Assessment of Coral Reef Damage in Aqaba, Jordan (Royal Diving Center) Oct 15th to 31st 1999 |
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Pierre MADL (Salzburg - AUT);
Fanni ASPETSBERGER (Vienna - AUT);
Maricela YIP (Mexico, DF); |
INTRODUCTION The coral disease survey was attempted for the first time in 1999 as part of the Marine Ecology Field
Course by the University of Vienna, Institute of Ecology. The main interest was focused on hard corals (scleractinians) because
they comprise most of the framework of a living coral reef, and they are home for a great number of marine organisms. Coral diseases, first reported in 1973 (Antonius), have not yet received the attention of marine biologists that they would deserve. With the onset of global climate change (a factor that should no longer be neglected), however, their frequencies and extent of damage are on the increase. Recent reports regarding diseased corals from around the world have focused on these dramatic events (Antonius, 1984). In order to avoid its continuos spreading and to attempt the conservation of healthy corals for future generations, coral disease monitoring deserves more attention today than in the past. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The goal is to avoid the continuous spread of diseases and to conserve healthy coral reefs for future generations - be it for recreational purposes or for other sustainable uses by mankind, e.g. as an additional source of proteins, as an important pool for the pharmaceutical industry in the extraction of prostaglandins and anticancer agents, etc. (Gosliner et al, 1996). Moreover, coral reefs represent the most diverse marine ecosystems. They provide habitats not only for fish and other marine organisms, but also form entire inhabited islands. Furthermore, coral reefs are essential wave blockers that reduce coastal degradation and erosion. Based on their vulnerability, reefs can be used as indicators of environmental stress, i.e. to monitor chemical pollution, eutrophication, sedimentation, sea temperature and salinity fluctuations, or excessive impact from tourism or from military facilities. |
![]() Map CD-0 Geographic location (95kB) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SITE DESCRIPTION The investigation of coral diseases was done at the narrow fringing reef, often referred to as a contour
reef, in front of the Royal Diving Center (RDC), 10 km south of the city of Aqaba and 3 km north of the Saudi Arabian border on
the eastern side of the Gulf of Aqaba - Red Sea. |
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A phosphate factory, located a few kilometers north of the RDC, might be a possible source of pollution in
that the supplying trucks with an improperly covered cargo can lead to airborne relocation of phosphate fertilizer. |
![]() Map CD-2 Close-up of RDC (170kB) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The left hand or southern side of the jetty, shortly before the reef crest, has an average depth of about 4 to 5 m and borders a sandy substrate, which bears an extensive sea grass bed. The northern or right hand side of the jetty, displays a steep and stony slope (mostly secondary hard substrate). Although coral growth persists beyond the reef crest, the lower sections of the slope are dominated by sandy substrates, limiting corals to isolated patches. In general, corals are abundant along the entire reef stretch, from just below the water line down to roughly 50 m. Only the upper 30 m were monitored. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MATERIAL AND METHODS In order to assess the general health of the corals, two monitoring approaches were conducted. The use of transects yielded a quick picture about the quantitative extent of damage, while selective analysis of diseased sites provided further information about the qualitative aspects, i.e. the types of symptoms affecting a particular coral colony. Only hard, reef-building (hermatypic) corals that exceeded 10 cm in diameter were selected. The corals were identified to the lowest possible taxonomic level.Material: The main instrumentation used throughout the survey involved the following items: A plastic slide-caliper, 2 measuring tapes (2 m and 30 m long, respectively), water-resistant digital thermometers, an underwater compass, polyurethane marking buoys tied to stones, plastic stakes, underwater writing slates, a 15 m long rope, aluminum nails and several underwater cameras.
