Robberg Nature Reserve
Robberg MPA has offshore reefs, which provide especially important habitat for commercially fished sparids from the genus Chrysoblephus, and endemic sparids such as Red steenbras (Petrus rupestris) and Black musselcracker (Cymatoceps nasutus). The MPA has offshore soft sediment areas close inshore between the offshore reefs. Although these areas are low in species diversity, they are important areas for East coast sole (Austroglossus pectoralis), Silver kob (Argyrosomus spp.) and Hake (Merluccius spp.). The Robberg MPA is a breeding area for the rare African Black Oystercatcher (Haematopus moquini). Many other seabirds are known to frequent the area, including a Whitebreasted Cormorant breeding colony of ca. 20 – 30 pairs. Globally threatened and CITES listed sea turtles have been observed in the area, including Loggerhead (Caretta caretta), Green (Chelonia mydas) and Hawksbill (Eretmochelys imbricata) turtles which are seen annually, and Leatherback turtles (Dermochelys coriacea) which are rare visitors. There have also been many species of marine mammals sighted and also stranded in the Robberg MPA, including various species of whales, dolphins and seals. There is a Cape fur seal (Arctocephalus pusillus pusillus) colony within the MPA, this colony is mainly a “haulout”, however some breeding does occur but these pups have a low survival rate. There is also a resident population of the CITES listed Humpback dolphin (Sousa chinensis). There are three species of fish known to be present in the MPA which are listed as “Vulnerable” under the Draft List of Threatened and Protected Species issued in terms of NEMA: Biodiversity Act. These species are the Great white shark (Carcharodon carcharius), White steenbras (Lithognathus lithognathus) and Red steenbras (Petrus rupestris).
Robberg Nature Reserve has an altitudinal range from sea level to 148.5 m above sea level; this has a significant influence on its vegetation. The effect of regular strong winds on the vegetation structure is clearly visible. Particularly along the crest and on the southern slope of the peninsula the plants have a stunted growth form. This is most prominent in the dwarflike growth form of the Keurboom (Virgilia divaricata), a common tree species usually associated with the Afromontane Forests. The vegetation consists of a mosaic of fynbos and subtropical thicket. The subtropical thicket occurs as small patches in sites that are protected against fires where the soils are loamy, whilst the fynbos is limited to the nutrient poor soils and open areas (Vlok & Euston-Brown 2002).
Three vegetation types occur on the reserve according to this map. The conservation status of each vegetation type is given in brackets: · Cape Seashore Vegetation (LT) · Garden Route Shale Fynbos (EN) · Knysna Sand Fynbos (EN) Detailed descriptions of these vegetation types are given in Mucina and Rutherford (2006).
According to the fine-scale vegetation map compiled for the Garden Route Initiative by Vlok et al. (2008), the reserve contains five vegetation units representing three biomes (Figure 10). A brief description of each (based on Vlok et al. (2008)) is given below as well as the conservation status according to Holness et al. (2010) and Vromans et al. 2010):
Marine biome: o Hartenbos Primary Dune (EN) – This unit occurs in patches as a very narrow coastal strip all the way from Witsand eastwards to Nature’s Valley. It has a few species present. Ammophila Arenaria (alien), Arctotheca populifolia, Gazania rigens, Hebenstretia cordata, Ipomoea pes-caprae, Senecio elegans, Scaevola plumieri, Tetragonia decumbens and Thinopyrum distichum are most prevalent. The plants tend to be sparse, but just inland (secondary dunes) the vegetation becomes rapidly denser and taller, with shrubs such as Metalasia muricata, Morella cordifolia, Passerina rigida, Searsia crenata and often somewhat stunted Sideroxylon inerme present. The latter constitutes the transition to Dune Thicket vegetation and the cut-off point between these two units is often difficult to determine. The absence of species such as Scaevola plumieri, Tetragonia decumbens and Thinopyrum distichum indicates the transition from Primary Dune to Dune Thicket units. The Primary Dune units act as a precursor to the Dune Thicket units. Wherever they are absent, often due to stabilization of the supporting Drift Sands habitat, wave action starts eating into the secondary dunes, undermining the sands of the Dune Thicket. Gladiolus gueinzii is the only uncommon plant species known from this unit – it has not yet been recorded from the RNRC.
Subtropical Thicket biome: Herolds Bay Littoral-Thicket (CR) – This unit is restricted to the granite and shale outcrops from Glentana eastwards to Stormsrivier. It has a higher succulent component present. Silene vlokii is endemic to this unit, but it is now regarded by some as only an ecotype of Silene primuliflora. o Wilderness Forest-Thicket (VU) - This habitat is restricted to the secondary dune systems, just inland of the mobile dune systems between Wilderness and Brenton-onSea. The matrix vegetation consists of Dune Thicket with typical species such Azima tetracantha, Carissa bispinosa, Cassine peragua, Euclea racemosa, Lycium cinereum, Searsia crenata, Searsia pterota, Mystroxylon aethiopicum, Muraltia spinosa, Putterlickia pyracantha often forming impenetrable stands as these shrubs are usually woven together with creepers such as Asparagus aethiopicus, Cynanchum ellipticum, Rhoicissus digitata, Sarcostemma viminale and Solanum africanum. A forest-like community of trees such as Olinia ventosa, Pterocelastrus tricuspidatus, Sideroxylon inerme and Tarchonanthus littoralis occur in the protected dune slack areas. Where these dune slack areas are deep these trees form a dense closed canopy that is well lifted above ground level, thus qualifying to be called a “Milkwood forest”. These forests are never very wide, although they can be quite long.
