Staghorn coral is listed as threatened under the U.S. Endangered Species Act. NOAA Fisheries has proposed it be reclassified as endangered. Photo by Albert Kok

Our oceans are taking a beating from overfishing, pollution, acidification and warming, putting at risk the many creatures who make their home in seawater. But when most people think of struggling ocean species, the first animals that come to mind are probably whales, seals or sea turtles.

Sure, many of these large (and adorable) animals play an important part in the marine ecosystem and are threatened with extinction due to human activities, but in fact, of the 94 marine species listed under the Endangered Species Act (ESA), only 45 are marine mammals and sea turtles. As such, these don’t paint the whole picture of what happens under the sea. What about the remaining 49 that form a myriad of other important parts of the underwater web?

These less charismatic members of the list include corals, sea birds, mollusks and, of course, fish. They fall under two categories: endangered or threatened. According to NOAA’s National Marine Fisheries Service (pdf), one of the groups responsible for implementing the ESA, a species is considered endangered if it faces imminent extinction, and and a species is considered threatened if it is likely to become endangered in the future. A cross section of these less-known members of the ESA’s list are described in detail below.

1. Staghorn coral (Acropora cervicornis), pictured above, is one of two species of coral listed as threatened under the ESA, although both are under review for reclassification to endangered. A very important reef-building coral in the Caribbean and the Gulf of Mexico, it primarily reproduces through asexual fragmentation. This means that its branches break off and reattach to a substrate on the ocean bottom where they grow into new colonies.

While this is a great recovery method when only part of a colony is damaged, it doesn’t work so well when most or all of the colony is killed—which often is the result from disturbances afflicting these corals. Since the 1980s, staghorn coral populations have steeply declined due to outbreaks of coral disease, increased sedimentation, bleaching and damage from hurricanes. Although only two coral species are currently on the ESA list, 66 additional coral species have been proposed for listing and are currently under review.

The white abalone population off the coast of California continued to decline even after the closure of its short-lived fishery in the 1970s. Photo by John Butler, NOAA

2. The white abalone (Haliotis sorenseni), a large sea snail that can grow to ten inches long, was the first marine invertebrate to be listed under the ESA but its population hasn’t recovered. The commercial fishery for white abalone collapsed three decades ago because, being spawners that jet their eggs and sperm into the water for fertilization with the hope that the two will collide, the animals depend on a large enough population of males and females being in close proximity to one another to reproduce successfully.

Less than 0.1% of its pre-fished population survives today, and research published in 2012 showed that it has continued to decline since its ESA listing more than a decade ago. The researchers recommended human intervention, and aquaculture efforts have begun in an effort to save the species.

Johnson’s seagrass is the first, and only, marine plant listed under the Endangered Species Act. Photo by Lori Morris, St. Johns River Water Management District

3. Johnson’s seagrass (Halophila johnsonii), the lone marine plant species listed, is classified as threatened and makes coastal habitats and nurseries for fish and provides a food source for the also-endangered West Indian manatees and green sea turtles. However, its most important role may be long-term ocean carbon storage, known as blue carbon: seagrass beds can store more carbon than the world’s forests per hectare.

The main threats to Johnson’s seagrass are nutrient and sediment pollution, and damage from boating, dredging and storms. Its plight is aggravated by its tiny geographic range–it is only found on the southeast coast of Florida. The species may have more trouble recovering than other seagrass species because it seems to only reproduce asexually–while other seagrasses can reproduce like land plants, by producing a flower that is then fertilized by clumps of pollen released underwater, the Johnson’s seagrass relies on the sometimes slow process of new stems sprouting from the buried root systems of individual plants.

Short-tailed albatrosses have made a remarkable recovery since they were believed to be extinct in the 1940s. They still face threats today though, from habitat loss to being caught unintentionally by fishing gear. Photo by U.S. Fish and Wildlife Service

4. The short-tailed albatross (Phoebastria albatrus) differs from some of its neighbors on the ESA list in that an extra layer of uncertainty is added to the mix: During breeding season, they nest on islands near Japan, but after breeding season ends, they spread their wings and fly to the U.S. In the late 19th century, the beautiful birds are thought to have been fairly common from coastal California up through Alaska. But in the 1940s, their population dropped from the tens of millions to such a small number that they were thought to be extinct. Their incredible decline was due to hunters collecting their feathers, compounded by volcanic damage to their breeding islands in the 1930s.

Today they are doing better, with over 2,000 birds counted in 2008, but only a few islands remain as nesting sites and they continue to be caught as bycatch, meaning that they are often mistakenly hooked by longline fishing gear.

Atlantic salmon used to be found in most major rivers in New England, now they are only found in a small section of Maine. Photo by E. Peter Steenstra/USFWS

5. Salmon are a familiar fish frequently seen on the menu. But not all species are doing well enough to be served on our plates. Salmon split their time between freshwater (where they are born and later spawn) and the ocean (where they spend their time in between). Historically, Atlantic salmon in the U.S. were found in most major rivers on the Atlantic coast north of the Hudson, which flows through New York State. But damming, pollution and overfishing have pushed the species to a point where they are now only found along a small section of the Maine coast. Twenty-eight populations of Pacific salmon are also listed as threatened or endangered. Efforts on both coasts are underway to rebuild populations through habitat restoration, pollution reduction and aquaculture.

The five organisms listed here are just a few of the marine species on the ESA’s list. In fact, scientists expect that as they learn more about the oceans, they will reveal threats to more critters and plants.

“The charismatic marine species, like large whales [and] sea turtles…were the first to captivate us and pique our curiosity to look under the waves,” says Jonathan Shannon, from the NOAA Fisheries Office of Protected Species. “While we are learning more about the ocean and how it works every day, we still have much to learn about the different species in the ocean and the health of their populations.”

 Learn more about the ocean from the Smithsonian’s Ocean Portal. 

Emperor penguins swimming. Photo by Polar Cruises

Penguins seem a bit out of place on land, with their stand-out black jackets and clumsy waddling. But once you see their grace in the water, you know that’s where they’re meant to be–they are well-adapted to life in the ocean.