Methods: The survey was based on two separate census techniques:
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The quantitative survey was limited to the northern section of the jetty, while the qualitative survey was
spread along the entire stretch of the RDCs shoreline (Map CD-2). | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
RESULTS
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Transect coverage: Coral coverage on the transects were 15.5% in transect T1, 16.5% in transect T2 and 31.7%
in transect T3 (Fig. 3). Coral coverage of T4 has not been estimated. Having included both soft and hard corals in the estimations
of coverage, only hard corals have been monitored in the disease-census. According to Fig. 4, transect T3 displayed a higher
coral coverage than the other three transects. |
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Disease-Survey: | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Within each transect, the extent of healthy and damaged corals was evenly distributed. Some common
symptoms observed were white patches, black bands across corals, algae overgrowth on or around bleached sites, denuded
skeletons, broken or detached corals, mucus secretion by vermetid snails, etc. These manifestations were found on several
hermatypic species (order Hexacorallia) of this contour reef, among them, the representatives of the families: Acroporidae,
Pocilloporidae, Poritidae, Faviidae and the solitary living Fungiidae. |
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Note that both the "blotched" and the "diseased" categories do not reflect
particular symptoms per se, but can be the result of several influences that we were unable to determine. One conclusion can be
drawn: coral bleaching does not seem to be a major cause of coral destruction within the examined reef section - indicating that
temperature fluctuations below and above the ideal limits are neglectable. |
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In general, the overall symptoms among branching corals outnumbered the symptoms on massive corals. It is possible that the morphological differences between these two types of corals influence the resistance against diseases. In Fig. 6, the same results are expressed as colonies per m2. Similar trends as in the proportional presentation can be observed. Click here to enter the "picture galery" of diseased coral colonies
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Patch Reefs: | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Another qualitative analysis was done on two different patch reefs - a larger and a smaller coral block
(refer to Map CD-2 for its location). |
![]() Fig 7: Larger Patch Reef in front of the reef crest (click to zoom in - 110kB) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Larger patch reef | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Sporadic algae were detected at several locations, but they seemed not to be correlated with the symptoms described below (sets of Fig’s. 8 and 9). The first two charts (Figure 8a and 8b) show the general state of health of the patch, while Figure 8c displays the degree of symptoms in percent of corals showing certain abnormalities. As this survey has been done solely by snorkelling, a differentiation between mechanical and biogenic damages could not be done due to methodological reasons. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Fig 8a: Diseased and healthy corals of the |
Fig 8b: Diseased and healthy corals of |
Fig 8c: Extent of coral symptoms grouped into categories | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
About 70% of all the corals observed showed no visible damage (Fig. 8b). Among the other 30%, which displayed some sort of damage, bleached corals were predominant, followed by mechanical damages and blotched symptoms. In general, the branching corals seemed healthier than massive corals (Fig. 8b). This distribution, which differed strongly from the ones found in the other surveys. It is most probably the result of improper behavior of the bathing public. The observed coral damages from Fig. 8b were further categorized into four groups, while symptoms were displayed separately in Fig. 8c. The most affected colonies were found to be already in an advanced stage, with the extent of damage peaking within the 26-50% range. Whereas, dead corals, which were treated in the damaged category ">75%", were rarely recorded.
Smaller patch reef
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The smaller patch reef, in close proximity to the larger one described above, measured about 2 m in height and was located at
more or less the same depth as the larger patch, thus it had a reduced risk of being exposed to the air. This fact is also reflected
in the homogeneous coral coverage (almost 100%) of the entire block, with no algae present at any site. Fig. 9a and 9b show
the general state of health of the smaller patch. Fig. 9c shows the degree of symptoms showing certain abnormalities (in percent).
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Fig 9a: Diseased and healthy corals of the
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Fig 9b: Diseased and healthy corals of
| Fig 9c: Extent of coral symptoms grouped into categories
| As in the larger patch reef, healthy corals outnumbered the affected coral colonies at a ratio of about 3:1. About 75% of all the corals observed showed no visible damage (Fig. 9b). Among the remaining 25%, damaged corals dominated over the bleached and blotched symptoms. Again, the branching corals seemed healthier than the massive corals (Fig. 9b). Categorization of damaged corals (Fig. 9c) revealed that the extent of affected corals was less than 25%.
