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BOT RIVER ESTUARY: Ecology
  Flora
Phytoplankton/Diatoms
Koop et al. (in press) have reported that the phytoplankton biomass of the Botriviervlei consists mainly of flagellates.  The standing stock of pnytoplankton is, however, relatively low, their growth possibly being limited by wind-induced turbidity.

Measurements of diatoms in the sediment also give low values and show that they are restricted to the top 5cm, predominating in finer sediments. (Ref 2)
Algae
Fairly substantial amounts of large algae are often deposited on the sandy beach in front of the Botriviervlei and Kleinmond estuary.  Frequently these algae are also washed into the estuary by waves overtopping the dune barrier, or when the estuary is open to the sea.

These driftline algae are mainly the giant kelps Ecklonia maxima and Laminaria pallida as well as smaller amounts of Macrocystis angustifolia.(Ref 2)
Koop et al. (in press) mention the presence of the alga Chara sp. throughout the vlei, but particularly dense near the head.  Dense beds of Chara were also found in the Lamloch swamps (82.08.23). (Ref 2)
The epiphytic alga Cladophora sp. has been reported to grow on submerged plants (Koop et al., in press).  This alga can break loose and form dense mats which float and are often deposited on the vegetation along the shoreline.  It does not appear to have a definite growth cycle and its occurrence is unpredictable.  It often grows rapidly for several months followed by an equally rapid decline. (Ref 2)
Aquatic Vegetation
Ruppia maritima is reported to be the most important aquatic plant in terms of biomass (Koop et al., in press).  This aquatic grass was found throughout the vlei in water shallower than 2,9m.  A similar plant, Potamogeton pectinatus, was found in dense isolated patches in the upper reaches of the vlei. (Ref 2)
Sporobolus virginicus might also be classified as an aquatic plant.  Although it grows predominantly in areas which are periodically inundated, it can withstand long periods of complete submergence and even support epiphytic algae (AEF Heydorn, pers.comm.).  It is found submerged mainly in the shallow waters along the southern parts of the Lamloch swamps. (Ref 2)

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Semi-aquatic Vegetation
There are a number of communities which make up the semi-aquatic vegetation of this system.  Possibly the most important of these are the Phragmites australis and Scirpus littoralis reeds swamps.  These form dense patches in very we and/or submerged areas.  They are found mainly  near the bridge at the head of the Botriviervlei and in the Lamloch swamp area.  Small patches are also found along the banks of the vlei, especially at the Afdaks River inlet. (Ref 2)
At the time of sampling (August 1982), the Lamloch swamp area was totally flooded.  Many land plants were found growing submerged or partly so.  The  most common of these was the marsh grass Chondropetalum tectorum with other restioids.  Where the water levels are lower, Juncus kraussii is an important constituent of the vegetation.  This role is taken over by Scirpus nodosus in the sandier dune areas and Juncus acutis nearer the head of the vlei. (Ref 2)
The other semi-aquatic vegetation type, broadly defined as 'marshes' was found in areas which are periodically inundated.  In the lower sandy parts of the vlei, these marshes consist mainly of the brakkweek (Sporobolus virginicus) with Sarcocornia natalensis in restricted areas.  S. decumbens was found in the Lamloch area while pure stnads of S. natalensis are to be found near the head of the vlei.(Ref 2)
Terrestrial vegetation
The hummock dunes have a sparse convering of marram grass (Ammophila arenaria), sea wheat (Agropyron distichum), klappiesbrak (Tetragonis decumbens), bietou (Chrysnathemoides monolifera), blombos (Metalasia muricata), and numerous other herbs and shrubs. (Ref 2)
As one leaves the fore-dune area, the vegetation becomes doniated by rooikrans (Acacia cyclops) and only small isolated patches of the natural hind dune vegetation remain in the form of bietou, taaibos (Rhus glauca), slangbos (Stoebe plumosa) and pipe grass (Ehrharta villosa).(Ref 2)
The area around the marina development is dominated by Port Jackson willow (Acacia saligna) with Australisn myrtle (Leptospermum laevigatum), that is, alien vegetation.

