Atlantic Ocean Islands, Coastal Ecology
Isolation index of different islands or group of islands in the Atlantic Ocean (compiled from the United Nations Environment Programme)
Tristan da Cunha
The Faeroe group comprises 1398 km2 of rugged and mountainous islands located just north of the United Kingdom, on the edge of the Rockall Rise. The coastline is indented, with fjord-like inlets, the marine life is abundant and the climate is mainly temperate oceanic.
As their situation in the transitional zone between the North Atlantic and the Arctic, the Faeroe Islands harbor a flora and fauna made up of both boreal and arctic species (Blindheim 1989). The phytoplankton productivity of this area is considered to be one of the greatest in the world oceans. The blooms occur in March and consist mainly of diatoms (Braarud et al. 1958). Compared to the spring bloom, the summer abundance of pelagic algae is rather poor, but more diverse (Blindheim 1989). The zooplankton bloom begins around March–April, in conjunction with the phytoplanktonic bloom. The summer pelagic fauna is dominated by copepods such as Calanus finmarchicus, Pseudocalanus minutus, and also by the arrow worms Sagitta elegans and Eukrohnia hamata. The Euphausiacea represent another important component of the zooplankton. Common pelagic fish in the waters off Faeroe are herrings, Greenland halibuts, blue whittings, redfish, cods, and haddocks.
On the vertical slopes of the coast, from the lowest water spring tide mark, every centimeter of the subtidal benthic zone is covered in a profuse carpet of life. Kelp and other algae are gradually replaced by sea anemones and sponges in deeper water.
Marine birds like the puffin Fatercula arctica and marine mammals such as the pilot whale Globicephala melaena and the white-beaked dolphin Lagenorhynchus albirostris are abundant.
Sable Island is located approximately 300 km southeast of the Canadian province of Nova-Scotia. The island itself is about 40 km long and 1 km wide, hence its temperate climate is markedly influenced by the sea. Ocean waters maintain winter air near freezing and keep summer temperatures below what would be considered room temperature. Fierce ocean currents sweep around the island causing the peculiar shifting of sand that constantly changes its contours. Between the dunes are numerous depressions usually filled with freshwater, and supporting a variety of aquatic plants and insects. A total of 179 species of terrestrial plants can be found on Sable Island. Along the coast, the moving sand is stabilized by the marram Ammphila breviligulata, the sandwort Honckenya peploides, and the beach pea Lathyrus maritimus.
Since all the shores of the island are sandy, benthic invertebrate diversity is low, although the sand dollar Echinarachnius parma, shrimp Crangon septemspinosa, and gastropod Lunatia heros are observed commonly. Among fish larvae, the pollock Pollachius virens and haddock Melanogrammus aeglefinus have been found around Sable Island. The American sand lace, smooth skate, yellowtail flounder, Atlantic cod, Atlantic mackerel, witch flounder, and spiny dogfish are also present.
Sable Island is the only known nesting place for the ipswich sparrow Passerculus sandwichensis princeps. Over 2500 pairs of terns, mostly Arctic terns Sterna paradisaea, nest on the island along with over 500 pairs of black-backed gulls Larus marinus and 2000 pairs of herring gulls Larus argentatus. A few sandpipers Calidris spp. and semipalmated plovers Charadrius semipalmatus also nest on the island and broods of black ducks Anas rubripes and red-breasted mergansers Mergus sarrator are produced near the ponds. During migration and after strong gales, nearly any species of bird in eastern North America may show up on Sable Island. About 300 Sable Island horses, introduced in 1738, are now living wild on the island. Sable Island also supports the largest breeding colonies of gray seals Halichoerus grypus and harbor seals Phoca vitulina in the western Atlantic Ocean. Harbor seals use Sable Island as a mating ground (Coltman et al. 1999).
Not far from Sable Island is the Sable Gully, which is the largest marine canyon in eastern Canada, and is considered an important habitat for a wide diversity of marine life, including over 200 vulnerable northern bottlenose whales (Hyperoodon ampullatus).
