Western Cape Rivers - Two Oceans Aquarium · 2014. 4. 25. · 2 Level 2 Volunteer Course: Freshwater Ecosystems May 18, 2013 Fig. 2. Percentage of Fresh Water vs. Sea Water1 Oceans

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Level 2 Volunteer Course: Freshwater Ecosystems May 18, 2013

Freshwater Ecosystems

Table of Contents Freshwater Ecosystems ........................................................................... 1 Western Cape Rivers ................................................................................ 2

How are Western Cape Rivers different to Eastern Cape and Southern

Cape rivers?................................................................................................ 4 Characteristics of a typical Western Cape river such as the Olifants

River. ....................................................................................................... 5 River Health is important for our health ................................................. 7 How do we affect our rivers? .................................................................. 9

Wetlands ................................................................................................... 15 Glossary of terms ................................................................................... 17

Key Concepts Underline or highlight the concepts as you read through the notes.

1. Western Cape River system

Characteristics of

Plants and animals

Threats to river ecosystem 2. Definition of wetlands and estuaries

Importance of 3. Importance of frogs in the environment

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Fig. 2. Percentage of Fresh Water vs. Sea Water1

Oceans

97%

Fresh water

3%

Western Cape Rivers

1. Precious Water Water is our most precious resource, without it the earth cannot continue to sustain life. It might seem that there is an abundance of water on our planet –especially when viewed from outer space - but the amount that humans can drink is very small.

Ninety seven Percent (97%) of the water on earth is found in our oceans with only 3% being freshwater.

11 However, the bulk of this fresh water - 68% of all the freshwater or 2.2% of all the water on

earth – is found in the polar icecaps. This leaves us with only 0.25% in surface water, and 0.74 %, in groundwater, of all the water on earth that is ‘available’ as freshwater for humans to use .

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1 Davies B and Day J (1998) Vanishing Waters p 39

Fig. 1. Percentage Land vs. Water on Earth

Land

30%

Water

70%

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Fig. 3. Distribution of Earth's Fresh Water

Ice

68%

Ground Water

23%

Surface Water

8%

Water in

Atmosphere

1%

Yet all we need do is go to a river, stream or lake nearest our homes or schools to realise that the percentage surface water available for us to drink or use is even less than we first thought.

2. South Africa a semi-desert region. South Africa has very few rivers compared to many other parts of the world. This is due to the low rainfall that we receive annually. The average rainfall in South Africa is approximately 500mm per annum, while the average in Europe is approximately 1000mm per annum.

2 Therefore particularly in South Africa water is our most precious –

and limited – natural resource. Our average rainfall is just over half of the world average which places our country within a semi-desert area. Furthermore rainfall and available water are very unevenly spread across the country 21% of the country receives less than 200mm per annum. This situation is made worse by the fact that our average evaporation rate per year is approximately four times more than our average rainfall per year. This means that four times more water is lost through evaporation than is received as rainfall. The map below shows the different climatic regions in southern Africa.

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The major rivers of the Western Cape are the Berg, Olifants, Breede and Gouritz Rivers.

2 Strahler A N (1975) Physical Geography Fourth Edition.

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How are Western Cape Rivers different to Eastern Cape and Southern Cape

rivers?

Cape Rivers originate in a variety of areas. The various ecological conditions include different: -

gradients of slopes,

climates of areas,

soils and rock formations and

types of vegetation. These varying conditions give rise to different types of rivers. For example types of rivers found include: -

perennial rivers or permanent rivers in the higher rainfall areas of the southern coastal region and eastwards,

seasonal flowing rivers in the winter rainfall area of the southwestern Cape and

non-perennial rivers or periodic rivers in areas receiving sparse rain at any time of the year as are found in the dry regions of the Western Cape.

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The table below compares the general features of the three ‘Cape’ water regions. Table 1: General characteristics of the hydrological (water) regions

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Region name

Flow rate Peak time of flow

Flow type Flood Characteristics

Type of substrate (bottom surface)

Turbidity or appearance of water.

Western cape

During winter the flow is moderate.

July/ August Flow is strongly seasonal Fast flowing Rivers.

River doesn’t stay in flood for long.

sandy

Tea- like /brown/ black in colour.*

Southern cape

Flow is not dependent on a season -Aseasonal.

