The Wilderness–Sedgefield Lakes Complex incorporates the Wilderness Section of the Garden Route National Park and the CapeNature Goukamma Nature Reserve along the coast east of Wilderness. In the north, it is bounded by a series of steeply rising slopes that represent the remains of ancient sea cliffs; to the south, it is cut off from oceanic influences by high, consolidated sand dunes. Overall, it lies below the 5-m a.s.l. contour.
The complex is made up of three discrete lake systems. From west to east, the first is the Wilderness system, which forms part of the flat Touw River floodplain and consists of a natural channel, the Serpentine, that links the Touw River and its estuary to Eilandvlei, near the town of Wilderness. Another channel runs between Eilandvlei and two other lakes, Langvlei and Rondevlei. The central system consists of a large lake, Swartvlei, which is usually connected to the sea by the Swartvlei Estuary near Sedgefield. Whenever this connection is periodically closed by long-shore drift, a lagoon dominated by fresh water forms. When the connection re-opens, the character of the Swartvlei system is transformed and it becomes flooded with sea water (35 parts per thousand), resulting in a dramatic freshwater–seawater gradient that can persist even after the estuary mouth closes again. The third system is a single landlocked lake known as Groenvlei, which does not have a connection to the sea. Collectively, these systems are the only warm-temperate coastal lakes in South Africa.
The lakes consist of a deep central area (pelagic zone), where the surface water is clear and open, bordered by a shallow area (littoral zone) of varying width. Fringing beds of semi-aquatic emergent macrophytes, such as Phragmites australis and Scirpus species, grow in the littoral zone. When water levels are low, exposed sand flats or mudflats appear at the edge of most of the waterbody. The lakes support a diverse community of estuarine macro-invertebrates and fish, which influence the biotic character of the area. The submerged macrophyte community, which grows in the lakes, channels and estuaries, provides foraging for a diversity of waterbirds, including herbivorous species and those that feed on the invertebrates in the submerged macrophytes. Variations in salinity, turbidity, water depth and the biomass of submerged macrophytes all interact in complex ways to influence the suitability of the lakes complex's habitats for waterbirds, with different conditions favouring different suites of species.
Recent research undertaken by SANParks indicates that waders, cormorants and gulls tend to prefer shallow waterbodies with high salinity, whereas ducks and grebes are more abundant in deeper waterbodies where the salinity level is lower. In addition, a stable water level increases the suitability of the habitat for herbivorous species, whereas fewer open periods in the estuary make the habitat less suitable for waders. These complex interactions therefore favour different suites of species periodically, but in the long term they support a high diversity of waterbirds.
The terrestrial vegetation in the Wilderness Section of the Garden Route National Park and the Goukamma Nature Reserve is mostly made up of fynbos and coastal plant species, with small remnants of forest habitat in some areas. The well-drained, sandy, floodplain soils support typical coastal maccia or fynbos. Towards the coast, true forest trees become scarce and dune forest elements, together with smaller shrubs, dominate. A 38-km stretch of coastline, including a series of high undulating coastal sand dunes, is protected within the national park and the neighbouring Goukamma Nature Reserve. Dune fynbos, including small-leaved and broad-leaved shrubs, grows in the latter.
The Wilderness–Sedgefield Lakes Complex supports an average of 10 868 non-passerine waterbirds every month; from 1980 to 1984, the monthly total ranged between 4 841 and 24 427. In the former Wilderness National Park alone, 262 bird species were recorded. The similarity in habitats means that the entire IBA supports a comparable number of species. Recent research conducted by Randall et al. (2007) suggests that there have been few changes in species composition since the original assessment. An additional 30 species that had not been previously recorded in the area were mostly vagrants and thus made no significant contribution to the biology of the lakes system. Although it appears that not many changes have occurred to the avifauna of the system, the threats outside the protected areas have increased.
The lakes complex is important for Palearctic migrant waders and southern African waterfowl, especially Anatidae, which feed and moult here. It is an important focus, with a constant exchange of waterbirds between the components, depending on the prevailing conditions in each one. The lakes support 72 waterbird species, including good numbers of Great Crested Grebe Podiceps cristatus, Black-necked Grebe P. nigricollis, Red-knobbed Coot Fulica cristata, White-backed Duck Thalassornis leuconotus and Southern Pochard Netta erythrophthalma, all of which tend to concentrate on Langvlei and Rondevlei. They also hold large numbers of Yellow-billed Duck Anas undulata and Cape Shoveler A. smithii. The latter is considered to be the most vulnerable waterbird in southern Africa owing to its relatively small range (it is endemic to the region), small population and specialised habitat requirements.