The island group of Bermuda is located in the western central region of the North Atlantic oceanic gyre known as the Sargasso Sea, approximately 1250 km southeast of New York City. Bermuda comprises about 130 islands and islets covering a land of just over 50 km2. The climate is wet subtropical. These islands are characterized by tidal and nontidal ponds, rocky coasts, sandy beaches, and shallow marine bays. They harbor the most northerly mangroves in the world and the most northerly coral reefs in the Atlantic, including coral/algal and algal/ vermetid reefs.
The ocean temperature of the surface waters off Bermuda varies seasonally between 18 °C and 28 °C. This island group can be considered a semi-tropical area where ocean conditions differ markedly from those encountered further south in the true tropics. In Bermuda, winter cooling and mixing of the surface layers occurs and a seasonal thermocline develops from late spring through fall (Morris et al. 1977). The phytoplankton of the Sargasso Sea that surrounds Bermuda shows low concentrations, especially during spring and summer with about 3000 cells L−1. The density of phytoplankton reaches a maximum in fall and winter with 50,000 cells L−1. In summer, the phytoplankton is mainly composed of coccolithophores, dinoflagellates, and diatoms. The main species, especially between late fall and spring, is the coccolithophore Coccolithus huxleyi. A spring bloom of diatoms, 200,000 cells L−1, occurs around April. Dinoflagellates dominate in late summer concurrent with the lowest productivity of the year.
The zooplankton of the waters surrounding the Bermuda reef platform and of the inshore waters are distinct from the oceanic species. The larvae of numerous benthic invertebrates are a significant component of the reef and inshore zooplankton, which is 5 to 10 times more abundant than in the Sargasso Sea, fluctuating around 2000 individuals m−3. Maximum zooplankton abundance generally occurs after the phytoplanktonic bloom in late spring-summer and again in winter, following the spring and fall increases of phytoplankton. Both zooplankton peaks are of only short duration and are followed by rapid population declines. Copepods are the most abundant members of the inshore populations and dominate in summer and fall, representing about 70–95% of all species present. In winter, the appendicularian Oikopleura graciloides dominate and fish eggs are prevalent in spring. Copepods nauplii and gastropod veligers are abundant in spring and again in early winter. Though less abundant, medusae, cladocerans, decapod and fish larvae are also part of the zooplankton of Bermuda (Morris et al. 1977).
The benthic habitats of Bermuda comprise rocky shores of the intertidal and subtidal areas, gullies, crevices and caves, muddy bottoms, mangroves, sandy-bottoms, and coral reefs. The coral reefs of Bermuda can further be divided into four different types: the ledge flat reef, the patch reefs, the coral knobs, and boiler reefs (Morris et al. 1977). The muddy substrata, mainly located in shallow protected areas, are associated with mangroves but also occur in the deepest bassin depressions. The sublittoral zones around Bermuda, including the surroundings of coral reefs, are mostly sandy. Numerous algae and sea grasses cover the shallows and offer home or shelter to various invertebrates. Burrowing species are the most abundant group of invertebrates present.
The rocky shore, sublittoral, and coral reef habitats shelter the greatest number of species. Overall, 118 common species are known from the rocky-shore subtidal area, including several algae, cnidarians, mollusks, and echinoderms. The rocky intertidal zone harbors 82 common species, dominated by algae, mollusks, and crustaceans. Many of these species live in the lower fringe or directly in tide pools. In the coral reefs, there are about 79 common species, mainly corals, but also algae, sponges, mollusks, and crustaceans. Mangrove swamps sustain about 21 species, dominated by algae, shrubs, mollusks, crustaceans, and bryozoans (Morris et al. 1977).
Macronesia encompasses the islands of Azores, Madeira, Canaries, and Cape Verde, which are located in the northeastern Atlantic.
The Azores consist of 10 Portuguese islands covering 2244 km2 and having a highly volcanic topography with many peaks and hollows (Bird 1985). They lie about 1500 km off the main coast of Europe and their climate is moist-moderate with abundant rainfall.