| Selected Coral Colonies: Qualitative analysis of diseased coral colonies in the waters in front of the RDC were restricted to 10
distinct sites, which revealed a broad variety of symptoms (for overviews, see Fig.s 2 and Tables 1 & 2). Coral bleaching,
band diseases and blotching, amongst other symptoms, were common. Mechanical damages on corals could be further separated
into natural causes (predation by parrotfish, echinoderms, epifauna or endofauna) and anthropogenic impacts mainly caused by
snorkelers standing on the corals, or by improperly balanced divers, etc. At the time of our investigation, October 1999, water temperatures remained around 25 °C. Year round
observation would be needed to reveal whether temperature fluctuations or peak temperatures affecting coral growth -
especially during the hottest months of the year. |
[m] |
T. [°C] |
cover |
Comment
Site-# |
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Acropora sp. | ||||||||||||||||||||||
Acropora sp. | ||||||||||||||||||||||
Acropora sp. | ||||||||||||||||||||||
Acropora sp. or Favia sp. | ||||||||||||||||||||||
Favia sp. | ||||||||||||||||||||||
Favia sp. | ||||||||||||||||||||||
Porites sp. | ||||||||||||||||||||||
Pocillophora sp. | ||||||||||||||||||||||
Stylophora sp. | ||||||||||||||||||||||
Stylophora sp. | ||||||||||||||||||||||
Porites sp. | ||||||||||||||||||||||
Legend: (2) BBD: Black Band Disease (3) TBL: Tissue Bleaching |
[m] |
T. [°C] |
NS : EW : Height |
Comment
Site-# |
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likely due to interspecific competition 9 (P1b) | |||||||||||||||||
trapped mucus, covered w/ sediment | |||||||||||||||||
partly overgrown w/ algae; whitish to blackish band extends in an EW direction; length about 450mm; prob. BBD2 F2 (11,2/99) | |||||||||||||||||
partly shaded by an over-hanging rock and subject to sedimentation | |||||||||||||||||
TBL3 (exc. for a small green spot on top) 32 (3/99) | |||||||||||||||||
Polyps: healthy 22 affected: 2; dead: 12 |
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partly shaded by an over-hanging rock and subject to sedimentation | |||||||||||||||||
white band which turned black; probably BBD2 | |||||||||||||||||
Further attempts to monitor the extent of the band by placing reference markers into the dead portion of the coral skeleton (aluminum nails) are listed below: | |||||||||||||||||
nail 2 (west): |
50mm |
70mm |
6(1) |
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nail 2: |
50mm |
70mm |
9(1) |
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probably TBL3L | |||||||||||||||||
top shows scratches; probably suffering from TBL3 A,8(X) | |||||||||||||||||
15 : 20 : -* |
probably TBL3A,8(X) | ||||||||||||||||
16 : 12 : -* |
parrotfhish bites and small turbellarians F6(5/99) | ||||||||||||||||
healthy branches 129; dead 119; affected 11; 9(P1b) | |||||||||||||||||
Legend: (*) dimension of affected spot on coral colony (1) likely that census errors accounted for the varying results (2) BBD: Black Band Disease (3) TBL: Tissue Bleaching |
DISCUSSION
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The northern section of the Red Sea of the Gulf of Aqaba receives slightly less solar radiation
than other coral reefs around the globe. An average of 1.68 J×
cm-2×min-1 penetrates the surface waters of the Gulf
(Rauschke et al., 1973). One might conclude, that the amount of photosynthetic active radiation (PhAR) reaching the
zooxanthellae in the corals could result in slower growth compared to other reef locations worldwide. It is likely though, that
adaptation of these organisms have led to an increase in photosynthetic activities, similar to extreme temperature fluctuations
of the surface waters within the Gulf. At this point, however, it cannot be determined whether slight deviations from normal
abiotic patterns are responsible for higher levels of coral diseases in this area. Furthermore, the increase in atmospheric
CO2 due to increasing greenhouse gases results in an elevated partial pressure, thus increasing it’s solubility
in the oceans. Again, one might deduce that elevated pCO2 fertilizes the zooxanthellae, thus increasing
productivity. Obviously, these topics go beyond the framework of the present study. In a thriving reef community, space can be seen as a resource limited in supply. Furthermore, severe inter- and intraspecific competition also results in fewer offspring and reduces fecundity (Begon et al., 1996). The fittest colony of each species may then be those that "escape" competition because they utilize the habitat in ways that differ most from those adopted by colonies of the other species. Such a fundamental niche is usually narrowed down to the realized niche as competition increases. Based on our present observations, niche partitioning is less important, because data of coral coverage do not support such claims. According to our observations, transect analyses revealed that coral distribution seemed to follow a
clustered rather than a random or even pattern. This would imply that such crowded aggregations not only facilitate the spread
of diseases, but in occasions, reflect a considerable impact of both inter- and intraspecific competition among coral colonies.
Having examined several sections of the RDC’s reef stretch, it can be excluded that space is of limited supply. Thus, neither
competition, nor facilitated spread of diseases due to cramped conditions can be held responsible for the elevated number of
diseased coral colonies. In addition, each modular organism may broadly be divided into those that concentrate on vertical growth
(branching corals), and those that spread their modules more or less laterally (encrusting or massive corals). The present study
focused on both branching and massive corals. Microbial infestation seem to play a role in the general state of health among hard corals. The fact that water pollution might boost the number of bacteria, viruses and funghi is further emphasized by the findings of definite pathogens, as recorded in the two BBD affected coral colonies (Fig’s. 10 and 11). Such findings have been also documented by investigations made in recent years along the shores of the Red Sea (Antonius, 1987, 1995). In general, all of the theoretical facts mentioned so far probably influenced the upper and lower reef slope to a lesser extent, than the corals of the reef flat and the reef front. A yet another interesting observation was made at the reef crest and the two patch reefs. Corals there seem to be in a better state of health than their reef flat counterparts and the corals of the reef slope. At this point it should be mentioned that the survey of the reef crest, patch reef and those along the reef slope have been made by different groups. Even though differences in perception could have influenced the survey, it is very unlikely that the observed facts could have resulted in major differences. Transect analysis along the slope revealed a more or less constant ratio of healthy and diseased coral
colonies. About 56% of the hard corals showed no visible symptoms; those that did were mostly affected by algae overgrowth of
already dead segments or affected by blotches. Both of these symptoms, however, did not represent distinct diseases, although
they could be the result of such influences. One has to keep in mind that even in healthy reefs, about 5% of the coral population
are dying of age-related diseases (Antonius, 1984). It is therefore obvious that the transected areas suffer somehow from severe
symptoms of stress. Many symptoms observed have been summarized in the "damaged" category. This simply
reflects the scarce knowledge about coral diseases and the typical appearance on different species. Furthermore, it is possible
that some symptoms due to biotic influences probably do not reflect a specific disease, but could be morphological variabilities.
A general trend within the transected areas indicated that diseased corals are more frequently found among massive corals rather
than on branching ones. In many cases, bleaching seemed to be another source of poor coral health. Floating plastic bags did
pose a problem along the sites of study, since they become entangled among the corals, depriving both branching and massive
corals of vital sunlight or simply ripping off segments of branching corals due to increased drag against wave action. It is most
likely that morphology, i.e. fast-growing branching corals, plays a role in lowered resistance against mechanical as well as
immunological factors (Wells, et al., 1992). | |||||||||||||||||
CONCLUSION
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We assume that the contour reef along the RDC does show signs of stress. Regular monitoring should provide more clues as to whether this is a temporary event or an ongoing trend. Further investigation should also focus on the sources and on the triggering mechanisms that cause such massive impairments. This information could eventually be used to improve the general state of health among corals in this area. Therefore, this survey should be seen as the first one in a series of many still to come.
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REFERENCES
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Assoc. Island Mar. Lab., Caribbean, University of Puerto Rico - Puerto Rico Antonius, A.; 1984: Human Impact on corals in Fringing Reefs near Jeddah, Red Sea; Symposium Coral Reef Environment; Jeddah - Saudi Arabia Antonius, A.; 1985: Coral Diseases in the Indo-Pacific - A First Record 6(3):197-218; Paul Parey Scientific Publishing; Berlin - FRG Antonius, A.; 1995: Pathologic Syndromes on Reef Corals - ISRS 2nd European Regional Meeting; Luxembourg - LUX Begon, M., et al; 1996: Ecology 3rd ed.; Blackwell Science Oxford - UK Gosliner, T.M. et al; 1996: Coral Reef Animals of the Indio-Pacific; Sea Challengers Publischers; Monterey CA - USA Hughes T.P., Connell J.H., 1987: Population dynamics based on size or age? A coral reef analysis; American Naturalist; University of Chicago Press - USA Price A., Roberts C.; 1992: Marine Ecology of the Arabian Region; Academic Press; London - UK Rauschke, et al., 1973: The annual radiation of the earth-atmosphere system during 1969-70 from Nimbus Measurements; Journal of Atmospheric Science; Veron, J.E.N., 1993: Corals of Australia and the Indo Pacific; University of Hawaii Press; Honolulu - USA Vine P. 1986: Red Sea Invertebrates; Immel Publishing; London - UK Wells S., Hanna N.; 1992: The Greenpeace book of Coral Reefs - Sterling Publishing Co. New York - USA Wood E.M., 1983: Corals of the World; T.F.H.Publications Inc. Ltd., Neptune City (NJ) - USA |