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Biogeography of Platberg, Eastern Free State, South Africa:

Links with Afromontane Regions and South African Biomes

131

change, CO

level fluctuations, fire and grazing are all responsible for the present day

species richness and diversity recorded on Platberg and its parent vegetation of the

Drakensberg. The Grassland Biome in South Africa is second largest of all eight Biomes (354

593.501 km²) after the Savanna Biome (412 544.091 km², Mucina & Rutherford 2006), with

both Biomes providing an enormous sink for Carbon as well as climate amelioration.

Between 30–55% of the Grassland biome has already been transformed with only 5.5%

protection. Grassland is under significant threat of continual transformation, the most severe

is ploughing, which disrupts the soil and releases not only moisture, but also nutrients and

Carbon (Mucina & Rutherford 2006).

Fig. 8. Platberg showing tracks of the major floristic influences (modified from Rutherford &

Westfall 1994).

Undisturbed grassland provides a significant Carbon sink, and should thus be given priority

status for conservation, which should include both the above ground and belowground

grass and soil ecosystems (Retallack 2001).

Historically in South Africa, areas for conservation were not selected primarily for ecological

reasons until the mid 1970’s (and then only in the Cape), but were rather based on other

criteria, such as national strategically protection of the watershed around dams; fragmented

forest areas to protect the water sources higher up in the mountains, or politically

determined boundaries such as the Kruger National Park. It was only between 1971 and

1982 in the Cape, that a few wilderness areas were established for scientific research in

natural ecosystems, aesthetic values they engendered and physical and spiritual

opportunities they afforded (Rebelo 1992). Biogeographical considerations such as fynbos

being ‘islands’ surrounded by forest were used as well as critical plant population size and

habitat. These parameters plus total land surface were selected in determining conservation

areas. It was found that for mountain areas, the minimum statuary size for reserves should

be at least 10 000 ha (Rebelo 1992). Human population growth and increased urbanisation

are seen as two major threats to natural ecosystems, with the implications for conservation

of the effects of unrestricted human population growth being considered (Rebelo 1992;

Ferrier 2002).

Biodiversity Loss in a Changing Planet

132

The scale of human impact on the biogeographical distribution of plants and animals will

only continue to grow globally, but specifically in Africa, with the continued existence of

many plant and animal species more dependant on human social, rather than on physical

environmental factors (Meadows 1996; Anderson et al., 2001; Mutke et al., 2001). The

African landscape, in particular East Africa, has had a long history of influence by humans,

i.e. the Savanna and Grassland Biomes (Meadows 1996). Globally, and in the context of the

use of resources and climate change in Africa, the human species now exerts an influence on

all other species of organism, which in its scale and intensity is critical in the future

evolution of the African flora and fauna (Kingdom 1989; Meadows 1996; Anderson 2001;

Mucina & Rutherford 2006).

The conservation value of Platberg is significant: is a link between high altitude C

grasses

and lowland C

grasses. It is also the best-preserved continuous high altitude grassland

within the Grassland Biome and has escaped agricultural activity which giving the site a

unique status, and leaves enormous scope for future research (Smith & Young 1987).

Platberg is an excellent natural history laboratory, which connects the present day

environment with geological, palaeo-environmental and evolutionary processes from

modern Holocene to Jurassic times (Scott et al.1997; Anderson 2001; Linder 2003; Mucina &

Rutherford 2006).

9. Acknowledgements

National Geographic (Grant number 7920-05) for the generous funds without which the

fieldwork and the study would not have been possible.

Snow on Platberg, Figure 4. Kind permission of Theunis Bekker.

Figure 8, Wetlands on Platberg is courtesy of Nacelle Collins.

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Biodiversity Loss in Freshwater Mussels:

Importance, Threats, and Solutions

Trey Nobles and Yixin Zhang

Department of Biology, Texas State University, San Marcos, Texas

The United States of America

1. Introduction

The loss of biodiversity worldwide has been well documented for decades, and while much

of the attention of the media and scientific community has been focused on terrestrial

ecosystems, other biomes such as freshwater lakes and streams have received less

consideration (Myers et al., 2000). Despite the current decade (2005-2015) being declared an

International Decade for Action – ‘Water for Life’ by the United Nations General Assembly,

freshwater ecosystems worldwide are as threatened as ever by the activities of a rapidly

growing human population. Surface freshwater ecosystems only constitute 0.8% of the

Earth’s surface, yet they contain almost 9.5% of the Earth’s known species, including as

many as one-third all known vertebrate species (Balian et al., 2008; Dudgeon et al., 2006).

The impact of human disturbances on this disproportionate amount of biodiversity has

made the extinction rate in freshwater ecosystems equal to that of tropical rainforests

(Ricciardi and Rasmussen, 1999).