Currently, 274 species of algae are listed in the Azores, including 45 Chlorophyta, 52 Phaeophyta, and 177 Rhodophyta, among which are 10 endemic species. Although the Azores share algal biotopes with the Atlantic coast of mainland Europe, intertidal and subtidal seashores in the archipelago mostly lack the functionally important community of fucoids and laminarians widespread in the North Atlantic. Large brown algae such as Fucus spiralis are sporadic in the Azores, while Laminaria ochroleuca is known from only one location. Other large brown algae (Cystoseira spp., Sargassum spp.) occur in deep sheltered pools, lagoons, and some subtidal biotopes.
The intertidal areas of the Azores typically present three distinct zones. The highest band is dominated by littorinids (Littorina striata, Melaraphe neritoides). The upper boundary of the second zone is marked by the presence of barnacles Chthamalus stellatus and some small shoots of Ulva rigida, Gelidium pusillum, Gelidium microdon, Ralfsia verrucosa, and Enteromorpha spp. The third zone comprises an extensive area dominated by G. pusillum and Centroceras capillacea. In the adjacent subtidal area, the algal community changes along the depth gradient. Ulva spp., Hypnea musciformis, and Asparagopsis armata dominate the shallow depths. The 10 m depth community is characterized by the algae Dictyota dichotoma, Halopteris spp., and Stypocaulon scoparia, while Zonaria tournefortii is dominant at 30 m depth. With the exception of mollusks Bittium spp., that can be found everywhere, differences in the invertebrate fauna are also observed along the depth gradient. Sponges are an example of this: Tethya aurantium, Halichondria panicea, Hymeniacidon sanguinea, and Timea unistellata occur in the intertidal zone, whereas Petrosia ficiformis, Erylus discophorus, Myxilla macrosigma, and Clathrina coriacea are found between 10 and 15 m depth (Neto and Avila 1999).
The southern oyster drill Stramonita (Thais) haemastoma preys intensively on the populations of Mytilus edulis, Patella candei, Patella aspera, Crassostrea virginica, Ostrea equetris, Ischadium recuvrum, Balanus eburneus, Balanus amphitrite, and Chthamalus stellatus which colonize the intertidal zone of the Azores. Sea urchins Arbacia lixula also common on the rocky shores.
Over 175 species of mesopelagic fish are believed to occur around the Azores. The most widely spread families are included in the Stomiidae, Gonostomatidae, Sternoptychidae, and Paralepididae. The yellowmouth barracuda Sphyraena viridensis is a common pelagic coastal predator, mostly preying on juvenile horse mackerels Trachurus picturatus.
Large numbers of juvenile loggerhead sea turtles Caretta caretta thrive off the coast of the Azores. The sperm whale Physeter macrocephalus is the most common whale in Azorian waters. A total of 23 species of cetaceans have been observed, including the false killer whale Pseudorca crassidens, Risso dolphin Grampus griseus, bottlenose dolphin Tursiops truncatus, common dolphin Delphinus delphis, stripped dolphin Stenella coeruleoalba and spotted dolphin Stenella frontalis. Balaneoptera acurostrata and Globicephala macrorhynchus have also been recorded in winter and early spring.
The Portuguese archipelago of Madeira consists of one large and several small islands lying some 600 km off the coast of Morocco and representing a total land area of 810 km2, mostly made up of extinct volcanoes. The climate is semi-arid subtropical. The slopes are steep, but well vegetated and terminated in high coastal cliffs. Beaches are mainly gravely, but beach borders are also found. The coastal marine fauna of Madeira is a mixture of species with Mediterranean affinities and distinctly tropical species that often reach their northern limit there (Wirtz 1999).
Little is known of the precise marine ecology of this group. The sea urchin Diadema antillarum is an extensive herbivore that preys on algal bed. Thirty-eight species of fish are easily observed in the coastal waters of Madeira. The endangered Madeira soft-plumaged petrel Pterodroma mollis madeira occurs there, as well as the Mediterranean monk seal Monachus monachus, which breeds on the island. In fact, Madeira is one of the most important remaining localities for this species threatened with extinction.