However, remnants of the natural flora include species such as Leucodendron modestum, Erica cordifolia, Spiloxene sp. and numerous Mesembryanthenaceae.  This indicates that the vegetation of this area might previously have constituted a diverse mosaic of wet coastal renosterveld and coastal fynbos. (Ref 2)

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Fauna
Zooplankton
Coetzee (1982)has recently published an extensive survey of the zooplankton of the Botriviervlei undertaken during 1980 and 1981.  He obtained a range of values of 8 - 298 mg dry mass per m3 of vlei water which appears to be within the range recorded from other South African estuaries. (Ref 2)
More than 99 percent of the zooplankton was made up of the copepods Pseudodiaptomus hessei, Halicyclops spp. as well as copepod nauplius larvae and various harpacticoid copepods.  Of  these four groups, P. hessei and its larvae constituted about 90 percent oand was thus clearly the most abundant zooplankton organism in the vlei. (Ref 2)
During the survey, the mouth of the vlei was opened in October 1981.  An interesting addition to the zooplankton in the estuary after it was opened to the sea was the appearance of arvae and post-larvae of the burrowing sandprawn Callianassa kraussi. (Ref 2)
Sandprawns have been shown to be unable to breed at salinities below about 17 parts per thousand (Forbes, 1978) and Coetzee (1982) concludes that the population in the Bot vlei had probably been unable to breed at least since the start of his study in July 1980 because salinities were never higher than 15 parts per thousand. (Ref 2)
Aquatic Invertebrates

There are no extensive rocky areas within the system and an invertebrate fauna typically associated with rocks, e.g. limpets, barnacles and periwinkles is absent.

Some rocks do occur around Witpunt as well as on the opposite shore of the Botriviervlei, north of the Afdaks mouth.  These are small areas and appear to support mainly mobile forms, particularly isopods and amphipods which are found throughout the system.  The largest proportion of the invertebrate fauna from both the Bot and Kleinmond estruaries are either benthic, living on or in the bottom sediments, or associated with the aquatic vegetation. (Ref 2)
The most striking feature of the results presented by Koop et al. (in press) is the paucity of the fauna.  A total of only 18 species of invertebrates was recorded.  Clearly some species may reach rather high densities, up to 4 000 individuals of the small snail Hydrobia per square metre being recorded, although this is still far short of the figure of up to 100 000 individuals per square meter found in other estuaries, for example, the nearby Palmiet (Branch and Day, 1981).  The nature of the esturary,with its closed mouth and lack of tidal exchange and its relatively uniform physical and chemical conditions throughout, leads to a fairly even distribution of invertebrates.  Thus the major species occur at all locations. (Ref 2)
There appears to be clear driftline fauna consisting of a staphylinid beetle, the amphipod Orchestia ancheidos, the sea louse or isopod Exosphaeroma hylecoetes and the polychaete worms Nephtys and Ceratonereis as well as a few individuals of the tiny snail Hydrobia.  The remaining species are fairly evenly distributed although the sand prawn Callianassa kraussi and the prawn Palaemon pacificus exhibit a rather patchy distribution with the sandprawns avoiding the muddier regions.  (Ref 2)
Insects

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Fish
The fish fauna of the system may be divided into four categories:

Freshwater species: these are species which occur in the upper reaches of the estuary where salinities are usually low:

  • Carp                Cyprinus carpio

  • Tilapia              Oreochromis mossambicus

  • Black Bass       Micopterus salmoides                                                                (Ref 2)

Marine visitors:  these are typically marine species which are much more abundant in the sea than in the estuary.  They are restricted to areas of high salinity although some of them may tolerate salinities of not lower than 8 parts per thousand (Whitfield et al., 1981).  They move freely in and out of the Bot estuary while it is open but may get trapped when it closes.

  • Sea barbel                                 Tachysurus feliceps

  • Gurnard                                     Trigla capensis

  • Maasbanker                              Trachurus capensis

  • Anchovy                                    Engraulis capensis

  • Strepie                                      Sarpa salpa

  • Blacktail                                    Diplodus sarga

  • Zebra                                        Diplodus cervimus                                         (Ref 2)

Species which breed in the estuary:  these are numerically the most abundant species, forming the backbone of the fish population in the system.  They are usually much less abundant in the sea than in estuaries.

