Why Do Scientists Want to Map Coral Ecosystems with Laser Line Scan Technology?
A key purpose of NOAA’s Ocean Exploration Initiative is to investigate the more than 95 percent of Earth’s underwater world that until now has remained virtually unknown and unseen. Such exploration may reveal clues to the origin of life on Earth, cures for human diseases, answers on how to achieve sustainable use of resources, links to our maritime history, and information to protect endangered species.
Coral reefs are one of the most biologically-productive ecosystems on Earth, and benefit humans in a variety of ways that include protecting shorelines from erosion and storm damage, supplying foods that are important to many coastal communities, and providing recreational and economic opportunities. In addition, these highly diverse biological communities are proving to be very promising sources of powerful new antibiotic, anti-cancer and anti-inflammatory drugs. Most drugs in use today come from nature. While almost all of these drugs are derived from terrestrial plants and microbes, recent systematic searches for new drugs have shown that marine invertebrates produce more antibiotic, anti-cancer, and anti-inflammatory substances than any group of terrestrial organisms. Particularly promising invertebrate groups include sponges, tunicates, ascidians, bryozoans, octocorals, and some molluscs, annelids, and echinoderms. For more information about drugs from the sea, see ‘More About Drugs from the Sea’ below. You may also want to visit the Ocean Explorer Web site for the 2003 Deep Sea Medicines Expedition (http://oceanexplorer.noaa.gov/explorations/03bio/welcome.html).
Even though they provide numerous benefits to humans, many coral reefs are threatened by human activities. Sewage and chemical pollution can cause overgrowth of algae, oxygen depletion, and poisoning. Fishing with heavy trawls and explosives damages the physical structure of reefs as well as the coral animals that build them. Careless tourists and boat anchors also cause mechanical damage. Some of the most severe damage appears to be caused by thermal stress. Shallow-water reef-building corals live primarily in tropical latitudes (less than 30º north or south of the equator). These corals live near the upper limit of their thermal tolerance. Abnormally high temperatures result in thermal stress, and many corals respond by expelling the symbiotic algae (zooxanthellae) that live in the corals’ tissues. Since the zooxanthellae are responsible for most of the corals’ color, corals that have expelled their algal symbionts appear to be bleached. Because zooxanthellae provide a significant portion of the corals’ food and are involved with growth processes, expelling these symbionts can have significant impacts on the corals’ health. In some cases, corals are able to survive a ‘bleaching’ event and eventually recover. When the level of environmental stress is high and sustained, however, the corals may die.
Prior to the 1980s, coral bleaching events were isolated and appeared to be the result of short-term events such as major storms, severe tidal exposures, sedimentation, pollution, or thermal shock. Over the past 20 years, though, these events have become more widespread, and many laboratory studies have shown a direct relationship between bleaching and water temperature stress. In general, coral bleaching events often occur in areas where the sea surface temperature 1º C or more above the normal maximum temperature.
In 1998, the President of the United States established the Coral Reef Task Force (CRTF) to protect and conserve coral reefs. Activities of the CRTF include mapping and monitoring coral reefs in U.S. waters, funding research on coral reef degradation, and working with governments, scientific and environmental organizations, and business to reduce coral reef destruction and restore damaged coral reefs. NOAA monitors reefs using a system of specially designed buoys that measure air temperature, wind speed and direction, barometric pressure, sea temperature, salinity and tidal level, and transmit these data every hour to scientists. Satellites are also used to monitor changes in sea surface temperatures and algal blooms that can damage reefs. Research and restoration projects on selected coral reefs are conducted by NOAA’s National Undersea Research Program (NURP). Using high-resolution satellite imagery and Global Positioning Satellite (GPS) technology, NOAA has made comprehensive maps of reefs in Puerto Rico, the U.S. Virgin Islands, the eight main Hawaiian Islands and the Northwestern Hawaiian Islands. Maps of all shallow U.S. coral reefs are expected to be completed by 2009.
