Littorally Unbelievable: Where Solid Ground Meets H2O -- in Pictures
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This is Portnoo Beach in Donegal, Ireland, showing the low-lying sands extending out into the blue tide. Much of the area you can see in the photo is littoral zone -- the loosely defined region where terrestrial habitats meet worlds of water. You could call it land's end -- or perhaps its beginning, depending on whether you happen to be equipped with lungs or gills. In any case, the littoral zone is the land in between Earth and ocean, where tough organisms thrive amid pounding surf, shadowy reefs, jagged rocks and burning sands. Read on to see more images of this turbulent middle world upon the tide.
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What people mean when they refer to the littoral zone varies, but it is generally understood to encompass the shores of lakes, rivers and oceans -- especially those that are affected by tidal forces -- and a segment of the shallows out to a moderate depth of about 30 feet (9.1 meters) beyond the low tide. Above, you can see the beach of Koh Phing Kan in the foreground and the erosion effects of the tide on the limestone base of the vertical column known as Koh Tapoo, literally "Nail Island," farther beyond. If this striking feature looks familiar to you, you may have seen it in the James Bond movie The Man With the Golden Gun (1974). Next, you'll see the way sediment accumulates in marine littoral zones.
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Most beaches are formed by the slow deposition of sediment, carried upward from the sea floor via tidal forces. However, accumulations of sand can pile up without giving way to mainland, and formations known as shoals or sandbars occur when sand or other granular materials heap toward the surface of the water on their own. Head over to the next image to zoom out from this idyllic seascape.
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This is the Maupiti Island complex of French Polynesia, lying peacefully in the middle of the Pacific Ocean. The sun is bright and the waters are clear, but that's not the only reason you can see as much sand strung out against the sea as you can. At the edges of these islands, coral and sand bars rise toward the surface of the sea and encircle tranquil inner lagoons. Next, you'll see a crawling inhabitant of the littoral zone.
Image Credit: Benoit Stichelbaut/Hemis/Corbis
Blue soldier crabs, formally of the genus Mictyris, swarm the sand flats of Urunga, New South Wales, Australia. Crabs are crucial fauna of the littoral zone, occupying both the saltwater shallows and the sunny grit of the exposed beach. Some crab species exhibit behaviors based on circatidal rhythms, meaning synchronized with the high and low tides. For example, Mictyris crabs tend to emerge en masse onto the exposed sands at low tide for scavenging and feeding. When high tide comes, they burrow into the beach below the waters. Check out the next image to see another littoral burrower.
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The horseshoe crab digs itself into the sand for protection. Looking at a horseshoe crab is like seeing into eons past -- in shape and appearance, they mimic life forms that dwelt in the ancient oceans of Earth long before human beings existed. The next animal you'll see is also a beach digger, but mainly when it comes to depositing eggs. Can you guess what it is?
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The littoral zone figures big in the reproductive cycle of the now-endangered loggerhead sea turtle -- an armored, foraging reptile found throughout the world's temperate oceans. While adult loggerhead turtles are confirmed saltwater dwellers, egg-bearing turtles venture to steep beaches with strong, high-energy wave activity to create nests and lay their eggs in the sand. Check out the next page to see a sea turtle hatchling saying hello to the world.
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After emerging from the coarse, gritty nests in which they are born, sea turtle hatchlings tend to head straight for the water. Early in their lives, sea turtles are highly vulnerable to predators. While the eggs themselves can be dug up and consumed by ghost crabs and small mammals like skunks, once the hatchlings emerge and begin to flop toward the surf, they become exposed to the vicious beaks of sea birds, and even once they're in the water, they can be attacked by large fish such as tarpon. Maintaining the integrity of littoral nesting sites is crucial to the continued survival of sea turtles like the loggerhead, as development and pollution can leave beaches unfit for egg deposition or unnecessarily dangerous to hatchlings. Next, you'll see the extent of tidal fluctuations.
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High-energy surf washes over a park slide. This is high tide -- a bad time to lose an earring or contact lens. The word "tide" refers to the usually (though not necessarily) twice-daily rise and fall of water levels in our oceans. The forces that control the tide are of such strange interest that many people find them hard to credit. Do you know who's responsible for pulling the oceans into our shores and then away again?
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Celestial bodies are to blame! Tides are caused by a complex interaction of gravitational and centrifugal forces. When facing the moon or the sun, Earth's great waters experience a very real gravitational pull from those far-away masses. Meanwhile, the sheer force of motion caused by Earth's rotation and orbits modifies this upward pull, creating a very complex global system in which some waters are pulled toward the sky and over land, while other waters are dragged away from the beaches toward a net swell elsewhere. The beach above shows a very low tide exposing a wide field of sand. Check out the next image to see how a really high tide can cause a problem for low-lying coastal settlements.