April 25 of each year is World Penguin Day, and to celebrate here are 14 facts about these charismatic seabirds.

1. Depending on which scientist you ask, there are 17–20 species of penguins alive today, all of which live in the southern half of the globe. The most northerly penguins are Galapagos penguins (Spheniscus mendiculus), which occasionally poke their heads north of the equator.

2. While they can’t fly through the air with their flippers, many penguin species take to the air when they leap from the water onto the ice. Just before taking flight, they release air bubbles from their feathers. This cuts the drag on their bodies, allowing them to double or triple their swimming speed quickly and launch into the air.

3. Most penguins swim underwater at around four to seven miles per hour (mph), but the fastest penguin—the gentoo (Pygoscelis papua)—can reach top speeds of 22 mph!

Gentoo penguins “porpoise” by jumping out of the water. They can move faster through air than water, so will often porpoise to escape from a predator. Photo: Gilad Rom (Flickr)

4. Penguins don’t wear tuxedos to make a fashion statement: it helps them be camouflaged while swimming. From above, their black backs blend into the dark ocean water and, from below, their white bellies match the bright surface lit by sunlight. This helps them avoid predators, such as leopard seals, and hunt for fish unseen.

5. The earliest known penguin fossil was found in 61.6 million-year old Antarctic rock, about 4-5 million years after the mass extinction that killed the dinosaurs. Waimanu manneringi stood upright and waddled like modern day penguins, but was likely more awkward in the water. Some fossil penguins were much larger than any penguin living today, reaching 4.5 feet tall!

6. Like other birds, penguins don’t have teeth. Instead, they have backward-facing fleshy spines that line the inside of their mouths. These help them guide their fishy meals down their throat.

An endangered African penguin brays with its mouth open, showing off the bristly inside of its mouth. Photo by Dimi P (Flickr), with permission

7. Penguins are carnivores: they feed on fish, squid, crabs, krill and other seafood they catch while swimming. During the summer, an active, medium-sized penguin will eat about 2 pounds of food each day, but in the winter they’ll eat just a third of that.

8. Eating so much seafood means drinking a lot of saltwater, but penguins have a way to remove it. The supraorbital gland, located just above their eye, filters salt from their bloodstream, which is then excreted through the bill—or by sneezing! But this doesn’t mean they chug seawater to quench their thirst: penguins drink meltwater from pools and streams and eat snow for their hydration fix.

9. Another adaptive gland—the oil (also called preen) gland—produces waterproofing oil. Penguins spread this across their feathers to insulate their bodies and reduce friction when they glide through the water.

10. Once a year, penguins experience a catastrophic molt. (Yes, that’s the official term.) Most birds molt (lose feathers and regrow them) a few at a time throughout the year, but penguins lose them all at once. They can’t swim and fish without feathers, so they fatten themselves up beforehand to survive the 2–3 weeks it takes to replace them.

An emperor penguin loses its old feathers (the fluffy ones) as new ones grow in underneath. Photo by Carlie Reum, National Science Foundation

11. Feathers are quite important to penguins living around Antarctica during the winter. Emperor penguins (Aptenodytes forsteri) have the highest feather density of any bird, at 100 feathers per square inch. In fact, the surface feathers can get even colder than the surrounding air, helping to keep the penguin’s body stays warm.

12. All but two penguin species breed in large colonies for protection, ranging from 200 to hundreds of thousands of birds. (There’s safety in numbers!) But living in such tight living quarters leads to an abundance of penguin poop—so much that it stains the ice! The upside is that scientists can locate colonies from space just by looking for dark ice patches.

13. Climate change will likely affect different penguin species differently—but in the Antarctic, it appears that the loss of krill, a primary food source, is the main problem. In some areas with sea ice melt, krill density has decreased 80 percent since the 1970s, indirectly harming penguin populations. However, some colonies of Adelie penguins (Pygoscelis adeliae) have grown as the melting ice exposes more rocky nesting areas.

14. Of the 17 penguin species, the most endangered is New Zealand’s yellow-eyed penguin (Megadyptes antipodes): only around 4,000 birds survive in the wild today. But other species are in trouble, including the erect-crested penguin (Eudyptes sclateri) of New Zealand, which has lost approximately 70 percent of its population over the past 20 years, and the Galapagos penguin, which has lost more than 50 percent since the 1970s.

  Learn more about the ocean from the Smithsonian’s Ocean Portal.

Beneath the seafloor, there is an ecosystem of microbes living in the oceanic crust, independent of sunlight. Here, the seafloor of McMurdo Sound in Antarctica. NSF/USAP photo by Steve Clabuesch

If you were to hit the seafloor and continue to travel down, you’d run into an ecosystem unlike any other on earth. Beneath several hundred meters of seafloor sediment is the Earth’s crust: thick layers of lava rock running with cracks that cover around 70% of the planet’s surface. Seawater flows through the cracks, and this system of rock-bound rivulets is enormous: it’s the largest aquifer on earth, containing 4% of global ocean volume, says Mark Lever, an ecologist who studies anaerobic (no-oxygen) carbon cycling at Aarhus University in Denmark.

The sub-seafloor crust may also be the largest ecosystem on earth, according to a new study by Lever, published this month in Science. For seven years, he incubated 3.5 million-year old basalt rock collected from 565 meters below the ocean floor–the depth of nearly two stacked Eiffel towers–and found living microbes. These microbes live far away from the thriving bacterial communities at mid-ocean ridges, and survive by slowly churning sulfur and other minerals into energy.

But just how big is this chemically-fueled ecosystem that survives entirely without oxygen? If the results from his sample, collected from below the seafloor off the coast of Washington state, are similar to those found across the planet, then diverse microbial communities could survive throughout the ocean’s crust, covering two-thirds of the earth’s surface and potentially going miles deep.

The sub-seafloor crust has plenty of space and energy-rich minerals–a welcoming potential habitat for a large microbial community–“but we have no idea what the ecosystem looks like,” says Julie Huber, a microbial oceanographer at the Marine Biological Laboratory in Woods Hole, Massachusetts. “Mark’s evidence would point to it being a very different world.”