No distinctive flow peak.

Flow and flood frequency highly unpredictable Period of flood is medium to long

sandy

Tea- like/ Brown/ black in colour.* River is clear and carries cool, acid, ‘black’ waters.

Eastern cape

Moderate to high

November and March

It has more places of slow flow along river.

River stays in flood for longer.

muddy

Warm and turbid, with neutral to slightly alkaline waters.

*Fynbos contain oils called tannins in its leaves to stop animals from eating it. When these leaves are shed into rivers the tannins leach into the ground and water causing the rivers passing through fynbos areas to be brown/ black in colour.

3 Scott H A and Hammond K C D (1984). Cape Conservation Series 5: Freshwater Fishes of the Cape. Cape

Department of Nature and Environmental Conservation, p2 4 Eekhout S, King J M and Wackernagel A. (undated). Classification of South African Rivers, Volume 1. South African

Wetlands Conservation Programme, Department of Environmental Affairs and Tourism p.65 and 56

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Characteristics of a typical Western Cape river such as the Olifants River. The conditions in and around a river changes as one travels from the mountain area where the river starts to the river mouth where it flows into the ocean. To understand these changes and how they affect the type of animals found in that section of a river it may be split into the following parts, the upper reach, middle reach and lower reach.

Activity: Go to the Sappi River Meander Ecosystem. What differences do you see in

these regions in the exhibit? Make notes on the accompanying figure.

Fig. 5. A River Catchment .5

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The following table5 shows how conditions in a river change as you move from the upper reach to the

lower reach of the river.

Table 2: Shows the three parts of a river and the typical conditions found in each.

FACTORS PART 1 UPPER

REACHES

PART 2 MIDDLE

REACHES

PART 3 LOWER

REACHES

Slope

Very steep Less steep Slight slope

Water speed

Very fast Slower Very slow

FACTORS PART 1 UPPER REACHES

PART 2 MIDDLE REACHES

PART 3 LOWER REACHES

Oxygen Abundant 02 (aq) Less 02 (aq) Little 02 (aq)

Width Very narrow Wider

Very wide

Bottom surface Stones/rocks Mainly stones Sand/mud/silt

Soil erosion causes an increase in the suspended particles in the water. The turbidity of the water is increased. This makes photosynthesis difficult because of no or little sunlight penetrating the water. Particles, which sink to the bottom, form a 'woolly' layer on the river bed which has a harmful effect on animal life

Vegetation

Plants are scarce because of harsh action of fast flowing water.

mosses/algae grow on rocks, little/no plankton,

forest / canopy vegetation on river/ stream bank.

algae/plankton in water.

more photosynthesis. plants along water's edge

Lots of water plants /algae /plankton

Bulrushes and reeds (such as palmiet) line the riverbanks.

Deforestation of riverbanks can have a negative effect on animal life, because it damages the habitat.

Sunlight

Very little sunlight per volume of water because of shade from vegetation on banks. Little photosynthesis.

River is more exposed therefore sunlight filters through water. Water is warmer.

Wide river allows more sunlight to filter through water. High rate of photosynthesis.

5 Juta (undated) Environmental Focus 3: Rivers as Ecosystems

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How is this achieved in the SAPPI river ecosystem? Water used in the freshwater part of the ecosystem comes from the municipality, normal tap water. Normal tap water is chlorinated and this may clog the gills of fish, so the water is passed through a carbon filter to extract the chlorine. The filtered water is introduced from the water fall area and over flows into the rest of the parts of the river. No air stones are required as the waterfall provides all the Oxygen needed for the system (exactly as is the case in a usual river system). The temperature of the water is maintained at max of 210 C but may drop to 180 C during winter. The fish in the upper reaches and middle reaches are indigenous to Western Cape river systems and prefer more acidic pH of water. So to lower the pH ( to under 7) of the water Ferric Chloride is added to the water. The water is recirculated in this exhibit and topped up with 60 litres per hour.

River Health is important for our health

A healthy river may provide us with a number of direct and indirect services such as: -

transporting and providing clean fresh water6

providing a suitable place for recreation, such as swimming and having picnics on the riverbank

providing water used for cattle and to irrigate crops. Along some areas of the river fish and reeds are harvested

being part of our cultural and religious beliefs e.g. performing baptisms in the river pools

chemical cycling of detritus and nitrogen

Purifying Water: Rivers are able to absorb a certain amount of pollution. The river vegetation along the banks of the river performs this function. The self-cleaning ability of rivers if protected can save thousands of rands that would otherwise have been spent on water purification plants.

