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KEURBOOMS RIVER ESTUARY: Ecology
  Flora
Phytoplankton/Diatoms
No data available
Algae
No data available
Aquatic Vegetation
Beds of Zostera capensis (eel grass) were found throughout the lagoon, growing intertidally and below the mean low water mark.  At the blind south-west end of the lagoon, these plants become relatively tall and dense and Halophila ovalis is also present.  The Zostera beds in the other parts of the lagoon do not seem to be as well-developed due to trampling, stronger currents and silt deposition. (Ref 1)
Semi-aquatic Vegetation
The saltmarshes of this system are very variable, primarily according to micro-topography, substrate and salinity regime.

The general marsh can be described in the following way:  at mid water mark, patches of Spartina capensis (strandkweek) and Sarcocornia decumbens (brakbos) are found.  Below high water mark, Salicornia uniflora, Triglochin bulbosa and T. striata are found together with S. decumbens.  At high water mark, Poeciolepis ficoidea, Cotula coronopifolia (gansgras) and Limonium scabrum (sea lavender) dominate with Chenolea diffusa (soutbos), Sarcocornia pillansiae and Sporobolus virginicus (quick grass) at the higher levels.  Any of the above species may become locally dominant to give a patchy effect.  Juncellus laevigatus and Sueda caespitosa were also found at the southern part of the lagoon. (Ref 1)
The saltmarshes around this lagoon, although well-developed, are not extensive.  The limited size of these marshes are due mainly to natural phenomena; however, in some areas, the marshes are subject to human disturbances, especially near recreation areas.  (Ref 1)
Terrestrial vegetation
The terrestrial vegetation of this area can be grouped into five types. 
Primary dune scrub:

This vegetation type is found primarily along the eastern spit with small patches on the northern shore of the lagoon.  The hummock dunes have a sparse covering of Arctotheca populifolia (sea pumpkin), Agropyton distichum (sea wheat). Ammophila arenaria (marram grass) and Tetragonia decumbens (klappiesbrak).  On the primary dunes, the creeping sand binders Ipomea pes-caprae (goat's foot) and Scaevola thumbergii (seeplakkie) are common.  (Ref 1)
Secondary dune scrub:

The secondary dunes are covered by a scrub consisting of Passerina vulgaris (gouna), Metalasia muicata (blombos), Cliffortia ilicifolia, (doringtee), Myrica codifolia and smaller herbs and grasses, e.g. Ehrharta villosa (pypgras), Stenotaphrum secundatum (buffalo grass) and Ficinia lateralis. 

Artificial stabilization has taken place in some areas, especially near the gull colony on the north-eastern spit.  This is done largely by planting Ammophila arenaria.  However, this grass is relatively short-lived and it is recommended that efforts be made to re-establish the scrub species; the easiest method would be sowing seeds. (Ref 1)
Hind dune scrub:

Although this vegetation type might have many species in common with the above, it is generally found in more protected areas, is far denser and can reach a height of up to 3m.  The most common species are Rhus glauca (taaibos), R. crenata, Chrysanthemoides monilifera (bitboubessie).  Sideroxylon inerme (milkwood) and Buddleia saligna (basteroelien) might also be present. (Ref 1)
Fynbos:

The areas north-west and east of the lagoon are largely used for farming.  However, many remnants, and in some areas, relatively large patches of fynbos are still to be found, although these are somewhat depauperate.  Species such as Erica peltata, Anthospernum aethiopicum (cattail) and Thamnochortus glaber dominate.  Although proteoids are not present, this vegetation is typical of coastal fynbos in the area. (Ref 1)
Alien dominated vegetation:

