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
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:
- "0", no syndrome found during the survey swim for 30 min (= one SCAN)
- "rare", 1-3 cases found during a 30min scan
- "moderate", 4-12 cases found
- "frequent", represents 13-25 cases
- "abundant", means 26-50 cases
- "epidemic", when 51-100 cases are found
- "catastrophic" is the end of the scale, >100, the number of diseases become uncountable
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).
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)
- 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.
- 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.
- 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.
- 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.
- If there are enough people, make another set of fish and lifeform transects a bit deeper e.g. 10m.
- 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.
- Repeat the fish transects, if possible, after 3 months to check for seasonal effects.
- Repeat all the monitoring after 12 months, or a minimum of 2 years.
- Record all data immediately into the computer and check for accuracy against the original data sheets.
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Related sites on the www: slide show about the Great Barrier Reef (1.6MB)