The Canary group comprises 7500 km2 of dry islands spreading close to the coast of northwest Africa. These Spanish islands are mostly surrounded by sandy beaches and rocky shores and their climate is semi-arid subtropical.
In the Canary Islands, the chlorophyll concentrations range from 0.09 mg m−3 to 0.25 mg m−3, with deep maxima between 75 and 100 m depth. The biomass in the shallower water corresponds to 2000–28,000 cells L near the coast (Ojeda 1996). Some coastal lagoons are characterized by the conspicuous presence of Cyanophyta and Chlorophyta up to 105 cells ml−1, thus imparting a green coloration to the water.
Primary productivity is high in the water off Canary Islands. The northern portion of the islands supports a high phytoplankton production where the Canary current collides with the coast. The biomass is not large but the turnover is pronounced. Bacteria associated with phytoplankton are abundant at the outer edge of the main phytoplankton concentration. Zooplankton accumulates in the marginal southern areas and is quite important in the upwelling area in the upper 50 m of the water column. The zooplankton community is generally composed of copepods, but mysidacea are usually important in all regions. Zooplankton also includes amphipods, ostracods, and mysids.
The sea urchin Diadema antillarum is commonly observed. Falcon et al. (1996) found 76 species of coastal fish around the Canary Islands, the most common being Abudefduf luridus, Canthigaster rostrata, Chromis limbatus, Sparisoma cretense, and Thalassoma pavo. Lorenzo (1995) indicated that many waders (Charadrius alexandrines, Calidris alba, Arenaria interpres) were found in intertidal lava platforms and in supratidal lagoons of the Canary Islands.
St. Helena and Ascension (United Kingdom)
St. Helena is an isolated volcanic peak rising 4400 m from the seafloor, slightly east of the mid-Atlantic ridge, about 1900 km off the coast of Angola. It covers 125 km2 as a deeply eroded volcanic cone. It has a dry subtropical climate. The bay on the south coast has a beach backed by calcareous dunes, which have been driven far inland by the southeast trade winds. The coastal areas are rugged and barren whereas the higher elevations in the center of the island present a lush vegetation (Bird 1985).
St. Helena’s isolated position in the South Atlantic has given rise to an unusual and remarkable land and marine flora and fauna. There are 60 species of flowering plants, of which 49 are endemic. Thirteen endemic species of ferns are present, almost all on the verge of extinction. Of 1100 land invertebrates, 400 are unique to St. Helena. At least six unique land birds once occurred on St. Helena, only one, the wirebird Charadrius sanctae helenae, survives today. Also, modest seabird populations nest on isolated cliffs and rocks. The island is home to the largest species of earwig, Labidura herculeana. Endemic species of shrimps Typhlatya rogersi and Procaris ascensionis are present in rock pools. Ten shore fishes are found only around the island, and 16 more are found only here and at Ascension. The green turtle Chelonia mydas, and the hawksbill turtle Eretomochelys imbricata may breed along the coast of St. Helena.
Ascension is a 97 km2 volcanic island isolated in the south Atlantic. The peak of a dormant volcano rises 3000 m above the seafloor and a further 859 m above sea level to the summit of Green Mountain. The vegetation is sparse with scattered guano deposits and the island has a dry tropical climate. Imposing sea cliffs line the more exposed eastern coast (Bird 1985). Beaches, intertidal rock pools, and rocky shores are mainly composed of bare rock, regularly covered by a layer of crustose coralline algae that has cemented all rubble into a uniform surface.
The general biodiversity of Ascension is not high, not only because of its isolation but also due to the absence of lagoons, estuaries, seagrass beds, mangroves, and coral reefs (Manning and Fenner 1990). Price and John (1978) concluded that the primary facet presented by the intertidal and sublittoral fringe on Ascension was still that of stark bare rock, sometimes abutting or adjoining clean sand. Other factors such as strong tidal surge, supplemented by rollers, enormous waves that assault the island, influence the shore and shallow depth colonization. Finally, the blackfish Melichthys niger is another important factor regulating the presence of other species, as it deters colonization by grazing all surfaces that it can reach (Day 1983), including the crustose algae described earlier. Stands of algae and colonies of sabellariid worms, barnacles, and solitary coral are limited to crevices, blowholes, and isolated tide pools where blackfish cannot penetrate (Manning and Fenner 1990).
