ESTUARIES IN SOUTH AFRICA

Main Page	General Information	Catchment Characteristics	Land and Estuary Uses	Water Quality
Threats	Mouth dynamics and Estuarine Hydraulics	Physical Features	Climate	References
Heuningnes: Ecology

	Flora
	Habitat within the Ramsar site can be broadly classified into three broad types, the estuary and associated river system, the dunes system and associated pebble slacks and vegetated areas. According to Acock's (1953) the vegetation of the area is classified as Coastal Macchia. Heydorn and Tinley (1980), however, describe the vegetation of the area as Dune Thicket and Coastal Heath, while Moll et al. (1984) describe it as South Coast Strandveld, being an open to closed (40 - 80% canopy cover) mid-high vegetation with evergreen and deciduous broad-leafed and less conspicuous succulent elements. Graminoid components and herbaceous species form the understorey. (Ref 2)
	In the past exotic plants (Acacia cyclops and Marram grass Ammophila arenaria) were introduced to stabilize the shifting dunes. Marram grass is a pioneer species and disappears as soon as competition from other plants increases. The Acacia on the other hand is highly invasive and has been removed. (Ref 2)
	Semi-Aquatic Vegetation Near the mouth, salt marshes on sandy substrate occur in three areas. Typical species here include Limonium species, Salicornia cf. meyerana and Sarcocornia species. Owing to road protection levees tidal activity has been curtailed on these areas and pioneer terrestrial species such as Tetragonia decumbens and Chrysanthemoides monilifera are starting to encroach. (Ref 2)
	Further upstream, salt marshes on more muddy substrates are found. Here the typical species include Sarcocornia perennis, S. decumbens, Chenolea diffusa, Sueda maritima, Limonium scabrum and Juncus kraussii. Flood plain vegetation above the salt marshes has been heavily grazed and degraded (outside the reserve). Species occurring here include Sarcocornia pillansia and Chrysanthemoides incana. Patches of reeds (Phragmites australis) occur at places along the riverbanks. (Ref 2)
	Fauna
	Aquatic invertebrates The Heuningnes estuary has a tidal influence for 12 km upstream and the mouth has been kept open artificially since 1976. This has resulted in a strong marine influence on the aquatic fauna of the estuary. As this is the southernmost estuary in Africa it is important for the documentation of southernmost extremities in the distribution of estuarine species. Examples of these are the Ginger Mud Prawn (Penaeus japonicus) the Giant Mud Crab (Scylla serrata) both tropical crustaceans, and a tropical gastropod Nerita albicilla.(Ref 2)
	Fish The presence of marine species such as baardman (Umbrina canariensis), galjoen (Coracinus capensis), zebra (Diplodus cervinus) and strepies (Sarpa salpa) not often found in estuaries illustrate the marine influence on the estuary. The occurrence of the sea horse (Hippocampus sp.) is also noteworthy. (Ref 2)

	Birds The site is of extreme importance to the Damara Tern (Sterna balaenarum), probably South Africa's rarest coastal bird. This species is listed by Brooke (1984) as Rare. The tern nests on the interdune pebble slacks along the coast on either side of the estuary, both within and outside the Reserve. The estuary is used for foraging and for pair formation prior to breeding. Counts indicate that in excess of 30 individuals of this species utilise the estuary and that between 5 and 7 pair's nest in the surrounding coastal dunes. This represents about 15 % of the national population of this species and flock sizes seen at the estuary are amongst the largest seen in southern Africa, (Cooper pers. comm.). Other bird species that regularly nest in the dunes within the site includes ą 300 pairs of Kelp gulls (Larus dominicanus) and several pairs of Caspian Terns (Hydroprogne caspia). Other breeding species include the African Black Oystercatcher (Haematopus moquini), the Blue crane (Anthropoides paradisea), the Spotted Prinia (Prinia maculosa), the Kittlitz Sandplover (Charadrius pecuarius) and the Egyptian Goose (Alopochen aegyptiacus) (Bickerton, 1981) (Underhill, 1984). The Pied Kingfisher (Ceryle rudis) also nests in the area. (Ref 2)