Much of the area around this lagoon is dominated by aliens.  Acacia cyclops (rooikrans) is most prominent and is found with remnants of a thorny riparian scrub forest near the blind end of the lagoon and with remnants of fynbos to the north-west of the lagoon.  A. saligna (Port Jackson) and A. mearnsii (black wattle) are also conspicuous, the latter especially along the lower reaches of the Keurbooms River.  These aliens destroy much of the natural vegetation and these areas become less resilient to natural perturbations such as flooding, dune slumping or blow-out erosion.  It is recommended that aliens be gradually removed from these areas and the natural vegetation allowed to become re-established.  (Ref 1)
Fauna
Zooplankton
According to J Grindley the zooplankton, at the time of his sampling programme in June 1969, was rich with a dry biomass of 2,9 to 108 mg/m3.  Catches with a 36 cm plankton net showed Pseudodiaptomus hessei as the dominant copepod and it is particularly abundant in the reduced salinity water above Keurbooms bridge.  Grindley (in litt.) recorded 39 taxa present in the Keurbooms Estuary in June 1969.  (Ref 1)
A variety of other copepods, amphipods, isopods, shrimps, mysids as well as the larvae of resident fishes and invertebrates are common in night plankton samples.  The mysid Gastrosaccus brevifissura is common and, as mysids are known to avoid small nets, it may for the bulk of the planktonic biomass as in some other estuaries (Day, 1981)  (Ref 1)
Aquatic Invertebrates

There are no extensive rocky areas within the system and an invertebrate fauna typically associated with rocks is scarce.

The bloodworm (Arenicola) and razor shell (Solen) are fairly common on the sand banks on the northern side of the lagoon with a limited distribution north of the Keurbooms/Bitou confluence.  The highest density recorded for Solen is 40 holes/m2 while the maximum for Arenicola is only 1 hole/m2.  The density of the benthic fauna in the mouth region was very low during the ECRU survey, probably due to the high current velocity inhibiting larval settlement and habitation.  

The bivalve Loripes clausus was abundant in most parts of the etuary while speciemns of the green prawn, Penaeus semisulcatus were collected during the ECRU survey.  The occurrence of these prawns is an extension of their recognized distribution range (Day, 1981) where Mngazana in the Transkei is regarded as the southernmost limit.  (Ref 1)
Insects
Insect species associated with the Keurbooms River (Harrison and Agnew, 1962).

  • Emphemeroptera :  Baetidae (Baetis harrisoni, Centroptilum sudafricanum, Pseudocloeon maculosum), Leptophlebiidae (Adenophlebia peringueyella)

  • Trichoptera:  Hydropsychidae (Cheumatopsyche afra ), Heoptiliae (Hydoptila sp.)

  • Ditpera :  Simuliidae (Simulium larvae), Chironomidae

  • Coleoptera :  Elmidae                                                                                                                                                    (Ref 1)
Fish
According to Le Roi Le Riche and Hey (1947), Monodactylus, Barbus and Sandelia spp. were found in the lower reaches of the Keurbooms River while the following freshwater fish species occur in the Bitou and Keurbooms rivers (P Skelton, pers.comm.)

Eastern Cape Redfin (Barbus afer), Slender Redfin (Barbus tenuis), Cape Kurper (Sandelia capensis), Cape Galawias (Galaxias zebratus), Brown Trout (Salm trutta), Longfin Eel ( Anguilla mossambica)   (Ref 1)

Wallace and Van der Elst (1975) found the following species in the Keurbooms Estuary, during sampling for juvenil estuarine fish species along the east coast:

Groovy Mullet (Liza dumerili), Largescale Mullet (Liza macrolepis), Cape Stumpnose (Rhabdosargus holubi), White Steenbras (Lithognathus lithognathus),  Southern Mullet (Liza richardsoni)

The main fishing banks are at the confluence and at the eastern end of the lagoon, while angling above both bridges is poor.  This could be due to the restricted channels under the bridges acting as a deterrent to the fish.  Mullet occur above both bridges and there are stumpnose (Rhabdosargus), Blacktail (Diplodus sargus), Zebras (Diplodus cervinus) and Tenpounders (Elops machnata).   (Ref 1)
Amphibians and Reptiles
A list of reptile and amphibian species has been compiled by A L de Villiers of the Cape Department of Nature and Environmental Conservation.
The species "likely to occur" were only included when it was established that their distribution ranges and habitat preferences coincided with the area and where there were confirmed distribution records in close proximity to the loci in question.  Some of the species listed are not directly associated with the estuaries concerned but are confirmed more to their catchments.  Lizards have been omitted from this list.  (Ref 1)

Frogs:

  • Xenopus laevis (Common platanna)

  • Heleophryne Regis ( Southern Cape ghost frog)

  • Bufo rangeri (Raucous toad)

  • Breviceps fuscus (plain rain frog)

  • Tomopterna delalandii ( Cape sand frog)

  • Rana angolensis (Common river frog)

  • Rana fuscigula ( Cape rana )

  • Rana fasciata (Striped grass frog)

  • Rana grayii (Spotted rana)

  • Cacosternum  boettgeri (Common caco)

  • Cacosternum nanum (Bronze caco)

  • Kassina wealii (Rattling kassina)

  • Afrixalus brachycnemis Knysnae  (Golden leaf folding frog)

  • Hyperolius horstockii (Arum lily frog)                                             (Ref 1)

Snakes:

  • Typhlops lalandei (Pink earth snake)

  • Leptotyphlops nigicans (Black worm snake)

  • Lycodonomorphus rufulus (Brown water snake)

  • Lamprophis aurora ( Aurora house snake)

  • Lamprophis inornatus  (Olive house snake)

  • Lamprophis fuliginosus (Brown house snake)

  • Lycophidion c. capense ( Cape wolf snake)

  • Duberria lutrix (Southern slug-eater)

  • Pseudaspis cana (Mole snake)

  • Amplorhinus multimaculatus ( Cape many-spotted snake) 

  • Psammophylax rhombeatus (Spotted skaapsteker)

  • Psammophis notostictus  (Whip snake)

  • Psammophis crucifer (Cross-marked sand snake)

  • Homoroselaps lacteus (Spotted dwarf garter snake)

  • Prosymna s. sundevallii (Southern shovel-snout)

  • Philothamnus hoplogaster  (South-eastern green snake)

  • Philothamnus natalensis occidentalis  ( Western Natal green snake)

  • Crotaphopeltis hotamboeia  (Herald snake)

  • Dispholidus typus (Boomslang)

  • Dasypeltis scabra  (Common egg-eating snake)

  • Hemachatus haemachatus  (Rinkals)

  • Aspidelaps lubricus (Coral snake)

  • Naja nivea ( Cape cobra)

  • Pelamis platurus (Yellow-bellied sea snake)

  • Causus rhombeatus (Rhombic night adder)

  • Bitis atropos ( Cape mountain adder)

  • Bitis arietans (Puff adder)                                                                  (Ref 1)

Birds
According to Day (1973) the aquatic avifauna is much the same as at other Cape estuaries.  During a brief survey, flocks of Yellow-billed Duck and a few Egyptian geese were observed on the marshes above the Bitou Bridge.  No aquatic birds were seen above the Keurbooms Bridge.  Colonies of gulls and terns nest on the bare sand spit between the northern end of the lagoon and the sea.  Commorants are present but not common and there are fair numbers of waders on the intertidal sands and muds including Curlew Sandpipers, Little Stints, Whimbrels and White and Grey Herons (Day, 1973 unpublished).  Waders are common near the confluence and duck, geese and coot frequent the Bitou marshes. (Day, 1981).  (Ref 1)
A census of numbers and distribution of waders and other birds in the Plettenberg Bay area was conducted by the Western Cape Wader Study Group in January 1979.  The eastern spit contained a large Kelp Gull colony fenced off from the public as part of the Keurbooms Nature Reserve.  Little and Cattle Egrets also breed within the fenced area.  The blind section of the estuary forms a high tide refuge for waders and other birds while the Plettenberg Bay sewage works also supports a good variety of waders.  (Ref 1)
Mammals
 

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