The sandy beaches of Ascension are high-energy areas made up of very coarse sand. Only digging crustaceans Hippa testudinaria have been found in the sand and crabs Grapsus spp. have been seen roaming over the open beaches at night. Isolated tide pools with rims of protective rock are often inhabited by dense beds of oysters Saccostrea cucullata (Manning and Fenner 1990).
Much of Ascension’s global conservation importance comes from the island’s remoteness, which has produced one of the most remarkable island floras and faunas in the world. It is of world significance for its 11 species of breeding seabirds, especially the unique Ascension Island frigate bird Fregata aquila. There are six unique species of land plants, nine of marine fish and shellfish, and over twenty of land invertebrates. Some 27 species of amphipods have been described in the pool habitats along the shore, and Manning and Fenner (1990) observed 74 species of decapods on Ascension. Of these, 41 occur in the western Atlantic, and most are common.
The echinoderm fauna of Ascension comprises 25 species, including brittle stars, sea cucumbers, sea urchins, and starfish. Eight of these species are amphi-Atlantic, one species is restricted to Ascension, three species are also known in the western Atlantic, four species are also found in eastern Atlantic, five species are circumtropical and four species are also found in St. Helena. These findings suggest that species dispersion by larvae is mediated by surface and subsurface transport of planktonic stages (Pawson 1978).
About 81 species of shore fishes are known, including 11 endemic species. Ascension has one of the most important breeding populations of green turtle C. mydas in the world. The green turtles mate and lay their eggs on sandy beaches, whereas hawksbill turtles E. imbricata less frequently seen along the shores.
Tristan da Cunha and Gough (United Kingdom)
Tristan da Cunha is a circular volcanic island of 103 km2 rising 2062 m above sea level. The island is bleak and barren, but zoned vegetation occurs above 1350 m. It has a wet temperate climate and is surrounded by rocky shores.
Gough is a deeply dissected volcanic island located 350 km southeast of Tristan da Cunha. High cliffs with hanging valleys and waterfalls surround the surface area of 65 km2. The luxuriant evergreen scrub forest thins out above the 300 m contour. The climate is a cool-temperate oceanic. The flora of Gough is typical of southern cold-temperate oceanic islands, with relatively low species diversity, and a large preponderance of ferns and cryptogams.
Both Tristan da Cunha and Gough are characterized by their isolation and high level of endemism near the shore. However, with increasing depth, the amount of faunal similarity increases between regions across the South Atlantic.
The marine area can be split into two distinct algal zones. From sea level to 5 m depth, algae consist mainly of bull kelp Durvillea Antarctica, and beyond 20 m are dominated by Laminaria pallida and giant kelp Macrocystis pyrifera. Forty species of algae have been recorded, of which two species are endemic to Gough. Most littoral species found at Gough are widespread on other southern ocean islands, and 79 invertebrate species have been recorded. The absence of limpets and bivalves in the littoral and subtidal zones is noted. Sea urchins Arbacia dufresnii are abundant in the marine area, as are whelks Argobuccinum sp., chitons, starfishes, sea anemones, bryzoans, barnacles, slipper limpets, nudibranchs and sponges. Important marine species include the Tristan rock lobster Jasus tristani (from close inshore to 400 m depth around Gough), and octopi. Both are economically exploited by fishermen under close regulation. About 51 species of fish are known to occur in nearshore waters of Tristan da Cunha and Gough.
