Oceans For Dummies
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The ocean is big — really, really big — both as a body of water and as a topic. It encompasses physical characteristics, its ecosystems and inhabitants, its influence on climate and weather, the sustainable use of its resources, and much more. This Cheat Sheet touches on a few key topics.

coral reef scene © Jag_cz / Shutterstock.com

Ocean ecosystems

An ecosystem is like a neighborhood in which a variety of lifeforms adapt to the environment and to one another, developing complex interdependencies. If something changes, even a tiny change, it affects everything else. The ocean has a variety of ecosystems, including the following:

  • Tidal pools: These puddle- to pond-sized ecosystems form when seawater fills depressions near shore. They support a variety of marine life, including algae, crabs, barnacles, mussels, sea stars, urchins, snails, anenomes, and even small fish.
  • Sandy beaches: While they may seem barren at times, sandy beaches are home to sand dollars, crabs, shellfish, worms, seals, and a variety of birds, not to mention the many fish and other organisms that hang out in the shallow waters near shore. Sandy beaches also provide vital nesting areas for sea turtles and many birds.
  • Estuaries: These areas where freshwater from rivers and streams mixes with salty seawater, can host a variety of ecosystems, including mudflats, marshes, mangroves, and oyster and coral reefs, each of which is home to a unique community of marine organisms.
  • Mudflats: These flat, stinky, muddy areas, uncovered at low tide, are a favorite spot for mussels and clams that filter-feed on the abundance of plankton, along with birds that feed on the abundance of mussels and clams.
  • Salt marshes: These swampy areas are composed of salt-tolerant plants and have a variety of residents including crabs, snails, mussels, and worms, along with fish and shrimp, which visit to feed and breed. They also attract birds who come mostly to feed.
  • Mangrove forests: Mangroves are salt-tolerant trees and shrubs with roots that reach down from above the waterline into the substrate below, providing sheltered breeding areas for many species. Mangrove forests support a variety of marine life, including crabs, shrimp, oysters, sponges, fish, and manatees, along with reptiles and small mammals. They also play a vital role in protecting coastlines from storm surges.
  • Kelp forests: Kelp is a large plant-like algae that grows from the seafloor up to about 50 meters (160 feet) tall, providing food and shelter for large, diverse communities of marine species, including urchins, otters (which eat urchins), sea horses, baby sea turtles, crabs, sea cucumbers, and more.
  • The Sargasso Sea: This unique ecosystem consists of a massive mat of floating algae called sargassum, which is concentrated in one area of the Atlantic Ocean by four currents that surround it. It provides a habitat for shrimp, crab, fish, and many other marine species that have adapted specifically to it. It also serves as a vital spawning site for certain eels and fish.
  • Seagrass meadows: Seagrass is a salt-tolerant plant that grows and reproduces underwater. In addition to providing food and shelter for a variety of small marine species, these meadows are popular grazing sites for manatees, dugong, and sea turtles.
  • Coral reefs: Formed by polyps that build their homes out of calcium carbonate, coral reefs are some of the richest and most colorful ecosystems in the sea. They feed and shelter nearly every type of creature, from sponges and octopi to sharks, rays, and dolphins.
  • Oyster reefs: Formed by colonies of oysters, these reefs provide habitat and safe nurseries for diverse communities of marine life, including commercially valuable fish like anchovies.
  • Polar ecosystems: The Arctic (north) and Antarctica (south) are cold, icy areas with significant seasonal variations in temperature and sunlight. They’re home to: krill (tiny shrimp-like creatures); cold-water fish; a variety of birds, including penguins (Antarctica only); and a variety of mammals, including seals, walruses (Arctic only), whales, and polar bears (Arctic only).
  • Open ocean: Far from shore, the light-rich surface waters of the open ocean are home to photosynthetic plankton (phytoplankton) and zooplankton that anchor a complex food web. These plankton are eaten by fish, rays, squid, whales, and many other marine animals. Numerous predators, including sharks, dolphins, and seabirds, feed on those smaller marine animals and on other predators.
  • Deep ocean: At the bottom of the ocean are several extreme ecosystems that develop around hydrothermal vents (extremely hot and rich in chemicals), cold seeps (where hydrogen sulfide, methane, and other chemicals flow up through the seafloor), and whale carcasses (micro-ecosystems called whale falls). Except for whale falls, these ecosystems are possible thanks to chemotrophs (bacteria that feed on chemicals) — in contrast to phototrophs, such as algae, which use the sun’s energy to create food mostly from carbon dioxide and water.