Microbes that get their energy from minerals, rather than from sunlight, are far from rare. The most well known of these so-called chemoautotrophic or chemosynthetic bacteria are those found at hydrothermal vents in the deep sea. Some of these bacteria live symbiotically with giant tubeworms, mussels and clams, providing chemically-produced energy to these larger organisms as they “breathe” the sulfur-rich water erupting from the vent–not unlike how plants convert sunlight into energy at the surface. Chemosynthetic microbes are also found in the rotting and oxygen-poor muck of salt marshes, mangroves and seagrass beds—“any place you’ve got stinky black mud, you can have chemoautotrophy,” says Chuck Fisher, a deep-sea biologist at Pennsylvania State University in College Park.

But what makes Lever’s sub-seafloor microbes different is that they don’t use any oxygen at all. The symbiotic bacteria at hydrothermal vents are often described as “life without sunlight,” but they still rely on sunlight indirectly by using sun-produced oxygen in the chemical reaction to generate energy. Chemosynthetic microbes in salt marshes feed on decomposing plants and animals, which got their energy from sunlight. Even deep-sea sediment is accumulated from an assortment of dead animals, plants, microbes and fecal pellets that relies on light energy.

The oceanic crust microbes, on the other hand, rely entirely on non-oxygen-containing molecules derived from rock and completely removed from photosynthesis, such as sulfate, carbon dioxide and hydrogen. “In that sense it’s a parallel universe, in that it runs on a different type of energy,” says Lever. These molecules provide a lot less energy than oxygen, creating a sort of microbial slow food movement. So instead of dividing and growing quickly like many oxygen-based bacteria, Fisher suspects that microbes in the Earth’s crust may divide once every hundred or thousand years.

A hydrothermal vent, covered with tube worms, spews black sulfur smoke on the Juan de Fuca Ridge. The oceanic crust microbes were collected hundreds of meters under the seafloor beneath this same ridge. Photo via University of Washington; NOAA/OAR/OER

But just because they’re slow doesn’t mean they’re uncommon. “There are lots of data that there is a large, very productive biosphere under the surface,” says Fisher.

In addition, microbial population sizes in different areas of the crust may vary greatly, Huber notes. Through her studies on the fluid found between the cracks in the crust,  she says that in some areas the fluid contains about the same number of microbes as standard deep-sea water collected at ocean depths of 4,000 meters (2.5 miles): around 10,000 microbial cells per milliliter. In other regions, such as at the Juan de Fuca Ridge in the Pacific Ocean where Lever found his microbes, there are fewer cells, around 8,000 microbes per milliliter. And in other regions, such as in non-oxygenated fluid deep in hydrothermal vents, there can be around 10 times more.

It’s not just the number of microbes that vary depending on location–it’s possible that different microbial species are found in different types of crust. “Different types of rock and different types of chemistry should result in different types of microbes,” says Andreas Teske, a deep-sea microbial ecologist at the University of North Carolina at Chapel Hill and co-author on Lever’s paper. The Juan de Fuca Ridge is a relatively hot area bursting with new rock, which tends to be made of more reactive minerals and thus able to provide more energy. Other parts of the crust are older, composed of different minerals, and cooler. And, in some regions, oxygenated water reaches down to the cracks.

It’s this infiltrating seawater that keeps this sub-seafloor ecosystem from existing on a completely separate plane from our oxygenated one. “The crust plays a significant role in influencing the chemical composition of the ocean and the atmosphere, ultimately influencing [nutrient] cycles on earth,” says Lever. Some of the compounds created by oceanic crust microbes from rock are water soluble, and will eventually enter the ocean. Sulfur, for example, is present in magma—but after the microbes use it for energy, it’s converted to sulfate. Then it dissolves and becomes an important nutrient in the ocean food chain.

Lever’s find of a microbial community in the crust could catalyze the scientific community to answer these questions. For example, what kinds of microbes are found where, do they interact through interconnected cracks in the rock, and what role do they play in mineral and nutrient cycling? In some ways, it’s very basic exploratory work. “A lot of what we do on the seafloor is similar to what we’re doing on Mars right now,” says Huber. “Controlling [NASA’s Mars Rover] Curiosity is very similar to operating an ROV under the ocean.”

  Learn more about the deep sea from the Smithsonian’s Ocean Portal.

Ribbon worms come in all shapes and sizes. This one, with white stripes along the body, was found off the coast of Mexico. Photo by Chris Meyer and Allen Collins

Whether they’re on a rain-soaked sidewalk, in the compost bin or on the end of a fish hook,  the worms most people know are of the segmented variety. But what about all the other worms out there?

With more than 1,000 species of ribbon worms (phylum Nemertea), most found in the ocean, there is a huge range of sizes and lifestyles among the various types. A defining characteristic of ribbon worms is the presence of a proboscis—a unique muscular structure inside the worm’s body. When attacking prey, they compress their bodies to push out the proboscis like the finger of a latex glove turned inside-out.

Here are 14 other fun facts about them:

1. The largest species of ribbon worm is the bootlace worm, Lineus longissimus, which can be found writhing among rocks in the waters of the North Sea. Not only is it the largest nemertean, but it may also be the longest animal on the planet! Uncertainty remains because these stretchy worms are difficult to accurately measure, but they have been found at lengths of over 30 meters (98 feet) and are believed to even grow as long as 60 meters (197 feet)—longer than the blue whale! Despite their length they are less than an inch around.

An illustration of a bootlace worm, which can be found at lengths of 30 meters (98 feet) or longer. From McIntosh/Publisher Selam Amare

2. The smallest ribbon worm species is less than a centimeter long, and resembles a piece of thread more closely than what we think of as a worm.

3. Ribbon worms have highly developed muscles that allow them to contract their bodies, shrinking to a tenth of their extended length when threatened.

4. Talk about stretching: ribbon worm muscles don’t just contract–they can also expand, allowing some species to swallow prey (such as other kinds of worms, fish, crustaceans, snails and clams) that are more than double the width of their narrow bodies

Ribbon worm (Nemertean) eating a polychaete annelid [edited] from LabNemertea on Vimeo.

