Structure and Function:
Kelps are the largest and most complex of all algae (Kingdom: Protista) known as seaweeds. In algae, the body of an individual organism is known as a thallus. Kelps belong to brown algae in the class Phaeophyceae in the order Laminariales. Kelps are frequently considered to be an “ecosystem engineer” which means that the kelp provides a physical substrate and habitat for kelp marine communities. Kelp is unique in that whereas most of the algae in the ocean are tiny and single-celled, kelp are large and multi-celled plants producing dense 3-dimensional forests. One of the characteristics of kelp plants is the presence of “anchors” called holdfasts among the kelp. Thus, instead of tree-like roots that extend into the substrate, these holdfasts grip onto rocky substrates and enable the kelp plants to grow toward the water’s surface. Kelp forests are tiered like a terrestrial rainforest with a canopy and several layers below. This function is enabled by the kelp stipe which is analogous to a plant stalk, allowing the kelp to extend vertically from the holdfast thus providing a strong support. The blade-like attachments that extend from the stipe are termed fronds and these are the sites of nutrient uptake and photosynthetic activity (Dayton, 1985). Especially unique to the kelp among all other marine plants as well as terrestrial plants is their especially high growth rate. Some species of kelp can grow as fast as half a meter a day, ultimately reaching 30 to 80 meters (100 to 260 feet). These vertical forests are maintained by pneumatocysts, which are gas-filled bladders that keep the upper portions of the algae afloat as well as maintaining an upright position in the water (NOAA, 2007). Kelp forest are extremely important in the kelp’s photosynthetic nature enabling them to be the primary food producers for the kelp forest ecosystem; therefore, supporting a vast number of marine habitats including: tubeworms, sponges, sea cucumbers, and sea otters (Berg and Hager, 2009).
Location and Growth Conditions:
On a global scale, kelp forests grow primarily on the Pacific Coast, from Alaska and Canada to the waters of Baja California. The kelp forests of the eastern Pacific coast are dominated by two canopy-forming, brown macroalgae species, giant kelp (Macrocystis pyrifera) and bull kelp (Nereocystis leutkeana). However, in the kelp forests of California, giant kelp is the most recognized species of brown macroalgae, which also dominates primarily the more southern kelp forests, from the southern Channel Islands, California to northwestern Baja (NOAA, 2007).
Kelp forests are especially abundant in relatively shallow waters of depth of about 25 m or about 82 ft. These large underwater forests grow along rocky coastlines and kelp favors nutrient-rich water with temperatures between 6 °C and 14 °C (43 °F and 57 °F). (Berg and Hager, 2009). On the California coast, these brown algae communities persist in clear water conditions through which light penetrates easily. Kelp thrives most efficiently in regions of upwelling as well as regions with continuously cold, high-nutrient waters. Upwelling regions are regions where the ocean layers overturn, bringing cool, nutrient-rich bottom waters to the surface, especially rich in nitrogen and phosphorus. The California kelp forest flourishes because of the cool California current off the coast. In contrast, kelp experiences reduced or negative growth rates in warm water. This is primarily because the amount of dissolved inorganic nitrogen decreases significantly in marine waters warmer than 20 °C (NOAA, 2007). This phenomenon is particularly evident along the southern California coast where giant kelp forests decline in the summer months. Especially important among the Los Angeles kelp forests is the competition between giant and bull kelp for sunlight, which the giant kelp usually dominates. Lastly, imperative to the growth of the kelp forests is the strength of the substrate. Meaning, the larger and stronger the rock which the kelp is anchored then the better chance of survival.
In the Monterey Bay National Marine Sanctuary, kelp forests range throughout most of the nearshore waters and kelp canopy cover typically about 25 square miles. Throughout all of California, the total area of kelp canopy is 119 square miles (76,000 acres) based on data from the California Department of Fish and Game. Therefore 21% of the kelp canopies in California occur in Monterey Bay National Marine Sanctuary (NOAA, 2007).