While these maps show where various reef habitats are located, they are unable to provide detailed information needed for effective management of complex coral reef systems. Side-scan sonar techniques are able to cover large areas, but cannot distinguish individual organisms in communities of fish, algae, and invertebrates. Video and photographic data can be collected by divers in areas shallower than 20 to 30 meters, and by towed cameras, remotely operated vehicles, and human-occupied submersibles in deeper waters. None of these methods, though, are able to collect the large amounts of visual data needed to make detailed maps of coral reef habitats.
A new technology called laser line scan (LLS) may provide a bridge between broad-scale approaches such as side-scan sonar and fine-scale video and still photography. LLS systems can detect objects as small as about one centimeter. This is much better resolution than is possible with side-scan sonar, but not quite as good as video. While LLS systems are unable to cover as much area as side-scan sonar, these systems provide two to five times the coverage of video. One of the most publicized uses of LLS was in the search for wreckage from TWA Flight 800, which went down off Long Island in 1996. In 2001, the Ocean Explorer program and NURP co-sponsored a field test of a commercial LLS system for imaging seafloor habitats. Results from this test confirmed the potential of LLS technology for mapping benthic habitats. The laser images revealed details of low relief sediments such as sand waves and ripples, and showed a variety of fishes, salp chains, sea anemones, sea pens, kelp and other macro-algae. These images allowed scientists to identify fish and invertebrate species within a given habitat, and to observe the relationships of these animals to their habitats. The purpose of the 2006 Laser Line Scan Expedition is to test the ability of LLS technology to provide detailed information about a variety of coral reef habitats in the Hawaiian Archipelago.
The overarching question driving the 2006 Laser Line Scan Expedition is, ‘Can laser line scan technology provide data needed to effectively manage coral reef ecosystems?’ Specific Expedition objectives include:
• Testing the capability of LLS technology to characterize benthic habitats in coral reef ecosystems and their associated living communities;
• Providing data needed for ongoing studies of deep-water coral reefs, precious corals, and essential habitats for commercially-important fishes;
• Demonstrating the ability of LLS technology to collect large amounts of visual data about coral reefs in precisely located geographic areas;
• Developing techniques for combining data from LLS and multibeam sonar systems to produce detailed maps of coral reef habitats; and
• Producing maps of coral reef habitats that will meet management needs in the Hawaiian Archipelago.
A Laser Line Scan system consists of five components: a laser, a scanner, a detector, control electronics, and data processing/display/recording hardware. The laser, scanner, detector, and control electronics are enclosed in a watertight pressure housing that is towed behind the survey ship. Display/recording equipment is onboard the ship where it is monitored by the LLS system operator. The scanner consists of two mirrors mounted on a rotating shaft. Light from the laser is reflected by one of the mirrors onto the seafloor, and illuminates an area about the diameter of a pencil. Light reflected from the seafloor is bounced by the other mirror to the detector (called a photomultiplier tube). As the shaft rotates, the mirrors move back and forth through a 70º arc. Operation of the laser, scanner, and detector is regulated by the control electronics. The data processing computer integrates information from the detector and scanner with ship speed, and sends an image of the seafloor, one line at a time, to the display and recording equipment. The typical size for a LLS system is about 13.8 in (35 cm) diameter by 5.1 ft (1.6 m) long, with an in-air weight of 300 lb (136 kg). For more information about LLS systems, visit http://www.csc.noaa.gov . You can see some LLS images at http://jaffeweb.ucsd.edu .
More About Reef-Building Corals
Corals are members of the class Anthozoa, in the phylum Cnidaria. Like all cnidarians, corals have stinging cells called nematocysts that are used for feeding and defense. The nematocysts of some cnidarians are dangerous to humans, particularly jellyfishes such as the Portuguese man-of-war and the sea wasps found near Australia. Reef-building corals belong to the order Scleractinia (stony corals), and produce a hard limestone skeleton. Many corals are colonial, and a single coral ‘head’ or boulder consists of hundreds of individual coral animals called polyps. In shallow waters, coral polyps often contain symbiotic algae (zooxanthellae) living inside the corals’ tissue. These algae are photosynthetic and provide at least part of the corals’ nutritional requirements. The vivid colors often associated with coral reefs are primarily due to photosynthetic pigments of the zooxanthellae; most corals are colorless.