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Reducing soil erosion: Dense vegetation on riverbanks slows or prevents soil erosion and the loss of topsoil.

6 www.csir.co.za/rhp/state_of_rivers/state_of_umgeni

7 Juta (undated). Juta: Environmental Focus 4: River systems and their ability to recover

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Indicators of River Health South Africa in an effort to better manage existing rivers has established the South African River Health Programme (RHP). This programme focuses on selected animal groups that represent the larger ecosystem.

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The RHP assessments are:- 1. Fish Assemblage Integrity Index (FAII) Fish are good indicators of long term influences by humans on a section of a river and the condition of its habitat, because fish live for a longer period of time than invertebrates and are more mobile.

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The absence of frogs and other amphibians from our wetland and river systems should serve as a warning to us that the system is not healthy. Frogs respire through their skin and are susceptible to chemical pollution in our freshwater systems. So if frogs are disappearing then soon we may too…….(see more on Frogs on page 16)

2. South African Scoring System (SASS) is a scoring system that is based on the presence of certain families of aquatic invertebrate present at a site. Invertebrates need specific types of water habitats and water quality conditions for part of their life cycle. Some of these invertebrates are unable to live in water of poor quality while others flourish in such conditions. The presence or absence of these indicator invertebrates is a sign of changes in the overall river condition. These are good indicators of the conditions of a section of river over a short-term for example a few months.

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Table 3: The scoring system of mini - SASS

You can assist the river managers by studying rivers close to your home or school by using the mini SASS scoring system. This system helps to identify which rivers are of concern, which rivers may need further monitoring. You could download or print the sample sheets from the following website: - www.riverhealth.co.za.

http://www.riverhealth.co.za/

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How do we affect our rivers? All human activities within a catchment indirectly or directly drive changes in the health of a river

6 . See

picture below.

a) Alien vegetation is thirstier than fynbos

Trees such as Black wattle, Port Jackson and Sesbania are alien to the Western Cape introduced from Australia to stabilize the sand dunes. They grow well in the riparian zone. These plants disperse their seeds into the stream resulting in rapid infestation of the riverbank downstream over a few years. These tall alien trees are also much thirstier than fynbos and need more water to grow. Thus an area infested with alien plants will produce less runoff water

8 and reduce river flow. These impacts on river

and wetland ecosystems, translating into less water in dams for agricultural, industrial and domestic use. Alien plants form a poor groundcover leaving a lot of soil uncovered. The uncovered soil is easily eroded thus rainwater runs off too quickly to soak into the soil. This runoff of water also results in the erosion, collapse and flooding of riverbanks.

3

Fires in alien vegetation are more intense than fynbos fires. The flames in alien fires can reach up to 15m high. The subsequent rains wash all the exposed soil into rivers or down the slope of mountains causing mudslides as experienced in the Cape Peninsula 2 years ago. These mudslides cause rivers and dams to fill up with sand thus reducing the space to store water.

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8 Cape Nature Conservation and Department of Water Affairs and Forestry (1996) Mountain Catchment area pamphlet

9 Working for Water (undated). What is an invading alien plant? Working for Water programme leaflet.

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Solution: Clearing these mountain catchment areas of alien

vegetation can increase water yields by more than 30%. Removing these trees, which ‘drink ‘ up the majority of the water, is far more affordable and environmentally friendly than building new dams.

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Disrupts ecosystems Fishes and invertebrates in these systems exist mainly on a detritus food web. Removal of natural fynbos vegetation can seriously disrupt these food chains as these fish and invertebrates rely on the leaves that fall into the rivers for food. A change in the type of vegetation, for example alien trees, can change the colour, amount of organic load of the water and the type of food source.

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For example, fynbos sheds its leaves mostly in summer, providing food during this period for the various animals and microorganisms living in the river. Alien trees, mostly from Europe, shed their leaves in a single pulse during autumn. The bulk of the food is therefore not available at times when it is ‘expected’ by the animals. And they can’t cope with this overload of food source at one period.