Marine organisms

Scientists have a formal system called a taxonomy for classifying all lifeforms on Earth. Organisms are classified first by domain, then kingdom, then into progressively smaller groups — phylum, class, order, family, genus, and species. The organism is then named using its genus and species, typically resulting in something that only someone with a PhD in Biology or Latin can pronounce; for example, the scientific name for the southern blue-ringed octopus is Hapalochlaena maculosa. Talk about a mouth full. Plus, these groupings can change and species can be scientifically re-assigned as scientists learn more and discover new things.

In Oceans For Dummies, we simplify the groupings and use the Latin and Greek names only when necessary (they are their proper names of course) or when they have a nice ring to them (aka, it’s easy to pronounce). Accordingly, we classify marine organisms into the following groups:

  • Microbes: Mostly single-celled organisms that you can’t see without a microscope, such as bacteria, microscopic algae, and some fungi.
  • Plants: In this group, we include bona fide plants, along with other photosynthetic organisms, meaning they use the sun to create food from water and carbon dioxide (impressive trick) but aren’t technically plants. Seagrass, algae, seaweed (kelp), and mangroves are all plants or plant-ish.
  • Simple invertebrates: Anything without a backbone falls into this group, including sponges, jellyfish, sea anemones, sea stars, sea urchins, and a variety of slimy worms.
  • Mollusks: Anything with a hard shell and a soft body, though the hard shell may be optional. This group includes snails, sea slugs, bivalves (clams, oysters, mussels, scallops), octopus, squid, and cuttlefish.
  • Crustaceans: Think of a baguette (crusty on the outside, soft on the inside). Now, add legs, eyes, a mouth, and antennae, and you have something that looks like a crustacean. In this group are crabs, lobsters, shrimp, krill, and barnacles.
  • Fish: This one’s easy — anything with scales, gills, a tail, fins, and usually a swim bladder (to help it stay afloat without having to swim around like crazy all the time).
  • Reptiles: These guys and gals are cold-blooded, air-breathers with scales. The ocean is home to only a few reptiles — sea turtles (of course), sea snakes, saltwater crocodiles, and marine iguanas.
  • Birds: Another easy one — warm-blooded air breathers with two legs, feathers, and a beak. Flying is optional — case in point: penguins.
  • Mammals: Wow, another easy one — warm-blooded air breathers with a layer of insulation consisting of hair or fat (blubber). Members of this group include whales, dolphins (a type of whale), seals, sea lions, walruses, otters, manatee, and polar bears.

Ashlan and Philippe Cousteau’s 10 favorite sea creatures

  • Nudibranchs (sea slugs): The name “sea slug” doesn’t do these creatures justice. They’re some of the most beautiful creatures in the ocean, they collect toxins from what they eat (for self-defense), they come in every color combination imaginable, and they’re some of the most graceful swimmers on earth. What more could you want in a slug?
  • Mantis shrimp: Imagine a creature that looks like a praying mantis in front and a lobster tail in back. Its front legs are like those of a praying mantis, but they end in spears (for impaling their prey) or hammers (for clubbing crabs and other prey into submission or bashing open oyster shells). Their punch can be faster than a speeding bullet and they have eyes that can move independently and see from the ultraviolet end of the spectrum through to the infrared. Oh, and the ones with the hammer hands are nicknamed “thumb splitters,” which is just cool.
  • Cone snail: A poison-tipped-harpoon-toting snail that swallows fish whole and comes in a gorgeous shell. What could be more awesome?
  • Dumbo octopus: Elephants can’t fly with their ears as depicted in Disney’s 1941 film Dumbo, but the dumbo octopus looks sort of like an elephant head (without the trunk) but with tentacles and prominent ear-like fins that enable it to “fly” through the water. And they’re gosh darn cute.
  • Giant pacific octopus: This largest of octopi grows up to nine meters (about 30 feet) long and weighs up to 50 kilograms (110 pounds). Like other octopi, the giant Pacific octopus is smart and talented — it can crawl and even walk on the seafloor, swim, find its way through a maze, pry open shellfish, twist the lid off a jar, recognize people’s faces, change its skin color and texture in seconds to camouflage itself, and more. (Full disclosure: we, especially Philippe, haven’t met an octopus we didn’t absolutely adore.)
  • Parrot fish: Numbering about 90 species, these very colorful tropical fish spend most of their day eating algae off coral reefs, which helps the corals stay healthy. Their teeth are cemented together to form a beak-like structure for chipping away at the rock-hard coral and grinding it up to get at the algae. In the process, they ingest a lot of coral, which comes out the other end as white sand poop. What’s not to love about a fish that cleans coral and contributes to the white sand beaches we love so much . . . with their fishy poopies.
  • Grouper: This diverse group accounts for more than 100 species of stocky fish with big mouths that can change color to blend in with their surroundings. They’re all born and mature as females but can change sex later (freaky but useful if your dating pool doesn’t leave you with a lot of choices). Speaking of size, the goliath grouper can grow up to 2.5 meters (about 8 feet) long and weigh up to 455 kilograms (1,000 pounds). Their size makes them unafraid of people, and they’re highly intelligent and possibly the friendliest of fish — kind of like the Labradors of the sea.
  • Great white shark: If you get into a fight in the ocean, you want one of these bad boys (or girls) on your side — the world’s largest predatory fish. The great white grows up to 6 meters (20 feet) long, weighs in at up to 2,200 kilograms (about 5,000 pounds), is shaped like a muscle-bound missile, and is equipped with powerful jaws lined with razor-sharp teeth (up to 3,000 of them). And yet, in spite of all that size and power, Great Whites move like graceful ballerinas under water.
  • Female Anglerfish: Living in the dark, deep ocean, these ladies of the night have a dorsal fin shaped like a fishing pole that protrudes from the center of their head and ends in a glow-in-the-dark lure that just happens to dangle down in front of their huge mouthful of teeth. And they can swallow fish twice their size.