Gough has been described as a strong contender for the title of “most important seabird colony in the world,” with 54 species recorded in total, of which 22 breed on the island and 20 are seabirds. About 48% of the world’s population of northern rockhopper penguin Eudyptes chrysocome moseleyi breed at Gough. Atlantic petrel Pterodroma incerta is endemic to Gough and the Tristan group of islands. Gough also harbors a major colony of the great shearwater Puffinus gravis with up to three million pairs breeding on the island. The main southern ocean breeding sites of little shearwater Puffinus assimilis are Tristan da Cunha and Gough Island, with breeding pairs numbering several million. The wandering albatross Diomedea exulans dabbenena is virtually restricted to Gough, with up to 2000 breeding pairs. The only survivors of southern giant petrel Macronectes gigantous also breed on Gough, with an estimated 100–150 pairs. Gough moorhen Gallinula comeri is found in fern bush vegetation areas, and estimates of population size vary from 300–500 pairs to 2000–3000 pairs. About 200 pairs of Gough finch Rowettia goughensis have been recorded, although recent estimates suggest that there may be 1000 pairs. Other seabirds breed on these islands, such as the yellow-nosed albatross Diomedea chlororhynchos chlororhynchos and the great shearwater P. gravis. The penguin Eudyptes crestata is present on Tristan.
Subantarctic fur seals Arctocephalus tropicalis (200,000 individuals and increasing), and southern elephant seals Mirounga leonina (about 100 individuals) are the only two native breeding mammals. The former breed at beaches all round the island, whereas the latter are restricted to the island’s sheltered east coast. Two other marine mammals are found in the area, namely the southern right whale Eubalaena glacialis australis and the dusky dolphin Lagenorhynchus obscurus. Reptiles, amphibians, freshwater fish, and native terrestrial mammals are absent, although the introduced house mouse Mus musculus is widespread and abundant.
Falklands (United Kingdom)
The Falklands include two main islands and several hundreds smaller islands and islets that cover about 12,000 km2. The coastline is lengthy and highly indented with numerous rias at the mouths of winding valleys. The landscape is treeless, with tussocky grasses and extensive peat bog mantles (Bird 1985). Some rocky coasts possess offshore kelp beds of Macrocystis. The climate is dry cool temperate.
The Falklands are exceptionally rich in marine life, including benthic and pelagic forms. Also, about 85% of the world population of the black-browed albatross (Diomedea melanophris), and the largest concentration of rockhopper penguins (E. chrysocome) are found on the islands. A total of 63 species of sea and land birds occur, including the night heron Nycticorax nycticorax cyanocephalus, ashy-headed goose Chloephaga poliocephala, kelp goose Chloephaga hybrida malvinarum, Garnot’s ground tyrant Muscisaxicola muscisaxicola macloviana, and the common diving petrel Pelecanoides urinatrix berard. The penguins Pygoscelis papua, E. crestata, Eudyptes chrysolophus, and Spheniscus magellanicus are present on the Falklands. The islands are breeding grounds for sea lions (Otaria flavescens), elephant seals (Mirounga leonoina) and fur seals (Arctocephalus gazella). Fifteen species of whales and dolphins occur in the surrounding seas. Pelagic invertebrates such as the squid Ilex argentinus are abundant near the coast and can be considered the basic diet of birds and mammals.
Scotia Arc Islands (United Kingdom)
South Georgia, South Sandwich, and South Orkney Islands combined represent about 10,000 km2 of land that peaks over 2000 m. They are known as the islands of the Scotia Arc. Most of them rise steeply from the sea and are rugged and mountainous. Their coastlines are generally cliffed and rocky, with many inlets and some bay beaches.
South Georgia is a remote island located 1330 km from any other land. It is largely barren and has steep, glacier-covered mountains. The climate is wet subpolar; it is variable, with mostly westerly winds throughout the year, interspersed with periods of calm; nearly all precipitation falls as snow. The South Georgia fauna is depauperated and consists mainly of direct developers. The intertidal fauna is of geologically recent origin. It is suggested that South Georgia shores stem from colonization by rafting from remote sources. There are abundant rocky shores with Macrosystis kelp offshore. Some 24 species of breeding seabirds and 26 visitors, 6 species of seals, and 10 endemic bottom dwelling fish are found around South Georgia. Penguins Aptenodytes patagonicus, E. chrysolophus, Pygocelis antarctica are present.
