Coastal dune forest pool, Mvoti River catchment, east coast South Africa

_th place in Biotope Aquarium Design Contest 2020

Volume: 220 litres
Dimensions: 120x45x45cm
List of fishes: Coptodon rendalli ,Enteromius trimaculatus, Potamonautes sidneyi, Melanoides tuberculata
List of plants: n/a
Description of decorations: Fine, light coloured sand was used that is approximately the grade, texture and colour of dune sand found in the environment. Dried Phragmites reed stems washed up in nearby river after heavy rains, and used as the reed beds. Various leaves were collected from the forest floor near the water systems, as well as dried seed pods from acacia (Senegalia spp.). All were boiled and soaked prior to use. Wood, bark, and twigs collected from river banks used in the leaf litter. Some of the same Phragmites material from above was used in leaf litter component. Dried palm frond leaf (Phoenix reclinata) was collected from the garden, dried, then soaked. These trees occur within the dune forests.
Description of equipment: Canister Filter – Eheim Classic 250 (2213) 440l/h, LED light strips x2 – one white, one white and blue mix
Water parameters: Unheated aquarium, average 20°C to 22°C going up to 26°C in summer, pH is 7.5, TDS ranges between 200 to 250, gH is 10
Additional info: Water changes at 25% done weekly, algae cleared from glass on the same schedule. Filter cleaned monthly. Run an airstone behind reed beds occasionally to dislodge fine materials for water changes. Leaves occasionally topped up after the Coptodon and Potamonautes consume a fair amount of this material.


Description of the area surrounding the biotope: This biotope is of one of the small stream and pond systems that occur among the coastal dune forests of KwaZulu Natal, South Africa. This particular pool represents calmer water near a reed bed located in the region towards the end of the Mvoti River. These small systems, although close to the sea, are not under tidal influence and represent fully freshwater environments. Such streams either reconnect to larger main rivers, or end blindly. There is often a strong link between the water resources of these systems and the water table of the coastal forest dune environments. The summer rainy season sees increased flow contributed from surrounding water sources.

The Mvoti River itself originates over 190km inland, is fed by several tributary rivers, and terminates at the Mvoti estuary on the coast. Much of the watershed has seen extensive development particularly in agriculture and industry, as well as human settlement, resulting in increased pollution and organic loads in the water. Despite this, it supports a remarkable diversity of aquatic and semi-aquatic life.

Trees surrounding the rivers and pools contribute strongly to the leaf litter layer. The dense plant growth of these forests can strongly shade the aquatic environment, although areas away from the water’s edge often receive much sunlight.

Description of the underwater landscape of the biotope: This environment is towards the end of the course of the river, and as such is low-energy. Streams become slow-flowing, occasionally forming ponds. This is especially true within the coastal forest areas, where fallen vegetation and debris obstruct flow. The slowed water allows silt to settle out, and a leaf litter layer forms over. Reeds and other marginal vegetation do well here. The water often appears very shallow because of the dense silt and leaf layer. Branches, twigs, and wood make up the largest structures in the underwater landscape, with no rocks present. The substrate consists of dune sand – almost like very fine beach sand – where the forest has over time overtaken former beach dunes. A detrital layer covers much of the sand, which itself is covered by a leaf litter in varying states of decay. Where water flow is more prominent, there is less deposition of leaf litter and silt, exposing the underlying dune sand.

Description of the parameters of the habitat: TDS: 380 to 400μS, pH between 6.5 and 7.0, Temperatures can be as low as 14°C in winter to about 26°C in summer, although individual sections may be warmer or cooler depending on the amount of shade received.

The water is usually clear, sometimes with a slight tannin stain. Turbidity increases with summer rainfall and increased incoming water from the nearby larger river. If the leaf litter or detrital layer is disturbed, the water can remain turbid for quite some time.

List of fishes and invertebrates occurring in the nature biotope: Fishes: Coptodon rendalli, Enteromius trimaculatus, Pseudocrenilabrus philander, Oreochromis mossambicus, Anguilla marmorata, Clarias gariepinus, Invertebrates: Potamonautes sidneyi, Melanoides tuberculata, Caridina natalensis, Caridina typus, Non-native fish species found include Xiphophorus helleri, Poecilia reticulata, Micropterus salmoides, and Cyprinus carpio.

List of plants found in the nature biotope: Phragmites spp., Nymphaena nouchali, Non-native: Pistia stratiotes, Salvinia molesta

Threats to the ecology: This coastal habitat is under a number of threats due to being near an urbanized space. Coastal dune forests used to be more widespread, but are now largely restricted to reserves or small, isolated patches. However, the greatest threats come from alien invasive species which have overwhelmed many of these environments. Many non-native fish species, including Micropterus salmoides, Cyprinus carpio, Poecilia reticulata, and Xiphophorus helleri have been recorded from these waterways. These out-compete or prey upon native species, and are more adaptable to human-modified habitats. Additionally, invasive plants have choked out certain areas, especially floating plants like Pistia and Salvinia. These excessively shade the underlying water column and limit productivity within the aquatic environment.

Sources of information:

  1. Freshwater Life: a field guide to the plants and animals of southern Africa, Griffiths et al., 2015
  2. A complete guide to the freshwater fishes of Southern Africa, Skelton, 2001
  3. The current ecological state of the Lower Mvoti River KwaZulu-Natal, Malherbe, 2006

Comments of the members of the jury of Biotope Aquarium Design Contest 2020