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Kelp is rich in dietary fiber, protein and iodine, potassium, magnesium and other minerals, eat seaweed can enhance the body's thyroid function, and promote the consumption of calories, weight loss and thus achieve the purpose of detoxification.
Oceanography 10, T. James Noyes, El Camino College 10E-1 Kelp Forests The Biology of Kelp Blades Kelp are one example of the many varieties of macroalgae (“large algae”), better know as “seaweeds.” Species of kelp grow larger than any other macroalgae, creating huge undersea “forests” close to the shoreline. Kelp keep themselves from being pushed onto Pneumatocysts beaches or drifting off into the ocean by anchoring themselves to the bottom with large rocks. They stretch up towards the sunlit surface using pneumatocysts, carbon-dioxide-filled “bladders,” helping their blades to carry out photosynthesis. Nutrients are absorbed directly Stipe out of the ocean water. The blades, pneumatocysts, and holdfast are Holdfast connected by a long, flexible “stipe” which can reach lengths of 100 feet (30 meters) or more. Rocks Pneumatocysts Kelp Forest. Courtesy of Kip Evans, Channel Islands National Pneumatocysts. NOAA. Marine Sanctuary, National Oceanic and Atmospheric Administration Pneumatocysts Oceanography 10, T. James Noyes, El Camino College 10E-1 Oceanography 10, T. James Noyes, El Camino College 10E-2 As with all algae, kelp need sunlight and nutrients to make their own food via photosynthesis. In addition, kelp prefer living in cold water, in part because their spores (repro- ductive cells) cannot survive in warm water. As noted above, kelp need a rocky bottom to hold themselves in place. Waves and currents are desirable for bringing nutrients into the kelp forest, but if they are too strong, they may break the stipe of the kelp or tear it loose from the bottom. Even if this happens, kelp can grow back amazingly fast. Under good conditions kelp can grow over 2 feet per day! Kelp Holdfast. Courtesy of Shane Anderson. Channel Islands National Marine Sanctuary, NOAA. Pneumatocysts Holdfast The kelp’s “holdfast” (which grabs onto the rocks) is not “roots,” because it does not absorb nutrients from the rocks or the water. However, the holdfast does host special blades which produce spores (for reproduction). Kelp have a fascinating and complicated method of reproduction. Kelp produce male and female spores which grow into small male and female “gametophytes” on the ocean bottom. The male gametophytes release “antherozoids” (like sperm) that fertilize the eggs of the female gametophytes. The eggs are then released as plankton, and when they settle in a good spot, grow into a huge algae. Oceanography 10, T. James Noyes, El Camino College 10E-2 Oceanography 10, T. James Noyes, El Camino College 10E-3 Benefits of Kelp and Kelp Forests Kelp is used for a variety of purposes. Of course, people eat kelp (e.g., sushi). Kelp is also used as fertilizer for crops on land (It is rich in nutrients absorbed from the ocean water.) and to make feed for livestock like cows, chickens, and pigs. In addition, kelp byproducts like algin are found in ice cream (makes it smooth by keeping ice crystals from forming) and in beer (keeps it foamy). Kelp is used in a variety of products, including paper and cosmetics (it keeps Yummy kelp. moisturizers moist and creamy and keeps them from becoming solid over time). Kelp keeps toothpaste thick (not too “runny”) and yogurt creamy (not too solid). Moreover, kelp is particularly good at absorbing iodine from ocean water1, an element which we need in small amounts (to avoid growing a goiter, an enlargement of the thyroid found in your neck, and prevent mental retardation in growing children) and is used in antiseptics and other pharmaceuticals. To harvest kelp for all theses uses and more, the top few feet of kelp forests are “mowed” periodically. 1 Most of the world’s iodine is dissolved in ocean water. All organisms, not just us, need a little bit of iodine, and kelp help iodine get into the marine food chain. Oceanography 10, T. James Noyes, El Camino College 10E-3 Oceanography 10, T. James Noyes, El Camino College 10E-4 Fish of the Kelp Forest. National Oceanic and Atmospheric Administration. Right: Garibaldi. Channel Islands National Marine Sanctuary, NOAA. Kelp forests are home to a wide variety of algae and animals, many of which we catch for food and other uses. However, like wetlands, few animals eat living kelp. Some simply use the forest as a place to hide, but many are there because of another food source. Kelp like to live in cold, nutrient-rich upwelling zones, the same environment preferred by phytoplankton. Many animals live on the kelp, using it as a way to stay close to shore in the nutrient-rich waters where phytoplankton (and small zooplankton attracted to them) are most abundant. The classic example is bryozoans, tiny “moss animals” that resemble sea anemones and form the white “splotches” that you often find on kelp that has washed ashore. Presumably many small animals find it easier to dine on small plankton than chew through thick, tough kelp. However, once waves break kelp free from the bottom and the kelp begins to decompose (“break down”), many organisms find it a bit tastier. Just think of all the “sand fleas” that one can see hopping around dead kelp washed up on the beach. Kelp detritus (dead, decaying kelp) is an important food source for many ocean organisms. bryozoans on a kelp blade Bryozoans on a Kelp Blade. USGS. Bryozoan. Courtesy of The Alpha Wolf (CC BY-SA 3.0). Ghost Forests If you look at old pictures of ocean life from California’s kelp forests, they show a variety of organisms (particularly large fish or tasty shellfish) that are rarely, if ever, seen anymore. Kelp forests host a lot of life now, but they use to have a lot more life. Given that regular monitoring only started within the last few decades, we probably do not even know what “normal” conditions are. Sadly, the latest generation of scuba divers and marine biologists may not even realize what they are missing. For this reason, many environmentalists have taken to calling our kelp forests “ghost forests,” ecosystems where some parts of the food web are only occupied by “ghosts” – for those who can see. Oceanography 10, T. James Noyes, El Camino College 10E-4 Oceanography 10, T. James Noyes, El Camino College 10E-5 “The damage is so pervasive that it may be impossible ever to know or reconstruct the ecosystem. In fact, each succeeding generation of biologists has markedly different expectations of what is natural, because they study increasingly altered systems that bear less and less resemblance to the former, pre-exploitation version. This loss of perspective is accompanied by fewer direct human experiences (or even memories) of once undisturbed systems.” − Dr. Paul Dayton, Marine Ecologist (1998) (Dr. Dayton has monitored California’s kelp forests for over 25 years.) Urchin Barrens Sea urchins are one of the few animals that eat live kelp. Typically, they are happy to catch and eat kelp detritus (dead, decaying kelp that waves have broken), but if there is not enough food drifting in the water, they will search out live kelp to dine on. Since sea urchins are benthic animals (bottom dwellers), they attack the kelp holdfast first, which causes the entire kelp to break free and die. Under certain circumstances (for example, few or no predators), they can eat and/or destroy an entire kelp forest. Little life remains afterwards (all the animals that depend on the kelp go away); the resulting ocean bottom where a kelp forest once stood is called an “urchin barren.” Sea urchins will keep the kelp forest from growing back again until they are eliminated from the area, typically by disease. Fortunately, kelp can grow back relatively quickly once the urchins are eliminated and the forest can be restored. Sea Urchins. Right: Courtesy of Greg Burton. Animals that Eat Sea Urchins: Sheephead and Sea Otter. Notice the sea urchin in the sea otters’ paws. Left: Channel Islands National Marine Sanctuary, NOAA. Right: NOAA Oceanography 10, T. James Noyes, El Camino College 10E-5 Oceanography 10, T. James Noyes, El Camino College 10E-6 Marine Reserves A solution to the overfishing problem that is growing in popularity is marine reserves. For example, inspired by a nature film, President George W. Bush created a huge marine reserve north of the Hawaiian Islands (2006). The essential idea behind marine reserves is that no animals can be harvested from the reserve (they are “no fishing” zones). Free from fishing, the populations of the animals inside the reserve will grow, and when they outgrow the reserve, fish and other animals will have to leave the reserve to find food and other resources. Once they are outside the reserve, fishermen can catch as many as they like. The beauty of the idea is that no matter how many animals fishermen take outside the reserve, there will always be a population inside the reserve to reproduce the next generation. Therefore, fishermen can never accidentally “overfish.” If natural changes in the environment cause the population to go down, then the fishermen will catch fewer fish, but the population will rebound inside the reserve once the environment improves and so will the fishermen’s catch outside the reserve. Thus, fishermen’s catch will go up and down with natural cycles. Marine reserves may seem like a good idea, but there are problems. Often the best places for reserves are the best fishing spots, so immediately after the reserves are put in place, fishermen will catch few fish and their incomes drop until the population inside the reserves grows large enough for fish to “spill” over the boundaries. Dozens of studies of marine reserves have shown that this can happen remarkably quickly (within a few years in some cases, but this is still a long time for fishermen to be out of work). Since 1999, California has been trying to institute a system of marine reserves called “marine protected areas” (MPAs). Talks were stalled for many years, but thanks in part to leadership by then-Governor Schwarzenegger, no fishing is allowed along 10% of the central coast2 of California (from Santa Barbara to Santa Cruz), and fishing is restricted along another 10% of the central coast. California’s recreational fishermen tend to be in favor of the reserves, hoping that they will bring back some rare species, but commercial fishermen remain skeptical for the most part, claiming that pollution from coastal cities and agriculture are the real reason for fish declines, not overfishing. In December 2010, the MPAs for Southern California were finalized; they restrict fishing along about 16.5% of our coast. Stay tuned, because the next decade should help us determine if marine protected areas could be an important part of the solution to California’s overfishing problem. At First: Later: No g No g in in F is h Fish 2 This is the easiest place to agree on, because it is the part of California where the fewest people live and fish. The system consists of 29 reserves, only half of which ban all fishing. Oceanography 10, T. James Noyes, El Camino College 10E-6
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