Corals reproduce sexually. Most (about 75%) stony coral species form hermaphroditic colonies that produce both male and female gametes, while the remainder are gonochoristic (the colonies produce either male or female gametes, but not both). In many coral species (and other sessile organisms such as sponges), neighboring individuals of the same species release their gametes almost simultaneously, a process known as ‘broadcast spawning.’ The gametes fuse in the water column to form floating larvae (planulae). Planulae usually swim toward the surface, then settle within two days, although the larval stage of some species may last several weeks or even months. The time between planulae formation and settlement is typically a period of very high mortality (mortality is lower in some coral species that brood the planulae within their bodies after internal fertilization).
Deep-water coral reefs are not as well-known as shallow reefs, but deep reefs are at least as diverse as their shallow-water counterparts. In fact, the majority of coral species live in colder, deeper waters. One of the most studied deep-water corals, Lophelia pertusa, is found in depths ranging from 200 m to 1,000 m throughout the Earth’s oceans except in polar regions. L. pertusa and other deep-water corals do not have symbiotic algae, and receive nutrition from plankton and particulate material captured by its polyps from the surrounding water. Complex biological communities are associated with L. pertusa reefs on continental shelves, slopes, and seamounts; about 800 species have been reported to be associated with these reefs in the North Atlantic. Very little is known about reproduction in L. pertusa, but colonies of the coral have been found on oil rigs that are far away from known locations of natural reefs, suggesting that this species may have long-lived planktonic larvae. L. pertusa reefs have been known to fishermen for centuries and are considered good fishing areas, especially for gillnets and longlines. In recent years, the use of heavy bottom trawls has greatly increased damage to L. pertusa reefs through mechanical disturbance and by stirring up large quantities of silt. Siltation is believed to be a major cause of L. pertusa reef degradation on a global scale. Oil exploration and extraction activities can also damage L. pertusa reefs by increasing sedimentation and discharging toxic chemicals. For more information on coral reefs visit the National Ocean Service Corals Discovery Kit at http://oceanservice.noaa.gov/education/kits/corals/welcome.html .
More About Drugs from the Sea
Some of the drugs derived from marine invertebrates are:
Ecteinascidin - Extracted from tunicates; being tested in humans for treatment of breast and ovarian cancers and other solid tumors
Topsentin - Extracted from the sponges Topsentia genitrix, Hexadella sp., and Spongosorites sp.; anti-inflammatory agent
Lasonolide - Extracted from the sponge Forcepia sp.; anti-tumor agent
Discodermalide - Extracted from deep-sea sponges belonging to the genus Discodermia; anti-tumor agent
Bryostatin - Extracted from the bryozoan Bugula neritina; potential treatment for leukemia and melanoma
Pseudopterosins - Extracted from the octocoral (sea whip) Pseudopterogorgia elisabethae; anti-inflammatory and analgesic agents that reduce swelling and skin irritation and accelerate wound healing
w-conotoxin MVIIA - Extracted from the cone snail Conus magnus; potent pain-killer
Most of these species are sessile invertebrates, which means that they live all or most of their lives attached to some sort of surface. This lifestyle may provide a clue to why these animals produce potent chemicals. One possibility is that they use these chemicals to repel predators, since they can’t run or hide. Another idea is that since many of these species are filter feeders, they are exposed to all sorts of parasites and pathogens in the water. Perhaps they use powerful chemicals to repel parasites or as antibiotics against disease-causing organisms. A third possibility concerns competition for space: If two species are competing for the same area of sea bottom, it would be helpful to produce a substance that would attack rapidly dividing cells of a competing organism. Since cancer cells often divide more rapidly than normal cells, the same substance might have anti-cancer properties.
For more information on drugs from the sea, visit: