Ecosystems (adapted from Government of Seychelles 2011 and GoS 2014, unless otherwise indicated)
What is an Ecosystem?
An “ecosystem is a dynamic complex of plant, animal and micro-organism communities and their non-living environment interacting as a functional unit” (CBD Secretariat 2014).
Which ecosystems are represented in the Seychelles?
The Seychelles archipelago consists of 115 granitic and coral islands spread over 1.3 million km2 of oceans. They are endowed with a rich diversity of terrestrial and marine flora and fauna which are supported by diverse ecosystems. Seychelles’ ecosystems can be roughly divided into the following: forest, inland waters, marine and coastal.
Each of these ecosystems supports a range of habitats, which are as follows:
Descriptions & Species
Granitic Islands: Typically littoral bush species on beach crest with broadleaf canopy starting some metres inland. Quite large patches of former coconut plantation can still be seen. Typical littoral species include Coconut palm (Cocos nucifera), Takamaka (Calophyllum inophyllum), Sea hibiscus (Hibiscus tiliaceus), Portia tree (Thespesia populnea), Porcher (Cordia subcordata), Tree heliotrope (Tournefortia argentea), Bay cedar (Suriana maritime), Whistling pine (Casuarina equisetifolia), Mapou (Pisonia grandis), Veloutier manioc (Scaevola sericea), Hernandia nymphaefolia, etc.
Native species in the lowland forest include the Indian almond tree (Terminalia catappa), Takamaka, the Looking-glass tree (Heritiera littoralis), and Porcher, while introduced species include Cinnamon (Cinnamomum verum), Agati (Adenanthera pavonina), White cedar (Tabebuia pallida), Coconut and various fruiting and ornamental species.
Throughout this habitat, the endemic fauna is diverse with Seychelles fruit bat (Pteropus seychellensis), Sheath-tailed bat (Coleura seychellensis), Seychelles wolf snake (Lycognathophis seychellensis), Seychelles tree frog (Tachycnemis seychellensis), Seychelles magpie robin (Copsychus sechellarum), Seychelles paradise flycatcher (Terpsiphone corvine), Seychelles Warbler (Acrocephalus sechellensis), Seychelles fody (Foudia sechellarum), Seychelles blue pigeon (Alectroenas pulcherrima), Seychelles bulbul (Hypsipetes crassirostris), Seychelles kestrel (Falco araea), Seychelles sunbird (Nectarinia dussumieri), Seychelles skink (Trachylepis sechellensis), Wright’s skink (Trachylepis wrightii), geckos (Phelsuma spp.), a caecilian (Grandisonia spp.), mollusc Aphanoconia theobaldiana, etc.
Native species include Sooty tern (Onychoprion fuscata), Brown noddy (Anous stolidus), Lesser noddy (Anous tenuirostris), White tern (Gygis alba), Wedge-tailed shearwater (Puffinus Pacificus), Audobon’s shearwater (Puffinus lherminieri), White-tailed tropicbird (Phaethon lepturus), and Bridled tern (Sterna anaethetus)
However, a range of introduced species also occurs here, including Rat (Rattus spp.), House mouse (Mus musculus), Common myna (Acridotheres tristis), Zebra dove (Geopelia striata), Madagascar fody (Foudia madagascariensis), Malagasy turtle dove (Streptopelia picturata), domestic cats (Felis catus) and dogs (Canis familiaris), Tenrec (Tenrec ecaudatus), Barn owl (Tyto alba affinis), species of African land snails (Achatina fulica, A. immaculate), etc.
Coralline Islands: Typically a dry broadleaf forest grading to open mixed bush, markedly less species diversity than the Granitic island equivalent.
Flora: i) Native: Beach gardenia (Guettarda speciosa), Bois d’amande (Pemphis acidula), Mapou, Veloutier manioc, Bay cedar, ii). Introduced: Coconut, Whistling pine.
Fauna: i) Endemic: Aldabra giant tortoise (Aldabrachelys gigantean), snail Cyathopoma picardense, Amber snail Quickia aldabrensis, Aldabra banded snail (Rhachistia aldabrae), Aldabra drongo (Dicrurus aldabranus)
ii) Native: Coconut crab (Birgus latro), Brown noddy, Lesser noddy, White tern, Sooty tern, White-tailed tropicbird, Red-tailed tropicbird (Phaethon rubricauda), Audubon’s shearwater, Wedge-tailed shearwater, Roseate tern (Sterna dougalli), Black-naped tern (Sterna sumatrana), Boobies (Sula spp.), etc.
iii) Introduced: Rats, domestic goats (Capra hircus), domestic cats, Wild boar (Sus scrofa), etc.
The vast majority of human habitation and development is found on the coastal plateaux. Historical exploitation and the impact of IAS has seen significant decline in occurrence and abundance of biodiversity (e.g. seabird colonies and endemic avifauna). Rats are a notable vector of human disease, and have had a major impact on native biodiversity as have various other IAS, such as domestic cats, common myna, tenrec, etc. Coastal forests today are entirely secondary but there have been excellent small-scale restoration projects that serve to maintain endangered endemic species.
Descriptions & Species
Broadleaf forest canopy with palm strands in drier areas. The mid-altitude forest of the main granitic islands supports the greatest diversity of endemic species but is nearly entirely secondary.
The endemic flora includes Capucin (Northia hornei), Horne’s pandanus (Pandanus hornei), Bois rouge (Dillenia ferruginea), Colea seychellarum, Campnosperma seychellarum, Bois merle (Aphloia seychellensis), etc.
Introduced species that occur here are Cinnamon, Agati, Albizzia (Paraserianthes falcataria), Santol (Sandoricum koetjape), Cocoplum (Chrysobalanus icaco), White cedar, Devil tree (Alstonia macrophylla), Honduras mahogany (Swietenia macrophylla), etc.
The endemic fauna includes Seychelles White-eye (Zosterops modestus), Blue pigeon, Seychelles bulbul, Seychelles kestrel, Seychelles sunbird, Seychelles scops owl (Otus insularis) (Mahé only), Seychelles tree frog, Gardiner’s Seychelles frog (Sooglossus gardineri), Seychelles palm frog (S. pipilodryas), a caecilian (Grandisonia spp.), a day gecko (Phelsuma spp.), Seychelles skink, Seychelles fruit bat, mollusc Aphanoconia theobaldiana, gastropod Cyathopoma blandfordi, land snail Pachnodus niger, etc.
Introduced species include rats, Common myna, Zebra dove, Madagascar fody, Malagasy turtle dove, Barn owl, domestic cats and dogs, Tenrec, African land snails, etc.
Despite being almost entirely secondary and dominated by exotics, this vegetation type supports the greatest diversity of Seychelles’ endemic species. This vegetation band plays a vital role in maintenance of water and soil cycles. Forest cover has expanded significantly in the last 60 years.
Descriptions & Species
This habitat holds a higher abundance of native plant species, including ferns, mosses and other epiphytes covering rocks, ground and trees. It often forms a refuge for endemic animal species such as Scops owl, frogs, and various insects (Seychelles Tourism Board 2005).
The endemic flora includes Pitcher plant (Nepenthes pervillei), Seychelles pandanus (Pandanus sechellarum), Capucin, Bois rouge, Latanier hauban (Roscheria melanochaetes), Vacoa de montagne (P. multispicatus), Bois cassant de montagne (Timonius sechellensis), Manglier de grand bois (Randia sericea), Bois charlot (Excoecaria benthamiana), Mimusops sechellarum, etc.
Introduced species include Cinnamon, Albizzia, San(g)dragon (Pterocarpus indicus), Devil tree, etc.
The endemic fauna that occurs in this habitat includes Seychelles white-eye, Seychelles blue pigeon, Seychelles bulbul, Seychelles kestrel, Seychelles sunbird, Seychelles scops owl, Seychelles swiftlet (Aerodramus elaphrus), Seychelles frog (Sooglossus sechellensis), Thomasset’s frog (S. thomasseti), a caecilian (Grandisonia spp.), a day gecko (Phelsuma spp.), Seychelles tree frog, molluscs (Aphanoconia theobaldiana, Pilula mahesiana), land snails (Edentulina moreleti, Pachnodus spp.), gastropod Punctum seychellarum, etc.
Even up here, introduced species can be found, among them rats, Common myna, Zebra dove, Madagascar fody, Barn owl, domestic cats and dogs, Tenrec, etc.
Predominantly secondary and highly invaded, forest cover in this range has increased significantly over the last 60 years and plays a vital role in maintenance of water and soil cycles. Important area for human aesthetic and leisure value.
Descriptions & Species
The islands of Praslin and Curieuse exhibit special palm forest climax vegetation communities including Coco de Mer (Lodoicea maldivica), which is endemic to the two islands. Palm forest communities also occur in dryer areas and on ridges of other forest categories e.g. intermediate and mountain forest. Other endemic species are the Seychelles stilt palm (Latanier latte, Verschaffeltia splendida), Latanier hauban, Thief palm (Latanier palm, Phogienicophorium borsigianum), Nephrosperma vanhoutteana, Palmis (Deckenia nobilis) accompanied by Pandanus species (Pandanus spp.) and Bois rouge.
Introduced species can also be found in the palm forest. Among them are Cinnamon, Cocoplum, Devil tree, various vine species, etc.
Endemic fauna is represented by the Seychelles black parrot (Coracopsis nigra barklyi) (on Praslin and Curieuse only), Seychelles blue pigeon, Seychelles Bulbul, several land snails found only on Praslin (Stylodonta studeriana, Pachnodus praslinus, P. niger subfuscus), White slug (Vaginula seychellensis), Giant bronze gecko (Ailuronyx trachygaster), Dwarf bronze gecko (A. tachyscopaeus), day geckos (Phelsuma spp.), etc.
Introduced species in the palm forest include rats and common mynas.
The Coco de Mer-dominated palm forest communities of Praslin and Curieuse with 6 endemic species of palm are of particular interest. Research has shown that natural regeneration of Coco de Mer is limited due to excessive nut harvesting, but the management of Fond Ferdinand since 2003 has seen enhanced protection and greater planting out of nuts.
Descriptions & Species
Inselbergs are isolated rock outcrops. Microclimatically and edaphically, they can be considered as arid islands. Thus, they bear a flora almost totally different from the surrounding vegetation (Barthlott & Porembski 1996).
Endemic: Jellyfish tree (Medusagyne oppositifolia; only on Mahe), Vacoa de montagne, Bois calou (Memecylon eleagnai), Café marron petite feuille (Erythroxylum sechellarum), Herbe rasoir (Lophoschoenus hornei), Bois charlot (Excoecaria benthamiana), Colophante (Soulamea terminaloides), Pitcher plant, etc.
Introduced: Cinnamon, Pineapple (Ananas comosus)
Important refuges for specific endemic flora. Human aesthetic and leisure value.
Descriptions & Species
The State lands and River Reserves Act 1976 lists 146 rivers and rivulets on the three main populated islands of Mahé, Praslin and La Digue. Watercourses are typically of short length and steep gradient.
Endemic: Horne’s pandanus, Seychelles pandanus, Latanier palm, Latanier latte, Balfour’s pandas’ (Pandanus before) and the indigenous Looking-glass tree and Bois mare grande feuille (Barringtonia racemosa).
Introduced: Albizzia, Breadfruit tree (Artocarpus spp.), bamboo (Bambusa spp.), etc.
Endemic: Seychelles chameleon (Calumma tigris), Seychelles scops owl, etc.
Introduced: rats, etc.
Vital for the preservation and maintenance of the water cycle. Higher reaches of the river gorges also still harbour relict flora assemblages.
Isolated by nearly 1,000 miles of sea water and 65 million years of evolution from continental landmasses the inland waters of Seychelles exemplify the CBD terminology of the geographically and ecosystems isolated during evolution and likely to be of particular biodiversity interest.
Descriptions & Species
This habitat type is probably the most degraded and threatened of any in Seychelles. The largest remaining wetlands are Grande Barbe on Silhouette, Police Bay on Mahé and La Mare Soupape on La Digue. La Mare Soupap is located on the western coastal plain of La Digue, which is the centre of human development and habitation and hence faces diverse pressures.
Native: Bulrush (Typha javanica), Water chestnut (Eleocharis dulcis), E. variegata, Persicaire (Polygonum senegalense), Nutsedge (Cyperus spp.), another sedge genus (Fimbristylis spp.), Indian almond tree, etc.
Introduced: Water hyacinth (Eichornia crassipes), Water lettuce (Pistia stratiotes), Willow primrose (Ludwigia octovalvis), White lotus (Nymphaea lotus), Elephant ears (Alocasia macrorrhiza).
• Endemic: the Seychelles subspecies of the Yellow-bellied mud turtle (Pelusios castanoides intergularis), the Seychelles subspecies of the Black mud turtle (P. subniger parietalis), Sharp-nosed caecilian (Hypogeophis rostratus)
• Native: Yellow bittern (Ixobrychus sinensis), Common moorhen (Gallinula chloropus)
• Introduced: rats, domestic dogs and cats, Commn myna, Mascarene grass frog (Ptychadaena mascareniensis), Red-eared terrapin (Trachemys scripta elegans; to date, only on Mahé), Left-handed pondsnail (Physella acuta), another species of small, air-breathing freshwater snail: Gyraulus mauritanius, etc.
Most threatened habitat type in Seychelles due to reclamation, drainage/colonization. Estimates that more than 90% has been lost in the last 200 years and the trend is ongoing. Important habitat for endemic/indigenous biodiversity. Important habitat for diverse and abundant migrant birds. Increasingly important for research and ecotourism activities.
Descriptions & Species
Highland wetlands in the Seychelles are restricted to just three sites: Mare aux Cochons on Mahé, La Plaine Hollandaise on Praslin and the Mare Aux Cochons on Silhouette. On Mahe, Mare Aux Cochons lies within the Morne Seychellois National Park and was designated a Ramsar site in 2010; on Silhouette, the site now also falls within a recently designated national park. These locations are of considerable interest harboring unique wetland biodiversity assemblages.
• Endemic: Horne’s pandanus, Seychelles stilt palm, Bois chevre (Gynura sechellensis), Mimusops sechellarum, Manglier de grand bois, Bois cafoul trois feuilles (Allophylus sechellensis), Campnosperma seychellarum, Canthium sechellense, etc.
• Introduced: Cinnamon, Cocoplum, Albizzia, Devil tree, White cedar, Soapbush (Clidemia hirta), etc.
• Endemic: various frog species (Sooglossus spp.), Golden panchax (Pachypanchax playfairii), caecilian Grandisonia spp., Caddisfly (Trichoptera spp.), Seychelles scops owl, diverse molluscan species, both endemic and indigenous, etc.
• Introduced: rats, mice, Tenric, etc.
Provides important habitats for endemic biodiversity. Vital areas for water catchment capacity and maintenance. Increasing importance for ecotourism and scientific research.
Descriptions & Species
A 2003 study of selected watercourses on Mahé and Praslin was undertaken to identify fish and crustacean species. This survey investigated 7 permanent water courses on Mahé and 5 on Praslin and identified 12 native species of crustacean, including the endemic crab (Seychellum alluaudi) and 17 native species of fish, including the endemic Golden panchax and the discovery of a new endemic species Parioglossus multiradiatus (Valade, P. et al 2004). Additional work is required on more rivers and in their higher reaches.
• Endemic: Sharp-nosed caecilian, Cooper’s black caecilian (Praslina cooperi), Seychelles tree frog, Golden panchax, Parioglossus multiradiatus, Paludomis ajanensis, the endemic crab Seychellum alluaudi, Allolestes maclachlanii, Seychelles stream damsel (Leptocnemis cyanops), dragonfly Zygonix luctifera, Hughscotiella auricapilla and Caddisflies (Oxyethira sechellensis, Ecnomus maheensi).
• Native: eel Anguilla bicolor, terrestrial crab Sesarmops impressum, Oceanic paddler crab (Varuna litterata), freshwater prawns (Macrobrachium spp, Caridinia spp.), sea snail Neritina gagates, dusky nerite (N. pulligera), freshwater snail Septaria borbonica, Grey heron (Ardea cinerea), Striated heron (Butorides striatus), Black-crowned night heron (Nycticorax nycticorax)
• Introduced: Guppy (Poecilia reticulate), Mozambique tilapia (Oreochromis mossambicus), freshwater snails (Lymnaea natalensis, Gyraulus mauritanius), etc.
The status of upper and mid-reaches of water courses has improved over the last 50 years with recovering catchment areas. Lower reaches are increasingly canalised and subject to enrichment pollution. Important habitat for endemic and indigenous biodiversity and for diverse and abundant migrant birds that visit Seychelles annually – see SBRC (2010) for full current details.
Marine and Coastal Biodiversity
Descriptions & Species
An intertidal habitat, which is amongst the most disturbed habitats in the Seychelles. The white sand of Seychelles’ beaches is formed from the breakdown of corals and coralline algae (seaweeds that have hard protective calcium carbonate in their ‘leaves’). Parrot fish play an important role in chipping off coral, digesting the coral polyps inside, and excreting the coral skeleton as small particles (sand) (Seychelles Tourism Board 2005).
This habitat is vital for nesting turtle populations (Chelonia mydas and Eretmochelys imbricata), but while turtles have received full protection under the law since 1994, protection of nesting habitat outside of Protected areas is lacking. The habitat is also vital for wading birds (native and migratory), various species of nesting sea bird, and diverse crab species, etc.
Flora: Veloutier manioc, tree heliotrope, Bois d’amande, White milkwood (Sideroxylon inerme), Coconut, Whistling pine, Takamaka, Indian almond tree, Procher, Hernandia nymphaefolia, Beach gardenia, etc.
Fauna: Hawksbill sea turtle (Eretmochelys imbricata), Green turtle (Chelonia mydas) (nesting habitat), terrestrial hermit crabs (Coenobita spp.), Coconut crab, Ghost crabs (Ocypode spp.), wading/coastal birds (see SBRC 2010), clams (Donax spp., Atactodea glabrata) etc.
Seabird colonies: Sooty tern, Masked booby (Sula dactylatra), Brown booby (S. leucogaster), Brown noddy, Wedge-tailed shearwater, White-tailed tropicbird, Caspian tern (Hydroprogne caspia), Crested tern (Thalasseus bergii), Roseate tern, Black-naped tern, etc.
Subject to extensive and widespread development and diverse and intensive human activity on populated islands. Increasingly heavily modified with growing problem of coastal erosion believed to be climate related. The beach crest is vital to the resilience of coastal ecosystems, including lowland forest, to extreme weather events and rising sea levels. Important habitat for diverse and abundant migrant birds that visit Seychelles annually – see SBRC (2010) for full details. The beach is also a vital economic asset, attracting high paying tourism and as the focal area for many social and cultural activities of the local population.
Descriptions & Species
Rocky shore is the most common shore habitat in the granitic islands and is typified by a limited vegetation structure consisting of species such as Sea Hibiscus, occasional stands of the endemic Balfour’s pandanus (Pandanus balfouri) and more extensive and typically planted stands of Coconut and Whistling pine. Veloutier manioc also occurs growing out of clefts and creepers (e.g. Beach morning glory [Ipomea pes-caprae]) and grasses abound. In their natural state and particularly on promontories and rocky islets such habitats historically supported important seabird populations and/or roosts including Bridled tern, White-tailed tropicbird, Pedge-tailed shearwater – the type of which can still be seen on reserve islands like Cousin and Aride.
The intertidal zone is rich in gastropods some of which are commonly exploited for food (e.g. Patella exusta and Cellana radiata). The toothed topshell )Monodonta australis) and the majority of Seychelles Nerites sea snails (Nerita albicilla, N. plicata, N. polita, N. textilis) are common in this zone as are various species of Littorinid sea snails (Littorina kraussi, L. scabra, L. undulata and Peasiella roepstorffiana). Tropical periwinkle (Planaxis sulcatus occurs) occurs in large colonies in this zone, the Morulas, Mulberry shell (Morula granulate) and Grape drupe (M. uva) are also common. The cowrie Cypraea caputserpentis is common in rocks clefts typified by stronger wave action. Rocky shores also harbour large crab populations (Grapsus and Geograpsus spp.) and occasionally the distinctive chiton Acanthopleura brevispinosa.
Descending into deeper water, the granite cliffs support foliose and encrusting corals and various species of algae that attract various reef fish assemblages. Various herbivorous fish species are also associated with underwater granite faces – e.g. the lined surgeon fish (Acanthurus lineatus), Butterfly fish (Chaetodon auriga, C. lunula), Scissortail sergeant (Abudefduf sexfasciatus), Daisy parrot fish (Chlorurus sordidus) and Tripletail wrasse (Cheilinus trilobatus). However, human impact is not absent, in particular two notable and formerly abundant species are now rare in this habitat following intensive exploitation in the latter half of the 20th century, namely the Potato grouper (Epinephulus tukula) and the Green snail (Turbo marmoratus). Other molluscs such as Drupes (Drupa morum, D. ricinis, D. rubusidaeus) are still abundant and in deeper water Murex spp. can still be found.
Flora: Balfour’s pandanus, Sea hibiscus, Coconut, Whistling pine
Fauna: Bridled tern, White-tailed tropicbird, Wedge-tailed shearwater, Groupers (Epinephulus spp.), Blennies (Blennidae spp.), Chitons (Chitonidae spp.), lightfoot crabs (Grapsus spp.), Geograpsus spp., sea snails (Littorina spp., Cellana cernica, Tetraclita spp, Nerita spp.) etc.
Growing development and intensive harvesting of shellfish on populated islands. Important habitat for sea and shore birds and diverse and abundant annual migrant birds – see SBRC (2010) for details.
Descriptions & Species
This intertidal habitat is often found where a river meets the sea. Mangroves are the typical species here as the Water is brackish (a mix of fresh and salt water) and the water level varies with the tide – both conditions that not many plants can cope with. The soil is mud or sand with a lot of organic matter.
Total natural mangrove area has declined steadily through much of the 20th century, but has been considered relatively stable at approximately 25 km2 since the 1980s.
Eight species of mangrove naturally occur in Seychelles (Avicennia marina, Sonneratia alba, Bruguiera gymnorhiza, Rhizophora mucronata, Lumnitzera racemosa, Ceriops tagal, Xylocarpus granatum, Xylocarpus moluccensis). The last continuous mangrove belt in the central archipelago is located between Port Launay and Port Glaud on the west coast of Mahé. Curieuse supports a diverse mangrove area on its west coast and Praslin retains a few isolated mangrove areas around river mouths; other very small areas also occur on other islands such as Cousin. In the outer islands, mangroves are only found in atoll environments, which provide the sheltered lagoon habitat suitable for their establishment. The most extensive forests are found on Aldabra, Cosmoledo and Astove.
Mangrove habitats are considered to serve important environmental roles such as coastal protection, sedimentation of solids from freshwater sources and as a nursery habitat for various fish species.
Fauna: Giant mangrove whelk (Terebralia palustris), bivalves Gafrarium tumidum and G. pectinatum, Ctena divergens, etc., sea snail Littorina scabra, crabs (Cardisoma carnifex, Scylla serrata, Geograpsus spp., Metopograpsus spp., Sesarma spp.), Fiddler crabs (Uca spp.) etc., Common mudskipper (Periophthalmus kalolo), Barred mudskipper (P. argentilineatus), Red-footed booby (Sula sula), Frigatebirds (Fregata spp.), Aldabra rail (Dryolimnas aldabranus) (Aldabra only), Grey heron, Striated heron, and numerous migratory wading bird species; Dugong (Dugong dugon) (Aldabra only).
Important habitat for diverse and abundant annual migrant birds – see SBRC (2010) for details.Mangrove trees were historically extensively exploited for its bark and timber – mangroves are no longer directly exploited.Mangroves on the developed islands are still extensively fished for fish and crab on a leisure or commercial basis.
Descriptions & Species
Sea grasses are actually flowering plants with very small flowers and completely adapted to the sea. It is often washed up on the beach. In the Seychelles, the following species occur: Thalassodendron ciliatum, Thalassia hemprichii, Syringodium isoetifolium, Cymodocea rotundata, Cymodocea serrulata, Halodule uninervis, Halophila ovalis and Enhalus acocroides. Green algae (e.g. Caulerpa spp., Codium spp., etc.) often occur together with sea grass.
The extensive shallow submarine banks of Seychelles support significant sea grass areas. A particularly large sea grass bed (estimated to be 45 km long and 15 km at its widest) lies on the Providence-Cerf bank. Many of the outer islands, such as the lagoons of Aldabra, Cosmoledo and Astove, support large sea grass communities. Sea grass habitats are also common around the granitic islands, notably in the St Anne Marine National Park and off Grand Anse-Amities coast of Praslin.
Sea grass beds play an important role in stabilizing sand and sediment, thereby protecting corals from sedimentation and coasts from erosion. Sea grasses are considered important as nursery and breeding habitat for commercial fish and diverse invertebrate communities. A brief survey of inshore sea grass bed substrate around Mahé recorded 58 species of infaunal invertebrates. Sea grass beds are also essential for many marine herbivore species, including megafauna such as the green turtle and the Dugong.
Fauna: Green turtle, Hawksbill turtle, Dugong (Aldabra only), grazing fish species such as Rabbitfish (Siganus spp.), diverse species of invertebrates such as polychaete worms, amphipods, mollusks, crustaceans, bivalves (e.g. Pinna muricata), and gastropods such as Money cowrie (Cypraea moneta), Tiger cowrie (C. tigris), Fighting conch (Strombus spp.), Shouldered drupe (Morula margariticola), etc.
There is evidence of the decline of seagrass beds near the shore of the main populated islands. Data for extensive offshore seagrass beds is lacking, but the collapse of green turtle populations is likely to be having a negative impact. Seagrass beds play a vital role in trapping and stabilising sand and sediment, thereby protecting the shores from erosion and providing coral reefs with water clarity. They also provide an important habitat/nursery for important commercial fish and invertebrate species.
Descriptions & Species
Most reef flats consist of a complex patchwork of habitats: areas of sand and gravel are interspersed with areas of coral rubble, coral outcrops, sea grass and algal growth. In their natural state these habitats are rich in life and commodity species such as octopus, lobster and sea cucumber. Mollusc fauna can be very rich with Cowries (Cypraea moneta, C. annulus, C. lynx, C. caurca and C. helvola being common), Cones (Conus leopardus, C. litteratus, C. virgo, C. maldivus, C. betulinus and C. quercinus) readily found in the seagrass; whilst snail species such as Bittium zebrum and Smaragdia rangiana can be found in algal mats.
Fauna: Rissoidae: Rissoina ambigua and R. plicata; Strombidae: Strombus gibberulus, S. mutabilis; Bursidae: Bursa bufonia, B. cruentata; Cowries (Cypraea moneta, C. annulus, C. Lynx, C. caurca and C. helvola being common), Cones (Conus leopardus, C. litteratus, C. virgo, C. maldivus, C. betulinus and C. quercinus), Bittium zebrum, Smaragdia rangiana, Octopus, Lobster and Sea cucumber species
Important habitat for diverse and abundant migrant birds that visit Seychelles annually – see SBRC (2010) for full current details. Important for gleaning fishing practitioners and as a leisure resource.
Descriptions & Species
Reefs are constructed by tiny living animals called coral polyps, which secrete a hard protective covering of calcium carbonate. The coral colony grows continually, but slowly (some coral heads may be several hundred years old). Thus the reef is a growing structure.
It is estimated that Seychelles has some 1,700 km2 of coral reef. The vast majority occurs around the southeastern islands. Prior to 1998, the coral reefs of Seychelles exhibited good live coral cover, rugosity and reef community diversity. Only some localised outbreaks of crown of thorns starfish in 1996 and ‘97 hinted that fishing pressure and enrichment pollution might be an issue of concern on reefs near the main populated islands of the central archipelago.
The whole scenario changed however with the ENSO-related severe bleaching event in 1998. The impact of the coral bleaching was most severe in the Western Indian Ocean and for Seychelles particularly on the Mahé Plateau. The reefs of the central archipelago were particularly badly affected with 80-90% mortality. Fast growing Acroporas and Pocilloporas suffered most and a phase shift from live coral cover to coral rubble/macroalgae dominated reefs was initiated. The outer islands were in general less badly affected with coral mortality more in the region of 40%. It has been postulated that this may reflect greater resilience due to reduced anthropogenic stress and an existing natural adaptation to greater temperature fluctuations.
Reef fish diversity showed a lag effect following the bleaching event with some impact noted on certain live coral dependent species but in general diversity was maintained. However, as time progressed recruitment of new individuals to fish populations appeared to be reduced, possibly related to degradation of the reef structure. Furthermore, studies on herbivorous fishes suggest that they will not prove effective in preventing the spread of macroalgae over the reef surface. This bodes ill for future coral reef community diversity and for various economically important fisheries.
In the ten years following the bleaching event natural recovery has been slow. Live coral cover in the central archipelago is still below 10% with less than 1% composed of the fast growing branched species so vital for the development of habitats.
General climate trends suggest that raised sea-temperature events will occur with increasing regularity in the future and as such temperature-induced coral bleaching remains the primary threat to coral reefs and their wider recovery in the Seychelles.
Fauna: Parrot fish (Scaridae, e.g. Scarus prasiognathus, Chlorurus sordidus), Groupers (Epinephulus spp., e.g. E. fuscoguttatus, E. polyphekadion) , Rabbitfish, Emperor red snapper (Lutjanus sebae), the endemic Seychelles anenomefish (Amphiprion fuscocaudatus), Octopus, lobster species, Hawskbill sea turtle, more than 400 coral species. Numerous mollusc species, including Lambis chiragra arthritic, Cypraea helvola and C. histroetc. Diverse elasmobranch populations, including the Grey reef shark (Carcharhinus amblyrhynchos), Blacktip reef shark (C. melanopterus), Blacktip shark (C. limbatus), Whitetip reef shark (Triaenodon obesus), etc. and Reticulate whipray (Himantura uarnak).
Important habitat for diverse and abundant biodiversity and specific biodiversity assemblages. Important source of protein and recreation to local population. Important tourism resource.
Descriptions & Species
The Mahé plateau is a shallow (generally not more than 50 m in depth) bank of some 39,000 km2, supporting important demersal fisheries such as Emperors (Lethrinidae), Snappers (Lutjanidae), Parrot fish, Sea basses (Serranidiae) and Rabbitfish.
Fauna: Sea cucumber species Holothuria nobilis, H. fucogilva, H. fuscopunctata, H. atra, H. edulis, H. scabra, etc. Carangid species (Trevally and Bludger), Snappers, Emperors, etc. Shark species such as Silvertip shark (Carcharhinus albimarginatus), Bull shark (C. leucas), Blacktip shark, Sandbar shark (C. plumbeus), Tawny nurse shark (Nebrius ferrugineus), Tiger shark (Galeocerdo cuvier), Hammerhead sharks (Sphyrna spp.), Whale shark (Rhincodon typus), etc. Spotted eagle ray (Aetobatus narinari)
Historical and ongoing socioeconomic importance in terms of fishery development, protein provision for local population, fishery exports, commodity value fisheries – shark fin, sea cucumber, lobster. Various fisheries are subject to overexploitation with cascading and potential phase shift effects for the plateau ecosystem.
Descriptions & Species
The pelagic ecosystem of the western Indian Ocean has experienced major historical and ongoing fishery impacts (whaling and industrial tuna fisheries respectively) the impacts of which are not clear and are likely still evolving. The reduction or extirpation of mega fauna (whales, pinnipeds, turtles, sharks, etc.) can reasonably be expected to have significant cascade effects through the food chain and on overall productivity. Bycatch issues (e.g. with regard to sharks and marine turtles) are an ongoing concern as are other potential secondary fishery effects – such as the impact on seabird feeding success caused by reduced tuna standing stocks.
Tuna species: Bonito (Katsuwonus pelamis), Yellofin tuna (Thunnus albacares), Bigeye tuna (T. obesus), Albacore (T. alalunga), etc. Billfish: Swordfish (Xiphias gladius), Marlins (Makaira spp.), Striped marlin (Tetrapturus audax), Indo-pacific sailfish (Istiophorus platypterus).
Shark species: Blue shark (Prionace glauca), Silky shark (Carcharhinus falciformis), Oceanic whitetip shark (C. longimanus), Mako sharks (Isurus spp.), Hammerhead sharks, Great white shark (Carcharodon carcharias), Whale shark, etc. Manta ray (Manta birostris).
Turtles: Green turtle, Hawksbill turtle, Leatherback sea turtle (Dermochelys coriacea), Loggerhead sea turtle (Caretta caretta), Olive ridley sea turtle (Lepidochelys olivacea).
Marine Mammals: 25 species of cetacean have been recorded in Seychelles waters including Humbpack whale (Megaptera novaeangliae), Sperm whale (Physeter microcephalus), Common bottlenose dolphin (Tursiops truncates), Spinner dolphin (Stenella longirostris), Risso’s dolphin (Grampus griseus), False killer whale (Pseudorca crassidens), Pilot whales (Globicephala spp.), etc.
Seabirds : Lesser crested tern (Sterna bengalensis), Caspian tern, Sooty tern, Masked booby, Brown booby, Southern giant petrel (Macronectes giganteus), etc.
Since mid-1908s vital and growing importance for national economic development through industrial and semi-industrial fishing activities and secondary land-based value adding processes. Management of said fisheries and bycatch issues is a major challenge and vital for regional fisheries productivity.
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Government of Seychelles (2011). Fourth National Report to the United Nations Convention on Biological Diversity. Environment Department, P.O. Box 445, Botanical Gardens, Mont Fleuri, Victoria, Republic of Seychelles. Report prepared by John Nevill.
SBRC (2010). Seychelles Bird Record Committee: http://www.seychellesbirdrecordscommittee.com
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