  • Estuarine round herring                         Gilchristella aestuarius

  • Cape silverside                                     Hepsetia Breviceps

  • Banded goby                                       Gobius multifasciatus

  • Klipvis                                                 Clinus sp.

  • Sand goby                                          Psammogobius knysnaensis

  • Pipefish                                              Syngnathus acus                           (Ref 2)

True migrants –species which never breed in estuaries but use them to a large extent.  Especially the juveniles of these species are often found in estuaries.

  • White Steenbras                       Lithognathus lithognathus

  • Cape stumpnose                       Rhabdosargus globiceps

  • Flathead mullet                        Mugil cephalus

  • Southern mullet                       Liza richardsoni

  • Elf                                          Pomatomus saltatrix

  • Leervis                                   Lichia amia

  • Kob                                       Artyrosomus hololeptidotus

  • Knysna half-break                  Hyporhamphus knysnaensis

  • Sand snake-eel                     Ophisurus serpens                         (Ref 2)

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Amphibians and Reptiles
Poynton (1964) records the following species of frogs from the Botriviervlei and Kleinmond estuary and immediate surroundings:

  • Racous toad                             Bufo rangeri

  • Leopard toad                           Bufo pardalis

  • Clicking stream frog                 Rana grayii

  • Arum frog                                Hyperolius horstocki        (Ref 2)
The following reptile and amphibian records have been compiled by AL de Villiers and RC Boycott of the Cape Department of Nature  and Environmental Conservation.  These do not include the four species mentioned above and the area covers the entire Bot/Kleinmond catchment.

Frogs:

  • Cape ghost frog                                    Heleophryne purcelli

  • Sand toad                                             Bufo angusticeps

  • Cape mountain toad                              Capensibufo rosei

  • Cape mountain rain frog                        Breviceps montanus

  • Cape river frog                                     Rana fuscigula

  • Banded stream frog                              Rana Montana

  • Cape chirping frog                               Arthroleptella  lightfooti     (Ref 2)
  • Padlopertjie                               Homopus areolatus               (Ref 2)
Snakes:

  • Blind snake                                         Typhylops delalandii

  • Common slug-eater                              Duberria lutrix

  • Spotted skaapsteker                            Psammophylax rhombeatus

  • Dapple-backed sand snake                   Psammophis notostictus

  • Spotted dwarf garter snake                   Elaps lacteus                     (Ref 2)
Lizards:

  • Marbled gecko                                       Phyllodactylus porphyreus

  •                                                             Pachydactylus geitjie

  • Golden sand lizard                                 Acontias meleagris

  • Tiger lizard                                            Nucras tessalatus

  • Anguine lizard                                       Chamaesaura anguina

  • Klip salamander                                    Cordylus cordylus

  •                                                             Pseudocordylus microlepidotus   (Ref 2)

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Birds
The large number of 118 species of birds recorded from the area, reflects the diversity of habitats represented.  Apart from the open ocean shoreline and the wetland habitats in the estuary, there is the scrub and bush around the river courses as well as mountain fynbos on the higher ground. (Ref 2)
The Botriviervlei and Kleinmond swamp area is an important wetland for avifauna.  It supports about 8 percent of the resident wader population between the Olifants River and Cape Agulhas and 2,4 percent of the resident plus migrant water (Summers et al.,1976).  (Ref 2)
The estuary also carries a very large coot population, which plays a major role in the ecology of the vlei(C Heyl, Department of Nature and Environmental Conservation and R Bally, Zoology Department, UCT, pers. comm.).  (Ref 2)
A study carried out recently by the Western Cape Wader Study Group showed that approximately 50 percent of all coots in the area between the Olifants and Great Brak River mouths were on the Botriviervlei.

This population also makes up 27,7 percent of the total number of coots that have been estimated to occur on all South African coastal wetlands in a study by the Percy FitzPatrick Institute of African Ornithology (J Cooper, pers.comm.) and thus probably represents a fair proportion of the total South African population.  (Ref 2)
Several birds recorded from the Bot/Kleinmond area are listed in the South African Red Data Book - Aves (Siegfried et al., 1976).  Five of these species are directly associated with the coastal area and the Botriviervlei and Kleinmond estuary while one, the Victorin's scrub warbler (Bradypterus victorini) is endemic to the souther Cape.  This bird is confined to mature mountain fynbos occurring in the upper catchment and can be considred vulnerable.  The white pelican (Pelicanus onocrotalus) is listed as vulnerable and in 1976 it was estimated that not more than 2000 breeding birds remained in South Africa although the species is not endangered.  Both the greater and lesser flamingo populations are subject to erratic fluctuations and although they are in no danger of extinction the conservation of breeding habitats is problematic.  (Ref 2)
The caspian tern is listed as vulnerable.  It occurs in small numbers along the South African coast and is common only in St Lucia.  The African fish eagle, a truly magnificent bird, is listed as vulnerable.  Although it is protected by provincial laws, its numbers in estuaries and around manmade dams are declining largely due to destruction of suitable habitat.  (Ref 2)
CWAC data shows that the estuary can support up to 60 different waterbird species and 10 000 individuals at any one time, although summer counts are generally higher due to the influx of migrants. Redknobbed Coot Fulica cristata is by far the dominant species - up to 8000 birds have been counted – comprising up to 75% of all waterbirds at the site. Other abundant species that can be seen regularly include Reed Cormorant Phalacrocorax africanus, Greater Flamingo Phoenicopterus ruber, Egyptian Goose Alopochen aegyptiacus, Yellowbilled Duck Anas undulata, Cape Shoveller Anas smithii, Kittlitz's Plover Charadrius pecuarius, Blackwinged Stilt Himantopus himantopus, Kelp Gull Larus dominicanus, Hartlaub's Gull Larus hartlaubii, Caspian Tern Sterna caspia and Swift Tern Sterna bergii. Migrant waders are dominated in summer by Ringed Plover Charadrius hiaticula, Common Sandpiper Tringa hypoleucos, Curlew Sandpiper Calidris ferruginea and Little Stint Calidris minuta with large flocks of Common Tern Sterna hirundo regularly recorded roosting near the mouth.

The estuary holds globally significant numbers of Great Crested Grebe Podiceps cristatus (152), Blacknecked Grebe Podiceps nigricollis (1 100), Yellowbilled Duck, (811), Cape Shoveller (404), Hartlaub's Gull (285) and Redknobbed Coot (7518).  (Ref 3)
Mammals
Stuart et al. (1980) and Stuart (1981) record the following species of mammal from the area immediately surrounding the Botriviervlei.

  • Chacma baboon                                  Papio ursinus

  • Caracal                                              Felis caracal

  • Small-spotted genet                            Genetta genetta

  • Egyptian mongoose                            Herpestes ichneumon

  • Southern elephant seal                        Mirounga leonine            (Ref 2)
A fur seal (Arctpcephalus pusillus) was seen in the lower reaches of the estuary while it was open to the sea at Sonesta and a skull of the Cape dune molerat (Bathyergus suillus) was also found (R Bally, pers.comm.)

Bats :

  • Big brown bat                                       Eptesicus melckorum

  • Slit-faced bat                                        Nycteris thebaica

Carnivores:

  • Cape fox                                              Vulpes chama

  • Honey badger                                       Mellivora capensis

  • Leopard                                               Panthera pardus

  • Cape grey mongoose                            Herpestes pulverulentus

  • Water mongoose                                  Atilax paludinosis

  • Aardwolf                                              Proteles cristatus            (Ref 2)

Rodents:

  • Cape porcupine                                    Hystrix africaeaustralis

  • Black rat                                              Rattus rattus

  • Striped mouse                                      Rhabdomys pumilio

  • Cape greater gerbil                               Tatera afra

Antelopes:

  • Common duiker                                    Sylvicapra grimmia

  • Grey rhebuck                                       Pelea capreolus  (Ref 2)
Both the leopard and the aardwolf are listed as rare in the South African Red Data Book - Large Mammals (Skinner et al., 1977).

The honey badger is listed as rare in the South African Red Data Book - Small Mammals (Meester, 1976).  It is protected in the Cape Province and although it is widely distributed it is nowhere common.  The Cape greater gerbil is also listed as rare and although it is not in danger it is included because it is endemic to the southwestern Cape. (Ref 2)

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