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This is the Piazza San Marco of Venice, Italy -- one of the most famous city squares in Europe. The very old and very low-lying city of Venice sometimes experiences an overwhelming acqua alta, meaning "high water." In 2008, water in the city rose to the height of 1.56 meters (more than 5 feet), prompting a public announcement from the mayor's office urging people to confine themselves to their homes. Sometimes, locals manage these floods by setting up temporary raised walkways made out of simple planks. Other times, however, you just need a good pair of tall boots. Next, you'll see the effects of the tide on stony shores and outcroppings.
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The ocean giveth and the ocean taketh away. While tidal forces help create beaches by depositing sediment along shorelines, they also manage to wear away even the strongest of rocks, when armed by the ally of time. These slowly fading columns happen to be limestone stacks, known as the "Twelve Apostles," off the coast of Victoria, Australia. See another face of mineral erosion in the next image.
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This porous rock lives near the water line at Salt Point State Park, Sonoma County, Calif. So it's fairly obvious how straightforward wave action erodes rocks over time through the sheer force of friction, but how could surf and salt spray cause these smooth, intricate honeycomb patterns in solid stone? There is some debate about the various possible causes, but one answer likely lies in chemical erosion. Rocks in the littoral zone are subject to some particular chemical conditions -- especially related to salt. As the salts from ocean spray accumulate on rocks over time, slow chemical reactions take place. These reactions lead to the tunneling of one mineral through another -- hence, these patterns.
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Tide pools, like these in Cable Bay, Galiano Island, are essential features of littoral ecology. Some intertidal zones happen to host water-bearing depressions, small pools that hold seawater -- and sometimes plants and animals -- deposited by waves or by the high tide. When the waters recede, these tiny ecosystems are left to their own jurisdiction. Tide pools are some of the best places on Earth to see littoral life up close. Check out the next image to see some of the strange organisms that brim in these shallow miniature seas.
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In this New England tide pool, one spiny sea urchin and two pink sea stars recline on a soft mattress of algae. Also known as starfish, sea stars are elegant but slow-moving and literally brainless predators. Most sea stars prey on other slow-moving animals, such as oysters and mussels, by prying open their shells, enveloping them with external digestive tissue and consuming their bodies. It's kind of like if you could pull your stomach out of your body, turn it inside out and drop it on a cupcake. Next, we'll take a look at some stunning freshwater littoral habitats.
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We've hit gator country. The various littoral structures of the marine world offer many different and exciting habitats to study, but the banks and shallows of freshwater and brackish environments can be even stranger -- and more unique to the parts of the world in which they're found. These cypress trees take root in the shallow bayous of Louisiana. In the bayou, as well as other wetlands, the division between water and shore is not always distinct, making it difficult to determine exactly what to call the littoral zone. Next, we'll see freshwater erosion in action.
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This is the Buotama River of the Lena Pillars National Park in Russia. River bank formation bears some interesting analogues to the different types of ocean shores we've seen. Here, you can see at the outside of the river bend, there is a steep, stony, deeply eroded bank, whereas at the inside of the bend, there is a shallower bank that seems to hold soil and sediment. Accordingly, the outer bank is considered "cut" by the waterway, while the inner bank gives rise to "point bars" of sand and other sediment. Next, you'll see a creature that dwells in the resource-rich freshwater littorals of the Amazon River Basin.
Image Credit: Serguei Fomine/Global Look/Corbis
This yellow-spotted Amazon River turtle takes some refuge among the rocks. These hard-backed reptiles have adapted to the Amazon's annual flooding, making their home in the tributaries and side-streets of the massive Amazon complex. Unlike many turtles, a member of this species cannot retract its head entirely under its carapace. Next, you'll see the plant life that takes up residence in freshwater shallows.
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You've probably seen the lazily buoyant green circles from above, but this is your backstage pass. Water lilies are freshwater littoral flora, growing from lakebeds to reach the surface for the sunlight they gobble up so hungrily. The flat, floating leaves of these plants can reach epic proportions in some species. The giant Amazon water lily, for example, can forge a floating platter that is 6 to 7 feet (1.8 to 2.1 meters) in diameter. Click ahead to glimpse another freshwater plant that could call itself the water lily's cousin.
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For thousands of years, the lotus plant has been cultivated within water gardens by some Asian cultures, where it has often carried an important symbolic and religious significance. Like the standard water lily, lotus plants put down roots in the mud or sediment at the freshwater floor and grow toward the sun. Next, you'll see what beach sand looks like at the microscopic level.