The South Sandwich Islands are of volcanic origin with some active volcanoes. They have a wet polar climate, and sparse vegetation of lower plants (lichens and mosses), richer around fumaroles with dense bryophyte communities. The penguins A. patagonicus, E. chrysolophus, Pygocelis papua, and Pygocelis adeliae are present.
The South Orkney Islands are located between the Antarctic Peninsula and South Georgia and they have a subpolar climate. The littoral zone is either lifeless or very poor. Scarce diatoms and a few species of chitons and gastropods are found along the littoral. At low tide, there are green and red algae in small rock pools, and amphipods and planarians under stones. At around 2 or 3 m depth, green and red algae appear with an increasing number of fauna including starfish, urchins, sponges, and ascidians. At around 8–10 m depth, new species of starfish appear and the general animal biomass increases with depth. At 30 m, ascidians, sea urchins, starfish, and brittle stars form vast colonies. The penguins P. antarctica, P. papua and P. adeliae are present around South Orkney.
Overall, the biota of the intertidal region is poor, even during summer, in the Scotia Arc Islands. Due to the rigorous conditions, most biota is confined to lower levels of the shore (Stephenson and Stephenson 1972). The midlittoral zone that is most exposed to air is characterized by the presence of the Porphyra algae followed by Ulothrix and Urospora along the center of the zone. There are also algae in the tide pools and crevices. Limpets Patinigera polaris occur in crevices, whereas amphipods, nemertines, and flatworms are found clustered under stones and rocks. The tide pools of the midlittoral are home to many Antarctic species of algae such as Leptosomia, Iridaea, Adenocytis that can also extend their distribution to the infralittoral fringe area with Desmarestia, Curdiea, Monostroma, and Plocamium. The infralittoral fringe is characterized by numerous algae, mainly of the genera Desmarestia and Ascosiera. The huge Phyllogigas grandifolius dominates this area and its blades harbor a small fauna comprised, among others, of worms, sponges, hydroids, and mollusks (Stephenson and Stephenson 1972).
There is no supralittoral fringe in many places, the mid-littoral fringe has a very restricted population but there is an increasing number of species in the infralittoral zone (Stephenson and Stephenson 1972). Several animals such as sponges, alcyonarians, pycnogonids, amphipods, isopods, polychaetes, and nemertine worms are giant representative of their group (Knox 1970).
The chlorophyll abundance in the surface waters shows a high degree of variability. The chlorophyll in South Orkney fluctuates around 4 mg m−3 in summer. High pigment concentrations have been found especially between South Orkney and the South Sandwich Islands. The main species that compose the phytoplankton biomass are diatoms. Chaetoceros neglectus, Chaetoceros dichaeta, Chaetoceros atlanticus, Nitzshia sp., Corethron criophilum are the most common reaching densities around 105 cells L (Zernova 1970). The standing crop of zooplankton in the subantarctic represents 55 g m 3 between 0 and 50 m depth. Around South Georgia, the relationship between the density of phytoplankton and zooplankton is inverse (Knox 1970). Copepods reach maximum densities at around 600 m depth, decreasing continuously toward the surface. The main species of zooplankton are Euphausia superba, Euphausia frigida, Thysanoessa spp., Parathemisto spp., and Salpa fusiformis. The main krill biomass is observed in areas of the island arc. The complicated underwater relief and coastline of this area leads to the formation of numerous gyres and local eddy currents trapping the krill (Makarov et al. 1970).
Krill has been found to be an important part of the diet of numerous fish living around the islands, including members of the families Rajidae, Paralepidae, Myctophidae, Scopelarchidae, Muraenolepidae, Gadidae, Moridae, Macruridae. The occurrence of various fish in the epipelagic waters of the Scotia Arc Islands, which are described by many authors as a highly productive krill zone, are also profitable to whales, seals, birds, and Antarctic fishes, but also to subantarctic and subtropical epipelagic species of the southern hemisphere. The crabeater, leopard, Ross and some other seals can be found in the Scotia Arc Islands.
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