The marsh and reedbeds surrounding the lakes hold African Marsh Harrier Circus ranivorus, Greater Painted-snipe Rostratula benghalensis, Little Bittern Ixobrychus minutus, Red-chested Flufftail Sarothrura rufa, African Rail Rallus caerulescens and small numbers of African Grass Owl Tyto capensis. The lakes complex also provides important habitat for Caspian Tern Sterna caspia and Greater Flamingo Phoenicopterus roseus, and there are rare records of Black Stork Ciconia nigra and Lesser Flamingo Phoeniconaias minor. The coastline holds significant numbers of African Black Oystercatcher Haematopus moquini. Up to 6 000 Palearctic waders, consisting primarily of Curlew Sandpiper Calidris ferruginea, Little Stint C. minuta and Ruff Philomachus pugnax, can be found within the system during the austral summer.
The well-wooded backwaters on Swartvlei and Groenvlei hold small numbers of African Finfoot Podica senegalensis and Half-collared Kingfisher Alcedo semitorquata. The surrounding vegetation supports many restricted-range species from two EBAs: South African Forests and Cape Fynbos. The forests hold Forest Buzzard Buteo trizonatus, Knysna Turaco Tauraco corythaix, Knysna Woodpecker Campethera notata, Chorister Robin-Chat Cossypha dichroa and Forest Canary Crithagra scotops. The fynbos holds Cape Spurfowl Pternistis capensis, Cape Bulbul Pycnonotus capensis, Victorin's Warbler Cryptillas victorini, Cape Sugarbird Promerops cafer and Orange-breasted Sunbird Anthobaphes violacea.
Globally threatened species are Crowned Eagle Stephanoaetus coronatus, Lesser Flamingo, African Black Oystercatcher, Eurasian Curlew Numenius arquata, Maccoa Duck Oxyura maccoa, Knysna Warbler Bradypterus sylvaticus and Knsyna Woodpecker. Regionally threatened species are Caspian Tern, Greater Flamingo, African Finfoot, African Marsh Harrier, Lanner Falcon Falco biarmicus, African Grass Owl and Half-collared Kingfisher. Restricted-range and biome-restricted species in the IBA that are locally common include Forest Buzzard, Cape Spurfowl, Knysna Turaco, Knysna Woodpecker, Cape Bulbul, Chorister Robin-Chat, Olive Bush-Shrike Chlorophoneus olivaceus, Black-bellied Starling Notopholia corrusca, Yellow-throated Woodland Warbler Phylloscopus ruficapilla, Swee Waxbill Coccopygia melanotis and Forest Canary. Uncommon restricted-range and biome-restricted species include White-starred Robin Pogonocichla stellata, Grey Cuckooshrike Coracina caesia, Knysna Warbler, Cape Sugarbird, Orange-breasted Sunbird, Protea Seedeater Crithagra leucoptera, Cape Siskin C. totta and Victorin's Warbler.
Species that meet the 1% or more congregatory threshold are Great Crested Grebe (average 187 individuals), Cape Shoveler (average 752 individuals) and Red-knobbed Coot (average 8 414 individuals). Species that meet the 0.5% or more congregatory threshold are Yellow-billed Duck (average 878 individuals), White-backed Duck (average 82 individuals), Little Grebe (average 585 individuals), White-breasted Cormorant Phalacrocorax lucidus (average 112 individuals) and Maccoa Duck (average 42 individuals).
The forests hold several endemic plant species, including Gladiolus vaginatus and Satyrium princeps. The endemic and threatened Knysna seahorse Hippocampus capensis occurs in the Swartvlei Estuary. The terrestrial vegetation around the wetland system supports the endemic long-tailed forest shrew Myosorex longicaudatus, forest shrew M. varius and plain rain frog Breviceps fuscus. The protected areas hold many mammal species, including Cape grysbok Raphicerus melanotis, bushbuck Tragelaphus scriptus, bushpig Potamochoerus larvatus, Cape dune molerat Bathyergus suillus, Cape grey mongoose Herpestes pulverulentus, Cape horseshoe bat Rhinolophus capensis, caracal Caracal caracal, Cape clawless otter Aonyx capensis, honey badger Mellivora capensis and leopard Panthera pardus.
The IBA is threatened by the burgeoning expansion of tourism demands on the coastal zone between Knysna and George, which has become one of the premier holiday resort sectors in South Africa. The urban development taking place leads to irreversible habitat transformation around the protected areas within the IBA. In future it is likely that these areas – the Wilderness Section of the Garden Route National Park and Goukamma Nature Reserve – will become 'islands' in a sea of development. Not only will urbanisation reduce the buffer zones around the protected areas, but it will make them more susceptible to environmental threats and permanent alterations to their natural functioning. It is fortunate that the critical habitats in this IBA are already formally protected by national legislation and are thus secure from encroaching development. However, isolating patches of natural vegetation can change their ecological dynamics and still lead to losses in biodiversity.
Development between the lakes may restrict and/or alter the natural water flow between the lakes and have an impact on how they function ecologically. In addition, the lakes are susceptible to high-impact recreational use. It is vital that development around the lakes and human activity on them be monitored and controlled to minimise anthropogenic impacts. Fortunately, the relevant protected areas are well managed in terms of tourism impact and currently activities in the national park are restricted to two of the lakes while the others are off-limits. This is an important move in that it trades recreational use in some areas against protection in others.
