5. Environmental Stresses: Coastal and marine environments throughout the tropical regions are becoming subject to increasing anthropogenic pressures (civilian or even military; i.e. 1991 Gulf war; 1996 nuclear testing in French Polynesia, etc.). Similar impacts have resulted in harmful environmental effects in the Gulf Region, the Red Sea, Phillipine archipelago, and the Caribbean Sea. Thus, these areas are no longer the pristine sea as they were 20 years ago. And still, many people, governments, countries or multinationals consider the sea a huge dumping ground - be it for household, medical, toxic, or even nuclear waste.
  • Pollution: Oil, domestic, urban and industrial pollutants (waste water) are a problem in several areas, notably in the Gulf, the Caribbean and South-East Asia. Overt effects include local eutrophication and algal blooms (fig.45). Although some data are available on concentrations of pollutants (e.g. petroleum hydrocarbons, heavy metals) in water, sediments and biota, their effects on ecosystem structure and function are generally not well known. Through much of the tropical regions, the coastal zone is fast becoming the repository of solid wastes. In the Red Sea and the Bismarck Archipel, ecological effects from industrial inputs such as mining as well as military activities are of increasing concern, particularly if extraction of deep sea metalliferous muds becomes extensive.


Fig.45 Pollution (70kB)
  • Habitat loss: More acute ecological problems have probably arisen from loss and degradation of productive coastal habitat, caused by coastal landfill, dredging, and sedimentation of related practices. Some states (e.g. Arabian Peninsula, the Mexican Peninsula of Yucatan, some Caribbean islands) up to 40% of the coastline has now been developed, and much of the shoreline of countries are now artificial. Waikiki beach on the Hawaii'an island of Oahu used to be a mangrove forest. It has been cleared completely and up till now, it requires 1000s of tons of sand each year just to compensate the loss due to the oceans erossive forces (fig.46). Habitat decline also extends to other parts of the world, where approximately 50 % of mangrove forests may be lost over the last 20 years.

Fig.46 Oahu (Hawaii) (150kB)
  • Agriculture and related activities: In addition to fishing, hunting of adult turtles and birds (and their eggs) is extensive in some areas. The collection of algae for fish bait is a longstanding practice in many countries, but appears to be sustainable. A lot more devastating are dynamite and cyanide fishing practices. Such rude methods not only kill the fish, but also destroy fish larvae, juvenile fish, corals, and other benthic organisms in the affected area.
    Of increasing concern is degradation of the coastal environment caused by agricultural and other activities inland, sometimes far from the coast (fig.47). For instance, the overgrazing effect in Australia, Oman, and in parts of Oceania, the forest fires in Amazonia and Indonesia, etc. result in watersheds causing siltation of productive coastal environments. Sedimentation is severly suffocating coral polyps - the best example is given by the Amazon river delta: even though the waters off the Brasilian coast have an optimal temperature range to promote coral growth, the load of silt and slick flushed into the Atlantic by the Amazon river inhibts their survival.
    The use of corals as building and construction material is a common practice of the people of Sri Lanka. The continous dredging of their reefs will sooner or later deprive the coastal habitats from their natural wavebreaker and will expose their shores to increased tidal action and facilitating coastal erosion and degradation.



Fig.47 Agriculture (130kB)
  • Recreation and Tourism: Degradation of coral reefs from heavy collecting, and other recreational and touristic uses is becoming more widespread, particularly in the Red Sea, the Philippine archipelago and the Caribbean Sea. The lagoon of fringing reefs usually form a shallow natural pool, which is very popular among the non-swimming public (fig.48), results in a steep gradient of coral destruction in the shallow water zones of impacted reefs. It can range from 100% mortality in lagoons, to roughly 60-70% mortality in highly structured Back Reefs. However, this kind of destruction disappears completely at the point where the water becomes too deep and too rough to walk. Swimmers and divers apparently do not affect reef-health in terms of dead corals. They may however, damage corals quite easily by uncontrolled movements and loosely hanging gear, or simply by selectively exterminating certain species by collecting.
    More trouble arise when tourism takes off at a big scale. It is well known that infrastructure is a main source polluter; roads, hotels, restaurants, etc. create a lot of silt while in the construction phase, but keep doing so even after completion when sewage treatment plants spill their raw contents into the sea causing eutrophication. Economic activities like container ports, ferry terminals, boat traffic, uncontrolled anchoring (with no buoys), etc. further increase the pressure acting upon a reef ecosystem. Even the booming diving industry keeps up the stress even under water by producing crowds of poorly trained divers that jump like kangoroos along the reef slope, stirr up sediments, and smash branching corals with their loosely hanging gear. In that way, snorkeler-related breakage that used to be limited to the first few meters are then extended further down the slope. Divers should also act carefully when visiting overhanging crevisces; the cause considerable damage upon exposure of benthic flora and fauna by trapped exhaust air. And finally, as popular as it may seem, fish feeding does not only replace a beneficial natural diet by a manmade substitute, but also interferes with the complex foodweb of that ecosystem and in many cases even cause death of the fed fish.