Origin and Evolution:
“I can only compare these great aquatic forests…with the terrestrial ones in the intertropical region. Yet if in any country a forest was destroyed, I do not believe nearly so many species of animals would perish as would here, from the destruction of the kelp. Amidst the leaves of this plant numerous species of fish live, which nowhere else could find food or shelter…”
-Charles Darwin, 1 June 1834, Tierra del Fuego, Chile
In terrestrial ecosystems, scientists are able to reconstruct the history of a forest or grassland from the fossilized pollen or leaves. However, kelp does not produce pollen and marine sediments do not preserve a good record of the plants. As a result, the scientists and researchers used depth charts of the southern California coastline and information from sediment cores on past nutrient availability to reconstruct potential kelp habitat as sea levels changed over the last 20,000 years (UC Davis, 2009).
Benefits and Uses:
The California kelp forest is one of the most diverse among all the kelp forests throughout the world; therefore, its vastness provides a considerable sources of oxygen alongside coral reefs for animals and humans. Kelp’s photosynthetic ability provides the nutrients necessary for life. Another main use from kelp forests is that humans harvest the kelp directly for extraction of alginic acid, which is used in products like toothpaste and antacids. Kelp forests provide food and shelter for large numbers of fish and shellfish. Kelp also protects coastlines from damaging wave action, acting as a buffer region (Gutierrez et al. 2006).
Sources of Kelp Forest Damage:
1. Natural causes --- Salinity, temperature change, turbulence, storms, seasons; El Niño Southern Oscillation (ENSO) events involve the depression of oceanographic thermoclines, severe reductions of nutrient input, and changes in storm patterns; winter storms and high-energy environments easily uproot the kelp and can wash entire plants ashore (Dayton, 1992).
2. Lack of symbiotic relationships --- sea otters vs. sea urchins. In California's kelp forests, the sea otter is a keystone species (a species that has an excessively large effect on its environment relative to its abundance in the ecosystem) which keeps the sea urchin population in check as well as effectively keeping the entire ecosystem in balance. Sea urchins are invertebrates that live on the sea floor and often completely remove kelp plants by eating through their holdfasts which has a large destructive chain reaction effect on the kelp ecosystem which many marine animals rely on kelp to feed and survive. Consequently, when sea otters decline, sea urchin numbers explode in number. By the early 20th century, sea otters were nearly hunted out of existence for their fur; therefore, kelp beds disappeared as well as the marine life that depended on kelp.
3. Human causes --- overfishing higher trophic levels that naturally regulate herbivore populations; greenhouse gas emissions cause global warming issues as well as an increase in global temperatures not favoring the kelp forest stability, warming the ocean waters and having a vital effect on kelp forests; pollution including sediment deposition and freshwater runoff carries all the pesticides and fertilizers used on land to control pests and crop harvest. A huge devastation to the California kelp forest occurred about 50 years ago in Palos Verdes when huge amounts of untreated raw sewage was dumped off the coast. As a result, there was a boom in sea urchins which not only graze on the sea floor but on particulate matter as well. The huge explosion in sea urchins completely removed the kelp beds from the coast of Palos Verdes as the entire sea floor was carpeted with sea urchins. Consequently, the treatment plants today in the Los Angeles basin have almost eliminated the release of raw sewage into coastal waters as the kelp beds are still recovering (Castro and Huber, 1997).
Conservation Status:
In recent years, Southern California's kelp forests have declined and reduced by up to 80% of their historic range. This is attributable to pollution, sewage, and storm runoff has made it harder for sunlight to reach the leafy algae (Barboza, 2011). Conservation groups have attempted to restore kelp forests by planting seedlings and scattering spores in places such as Laguna Beach, Crystal Cove and Malibu, where there is a rocky seafloor for them to anchor onto. The results seemed to be initially poor as warm-water climate patterns continued to devastate the kelp. However, giant kelp has recovered in the last few years, not in response to made-man reefs but mostly because of a “series of mild summers and an influx of cool, nutrient-rich water.” Recent aerial surveys show the spread of kelp forests at "near historical highs" not seen since the 1950s, said Ed Parnell, a marine ecologist with the Scripps Institution of Oceanography (Barboza, 2011).
Most of these causes of kelp forest damage seem to only have slight effects on the long-run because of the very impressive growth rate of kelp. Once kelp is anchored, it can grow to about half a meter a day, so the effects seem to be minimal. However, over-polluting the coastal waters may have a significant effect on water quality that many marine habitats and humans depend on. Overall conservation status seems to be okay due to the fast recovery rate of kelp, but measures to improve overall kelp forest and marine wildlife should be excelled.
