the medusas are tiny and when they bud off from the polyp they dive down into the depths. Just about everything about velella is backwards from what we expect. The medusas mate in the deep and their babies cruise up to the surface where they develop into the floating form. Velella polyps show differences in the orientation of their sails depending on where they live. In the center of ocean basins it's hypothesized that velella polyps have sails angled so they're carried both east and west. But closer to shore; polyps have sails oriented so prevailing winds keep them in the ocean.  When large storms or anomalous winds kick up they drive the velella on the water into the shore. And that's the source of Monterey's large stranding.

Velella has few threats to its continued existence so thankfully we can expect these amazing animals to be around for quite a long time. There is the possibility that the larger storms that come along with global climate change will cause more frequent strandings. So as always doing what you can to cut back on carbon emissions is a great way to help make sure the age of sail continues for these wonderful animals.

Sail on my friends, sail on.
Courtesy PowderPhotography via Flickr

References:

http://eol.org/pages/1006207/details

http://animaldiversity.ummz.umich.edu/accounts/Hydrozoa/

http://ocean.si.edu/jellyfish-and-comb-jellies#section_The_Stings:_Nematocysts_and_Colloblasts

K.J. Eckelbarger and R.Larsen. Ultrastructure of the ovary and oogenesis in the jellyfish Linuche ungiculata and Stomopolus meleagris, with a review of ovarian structure in the Scyphozoa. Marine Biology #114, 1992. Accessed via: http://link.springer.com/article/10.1007%2FBF00357260#page-2

http://animaldiversity.ummz.umich.edu/site/accounts/information/Velella_velella.html