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Sand is made of finely granulated minerals -- some from ground-down rocks, some from seashells, coral and other biological particles. The most common material making up the world's beaches is known as quartz or silica, which is a solid molecule made from a combination of silicon and oxygen that is abundant in Earth's crust. This photograph shows coral sand at 45 times magnification. The extent to which these bits look like some off-brand sugary breakfast cereal is probably just a coincidence. Next, we'll take a look at how human civilization affects beaches and littoral zones.
Image Credit: Dennis Kunkel Microscopy, Inc./Visuals Unlimited/Corbis
Human activity has greatly altered the character of beaches and intertidal zones around the world, leaving the fate of many littoral-dependent organisms hanging in the balance. Even beaches that aren't destroyed or polluted can be ruined as habitats by the mere proximity of human civilization. As just one example, the installation of artificial lighting on or around beaches is a major threat to sea turtle hatchlings. When young sea turtles first emerge from their eggs, they tend to head straight for the brightest light -- which, under natural circumstances, is usually the moon and stars reflecting over the ocean. If there is artificial lighting on or near the beach, however, hatchlings can end up disoriented, scooting through streets, parking lots and beachfront yards, where they are vulnerable to predators and the elements.
Image Credit: Cydney Conger/CORBIS
Of course some littoral zones face even harsher threats. Many beaches around the world are left toxic and disease-infested by pollution, including litter, improper dumping and draining, and poor waste management practices in general. Next, you'll see what a sandy intertidal zone looks like after an oil spill.
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An oil spill can be one of the most devastating events for the health of a beach. In 2010, after the Deepwater Horizon oil spill in the Gulf of Mexico, beaches along the southern coast of the United States were contaminated with lethal oil toxicity and dangerous bacterial blooms. Fish, water birds, sea turtles and other creatures that make their living in the ocean, neritic and littoral zones were left in danger because of the spill. Carol Browner, who was White House energy adviser at the time, called it the worst environmental disaster ever to affect the United States.
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In addition to the fish, invertebrates, reptiles and birds that we've seen, there are warm-blooded mammals that roost in the littoral and intertidal zones as well. Among them, seals are front and center. This Galapagos fur seal lies down on the sandy shore when it's time to enjoy the sunlight and catch up on some sleep. Among all seals, the Galapagos fur seal is particularly land-oriented, cruising the waves for only about 30 percent of its time. Next, have you ever seen a seal go surfing?
Image Credit: Keith Levit/Design Pics/Design Pics/Corbis
This wide-eyed pup rides the tide like a pro. Seals can sometimes be observed surfing the incoming waves in order to bask on the beaches, as is their wont. To maintain this wonderful and insulating brand of blubbery physique, one can imagine a seal probably needs plenty of rest.
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Flamingos and other "wading birds" depend on shallow littoral environments for survival. Often seen standing in the water on one leg at a time, flamingos prowl the shore-side brackish waters of swamps and lakes, feeding on what they can graze from the aquatic field below their feet. Examples of their prey include all manner of littoral residents, including mollusks, insect larvae, brine shrimp and algae. Next, check out a massive colony of creatures who do their best to become permanent residents of the tide pools they inhabit.
Image Credit: Corbis
The mussel is another central player in littoral ecology, clinging to rocks in the intertidal zone, where it filters the water for small particles of food, and where the mussel itself is preyed upon by starfish, some marine snails, as well as any large animal capable of giving its tough outer shell a sufficient prying. In the photo above, a mussel fisherman harvests these creatures from intertidal beds in a contained mussel aquaculture. Check out another tide pool treat in the next photo.
Image Credit: Gary K Smith/Loop Images/Corbis
You can see the spongy beds of kelp lining these pools at low tide in Howe Sound, British Columbia. Kelp makes up the forests of the ocean, growing in shallow, chilly waters where the right amount of sunlight is available. Kelp is, after all, a plant, and like all plants, it gets its energy from sunlight, photosynthesizing the sun's rays to turn them into food. Other littoral and tide pool-dwelling organisms, such as sea urchins and kelp crabs, feast and make their homes within these forests of kelp.
Image Credit: David Fleetham/Visuals Unlimited/Corbis
Schools of small fish swarm this pier structure in Papua New Guinea. The pilings of a pier are, in their own way, subject to tidal changes and littoral habitation. One can see tidal zones reflected in the different phases of weathering on these beams, and all the familiar creatures, including small fish, sea stars and mollusks take up real estate on this underwater skyscraper.
Image Credit: Michele Westmorland/Science Faction/Corbis
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