What about the guys? This is where it gets really freaky. They’re usually much smaller than the females, and when a male finds one of these lovely ladies, he attaches himself to her, as a permanent parasite. After a while, he loses his eyes and all his organs except his testes, physically fusing his body with hers — a case in which moving in together is taken way too far. What’s more is that females can do this body meld thing with multiple mates at the same time (and why not?).

  • Sea otter: Cuteness incarnate, that’s why we love sea otters . . . that and the fact that they eat lots of sea urchins, keeping urchin populations in check so that they don’t devour all the kelp forests. Sea otters use tools (rocks) to open their food, and even keep their favorite rock in a little fur pouch near their foot. They wrap themselves and their babies in kelp so they don’t float away while napping (so smart). They’re the furriest animals on Earth, with up to 1 million hairs per square inch (compare that with the average human who has 100,000 hairs on their whole head!) And come on, look at those adorable faces!

10 biggest threats to ocean health

The ocean that cares for us in so many ways is under serious threat from human activities. Here are the ten biggest threats to ocean health:

  • Greenhouse gasses: Carbon dioxide, methane, nitrous oxide, and other greenhouse gasses trap heat in the atmosphere, resulting in global warming and an increasing ocean temperature overall. In turn, global warming is impacting weather, precipitation, and currents; melting polar ice, and destroying entire ecosystems that have evolved over millions of years, such as coral reefs. Many of the ecosystems at risk are vital to feeding a growing human population.
  • Acidification: The ocean absorbs a huge portion of the excess carbon dioxide emitted by the burning of fossil fuels, but the chemical processes that occur when carbon dioxide reacts with water make the water more acidic. Ocean acidification is especially hard on corals, many forms of plankton, and mollusks that live in calcium carbonate homes, because the acidity dissolves the calcium they need to form their protective coverings. Ocean Acidification is eating away at many of the fundamental building blocks of ocean life, including planktonic organisms, which form the foundation of entire ocean food webs, and coral reefs which are the most biodiverse ecosystems on Earth.
  • Overfishing: Harvesting too many fish and using methods that harm ecosystems and other wildlife is resulting in a situation in which the ocean is being fished out of fish. Right now, 90 percent of all fish stocks around the globe are fished to capacity or are over fished. Fortunately, over time, effective fisheries management and more marine protected areas can help to restore fish populations while increasing harvests.
  • Oil and gas drilling and pipelines: Drilling through the seafloor and laying gas and oil pipelines at the bottom of the ocean . . . hmmm, what could possibly go wrong? Mistakes happen. Equipment fails. Pipes leak. Risks rise considerably when countries like Venezuela experience political and economic instability that leads to poor maintenance and improper use of equipment. Nothing is more heartbreaking than to see than countless fishermen out of work, fish floating dead in a sea of oil, or birds and mammals choking on it.
  • Polluted runoff: Water carrying pesticides, chemical fertilizers, human and animal waste, and other harmful substances eventually makes its way from land to the ocean, killing wildlife directly or fueling harmful algae blooms that result in the death of large populations of fish and other marine creatures and pose a huge threat to human health.
  • Plastics: Plastics are synthetic products that never decompose They just break up into smaller pieces that pollute the water and kill wildlife. More than 300 million tons of plastic are produced every year, and at least 8 million of it ends up in the ocean. Marine animals get tangled up in it, or they eat it, sometimes starving to death on full stomachs (full of plastic, that is).
  • Inadequate protection: Only about 5 percent of the ocean is protected from abuse by being designated and managed as no-take Marine Protected Area. These areas provide a safe haven for marine life to live and reproduce, and the benefits extend far beyond the borders of the protected area.
  • Coastal development: Who doesn’t dream about living on a beach? About 37 percent of the world’s population live in coastal communities, and these same areas are hotspots for tourism. The problem is that coastal development can destroy the natural barriers, such as mangrove forests, saltwater marshes, and coral and oyster reefs, that protect the inland areas where humans tend to live. In addition, a great deal of wildlife depends on coastal habitats for their survival.
  • Shipping: Ninety percent of all goods shipped between countries crosses the ocean. Add to that cruise liners, personal boats and other watercraft, and you have a boatload of traffic. It negatively impacts ocean health in the form of oil spills, polluted ballast water (sometimes carrying invasive species), anchor damage, ship groundings and the massive amount of noise (sound pollution) created by all the vessels, which is devastating to animals like whales that use sound to communicate.
  • Aquaculture: Farming the ocean or raising aquatic animals in tanks near coastal areas can be a great solution to overfishing, as long as it’s done properly. However, when done improperly, it can be a source of: pollution; increased parasite infections in nearby wild fish populations; massive destruction of coastal areas like seagrass beds, mangroves, and more; the source of genetically engineered frankenfish that escape and throw the natural balance out of whack; and overfishing — caused when wild fish are used to make food for the farmed fish.