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The peak flow of Western Cape rivers is during winter- this means that all the leaves of alien trees are washed down into the lower parts of the rivers and could cause a blockage of the river course and flooding.

Aquatic alien plants such as Water hyacinth and Parrot feather are both South American natives

and are major economic pests. Water hyacinth for example prevents recreational activities such as boating, skiing and angling by blocking the river flow making it impossible for boats to pass through. Water hyacinth disrupts the water flow in irrigation channels and it block sluices creating conditions for malarial mosquitoes and bilharzia carrying snails to breed.

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Invasive alien vegetation blocks river courses and increases flooding while most indigenous river plants are adapted to occasional flooding and are able to bend with the water. These dense mats reduce light penetration into the water, reducing phytoplankton production and impacts on the rest of the ecosystem.

b) Introducing alien fish

Alien fish are fish that have been introduced from a different area or country - a species that doesn’t belong naturally in an area.

3

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Gigher I G, Hammon K C D and Thorne S C (1980) The Distribution, conservation status and factors affecting the

survival of indigenous freshwater fishes in the Cape Province.

Water Hyacinth Parrot feather

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Introducing alien fish into rivers is the second largest threat to the survival of many of the world’s 10 000 freshwater fish species.

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In the past indigenous fish were thought to be unsuitable for angling and eating. Therefore species such as trout and black bass were imported from Europe and North America for recreational angling. Table 4: Examples of Indigenous fish species

12 13

and their ecological status

For further information read the following:- Envirofacts 22: Freshwater fishes

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Cambray J (2003). Science in Africa: Africa’s first On-line Magazine. Alien alert: the aliens are here! So are the

ecotourists. 12

Skelton P (2001). Freshwater Fishes of Southern Africa 13

Garrow C. and Marr S. (2012). Swimming on the Edge of Extinction

Name of fish Picture Status Why is it threatened

1. Clanwilliam redfin

Vulnerable

Habitat is reduced. Introduction of predatory fish and excessive water abstraction

2. Cape Kurper

Found in southern and south western Cape rivers

Threatened Habitat destruction and introduction of alien fish species e.g bass, sharptoothed catfish and rainbow trout

3. Clanwilliam sandfish

Live in clear pools in Olifants river - only found here. May migrate upstream to breed

Critically Endangered (50% probability of extinction within 5 years or 2 generations)

Dams block breeding migration of fish Reduced water flow and introduction of alien fish

4. Clanwilliam sawfin

Endangered Introduction of bass, habitat destruction and dam obstructions

5. Clanwilliam yellowfish

Only found in slow flowing regions of Olifants river. Migrate upstream to

spawn

Vulnerable (10% probability of extinction in 100 years)

Construction of dams, abstraction of water and introduction of bass

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Table 5: Examples of alien fish

3 to Western Cape rivers include:-

(The names of the fish in bold are found in the lower reaches of the Sappi River Ecosystem)

Unfortunately these alien fish species are mostly carnivorous and indigenous fish soon fall prey to these efficient predators, as the indigenous fish had developed in systems where such carnivores were absent.

3

These alien fish may have positive attributes. However in the absence of natural limiting factors such as diseases or predators they spread and displace indigenous fishes of that area.

3

With the ever-present threat of drought, water is transferred from catchments with good water supplies and low water demand to those where demand for water is high and the supply is poor. This results in mixing of fish species from these two different river systems. Such introductions result in indigenous fish from one river system becoming ‘aliens’ in their new habitats.

Name of fish Picture Country / continent it originates from

Threat to ecosystem

1. Large mouth black bass

Central and Eastern America

Mainly a fish eater but will eat anything including crabs, frogs, snakes and small mammals

2. Rainbow trout

North America introduced via England -sport angling in 1897

Opportunistic feeder preys on insects, crabs, fish and frogs.

