February 8, 2013
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.
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.
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 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.
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.
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.
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.
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.”
January 10, 2013
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).
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.
December 18, 2012
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 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.
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 fins
ning; 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 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.
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
November 8, 2012
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.
“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.”
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.
October 17, 2012
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).
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.