6 win-win opportunities in the blue economy

The concept of a Blue Economy encourages the sustainable use of ocean resources for economic development, job creation, and improving people’s lives, while at the same time preserving the ocean for future generations. In other words, it involves engaging in profitable activities that benefit the ocean — win-win opportunities. Here are six Blue Economy opportunities:

  • Fish less, catch more. This statement may seem counterintuitive, but it’s true. Ninety percent of the world’s fish stocks are overfished or fished to capacity. Overfished means not enough fish are left to rebuild the population. So, if we stopped overfishing (fished less) more fish would be left to rebuild fish stocks and voila! more fish to catch. Setting aside no-take marine reserves, reducing bycatch, and limiting fish catch are all ways to increase the amount of life in the ocean.
  • Harvest ocean energy. By harnessing the power of wind, waves, tides, and other sources of energy in and near the ocean, greenhouse gas emissions can be reduced, mitigating the effects of acidification and climate change on the ocean. In addition, this green energy could eliminate the need for offshore gas and oil drilling, which would mean fewer oil spills and related pollution. Yay!
  • Farm the ocean to increase its productivity. The ocean can support far more life than it currently does, enabling us to harvest more food from the ocean while reducing our dependence on marine wildlife for food. Done sustainably, this has a tremendous potential to help people and the planet.
  • Restore wetlands and mangrove forests to sequester carbon. Extracting carbon from the atmosphere and storing it (like forever) is complicated and expensive. Mangrove forests and wetlands can do the job for the cost of restoring them, while providing habitat for marine life to flourish.
  • Preserve ecosystems to profit from ecotourism. Instead of extracting resources from the ocean to sell, promote the beauty of these ecosystems through ecotourism without having to destroy them.
  • Restore natural coastal barriers to reduce costly property damage. A great deal of property damage inflicted by storms is due to coastal development, which has destroyed the natural coastal barriers such as reefs, wetlands, and mangrove forests. Restoring these barriers would significantly reduce the amount of damage and the costs of repairs related to coastal storms and flooding.

About This Article

This article is from the book:

About the book authors:

Ashlan and Philippe Cousteau are world-renowned environmental advocates, filmmakers, and authors with a passion for adventure. Philippe is the founder of EarthEcho International, a leading global voice for ocean conservation. Ashlan is a journalist and storyteller who has explored all seven continents.

Ashlan and Philippe Cousteau are world-renowned environmental advocates, filmmakers, and authors with a passion for adventure. Philippe is the founder of EarthEcho International, a leading global voice for ocean conservation. Ashlan is a journalist and storyteller who has explored all seven continents.

Ralph R. Roberts has been investing in foreclosed properties for over 30 years. He knows every step of the process, from scouting properties to cashing out after the sale, from helping distressed homeowners keep their homes to buying those homes when the owners can no longer afford them. He also has assisted homeowners who have been taken advantage of by unscrupulous investors.

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