The normal flooding regime of the system has been disrupted because the mouth of the Touw Estuary has to be actively managed to protect low-lying properties from being inundated. In the early 1980s it became clear that the artificial opening of the mouth, which had resulted in lower than average water levels, had caused an expansion of emergent macrophytes, which were interfering with ecosystem processes and recreational activities. The primary concern on the floodplain should be to improve water exchange whenever possible. It would appear that flood control and selective dredging may be necessary to improve the flow regime of the estuary.
Increasing salinity in Swartvlei has led to changes in the macrophyte community, which in turn have caused a large drop in the numbers of Red-knobbed Coot and other herbivorous birds such as ducks. This situation is temporary, however – the estuary was open for an extended time that coincided with a period of reduced freshwater inflow – and the salinity is likely to decrease in due course.
Another threat to the ecology of this system is an alteration in the natural frequency of fires. Specific intervals between fires are an essential component of fynbos ecology and at present fires are not occurring regularly enough to maintain the vegetation's natural dynamics. This is the result of residential developments, which isolate patches of fynbos and preclude burning due to the danger to humans and their homes. Changes in fire frequencies can prevent certain longer-lived fynbos plants from seeding. Their abundance in the landscape is therefore decreased, with an impact on the bird species that rely on these plants.
Invasive alien vegetation, including Eucalyptus and Acacia species, within the IBA, on private and State-owned land and in the catchments of rivers feeding into the IBA poses a significant threat. Clearing programmes are being conducted on the SANParks and CapeNature land, but it is difficult to tackle this issue on privately owned properties. Infestations in the catchment of the lake areas are particularly damaging to the IBA as they reduce water flow to the lakes and alter the water-flow regimes necessary for maintaining the lakes' ecological functioning.
Alien fish, such as Mozambique tilapia Oreochromis mossambicus, carp Cyprinus carpio and mosquito fish Gambusia affinis, have been introduced to the lakes and are causing problems by competing with indigenous fish species. Illegal fish-netting in the lake systems that targets indigenous fish will reduce the fish populations over time. This in turn will impact on the bird species that rely on this prey source. Raptors such as Western Osprey Pandion haliaetus and African Fish Eagle Haliaeetus vocifer, as well as African Darter Anhinga rufa and cormorants Phalacrocorax species, are likely to be affected by changes in fish abundance.
Pollution is also of primary concern as it may seriously disrupt ecosystem processes. Effluent from residential and industrial or agricultural sectors, including dairy farming, should be monitored to detect changes in pollution levels. Dairy farming in the catchment areas leads not only to pollution, as pollutants and excess nutrients flow into the lakes, but also to a reduction in the run-off into lakes when farmers abstract water. This impacts on the natural flow regime necessary to maintain an estuary.
Climate change may impact on the lake systems in the short term. Severe droughts are likely to reduce the water flow through the systems, leading to hyper-salinity; excessive flooding may alter the area's topography by removing large amounts of soil. An overall drying trend predicted for the southern Cape could have serious consequences for this and other wetland systems across the region.
As a designated Ramsar site, the Wilderness Lakes is recognised as a wetland of international importance. It was brought under the management of the National Parks Board (now SANParks) in 1985, officially proclaimed in 1987 and subsequently expanded to include Rondevlei in 1991. The Wilderness Section of the Garden Route National Park incorporates Swartvlei, Rondevlei, Langvlei, Eilandvlei and the Touw River estuary. The adjacent Goukamma Nature Reserve, established in 1960, includes Groenvlei, the lower sections of the Goukamma River and its estuary, extensive sand dunes and 14 km of rocky coastline, beaches and marine reserve. The national park also incorporates parts of the terrestrial matrix lying between the lakes. Much of the IBA thus falls under the formal protection of SANParks and CapeNature. These protected areas constitute the important bird habitats in the IBA. The proclamation of these areas under NEM:PAA ensures the long-term maintenance of these sites by preventing unsustainable development and limiting the kinds of activities that may take place. In addition, scientific authorities provide capacity for research that informs detailed management plans for the protected areas, thus ensuring their sound ecological management to the benefit of biodiversity. The national and provincial management authorities undertake all necessary conservation actions in these areas, in accordance with their mandate.
Further conservation action could be considered for parts of the IBA that fall outside the formally protected areas, in particular the privately owned land that is heavily infested with alien vegetation. Private landowners and farmers on land around the protected areas should be approached to form conservancies and, if possible, encouraged to follow best-practice guidelines in order to minimise environmental impacts in the buffer zones. The Garden Route Initiative, led by the Eden District municipality, has secured funding to undertake a process to register the Garden Route Biosphere Reserve. This provides a platform for all the NGOs, government departments and civil society organisations involved in conservation across this region to collaborate on environmental projects and develop a shared vision for environmental management.
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