5. The proboscis varies among the species. Some are sticky or have suckers to help grasp prey, and some species, like those in the order Hoplonemertea, even stab their prey with a sharp spike, called a stylet, on the proboscis.

6. Because the stylets often are lost during an attack, the worms continually make and use replacements that they have in reserve in internal pouches.

7. As a second line of defense, many ribbon worms are poisonous and taste bad. Several species contain tetrodotoxin, the infamous pufferfish venom that can induce paralysis and death by asphyxia. It’s still not known exactly how the toxins are produced—they may linger in the worms from ingested bacteria—but they deter predators from taking a bite. Some even eject toxins from their proboscis.

8. Some ribbon worms sneak up on their prey, lying in wait buried in the sandy seafloor. One species of worm will pop up from its home in the sand when a fiddler crab walks over. The worm will cover the prey with toxic slime from its proboscis, paralyzing the crab so the ribbon worm can slide into a crack in the shell and eat the crab from the inside out.

9. Not all ribbon worms are predators – some are parasites. One genus of ribbon worms, Carcinonemertes, lives as a parasite on crabs, eating the crab’s eggs and any animals that it can find from the confines of its host.

A parasitic ribbon worm, seen in this picture with the crab eggs it persists on.
Photo by Sadeghian and Santos

10. Most ribbon worms produce a slippery mucus that covers their bodies and helps them to navigate through the mud and rocks on the ocean floor.

11. Some also use the mucus as a protective coat to keep from drying out when exposed to air during low tides. Others use their proboscis to move by attaching it to an object and pulling themselves forward. This same mucus makes them hard to catch! And not only by predators: scientists trying to catch the worms have a difficult time.

12. Marine ribbon worms usually have separate sexes and temporary sex organs. Rows of gonads line the inside of their bodies to produce either eggs or sperm. When they are ready to be released, the gonad ducts form on demand and are reabsorbed after reproduction.

13. Most ribbon worms have direct development: a miniature version of the worm hatches from a fertilized egg. However, the young of one group of ribbon worms, the heteronemerteans, emerge in a bizarre larval stage that looks like a flying saucer. After a few weeks to months living and feeding in the open ocean, a small worm develops inside and, when it’s ready, it eats its way out of the original larva encasing. Then the worm falls to the sea floor where it spends the rest of its life.

14. Many ribbon worms can regenerate when a predator takes a bite, healing their broken ends. One worm species, Ramphogordius sanguineus, has an exceptional ability to regenerate: if any part of their body is severed (except for the very tip of their tail where there are no nerves), it can regrow into a new worm. This new individual may be smaller than the worm it came from, but more than 200,000 worms can result from an individual that is only 15 centimeters (6 inches) long!

 Learn more about the ocean from the Smithsonian’s Ocean Portal. 

Two waved albatrosses, the only tropical albatross species, courting one another on the Galapagos Islands.
Photo by Flickr User James Preston

We often hear stories of animal love—tales of rare monogamy in the animal kingdom where life-long love is implied. But there is a distinction between romantic love and an efficient mating system. Here’s a look at some ocean animals to see what is really going on.

Albatrosses Get ‘Romantic’ to Increase Chick Survival

Albatross relationships seem especially relatable to humans. These long-lived and highly-endangered birds will court each other through ritual dances for years. Albatrosses are slow to reach sexual maturity, and some species even delay breeding for several years to learn specific mating rituals and to pick the perfect partner. The courtship behavior slows down once the pair bonds (an all too familiar aspect of human relationships). Once a pair is comfortable and breeding commences, they will return to each other and the same spot each year; for most albatross species, the bond lasts their entire life.

So is it love? The biological reality is that albatrosses only lay a single egg a year. With both parents fully invested in chick survival, their genetic heritage is most likely to survive. It may seem like love, but with those low reproduction rates no parents can afford to be deadbeats.

A waved albatross looks after its chick on the Galapagos Islands.
Photo by Flickr user James Preston

Seahorses Bond to Improve the Odds of Birth

If albatross relationships are reminiscent of fairytale romance, seahorses might be considered the swingers of the sea. Many seahorse species will bond with a mate, but that bond often lasts only through a single breeding season or until a more attractive female comes along. But, monogamy in this case is useful since it can be hard to find fellow seahorses due to poor swimming skills and low densities.

There is evidence that the longer that partners are together, the more successful at breeding they become and the two are able to produce more offspring per brood. One species of seahorse does appear to stick with a single mate for life: the Australian Hippocampus whitei. Practice makes perfect!

Two thorny seahorses (Hippocampus histrix), tails intertwined.
Photo by Bettina Balnis/Guylian Seahorses of the World 2010, Courtesy Project Seahorse

Two Angelfish Make a Strong Defense

Typically in pairs, French angelfish (Pomacanthus paru) help each other defend their territory against other fish. The couples have been observed spending extended periods of time together, exhibiting more of a monogamous social structure. Genetic monogamy (i.e. testing fertilized eggs to confirm they come from a single father) hasn’t been confirmed, but there have been observations of pairs traveling to the water’s surface to release their eggs and sperm together.

Monogamy is not that common in fishes, and it is mostly found in tropical and subtropical waters. Care needed from two parents, joint defense of territories, and difficulties in finding a mate all can play a role.

A pair of French angelfish off the coast of Brazil.
Photo by Barry Peters

A Permanent Glass Home for Shrimp

These intriguing glass sponges, called Venus’s flower-baskets (Eupectella aspergillum), are made of flexible silica that can better transmit light than our man-made fiber-optic cables. And many of these beautiful deep-sea sponges are also home to a monogamous pair of shrimp.

Several species of shrimp find refuge in these sponges, but due to the limited space found within the fine-mesh silica, only two adult shrimp can fit inside—and they are stuck there for life. The two spend their days cleaning the sponge and eating whatever bits of food manage to flow through. After they breed, their small offspring can squeeze through the holes in the mesh to escape, but eventually they will settle into a new home with their own imprisoned mate.

The  silica home of a male and female shrimp – the deep-sea sponge Venus’s flower-basket.
Photo via NOAA

The gift of this sponge, taken from the deep with the two dead shrimp still trapped inside, is considered good luck for couples marrying in Japan. It seems as though young human couples are not the only ones to share tight living spaces.

 Learn more about the ocean from the Smithsonian’s Ocean Portal. 

A close-up photo of the common sunstar (Crossaster papposus), a starfish found in the North Atlantic and Pacific oceans. Photo: © Alexander Semenov

Invertebrates close-up never fail to please: with their bright colors and strange structures, they begin to take on patterns that are more art than animal.

So is true of this series of close-up photographs of starfish taken by researcher and photographer Alexander Semenov. But it isn’t enough to call them art: why are all those finger-like appendages waving around? And what are those bulbous spikes (or floral bouquets, if you’re feeling romantic)?

Lucky for us, two floors up from the Ocean Portal office sits Dr. Chris Mah, an expert on echinoderms (a group of ocean animals that includes starfish, sea urchins and brittle stars) at the Smithsonian National Museum of Natural History. He helped us to fill in some of the details.

Asterias rubens is the most common starfish found in the north-east Atlantic Ocean. Photo: © Alexander Semenov

The Worm-Like Soft Bits: The vast garden of waving worms isn’t a starfish experiment in cultivation, but how they breathe on the seafloor. Sea stars breathe passively, letting oxygen-rich seawater flow over those finger-like sacs, called papulae, which peek through the cracks in their protective plates. Like fish gills, papulae absorb the oxygen in seawater.

Solaster endeca is a yellow, orange, pink, purple or red seastar shaped like the Smithsonian logo. Here, its translucent yellow papulae filter oxygen from seawater. Photo: © Alexander Semenov

Such fleshy little fingers would make an excellent snack for a passing shrimp or another small predator. To defend themselves, starfish can retract their papulae to make them less obvious targets, as this Mithrodia clavigera, pictured below, has done.

The tropical nail-armed sea star (Mithrodia clavigera) has five long, spiky arms–up close, its papulae have retracted, leaving behind purple cups. Photo: © Alexander Semenov

The Bald, Grooved Patches: Starfish are powered by plumbing: a series of pipes carry food and oxygen through their bodies. Water pressure builds up in these pipes, which helps to support their bodies. It was long-thought that this water pressure also created suction, allowing starfish’s hundreds of tiny tube feet to attach to surfaces and slowly creep across the seafloor. But recent research has suggested that tube feet are more like sticky pads than suction cups.

How does water get in and out of this plumbing system? It goes through the sieve plate (also called a madreporite), a small bald patch on the starfish that, close up, looks like a tiny, grooved maze. While it’s not the only way that water can enter the plumbing, it’s a major intake valve for starfish.

Check out the madreporite on that Asterias amurensis! This starfish, native to Northern Japanese waters, invaded the colder waters of Australia in the 1990s and completely carpets the seafloor in some places. Photo: © Alexander Semenov

Most starfish only have one sieve plate, but larger ones with many arms can have far more. For example, the coral-devouring crown of thorns starfish can have up to 15 to power its many arms. And starfish that reproduce asexually by splitting their bodies in half sometimes end up with more than one.

Patiria pectinifera only has one sieve plate–the blue bald patch in the center right. Incidentally, in the center orange patch you can also spot the starfish’s white anus. Photo: © Alexander Semenov

The Spiked Clubs: Humans aren’t the only species that came up with the mace as weaponry. Instead of being offensive tools, starfish spines (as they’re known) protect them from the smothering force of mud and debris. It’s likely that they also protect against predators, but a starfish’s first line of defense is stinky and poisonous chemicals.

Crossaster papposus is speedy for a starfish–it can move more than 5 meters in 12 hours. Here, wafting papulae are interspersed by spiky spines. Photo: © Alexander Semenov

Not all starfish spines are spiky. These purple spines of Evasterias retifera (below) in a field of orange papulae are low and stubby with lovely white notches. Other species have more architectural spines shaped like pyramids or tall spires.

Evasterias retifera, found in cold, northern waters, has blunt purple spines among orange clusters of papulae. Photo: © Alexander Semenov

The Tiny, Bitey Mouths: A slow-moving lifestyle puts starfish in danger of becoming overgrown with algae or other encrusting organisms. As a defense, many starfish are speckled with small, extendable “claws” called pedicellariae, which you can see in the photo below. In some species, the pedicellariae surround the spines and, if the starfish is threatened, will extend out to the spine’s full height! In other species, they are flat and spread out over the starfish’s skin. “They can look like a pair of lips or small jaws,” said Mah. “They probably look like monsters if you’re small enough to appreciate them.”

The tiny white bumps surrounding the larger white bumps (spines) on this Aphelasterias japonica are its pedicellariae. Photo: © Alexander Semenov

  Learn more about ocean invertebrates from the Smithsonian’s Ocean Portal.

The gooseneck barnacle (with a relaxed penis at arrow) is capable of a method of sex previously unobserved in barnacles, upending 150 years of theory. Image via Barazandeh, et al. Proc. R. Soc. B.

Barnacles are renowned for the size of their penises. The strange-looking creatures, which live inside shells glued to rocks or boat hulls, have outsized members that are among the longest in the animal kingdom relative to their size—their penises can stretch up to eight times their body length. Barnacles can even change the size and shape of their penis depending on the amount of wave action in their ocean real estate.

Perhaps this is why the sex lives of barnacles have long been of interest to scientists—luminaries such as Darwin, among others, closely studied the subject. Until recently, though, scientists recognized just two methods of reproduction in the species, and both left unanswered questions.

Pseudo-copulation, in which the penis enters a neighboring barnacle’s shell and deposits sperm, has been observed, but this method restricts them to reproducing only with others in their vicinity. Scientists have also observed that individual barnacles with no neighbors can reproduce, and they assumed this was accomplished through self-fertilization, because most barnacles are hermaphrodites.

Gooseneck barnacles (Pollicipes polymerus) taken at Limekiln Point on San Juan Island. Photo: Biriwilg, Wikimedia Commons

Now, though, researchers at the University of Alberta, Edmonton and Bamfield Marine Sciences Centre in British Columbia seem to have discovered a new reproduction method while studying the gooseneck barnacle (Pollicipes polymerus), upending more than 150 years of theory. Previously, the researchers had noticed that in other studies of the gooseneck barnacle, self-fertilization was never observed. They also saw sperm leaking from the barnacles in the field, which made them consider the possibility that barnacles could pick up sperm from the water.

In the study, the scientists collected gooseneck barnacles—both isolated and in pairs—along with their fertilized eggs from Barkley Sound in British Columbia to take back to the lab so they could genetically analyze the paternal combinations. The DNA of the fertilized eggs revealed that none of the isolated barnacles had produced embryos through self-fertilization—so one hundred percent of these eggs must have been fertilized by capturing sperm from the water.

Surprisingly, though, even some of the barnacles that resided in pairs had embryos that had been fertilized with sperm from a non-neighbor. This left one possibility: that the barnacles release their sperm into the ocean and let the water carry it to distant neighbors. This type of fertilization has been observed in other marine animals that can’t or don’t move, but it was always assumed that barnacles can’t reproduce in this way.

The authors point out that this mode of reproduction may be unusually common in this particular barnacle species because of the small size of their penis—but the fact that this phenomenon occurs at all opens the door to re-thinking the biology of these creatures. Other barnacle species might also have more mating options, with fathers coming from farther afield than previously thought.

 Learn more about the ocean from the Smithsonian’s Ocean Portal. 

Small red boring sponges embedded in star coral, killing the coral polyps immediately surrounding them. Image via Sean Nash, Flickr

Whenever anyone talks about ocean acidification, they discuss vanishing corals and other shelled organisms. But these aren’t the only organisms affected—the organisms that interact with these vulnerable species will also change along with them.

These changes won’t necessarily be for the good of the shell and skeleton builders. New research published in Marine Biology shows that boring sponges eroded scallop shells twice as fast under the more acidic conditions projected for the year 2100. This makes bad news for the scallops even worse: not only will they have to cope with weakened shells from acidification alone, but their shells will crumble even more quickly after their cohabiters move in.

Boring sponges aren’t named thus because they’re mundane; rather, they make their homes by boring holes into the calcium carbonate shells and skeletons of animals like scallops, oysters and corals. Using chemicals, they etch into the shell and then mechanically wash away the tiny shell chips, slowly spreading holes within the skeleton or shell and sometimes across its surface. Eventually, these holes and tunnels can kill their host, but the sponge will continue to live there until the entire shell has eroded away.

Alan Duckworth of the Australian Institute of Marine Science and Bradley Peterson of Stony Brook University in New York brought boring sponges (Cliona celata) and scallops (Argopecten irradians) into the lab to examine the effects of temperature and acidity (measured through pH) on drilling behavior. They set up a series of saltwater tanks to compare how much damage sponges did to scallops under current temperature and ocean conditions (26°C and pH 8.1), projected conditions for 2100 (31°C and pH 7.8), and each 2100 treatment alone (31°C or pH 7.8).

Cliona celata (yellow), the boring sponge species used in the study, is commonly found on oysters and scallops and lives throughout the Atlantic and Mediterranean. Here, numerous sponges have drilled into coral. Image via Bernard Picton, National Museums Northern Ireland

Under higher acidity (lower pH), boring sponges drilled into scallop shells twice as fast, boring twice as many holes and removing twice as much shell over the course of the 133-day study. The lower pH alone weakened the shells, but after the boring sponges did their work, the scallop shells were an additional 28% weaker, making them more vulnerable to predation and collapse from the sponges’ structural damage.

The sponges weren’t entirely thrilled by the water’s higher acidity, which killed 20% of the them (although the researchers aren’t sure why). Despite this loss, 80% of the sponges doing twice as much drilling meant more damage to shelled organisms in total. Temperature did not affect sponge behavior at all.

This study illustrates a classic positive feedback loop, where weakness in the shells leads to more weakness. And not through the sponge-drilled holes alone: the addition of sponge-drilled holes creates more surface area for acidification to further erode the shells, hastening each scallop’s inevitable collapse. It’s tempting to speculate out to the rest of the system—that the sponges are destroying their own habitat more quickly than scallops can produce it—but we don’t really know whether in the long run this is also bad news for the sponges.

Though a small and specific example, this study illustrates how a seemingly small change—more acid and weaker shells—can ripple out and affect other organisms and the rest of the ecosystem.

  Learn more about coral reefs from the Smithsonian’s Ocean Portal.

2012 was a big year for squid science. Photo Credit: © Brian Skerry, www.brianskerry.com

Despite covering 70 percent of the earth’s surface, the ocean doesn’t often make it into the news. But when it does, it makes quite a splash (so to speak). Here are the top ten ocean stories we couldn’t stop talking about this year, in no particular order. Add your own in the comments!

2012: The Year of the Squid From the giant squid’s giant eyes (the better to see predatory sperm whales, my dear), to the vampire squid’s eerie diet of remains and feces, the strange adaptations and behavior of these cephalopods amazed us all year. Scientists found a deep-sea squid that dismembers its own glowing arm to distract predators and make a daring escape. But fascinating findings weren’t relegated to the deep: at the surface, some squids will rocket themselves above the waves to fly long distances at top speeds.

James Cameron Explores the Deep Sea Filmmaker James Cameron has never shied away from marine movie plots (See: Titanic, The Abyss), but this year he showed he was truly fearless, becoming the first person to hit the deepest point on the seafloor (35,804 feet) in a solo submarine. While he only managed to bring up a single mud sample from the deepest region, he found thriving biodiversity in the other deep-sea areas his expedition explored, including giant versions of organisms found in shallow water.

Small fish, such as these schooling sardines, received well-deserved attention for being an important part of the food chain in 2012. Photo Credit: © Erwin Poliakoff, Flickr

Small Fish Make a Big Impact Forage fish—small, schooling fish that are gulped down by predators—should be left in the ocean for larger fish, marine mammals and birds to eat, according to an April report from the Lenfest Forage Fish Task Force. These tiny fish, including anchovies, menhaden, herring and sardines, make up 37% of the world’s catch, but only 10% are consumed by people, with the rest processed into food for farmed fish and livestock. With the evidence mounting that forage fish are worth more as wild fish food, state governments and regional fishery management councils are making moves to protect them from overfishing.

Marine Debris and Plastic Get Around In June, a dock encrusted with barnacles, sea stars, crabs and other sea life washed ashore on the coast of Oregon. It had floated across the Pacific from a Japanese port more than 5,000 miles away—a small piece of the estimated 1.5 million tons of marine debris set afloat by the 2011 Tohoku tsunami. But that’s not the only trash in the sea. Researchers found ten times as much plastic in the “pristine” Antarctic oceans than they expected. Some species are even learning to adapt to the ubiquitous ocean plastic.

These tropical tangs and their coral reef habitat are protected at Hawaii’s Papahanaumokuakea Marine National Monument. Photo Credit: Claire Fackler, CINMS, NOAA, Flickr

Taking Measure of Coral Reef Health Australia’s iconic Great Barrier Reef, so large it can be seen from space, is not doing well. An October study found that since 1986, half of the living coral has died because of warming water, predation and storm damage. And it’s not just Australia: the December Healthy Reefs report gave most Mesoamerican reefs a “poor” rating. It’s hard to escape that gloom, but there were glimmers of hope. Some coral species proved able to adapt to warmer water, and changing circulation caused by the warming ocean may create refuges for coral reef habitat.

Shark Finning Slowing Down? The fishing practice of shark finning—slicing off a shark’s fins before tossing it back in the ocean to slowly sink and suffocate—began its own slow death in 2012. A steady stream of U.S. states have banned the sale of shark finsning; the European Union will now require fisherman to land sharks with their fins on; four shark sanctuaries were created in American Samoa, the Cook Islands, Kosrae and French Polynesia; and, in July, China announced that official banquets would be prohibited from serving shark fin soup (although the ban may take up to three years to go into effect).

Arctic ice reached an all-time low in 2012. Photo Credit: NASA/Kathryn Hansen

Arctic Sea Ice Hits All-Time Low On September 16, sea ice extent reached a record low in the Arctic, stretching 3.41 million square kilometers—that’s 49% lower than the 1979-2000 average minimum of 6.7 million square kilometers. What’s more, its melt rate is increasing: 2012 had the largest summer ice loss by more than one million square kilometers. This change is expected to affect ecosystems—from polar bears to phytoplankton—and accelerate warming in the area, eventually melting Greenland’s ice sheet and raising sea level dramatically.

Hurricane Sandy Elevates Awareness of Sea-Level Rise This year certainly opened our eyes to the severity of climate change and sea-level rise. The east coast of the U.S., where scientists project sea-level will rise three to four times faster than the global average, got a glimpse of its effects when Hurricane Sandy caused $65 billion in damage, took at least 253 lives, and flooded Manhattan’s subways in October. The disaster inspired The Economist, Bloomberg Businessweek and other major news sources to take a closer look at climate change and what it means for us all.

Using satellite photos, researchers counted twice as many emperor penguins living in Antarctica than they thought existed. Photo Credit: Martha de Jong-Lantink, Flickr

Counting Ocean Animals from Space Scientists took advantage of satellite technology this year to learn more about ocean wildlife. The first satellite-driven census of an animal population discovered that there are twice as many emperor penguins in Antarctica as previously thought, including seven new colonies of the large flightless birds. A second study tracked the travels of sea turtles by satellite, which could help researchers get a better idea of where they might interact with fisheries and accidentally end up caught in a net.

The Ocean Gets a Grade The first tool to comprehensively assess ocean health was announced in August 2012—and the ocean as a whole received a score of 60 out of a possible 100. This tool, the Ocean Health Index, is novel in that it considered ten ways the ocean supports people, including economies, biodiversity, and recreation. The U.S. scored a 63, ranking 26th globally, while the uninhabited Jarvis Island took home an 86, the top grade of the 171 rated countries.

–Hannah Waters, Emily Frost and Amanda Feuerstein co-wrote this post

  Learn more about the ocean from the Smithsonian’s Ocean Portal.

Photo by Nick Hobgood

During the holiday season, even the ocean gets in the spirit! The Christmas tree worm (Spirobranchus giganteus) is a type of polychaete, a group of segmented worms mostly found in the ocean. It lives on tropical coral reefs and resembles a fluffy fir tree adorned with colored ornaments. Each worm has two tree-like appendages that are used to breathe and to catch meals of plankton floating by.

The Christmas tree worms are sedentary, attaching themselves to coral cover that act as their home base. Once attached, they create a calcium carbonate tube that they can then retract into for protection. The fluffy, eye-catching section of the worms that attract divers are small in size, usually not bigger than a few inches, but the remainder of the worm (hiding in its burrow) can be almost twice that size.

Check out more holiday-themed ocean animals and phenomena on the Ocean Portal! 

Photo by Nick Hobgood

A colorful “forest” of Christmas tree worms. Photo by Nick Hobgood

Read more articles about the holidays in our Smithsonian Holiday Guide here

 Learn more about the ocean from the Smithsonian’s Ocean Portal. 

New research reveals that corals send out chemical signals to recruit the help of Goby fish in removing toxic seaweed. Image courtesy of Danielle Dixson

Corals are constantly under attack. Sea stars and other predators would love to take a bite, coral diseases lie waiting to take them out and many human-caused stresses persist in the water they inhabit, such as pollution, warming temperatures and rising acidity.

One of the first signs of a sick reef is the takeover of seaweeds, which continually threaten even healthy corals. However, corals aren’t alone in the fight against greenery, according to new research published in Science. When attacked, some corals send out chemical signals to their bodyguards—small goby fish—who scrape off or eat the coral-choking seaweeds.

Turtle weed (Chlorodesmis fastigiata) threatens corals because, upon contact, it releases a noxious chemical that disrupts their food source, the photosynthetic algae (zooxanthellae) that live inside their cells, ultimately leading to coral bleaching. Although most fish don’t have a palate for such toxic seaweed, authors Mark Hay and Danielle Dixson from the Georgia Institute of Technology observed coral gobies—small fish that spend their lives living in a single coral colony—eating it, and they wondered if there was more to this behavior than taste.