Protection:
Protecting keystone species, such as sea otters, is one of the main priorities for conservationists along the California coast due to the profound effect on kelp ecosystems from a decline in sea otters. One of the methods that conservationists implanted to refuel the sea otter species along the California coast during the 20th century was to move some of the remaining sea otters from Big Sur to Central California (NOAA, 2007). As a result, the sea otter population gradually increased, thus resulting in a decline of sea urchins, and the kelp began to grow again. Furthermore, as the underwater forests grew, other species reappeared as well (Castro and Huber, 1997).
Another main goal of conservationists is to advocate a substantial decrease in fishing of the coastal ecosystems in order to maintain the large biodiversity within kelp forest and marine habitats at large. There are many groups in the world dedicated to saving the kelp forests, such as the Nature Conservancy and these groups work to educate people about the destruction of kelp forests in addition to expanding the marine conservation toolbox. To maintain balance between people and the ecosystem, they encourage governments to crack down on pollution, both into the ocean and into the air, which causes global warming. They encourage visitors to visit kelp forest and to be careful not to harm them. They even build artificial reefs to replace the reefs that have been destroyed.The future of kelp forests seems to be stable mostly because of the high growth rate of kelp. However, several key steps can be implemented to drastically help support the viability of kelp forests: Reduction in carbon dioxide emissions, elimination of sewage runoff, government funded grants for studying and monitoring the symbiotic relationships among kelp (may be more difficult) and most importantly raising awareness about the important of kelp forests for mankind by hopefully starting a Kelp Forest Awareness Organization on the UCLA campus.
Literature Cited:
Barboza, Tony. Man-made rock reef is part of a welcome seaweed change. Los Angeles Times. 2011.
Berg, Linda R. and Mary Catherine Hager. Visualizing Environmental Science. Second Edition. John Wiley & Sons, Inc. 2009
Berg, Linda R. and Mary Catherine Hager. Visualizing Environmental Science. Second Edition. John Wiley & Sons, Inc. 2009
Castro, Peter and Michael E. Huber. Marine Biology. McGraw Hill Higher Education, 1997.
Darwin, Charles. Voyage of the Beagle. 1839
Dayton, P.K. 1985a. Ecology of kelp communities. Annual Review of Ecology and Systematics 16: 215-245Dayton, P.K., M.J. Tegner, P.E. Parnell and P.B. Edwards. 1992. Temporal and spatial patterns of disturbance and recovery in a kelp forest community. Ecological Monographs 62: 421-445
Gutierrez, A., T. Correa, V. Muñoz, A. Santibañez, R. Marcos, C. Cáceres and A.H. Buschmann. 2006. Farming of the giant kelp Macrocystis pyrifera in southern Chile for development of novel food products. Journal of Applied Phycology 18: 259-267.
National Oceanic and Atmospheric Administration (NOAA). Kelp Forest Sanctuaries. 2007
Sala, E., C.F. Bourdouresque and M. Harmelin-Vivien. 1998. Fishing, trophic cascades, and the structure of algal assemblages: evaluation of an old but untested paradigm. Oikos 82: 425-439
Steneck, Robert S. et al. Kelp forest ecosystems: biodiversity, stability, resilience, and future. Envrionmental Conservation 29 (4): 436-459. 2002
University of California - Davis. "California's ancient kelp forest." ScienceDaily, 11 Nov. 2009. Web. 21 Nov. 2011.
Figures:
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Giant Kelp Forest in Catalina Island (Source: Underwater Photography Guide)
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| Steneck, Robert S. et al. Kelp forest ecosystems: biodiversity, stability, resilience, and future. Envrionmental Conservation 29 (4): 436-459. 2002 |
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| California Kelp Forest Map (Source: Sanctuary Integrated Monitoring Network) |
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| Kelp Structure |
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| Sea Otter |
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Sea Urchin
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| Kelp - Human Impacts |
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| Kelp Destruction - The Aftermath |
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| Steneck, Robert S. et al. Kelp forest ecosystems: biodiversity, stability, resilience, and future. Envrionmental Conservation 29 (4): 436-459. 2002 |