Fig.48 Tourism (170kB)
  • Climate change: Among the possible long-term ecological impacts on marine life of the region are increasing concentrations of greenhouse gases, global warming and sea level rise (fig.49); acid deposition; and large-scale marine ecosystem instability. The significance of these impacts, in particular, are at present mainly speculative. Sea surface rise is already taking place and no one knows for shure whether reef growth is able to catch up. It is probably not too difficult for an individual coral colony to keep up with the rise of the midwater line, but erossive forces like storms, earthquakes, or naturally occuring bioeroders (e.g. sea urchins, coral boring sponges, etc.) may break them to rubble before even reaching the top.

Fig.49 Rising Sea Levles (130kB)
6. Ways to monitor Coral Reefs

To assess the health condition of coral reefs, semi-quantitative and quantitative methods can be used. Both require the ability to recognize coral diseases and the affected species in situ under water. The methods under consideration here are fast and easy-to-apply techniques. They can be carried out either by snorkeling or by using SCUBA gear, depending on reef morphology and the depth-zones surveyed. The belt and point method are rather simple-to-use techniques to survey large tracts or to pinpoint any diseased spots.
They also represent a simple tool to detect any impacts on corals other than genuine diseases.
  • The Belt Method: It is relatively easy to note down all cases of active diseases on corals that are encountered while surveying a coral reef. It requires only a watch, a writing slate , and a pencil. The only standardization necessary involves:

  • i) a time frame limiting the duration of each individual survey swim, and
    i) organizing the number of every disease encountered into categories.

    The time-frame of one single survey swim is usually half an hour during which the diver swims fairly close to the reef surface and registers all pathologic syndromes on corals in a path (or belt) about 2m wide. The speed may vary according to the substrate confronted (less in densely populated areas and quicker in scarcely populated reef areas such as sandy patches).

Seven categories have been established:

  1. "0", no syndrome found during the survey swim for 30 min (= one SCAN)
  2. "rare", 1-3 cases found during a 30min scan
  3. "moderate", 4-12 cases found
  4. "frequent", represents 13-25 cases
  5. "abundant", means 26-50 cases
  6. "epidemic", when 51-100 cases are found
  7. "catastrophic" is the end of the scale, >100, the number of diseases become uncountable
  8. The method described, neglects the portion of completely dead corals. Thus, if desired, an account of dead versus living reef has to be given separately.

  • Manta Tow: A somewhat modified belt method, that consists of two minute snorkel tows (minimum of 9) behind a boat at slow speed with stops to record percent cover of live, dead corals, patches of damaged corals, etc. Using the Manta Tow, the whole reef boundary should be surveyed if possible (fig.50). The tows are used to select the transect monitoring sites to ensure that they are representative of the whole reef. Where visibility is poor, some Manta Tows could be performed using Scuba gear to asses deep slopes.









Fig.50 Manta Tow (50kB)
  • Point Method: Another simple and fast method that requires only a transect line (usually 100m long) that is strung over the reef. The line is marked at evenly spaced intervals, at which points the underlying substrate is recorded (e.g. 0.5m intervals - fig.51). In contrast to other line transect methods, sandy bottoms, rubble, sponges, and soft or hard coral, sea grass, etc. are not measured, instead only the point of contact is recorded. In order to obtain the additional information on reef health, not only the coral species is registered, but also the disease (even though the diseases area is not exactly below the transect pin).

Fig.51 Point Method (10kB)
To compare in quantitative terms both ecological characteristics of the stony coral fauna at various reef sites some more accurate methods deserve description. The methods listed below are restricted to reef characterization to the nearly horizontal reef tops at relatively shallow depths of 3-5m. Reef sides and slopes at greater depths should not be scanned due to possible depth zonation effects.
Besides providing detailed information about diseased corals, these methods would allow the determination of the total coral coverage, density, and diversity index (e.g. Shanon Index - not further described in this report).
  • Intersected -Length Method: The sample consists of a line transect of 10m length overlaying the desired reef area (fig.52). It is advisable to mark transect start and finish with steel stakes. The preferred method uses 5 line transects with the parameters either recorded as "lifeforms" or as species. All organisms must be capable of being compared statistically. The intersected length of any coral species underlaying the line is recorded to the nearest centimeter. The method is based on the premise that:
    Coral coverage (frequency) = total length area of the coral population/total transect line

    Similar techniques, like belt and video transects, are comparable and can be either inter-calibrated with the lifeform transect with little difficulty to provide baseline data.