Hay and Dixson placed turtle weed on small staghorn coral (Acropora nasuta), a common reef-building coral found in the Pacific and Indian oceans, while in the presence of two goby species. The gobies cleaned up quickly: Within three days, 30% of the turtle weed was gone, and coral bleaching dropped by 70-80% compared to a goby-less seaweed invasion.

Without the protection of goby fish, corals are much more likely to become overgrown with seaweed. Image via Ocean Portal/Wolcott Henry

“These little fish would come out and mow the seaweed off so it didn’t touch the coral,” said Hay in a press release. “This takes place very rapidly, which means it must be very important to both the coral and the fish.”

In a series of experiments, the researchers worked out how the coral contacts the gobies to let them know that they need their hedges trimmed. Once the coral gets hit with chemicals from the invading turtle weed, it releases its own chemical signal—an emergency call to gobies—within 15 minutes. And, within another 15 minutes or less, gobies receive the message and swoop in to nibble away at the encroaching foliage.

What are the gobies getting out of this arrangement? The broad-barred goby (Gobiodon histrio) got a boost in its own defenses. It produces its own poisonous mucus to deter predators and, after eating the noxious turtle weed, this mucus impaired their predators’ swimming ability more than twice as fast, the researchers found. But the other goby species—the redhead goby (Paragobiodon echinocephalus)—doesn’t eat the seaweed, simply shearing it off the coral. What is its benefit?

“The fish are getting protection in a safe place to live and food from the coral,” Hay said. “The coral gets a bodyguard in exchange for a small amount of food. It’s kind of like paying taxes in exchange for police protection.”

Goby fish spend their entire lifetimes with the same coral. Image courtesy of Georgia Tech/Joao Paulo Krajewski

This kind of chemical signaling system is the first observed in coral reef organisms—but it surely isn’t the only one. Many coral reef organisms are interdependent, relying on one or two other species for food or habitat, which means that the loss of just a few species can accelerate the disappearance of many others. For example, if these coral-cleaning gobies were overfished, say for the aquarium trade, the reef would be threatened by seaweed takeover, which could then degrade the entire community.

“Who would have thought that such a small, seemingly insignificant fish might play such a large role in keeping corals from being killed by seaweeds?” said coral reef biologist Nancy Knowlton from the Smithsonian National Museum of Natural History, who did not participate in the research. “It’s a compelling example of why maintaining biodiversity is so important.”

It’s also possible that such subtle chemical signals could be disrupted by ocean acidification. Clownfish and damselfish raised in seawater with the acidity scientists predict we’ll see in the year 2050 have trouble identifying scents in seawater to find their homes or avoid predators. If these gobies have similar problems, the impacts of acidification on reef communities could be greater than expected.

Learn more about coral reefs from the Smithsonian’s Ocean Portal.

Pacific hagfish (Eptatretus stoutii) in a hole at 150 meters depth at the Cordell Bank National Marine Sanctuary in California. (via Linda Snook of NOAA/CBNMS / Flickr)

Hagfish are widely considered the most disgusting animals in the ocean, if not on earth. The eel-shaped creatures use four pairs of thin sensory tentacles surrounding their mouths to find food—including carcasses of much larger animals. Once they find their meal, they bury into it face-first to bore a tunnel deep into its flesh.

Despite the fact that they seem repulsive, they are undoubtedly unique—and just because animals are disgusting to human sensibilities doesn’t mean they don’t deserve our attention and protection. That is the message behind Hagfish Day, which occurs every year on the third Wednesday of October: that we can find beauty in the ugly and protect all ocean animals. Here are 14 fun facts about the unusual group of animals:

1. The estimated 76 species of hagfishes live in cold waters around the world, from shallow to as deep as 5,500 feet (nearly 1,700 meters).

2. Hagfish can go months without food.

3. Hagfish can absorb nutrients straight through their skin.

4. They are sometimes called “slime eels”—but they are not eels. They are in the class Agnatha, designated for fish without jaws (around 100 species in total).

A Pacific hagfish hides under a rock. Image via Wikimedia Commons/Stan Shebs

5. Although they are jawless, hagfish have two rows of tooth-like structures made of keratin that they use to burrow deep into carcasses. They can also bite off chunks of food. While eating carrion or live prey, they tie their tails into knots to generate torque and increase the force of their bites.

6. A 2011 report from the International Union for Conservation of Nature (IUCN) found that 12% of hagfish species are at an elevated risk of extinction. One hagfish species is critically endangered, two are endangered, six are vulnerable to extinction and two are near-threatened.

7. No one is sure whether hagfish belong to their own group of animals, filling the gap between invertebrates and vertebrates, or if they are more closely related to vertebrates.

8. The only known fossil hagfish, from 300 million years ago, looks very much like a modern hagfish, leading some scientists to speculate that it has changed little since then. “It’s an indication, not that they’ve stalemated and are not evolving, but that they have arrived at a body plan that is still very successful today,” says Tom Munroe, a fish zoologist at the Smithsonian National Museum of Natural History.

9. To ward off predators and other fish trying to steal their meals, hagfish produce slime. When harassed, glands lining their bodies secrete stringy proteins that, upon contact with seawater, expand into the transparent, sticky substance. According to common hagfish mythology, they can fill a 5-gallon bucket with the stuff in mere minutes.

10. This slime gives hagfish a slippery exit when attacked by predators. A larger fish looking for a meal instead gets a mouth full of slime, while the hagfish can slide away.

11. To prevent choking on its own slime, a hagfish can “sneeze” out its slime-filled nostril, and tie its body into a knot to keep the slime from dripping onto its face.

12. Although their eating habits seem disgusting, hagfish help clean and recycle dead animals from the seafloor. They also serve as a food source for fish, seabirds and seals—at least those that can make it through the slime.

13. Not only are hagfishes jawless, but they are also boneless. They have a skull made of cartilage, but no vertebrae.

14. Hagfish are threatened from both intentional fishing and unintentional bycatch. Hagfish weren’t always fished, but because several more preferable fish species are overfished and hard to catch, fishermen have moved down to catching hagfish.

Learn more about the ocean from the Smithsonian’s Ocean Portal.