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Habitat alteration is defined as a change in the particular environment or place where organisms or species tend to live. Habitat alteration is a topic that, by definition, includes many other issues such as pollution, invasive species, overfishing, and aquaculture. However, there are issues that are having a negative impact on our ocean which are not included within these other categories.

Physical damage is one type of environmental damage not included within the other areas.  This destruction can be caused by poor fishing gear, cruise ships or even coastal development.

Bottom trawling (illustration courtesy:  www.Oceana.org) is a commercially used fishing method where large bag-shaped nets are pulled along the sea floor. This technique is used in search of bottom dwelling species such as shrimp, cod, rockfish and flounder. The nets are used from shallow depths as little as 50 ft (15.2 meters) all the way to depths of 6,000 feet (1829 meters) on the continental shelf. The nets can rise to 40 feet (12.2 meters) tall and be as wide as 200 feet (60.9 meters). This type of fishing was originally used primarily in sandy flat bottom areas in search of fish like flounder. However, with technical innovations such as the use of rollers and rockhopper devices, these same techniques are now used in much more sensitive complex ecosystems such as deep-sea coral forests, rock pinnacles, and boulder-covered areas. 

As this fishing gear drags and rolls along and digs into the sea floor, the result is often habitat destruction. Some single rockhopper devices weigh several hundred pounds, each having great potential to cause serious long-term damage to the ecosystem along the seafloor. This type of fishing often sweeps up or kills non-targeted marine life.  See our section on By catch for more information on this topic. According to information contained in the PEW Oceans Commission 2003 Report on America's Living Oceans, "typical trawl fisheries in Northern California and New England trawl the same section of sea bottom more than once per year on average. (Pew Oceans Commission, 2003, p. 5; Friedlander et al, 1999; Auster et al, 1996) Bottom-dwelling invertebrates can take up to five years or more to recover from one pass of a dredge." (Peterson and Estes, 2001)  This results in sea floor areas that never get a chance to return to their natural state.

The cruise ship industry is known to cause several different types of environmental damage.  Within the habitat destruction category, some are accidental such as groundings, which can be devastating.  Other causes are, unfortunately, the result of more regular practices and are, hence, avoidable. One issue is their massive anchors, weighing up to 5 tons, which along with the chains, devastate the sea floor which ranges from sensitive coral reefs to sea grass beds. Just one anchoring in calm seas with no wind can do damage that will take a reef 50 years to repair. (Smith, S. H., 1988) Government scientists in Grand Cayman report that more than 300 acres of coral reefs have been lost to cruise ship anchors just in the harbor of George Town alone. (Pattullo, 1998)  In the U.S. Virgin Islands National Park, a single anchor drop from a cruise ship in 1988 led to the destruction of almost 300 square meters of reef.  Monitoring at this site reveals no significant recovery of hard coral 8 years later. (Rogers, C. S., 1993)  For more information on other types of damage caused by cruise ships, click here

"A survey of 186 boats in 1987 revealed that 32% were anchored in seagrasses and 14% in coral communities. About 40% of the anchors in coral and 58% in seagrass beds caused damage (Rogers et al, 1988). Small boats continue to run aground on reefs within Buck Island Reef National Monument and Virgin Islands National Park. The installation of mooring buoys and limits on the size of vessels allowed in park waters have resulted in less pressure on these reefs, but in some areas there is little coral left to protect." (Smith et al 1997, p 352)


Coastal development (illustration courtesy: PEW Oceans Commission) is becoming an increasing threat to our oceans as more and more people move closer to the coast.  As of present time, 60% of the world's 6 billion people live within 60 miles of a coast. Within the United States, the state of Florida has experienced some of the greatest population growth, increasing from less than 2 million in 1940 to now over 14 million. As a result of development, over half of the Everglades have been lost. In California, according to information published in California's Ocean Ecosystem 1995 draft by The Resources Agency of California "Land reclamation activities, including agriculture and urbanization, have resulted in the loss of more than 90% of the state's historic distribution of riparian and freshwater wetlands." California's Ocean Ecosystem also states  that "ninety percent of emergent wetland habitats and more than half the mudflats in the enclosed waters zone have disappeared" and that more than two thirds of the states estuaries and bays have been eliminated. (The Resources Agency of California, 1995, p. 2) The PEW Oceans Commission reports that "Sprawl development is consuming land at a rate of five or more times the rate of population growth in many coastal areas." (Pew Oceans Commission, 2003, p. 5)

Coastal development threatens our oceans primarily by removing or changing our coastal marshes and estuaries. These areas are of vital importance because they serve as nurseries and spawning areas for aquatic wildlife.  These natural areas also filter out pollutants and sediments. They also help to regulate peaking flood levels. Marsh areas in the U.S. alone are disappearing at a rate of 20,000 acres per year.  Louisiana has lost half a million acres of wetlands since the 1950's. (Pew Oceans Commission, 2003, p. 5)

The threat to the coastal ecosystem in not always a result of direct development within the estuary or marsh area. In fact, most of the damage occurs as a result of altered natural water flow to these areas which often is a result of the creation of dams, bridges, roads and impervious surfaces such as parking lots.  Roads, parking lots, rooftops, and other impervious surfaces typically make up about 40% of the surface area of suburban development. The impervious surfaces not only alter the natural flow of fresh water to the oceans but they also collect pollutants from automobiles, fields, lawns, and the like which provide a quick transfer to rivers, estuaries, and finally to our oceans. For example, a one-acre parking lot produces about 16 times the volume of runoff that would come from a one-acre meadow. (Pew Oceans Commission, 2003, p. 56) Numerous studies show that when more than 10% of the acreage of a watershed is covered with impervious surfaces, its aquatic biodiversity begins to decline. (Pew Oceans Commission, 2003, p. 56)  


What can you do to help?


  • Buy your seafood from fisheries using non-destructive fishing techniques. A wallet-sized, easy to use list of fish that are caught in a sustainable fashion and are not toxic or hazardous to your health, can be down loaded from the Monterey Bay Aquarium's Seafood Watch. Another good source of information is the Seafood Choices Alliance.

  •     Choose cruise lines with known good environmental practices. If you vacation on cruise lines, ask what anchoring practices are used. If possible, select destinations where anchoring is not necessary or where a specific anchoring area has been specified outside of the most sensitive areas. Let the cruise line know that you value the ocean environment.

  •     Landscape with native plants that need less water. Less irrigation results in less runoff. Limit paved surfaces as they prevent water from percolating down into the ground, causing runoff to accumulate. Paved surfaces also transfer heat to runoff thereby increasing the temperature of receiving waters. Native species of fish and other aquatic life can often not survive in these warmer waters that are created due to such practices.

  •    Conserve water by purchasing water-efficient showerheads, faucets, and toilets. This will limit the total amount of wastewater and lessen the total runoff.

  • Your Voice counts. Use our letter writing area to make sure your opinions and concerns are heard by government and industry leaders.



To continue learning about other threats to our marine environment, read our Dangerous Debris page.


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