Fig.52 Intersect Length Method (10kB)
  • Point Centered Method: A transect line of 10m, with equally spaced sample points each 1m apart is used. Each point is considered the center of 4 quarters (fig.53). The distance from the sampling point to the center of the nearest individual coral colony is measured in each of the 4 quarters at each point. The coral species and the approximate area of the coral tissue (using the diameter of hemispherical specimens or the length and width of nearly rectangular specimens) is recorded. The mean of the 40 distances from the 10 sampling points is equal to the square root of the mean coral population area. This area describes the average empty area surrounding a coral as a point source.


Fig.53 Point Centered Method (14kB)
  • Belt Quadrat Method: A 30m line is used as a guide along which a continuos strip of adjoining quadrats, each 0.5m2 in area are photographed (fig.54, 55). In the laboratory, the photographs are analyzed using a binocular microscope and a grid overlay of 50 squares, each representing 100cm2 of actual bottom area. Photographing the scanned area provides a realistic image of the in-situ condition of the pathogenic condition of the species involved. If less time is available for such a reef health assessment, modification of this technique by using a meter rather than the camera allows a quick but less precise quantification of diseased corals. On both sides of the transect line, the meter-stick is laid down at every interval point to outline an imaginative area that is surveyed in more details.

Fig.54 Point Quadrat Method (17kB)

Fig.55 Video Transect (70kB)

  • Permanent Quadrat: If time permits, monitoring teams are encouraged to establish permanent, marked quadrats (e.g. 1m2 - fig.56) which are assessed regularly, either by photography or mapping to measure growth rates of corals and results of interspecific interactions. Quadrats are particularly used to follow new coral recruits to determine the ability of a reef to recover from stress. A very important site for monitoring will be reef areas that are almost bare of corals e.g. reefs that have been damaged (storms, blast impacts, ship wrecks, fresh water flows, pollution, sediment damage). Several permanent quadrats, 1m2 should be marked permanently with steel stakes (preferably stainless steel) at around 3 to 5 m depth (or where coral growth is normally highest). These quadrats are set up near the start of the Intersected -Length transects. Corals and other benthos in the quadrat can be photographed or marked on underwater slates. A portable quadrat divided into 25cm by 25cm squares with tight string will help map the quadrat. If examination of settling corals should be done in the area, terracotta tiles can be placed before corals breed and then collected to examine for juveniles under a microscope.


Fig.56 Permanent Quadrat (60kB)
A suggested monitoring program for a medium sized Reef (according to AIMS)
  1. Obtain a map or drawing of the reef. Mark on it the major reef and adjacent land features, and the compass directions. If possible, mark GPS coordinates.
  2. Manta tow the outside of the reef to obtain an overall picture - this will require a minimum of 9 by 2 minute tows recording coral cover, coral health, and unusual features like crown-of-thorns starfish, sea urchin numbers, giant clams, blast (dynamite) scars, etc.
  3. First select a typical transect site near the major wave exposure part. This area should be like most of the areas of the reef - NOT the area with the highest or lowest coral cover. It is best to monitor a site near where the major waves come, but usually not in them, as this can be too dangerous and difficult to visit regularly (e.g. select the north east face of reefs, if waves come mostly from the southeast). Select a depth where normally most coral grows. On many reefs, this is between 3 and 6m below low water mark. On reefs with large waves, this will be deeper, around 10m. Mark the start of the first transect with a steel stake. Mark the ends of all transects with stakes. Put down 3 transect lines each 50m long and wait 5 to 15mins and then count the fish along 3 by 50m lengths. Do the fish censuses first and then do coral cover.
  4. Set up 5 by 20m transects at 3m using the fish transect lines. Each 20m transect should be randomly placed along the fish transect lines.
  5. If there are enough people, make another set of fish and lifeform transects a bit deeper e.g. 10m.
  6. Repeat the process at 2 more sites on the reef, if you have enough time and more divers to do the job. This will give a good statistical sample - better than just one set of 150m fish and 100m benthos transects.
  7. Repeat the fish transects, if possible, after 3 months to check for seasonal effects.
  8. Repeat all the monitoring after 12 months, or a minimum of 2 years.
  9. Record all data immediately into the computer and check for accuracy against the original data sheets.

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         int. Coral Reef Symposium, Vol.2; Manila - Philippines
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Antonius A.; 1985: Coral Diseases in the Indo-Pacific - Marine Ecology 6(3):197-218;
         Paul Parey Scientific Publ. Berlin - FRG
Antonius A.; 1985: Black Band Disease Infection Experiments on Hexacorals and Octocorals;
         5th Int. Coral Reef Congress, Vol. 6; Tahiti
Antonius A.; 1987: Survey of Red Coral Reef Health. 1-Jeddah to Jizan; Saudi Biological Society;
          Proceedings on the 10th Symposium on the Bio. Aspects, Saudi Arabia
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Related sites on the www: slide show about the Great Barrier Reef (1.6MB)




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