Noetzie Proteoid Fynbos (LT) – This unit is limited to the area between Knysna and Plettenberg Bay. Subtropical thicket patches are absent as most of the habitat is exposed to periodic fire, but when physically disturbed the vegetation can be quite grassy. Another differentiating feature is the periodic occurrence of seasonally wet sites in which robust sedges such as Tetraria bromoides are locally dominant. Unlike the upland Montane Fynbos water loving species such as Berzelia intermedia and Grubbia rosmarinifolia are absent from these sites. Overstorey proteoid shrubs such as Leucadendron eucalyptifolium, Leucadendron salignum and Protea neriifolia are often locally abundant, along with ericoid shrubs such as Erica formosa, Erica sparsa and Erica versicolor. This habitat is not very rich in geophytic species, but some orchids such as Disa hians, are often locally abundant. Some of these geophytes, such as Pterygodium newdigateae, are threatened species.
Noetzie Thicket-Fynbos (VU) – This unit occurs in a narrow strip along the coast in the higher rainfall zone from Brenton-on-Sea to Plettenberg Bay. Thicket and Forest patches are more abundant and it has water-demanding species such as Erica glandulosa subsp. fourcadei present.
The current plant species list for the reserve stands on 175 species, based on specimens collected on the reserve. This list is by no means complete and is constantly being updated through baseline data collection. Species lists are available on request from Scientific Services, Assegaaibosch Nature Reserve, Jonkershoek Road, Stellenbosch. At least five of the plant species on the reserve are threatened or of conservation concern (Raimondo et al. 2009): o Agathosma acutissima (VU) o Disa hallackii (CR) o Erica glumiflora (VU) o Selago villicaulis (VU) o Wahlenbergia sp. nov. – a species that is restricted to the Plettenberg Bay area according to Goldblatt and Manning (2000). All these species are restricted to the fynbos vegetation units.
Invasive Alien Plants The major alien invasive threats to the reserve are due to infestation from neighbouring properties, which include Acacia cyclops and Acacia saligna. The dense stands of Acacia cyclops that used to occur in the area known as Witsand have been removed with only a small section that remains on the northern cliff face, which is inaccessible. Biological control agents are used to limiting new seed production in these areas. Annual maintenance is conducted to eradicate new plants from establishing on the reserve
Thirty-one species have been recorded in the reserve complex. Threatened marine species include the Humpback whale (Megaptera novaeangliae; VU), Humpback dolphin (Sousa chinensis; VU), Indian Ocean bottle-nosed dolphin (Tursiops aduncus; VU) and the Southern elephant seal (Mirounga leonina; EN), which is a vagrant to the reserve. There is a Cape fur seal (Arctocephalus pusillus pusillus) colony within the RNRC.
One hundred and twenty four bird species have been recorded on the reserve and the surrounding MPA (BIRP 2011). The marine portion of the reserve contributes some species to the reserve that would not normally be recorded on a terrestrial coastal reserve, e.g. Parasitic Jaeger (Stercorarius parasiticus) and Northern Giant Petrel (Macronectus halli). Threatened species recorded for the reserve are listed in Table 2 below.
In terms of population sizes, approximately 170 Cape Cormorants (Phalacrocorax capensis) are roosting and ca. 20 – 30 pairs of Whitebreasted Cormorants (Phalacrocorax carbo) are breeding in the RNRC.
Sixteen species of reptiles have been recorded in RNRC, according to the CapeNature State of Biodiversity (SOB) database. One of these, the Loggerhead turtle (Caretta caretta) is listed as EN. This species does not use the terrestrial part of the reserve for breeding but may utilise the marine protected area for foraging.
Five species of frogs have been recorded from the RNRC. None of these are listed as Threatened.
Only five marine fish species have been officially recorded in the RNRC (according to the SOB database). None of these are listed as Threatened. It is known that there are many more species present in the MPA, but these need to be properly documented.
Twelve invertebrate species (butterflies, spiders and scorpions) have been recorded from the reserve, none of which are listed as Threatened. The invertebrate list for the reserve is incomplete and needs focusing attention.
The alien Mediterranean mussel (Mytilus galloprovincialis) occurs in the intertidal zone of the rocky shoreline.
The Cape Fur Seal Colony at Robberg – implications for future zonation and management Robberg derives its name from a historic colony of Cape fur seals estimated at 3000 animals in the late 1800s but harvested to extirpation between the 17th and early 20th centuries. Seals returned to the Robberg Peninsula in small numbers during the early 1990s and their numbers subsequently increased to over 4000 (Huisamen et al. in press). The colony at Robberg is the first new colony to develop on the coast east of Agulhas since the 1970s. The colony is currently still in a transition phase with low numbers of pups born on the colony (still < 100 per year). In order to aid the recolonisation of the easternmost tip of the Robberg Peninsula (‘Seal Point’) by seals and further growth of the colony, rezoning of the current Nature Access Zone to restrict access, and re-routing the hiking trail along the periphery of the Peninsula may be required. Secondly, the marine area at Seal Point may be declared a no-take zone for boat and shore-based fishing. This would be appropriate in terms of the zoning policy for MPAs.