3. Bluegill sunfish

Declared noxious because of its potential to overpopulate rapidly

4. Carp Europe Breeds rapidly and its bottom feeding habits make natural waters very muddy

5. Small mouth black bass

Central and Eastern America

Preys heavily on indigenous fish

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c) Farming practices

Poor farming methods such as overgrazing and ploughing down a slope can cause excessive erosion of the lands. Erosion of large farming areas may result in a build up of silt in rivers, which in turn affects the spawning beds of fish and may lead to flood damage during heavy rains. Some farmers enrich their lands with fertilisers – nutrients- in order to increase crop yields. A large proportion of these nutrients is either washed off the soil into rivers or leaches through the soil into the ground water and then into rivers. On reaching the rivers these nutrients are as effective in increasing plant production as they are on land. When present in excess, they stimulate the development of blooms of algae and floating pest plants. This build up of nutrients in a river is called eutrophication. [(see page 9 a) Introducing alien plants]

d) Water extraction

Water is pumped out of rivers and used for irrigation, industrial processes and domestic purposes.14

This is particularly devastating during the hot summer months of the Western Cape when farmers remove water from already depleted rivers.

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This may lead to :-

sections of the river drying out and many fish and other animals dying.

an increase in salt concentration (salinity) of freshwaters.11

an increase in the effects of pollution by concentrating pollutants. e) Damming of rivers

Dams restrict the movement of migrating fish ( page 11, Table 4 Indigenous fish) and break populations into smaller units, which are then more susceptible to other threats such as pollution or sedimentation. The quantity and timing of flows in a river are critical to the maintenance of the ecosystem. Low flows may influence the diversity of species or trigger spawning in fish, while flooding might flush out poor water and trigger migration of fish and germination of seeds. Dams prevent a river from flowing and thus change these environmental cues on which some organisms rely and change the riverine habitat from flowing water to still water.

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If we use water wisely there may be no need to build more dams. f) Habitat damage

Where development results in habitat changes certain animals may not return to that part of the river even after the disturbance has stopped.

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Share net (1999) Envirofacts 22: Freshwater fishes 15

Major N (2001). Notes from Two Oceans Aquarium Volunteers Freshwater fish Workshop

Did You Know! In the SAPPI river system ecosystem the alien fish include Carp, large mouth black bass and Sharptoothed catfish and are in the lower reaches. The alien freshwater fish are fed once daily with khoi or flake fish food. The Sharptoothed catfish is fed twice a week with mullet. The indigenous freshwater fish are in the upper and middle reaches of the exhibit. They are fed twice daily with flake food, crickets and mealworms.

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Examples of these kinds of changes are draining of wetlands, canalisation of riverbeds, or removal of vegetation on banks and margins. For a river to function naturally with a diverse animal and plant community, a number of different habitats are needed.

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Canalisation

The purpose of canalisation was originally to prevent flooding of properties in low-lying parts of the catchment and to route stormwater in the most direct (and rapid) way out of the area. The bed and banks of a natural river is replaced with virtually smooth concrete on which no organic material can be trapped and therefore few animals live in these canals. Such stretches do no more than channel water from source to sea or discharge point.

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Solution: A better way of managing or rehabilitating a riverbank is to use gabions (stone filled baskets). The gaps facilitate plant and animal growth and therefore maintain a natural habitat. Drilling one metre holes through the bottom of the canal reconnects the river with its sediment. This allows for the accumulation of organic and inorganic material in the cores and some of the natural functioning of the river and its organisms to redevelop. These functions include decomposition of decaying material, shelter for invertebrates during flooding and habitat for burrowing animals’.

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i) Pollution

Water pollution occurs when chemicals or nutrients enter water faster than natural processes can remove it. Pollutants include: sewage, oil, silt, industrial chemicals, heavy metals, air-borne man-made chemicals dissolved in rain water, pesticides, fertilisers and herbicides leached from the land.

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Water pollution comes from ‘point’ and ‘non-point’ sources. Point sources include pipe outlets and other direct and observable sources of pollution. These sources may be easily identified and controlled. Non-point sources include acid precipitation and the run-off of fertilisers from large farming areas. These pollution sources are less easy to identify and control.

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Litter itself is seldom seriously damaging to water environments unless it is in such a large quantity to physically damage aquatic habitats.

1 Litter such as plastic bags, paper, cooldrink tins etc. in rivers

are unsightly, especially because it takes years to decompose if at all.

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Shelembe E B (1995). Monitoring Visible Water Life.

A canalized river

A river with Gabions

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Wetlands

1. What are wetlands?

__________________________________________________________________________

2. The three important characteristics or features of wetlands are:- ____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

Summary of importance of wetlands

1. _______________________________________________________________________________

2. ________________________________________________________________________________

3. ________________________________________________________________________________

4. ________________________________________________________________________________

5. ________________________________________________________________________________

6. ________________________________________________________________________________

7. ________________________________________________________________________________

8. ________________________________________________________________________________

9. ________________________________________________________________________________

Further reading : Envirofact sheet 2: Wetlands and Envirofact sheet 3: Estuaries

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Why are Frogs important?

1. Amphibians are the only group of animals able to truly live and exploit both aquatic and terrestrial environments. [The word amphibian is derived from two Greek words viz. amphi meaning double and bios

meaning life hence ‘living a double life’] 2. Amphibians are extremely interesting animals. They are also extremely varied, showing a tremendous range of shapes, colour patterns, behaviour, different vocalisations, breeding habits and habitats. They live in habitats that range from mountain tops to lowland wetlands and extremely arid deserts to humid forests. 3. Amphibians form a very important part of the food web, especially in wetlands.

Tadpoles eat large quantities of algae, which makes them primary consumers or herbivores. The tadpoles are in turn eaten by dragonfly larvae, fishes or waterbirds. Conversely the adults are secondary consumers or carnivores eating large quantities of insects and other invertebrates. This makes them useful animals for use as biological controls. So would you notice if there were no more frogs? Frogs in turn are food for fish, waterbirds, snakes, monitor lizards, young crocodiles and otters. Interestingly the eggs are protected from predators by toxins and do not form part of the food chain.

4. Amphibians act as monitors of water quality and general environment quality/early ecological warnings. Frogs are sensitive to various pesticides (e.g. DDT used in malaria affected areas), fertilizers and pollutants .If frogs have contact with any of these they die. Severe decline in amphibian population world wide may be due to increased acid rain, global warming, ozone depletion, pollution AND increase in urbanisation which has reduced natural habitats such as wetlands. Ozone depletion has resulted in an increase of ultraviolet light. An increase in UV light has caused the chytrid fungus to grow on frogs’ skin. The frogs are now unable to breathe through their skins, suffocate and die on a large scale. Instances of chytrid fungus have been discovered on frogs in Panama, South America as well as in Australia.

5. Amphibians are walking pharmaceutical factories, the skins producing, amongst other things,

antibiotics and painkillers. [They do not have to be killed to extract these chemicals] 6. The amphibian the platanna or African clawed toad was used as a human pregnancy test from

1933 and was only abandoned in the 1960s.

[A female plattana would produce eggs if injected with a little urine from a pregnant woman].

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Glossary of terms

Alien species

A species which has been introduced from another area or country; a species that doesn’t belong naturally in an area.

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Bilharzia

Bilharzia is a waterborne disease caused by parasitic flatworms. It is spread when an infected person urinates in river water.

Bio indicators

Animals which are used as an indicator of river health or pollution.

Bio Pollution

Introducing animals or plants to an area where they are not normally found.

Deforestation

Clearing of forests

Detritus

In ecological terms, the remains, often pieces, of plants and animals

Endemic

Animals found nowhere else but in a specific area. This term is used for species within a restricted range.

Eutrophication

A build up (excess) of nutrients

Groundcover

Low-growing, spread plants that help to stop weeds growing.

Indigenous

One which occurs naturally in the area it is found, i.e. its natural home range

Intercatchment link or Interbasin transfer

The transfer of water from one catchment area to another by means of tunnels and canals

Invertebrates

Animals which don’t have a backbone or internal skeleton

Non Perennial

Referring to a river which does not flow all year round.

Nutrients

Elements needed for life processes e.g. nitrogen, phosphorous and potassium are the most important nutrients.

Perennial

Refers to a river which flows all year

Riparian

Refers to a river bank

River Catchment

It is all the land from the mountaintop to seashore, drained by a single river and its tributaries.

Siltation

This is a buildup of sand or mud in either rivers or dams.

Turbidity

The immediate visual effect of a change in water is a change in water clarity. In other words the degree of visibility in water

Western Cape Rivers - Two Oceans Aquarium · 2014. 4. 25. · 2 Level 2 Volunteer Course: Freshwater Ecosystems May 18, 2013 Fig. 2. Percentage of Fresh Water vs. Sea Water1 Oceans

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