Part II - The Status Quo

Coral reefs are a critical global resource; both biologically, and in socio-economic terms. They are the most diverse marine habitat, with an estimated one million different species. They are also widely used by coastal communities as a source of food and as the basis for a major tourism industry, providing both a livelihood and foreign exchange earnings for many communities and developing nations.

a) The Human Factor: The increasing population is probably the most pressing issue of this nation. Currently, 79E3 Seychellois share some 490km2 of land area - of which almost 40% are younger than 15 years of age, and a staggering 70% of all inhabitants are younger than 30. The surrounding fringing reefs (one of the country's most ecologically important yet sensitive areas), the influence of human activities is clear - but the parameters are still poorly understood. Although, basic ecological and physical oceanographic information is available, the interrelationships between marine organisms and physical processes are known only rudimentarily. Another reason rendering the situation more complicated is based on the fact that the marine environment varies greatly through both time and space. In addition, links between the coastal habitats (i.e. mangroves and sea-grass beds of the coastal zone and the shelf proper) are likewise poorly understood. It is thus not surprising that the impact of humans on the surrounding reef communities is most evident in the densely populated main islands of Mahé and Pralin, with the former probably showing the greatest signs of stress.

Tropical Fisheries: Current fishing practices are not a real threat, but these may become so as more and more visitors along with the booming local population gradually increase the pressure on eatable reef-fish fauna. According to Spalding et al (2001), already today, the per capita fish consumption reaches some 65 kg/year - compared to those of Kiribati (182), Palau (108), and Japan (67). Fishing has a varied impact on the surrounding reef communities, but is most evident around the granitic islands. Most of the national fish consumption is of nearshore fishes, a large proportion of which are reef associated. The reefs of the inner islands are thus quite heavily utilized, and there are clearly documented examples of overfishing from a few localities. Fishing pressure in the outer islands, by contrast, is relatively low. There is some fishing by visiting vessels, but also some small commercial fisheries operations run from a few of the inhabited islands. The offshore tuna population is the center of a major export fishery, with a tuna cannery in Mahé serving a large number of vessels from the Indian Ocean.
Likewise, harvests of many marine invertebrate species are of commercial value. This includes molluscs (green snail, pearl oysters, gastropods and bivalves for the shell trade, a wide range of edible species, including octopus and squid), crustaceans (spiny lobsters, crabs, prawns), coral (black and stony corals for the curio trade; stony corals for construction and lime) and echinoderms (sea cucumbers). It has not been possible to do a full review on this information. For example, Cosmoledo and Aldabra are important areas for green snail in the Seychelles (IUCN/UNEP, 1984). Subsistence fisheries for numerous invertebrate species take place throughout the region.



Intensive bioerosion on dead reef sections increases suspended particle load (110kB)



The local fishing industry (150kB)



Left: Panulirus versicolor (Palinuridae) preys on molluscs, other invertebrates, and detritus. Right: Diodon sp.? (Diodontidae) feeds on molluscs and crustaceans (130kB)



A submerged basket fish trap used by locals (90kB)

Agriculture: Even though of less importance, there are some agricultural activities taking place on the inner islands. These range from tea and coco-plantations, to less intrusive activities of vanilla and cinnamon, among others. Fertilizers, pesticides and other agricultural chemicals from plantations are washed into the creeks and ultimately into the sea, augmented by increased run off from erosion due to the degradation of native highland vegetation, as well as lowland mangroves (land reclamation).



Octopus sp. (Octopodidae) - these day active couple has been pictured during a mating attempt (150kB)

Tourism: Tourism is a critical industry in the Seychelles, being one of the main providers of employment and the main foreign exchange earner. Virtually all tourism is coastal and beach oriented, with a large proportion of visitors on diving holidays, and many others making day trips to the reefs. Most tourists remain on the granitic islands, but there are now also some exclusive developments on the outer islands. Land reclamation for the International airport, the Inner Harbor, along with other infrastructure destroyed a large area of the fringing reefs of east Mahé, which were once the best developed fringing reefs in the country. Such activity even affected adjacent reefs through heavy sedimentation. Elsewhere, terrestrial sources of sewage pollution, sediments, and solid waste are problematic, while the increase in tourism is bringing these problems to new areas. It is a well-known fact that such substances have an altering effect on the food webs on inshore reefs - mostly likely due to those excess POM / DOM (particular / dissolved organic matter).
The booming diving industry of the Seychelles is mainly boat operated. Almost all reef sites visited by dive-operators still approach their spots without the use of mooring buoys. At Beau Vallon Bay, main island of Mahé, some three dive operators offer two to three trips a day out to the most popular diving spots and discharge divers into these areas. Without buoys, they drop their anchors onto coral heads, they drag, and then break the corals as the currents pushes the anchored vessels back and forth.
The impact of tourism is also felt in another degrading way - the curio trade in particular is of worrying concern. The shells of reef molluscs, e.g. cowries (Cypraea tigris, C.moneta, etc.), the giant triton (Charonia tritonis), cone shells (Conus geographus, C.leopardus and C.litteratus) horned helmet (Cassis cornuta), spider conch (Lambis scorpius and L.chiragra), horse conch Fasciolaria trapezium = Pleuroploca t. (?), Spiny Oyster Spondylus sp., ramose murex Chicoreus ramosus, inflated porcupine fish (Diodron sp.) or jaws and fins of sharks among numerous scleractinian corals. Shell for sale on the streets of Seychelles cannot be considered at a low level activity - it probably exceeded the levels of sustainability.

 

 



Cyprea tigris (Cypraeidae) - this member of the order Mesogastropods feeds on algae and small invertebrates (100kB)

 



Curio trade at the main market in Victoria/Mahé (150kB)

b) ENSO (El Niños - Southern Oscillation)

Coral reefs are also highly sensitive to climatic influences and appear to number among the most sensitive of all ecosystems to temperature changes, exhibiting the phenomenon known as coral bleaching when stressed by higher than normal sea temperatures. Coral tissue bleaching is the term used for a loss of color in reef-building corals and the subsequent visibility of the underlying (white) skeleton. Reef-building corals are highly dependant on a symbiotic relationship with microscopic algae (a type of dinoflagellate known as zooxanthellae) which live within the coral tissues. The bleaching results from the ejection of the zooxanthellae by the coral polyps and/or by the loss of chlorophyll by the zooxanthellae themselves.

This reaction of corals has been widely observed for many years: corals usually recover from bleaching but they can die in extreme cases when these abiotic stress factors persist for extended periods. Tissue bleaching is caused by various types of stress, including temperature extremes, pollution and exposure to air. It is the temperature related stresses, however, which have been most widely reported, and which are of particular concern in relation to climate change. On any particular coral reef, the normal range of sea temperatures throughout the year is narrow, usually within 4°C, though the range of temperatures tolerated by reef-building corals worldwide is much wider (16 - 36°C). It would appear that corals in individual regions and localities have become highly adapted to these relatively narrow temperature regimes. Studies have shown that temperatures of only 1 - 2°C above the normal range (threshold temperatures) for a few weeks are sufficient to drive a ‘mass-bleaching’ event (where a significant proportion of corals across the reef are bleached).



Bleached coral during the 97/98 ENSO event (55kB)


Myripristis sp. (Holocentridae) over dead hard corals (100kB)

The coral reefs of the entire archipelago were heavily impacted by the 1997-98 ENSO event, with Coral Tissue Bleaching (TBL) occurring on 60-95% of corals, and subsequent coral mortalities of 50-90%. Reef sections of the outer islands and in the south were only slightly affected. At the peak of this bleaching event, corals within the first 10m depth range were the most affected. Staghorn coral gardens (e.g. corals of the family Acroporidae) were completely denuded and are currently subject to massive bioerosion (internally by boring Clionid sponges and externally by grazing Scaridae). Only massive species like those of the family Poritidae (Porites lutea) that can be found beyond that depths, have survived this event mostly unharmed. Now, that the Seychelles have gone through the whole coral bleaching cycle, they find themselves amidst in the aftermath stage. The massive coral mortalities allowed many former corals to be externally overgrown with algal species, whereas endolithic bioeroders decompose the calcium-carbonate skeleton (the latter, responsible for increased turbidity due to suspended particles). In turn, it mediated a boost in both herbivorous as well as secondary trophic predatory fish fauna. The longer-term impacts on the reef communities are somewhat unpredictable given the scale of damage in all areas. During our visit in October of 2001 the inner islands showed signs of a slow recovery, we noted the emergence of new "coral plaques" on many reefs on the inner islands. These are the first signs of new branching coral re-colonization and growth after the bleaching event. We were even told that the outer islands show a massive re-growth of branching coral forms which seems to stem from latent coral polyps of the original colonies becoming awakened and re-colonizing the original coral skeletons. Unfortunately, an observation that we could not confirm as we have not had the chance to go there.



Chromodoris albopunctata (Chromodorididae) this nudibranch is often found among coral rubble (190kB)



Porites lutea (Poritidae) along with Arothron nigropunctatus (Tetradontidae) at 13m depth (75kB)



Juvenile Acropora sp. (Acroporidae) resettling on coral rubble (165kB)

Mr. Rowat, Chairman of the Marine Conservation Society of Seychelles described the situation as the following: The inner islands suffered from a lot of hard coral mortality, mainly of branching Acropora species. However, it did not have severely affected fish life. On the contrary, in sharp contrast to some of the published articles, the majority of their reef fish are algal grazers and there seems to be a bit of a population explosion of the various herbivores. Only a few of the dedicated coral feeders such as butterfly fish and file fish seem to have decreased so far. The Inner islands are also in an advantageous position in that the underlying reefs are granite. As such, much of the structures remain irrespective of what coral formations do; in that there are still the hiding places and protection for the different species and thus abandonment by the reef fish was less likely. The southern islands, with no granitic underlying structure and a slightly different set of parameters have even done better. The atolls with steep walls have faired a lot better than those with shallow sloping reefs. The walls of Astove and Cosmoledo still have amazing gorgonian fan formations and associated soft corals and sponges as well as their attendant fish life. Islands and atolls with shallow reef areas have not faired so well and have lost much of their hard coral cover, just as in the inner islands. However, the redeeming factor for the atoll formations is the presence of the lagoons which direct the growth and sustenance of the local fish populations to a large extent.

 



The herbivore Bolbometopon muricatum (Scaridae) foraging over a field of crumbled Acropora (80kB)



Scarus ghobban (Scaridae) in his mucus bubble; in huge number a serious bioeroder (100kB)

In order to fully comprehend the destructive pattern of the ENSO event, here some census results (Bigot, et al. 2000):

  • Trig Point in the Ste Anne Marine Park, East coast of Mahé; this site is subjected to high sedimentation from the capital Victoria and nearby catchment areas. Furthermore, the area was dredged to build embankments on East Mahé between 1985 and 1992, but monitoring data were not available.
  • Ternay Bay, West coast of Mahé, also part of a marine park, is a more protected bay in the marine park, with reduced human impacts. Reef flat cover in 1999 was mainly abiotic forms e.g. dead coral, with no living coral on the transect. Turf algae (2.8%) were the only living material. This shallow zone (1m low tide) was severely impacted during the 1998 ENSO with around 95% coral mortality. In 2000, some living corals appeared (0.9%), along with zoanthids (Palythoa - 10%) and algae (12.3% - calcareous and macroalgae - Turbinaria). There were no new Acropora recruits, but the calcareous algae will constitute a good substrate for new coral settlement. On the outer slope, there was a low cover of living corals (2.1%), mostly massive forms and some soft corals. All the branching Acropora disappeared during the 1998 bleaching event. Some coral recovery was observed in 2000 with 0.5% branching Acropora, and a definite increase, although not quantified, of non-Acropora forms, mostly massive and soft corals. Algae were just 6.2% of cover, mostly calcareous algae (2.3%) and a few Turbinaria sp.
  • Finally. the Silhouette granite island 35km north-west of Mahé, which was added in 2000. The reef flat is heavily impacted by the south-east monsoons and has always had low coral cover. The site at 2m depth has no Acropora, a 9% cover of non-Acropora (encrusting and massive corals), and some soft zoanthids (Palythoa). Most of the cover (over 50%) was dead coral rubble and sand. The outer slope (5-6m depth) had alive and dead massive corals (>15%) scattered over a sandy zone, with submassive corals (>15%), some encrusting corals, and 0.7% branching, very young Acropora which showed signs of fish grazing. This site appeared to escape most of the 1998 ENSO bleaching, possibly due to better water exchange with the cooler deeper waters.

Comparison of 1997 - 2000 data:
Coral cover on the Ternay Bay outer slope dropped from 54.6% in November 1997 to 3.5% in June 1998, 2.1% in January 1999 and 5.1% in March 2000. Acropora was more affected (29.1% in 1997, 0% in 1998 and 1999, and 0.5% in 2000) than non-Acropora massive corals (25.5% in 1997, 3.5% in 1998, 2.1% in 1999 and 4.6% in 2000). Soft corals appear to be fast growing, opportunistic species. As a reflection of these changes, abiotic forms went from 37% in 1997 to 92.3% in 1998, 92.8% in 1998 and 86.8% in 2000. These losses can be attributed to the 1998 bleaching phenomenon, as human activities are limited, and recovery is predicted for good coral cover, provided bleaching does not happen again within the next few years. A similar pattern was evident on the reef flat with a total loss of coral after the 1998 bleaching event; here recovery is predicted to be very slow.



Map of permanent sites (20kB)



The nocturnal Tonna perdix(?) (Tonnidae) crawling over a bioeroded reef-stretch in search for other molluscs and sea cucumbers (100kB)



Palythoa sp. (Zoanthidae) - a typical representative of shallow water reef communities (150kB)



A severely affected coral colony of the family Faviidae (140kB)



A (stressed?) Goniopora sp. (Poritidae) with almost retracted tentacles (!) and epizoic growth (140kB)