1.1 Freshwater ecosystem services

Because we depend on water both as a biological necessity and for the myriad of resources and

services it provides us, over half of the world’s population lives within 20 km of a permanent

river or lake (Small and Cohen, 1999). Direct benefits and ecosystem functions of freshwater

lakes, streams, and wetlands include providing sources of water for municipal and industrial

use, irrigation, hydroelectric power generation, transportation corridors, recreation, and

producing fish and other resources used for food and medicine. Freshwater ecosystems also

provide many indirect ecosystem services such as water filtration, buffering against storms

and flooding, cycling of nutrients and organic matter through the environment, and

supporting ecosystem resilience against environmental change (Aylward et al., 2005; Jackson

et al., 2001). These indirect ecosystem services have very real economic values. One study

valued the ecosystem services of freshwater aquatic ecosystems worldwide at $6.5 trillion

USD, or 20% of all the world’s ecosystem services (Costanza et al., 1997).

As human populations continue to develop aquatic resources to maximize a few of these

anthropogenically beneficial services such as water storage, generation of electricity, and

fish production, other environmental services that are less directly important to humans are

being reduced or lost (Bennett et al. 2009). The reduction of these ecosystem functions can

significantly alter an ecosystem’s natural character. After more than a century of

Biodiversity Loss in a Changing Planet

138

unprecedented human population growth and global economic development, we have

created widespread and long-term ecological disturbances to freshwater ecosystems in

almost all parts of the inhabited world (Strayer and Dudgeon, 2010).

Table 1. Ecosystem services provided by freshwater lakes, rivers, and wetlands (after Postel

and Carpenter, 1997).

1.2 Human disturbances to freshwater systems

Humans now capture more than 50% of the world’s precipitation runoff behind dams for

electricity generation and water storage, and through diversion canals for irrigation. 16% of

all runoff is consumed, or not returned to the rivers after use, while the remainder of the

captured runoff is returned but with altered timing, amount, and quality (Jackson et al.,

2001). Water pollution, including siltation, is endemic to almost all inhabited parts of the

world and is consistently ranked as one of the major threats to freshwater ecosystems

(Richter et al., 1997). Pollution in aquatic ecosystems not only consists of chemical toxicants

like heavy metals, industrial waste, and pesticides, but also includes excessive nutrient

enrichment and pharmaceuticals and personal care products (PPCPs) (Jobling and Tyler,

2003; Smith et al., 1999). Habitat loss and habitat degradation are also major reasons for

worldwide biodiversity loss in aquatic ecosystems, and are caused by a multitude of

anthropogenic disturbances (Allan and Flecker, 1993; Richter 1997 et al. 1997). Many

freshwater species are also being overharvested for human consumption or the pet trade.

This affects mostly vertebrate species, especially fishes, but can impact invertebrate species

like mussels and crustaceans as well (Dudgeon et al., 2006). The threat of global climate

change is pervasive across all of the Earth’s ecosystems, and is also often cited as a major

threat to freshwater biodiversity (Sala et al., 2000; Strayer and Dudgeon, 2010).

All of these environmental disturbances alter the “natural” chemical, physical, and

biological patterns of a system, and when those conditions are changed, both the absolute

and functional biodiversity of that system can be threatened. This loss of biodiversity can in

turn create a feedback loop that further alters ecosystem functioning. The theory that

ecosystem services depend on the biological diversity of the system is well supported for

terrestrial ecosystems (Kinzig et al., 2002; Loreau et al., 2001), and recent studies have shown

that maintaining biodiversity in aquatic ecosystems is crucial to the continued functioning of

ecosystems and the delivery of ecosystem services as well (Covich et al., 2004).

It is widely accepted that freshwater ecosystems worldwide are suffering from a

“biodiversity crisis”, with estimates of 10,000-20,000 species currently extinct or threatened

Biodiversity Loss in Freshwater Mussels: Importance, Threats, and Solutions

139

(Abell, 2001; IUCN, 2007; Strayer and Dudgeon, 2010). While almost all taxonomic groups of

freshwater organisms are facing unprecedented declines, some groups are especially

affected.

Fig. 1. Conservation status of selected groups of terrestrial and freshwater organisms using

NatureServe conservation status designations (after Master et al., 2000).

2. Freshwater mussels: North America’s most threatened animals

Of all groups of threatened aquatic animals, freshwater mussels (also known as unionid or

pearly mussels) are the most imperiled, with 67% of North American species considered

threatened (Williams et al., 1993). 35 North American freshwater mussel species have gone

extinct since 1900 (Williams et al., 1993), and some scientists have estimated a 1.2% per

decade extinction rate for this group, with others predicting that unless effective

conservation action is taken 127 more species will become extinct over the next 100 years

(Ricciardi and Rasmussen, 1999).

2.1 Classification of freshwater mussels

Freshwater mussels (order Unioniformes) belong to the subclass Paleoheterodonta, class

Bivalvia, and phylum Mollusca. A total of 18 bivalve families have at least one species found

in freshwater, although only about 9 have radiated to any degree there (Bogan, 1993). The

order Unioniformes contains the largest number and diversity of groups with 180 out of 206

genera and 797 out of 1026 species. Within the Unioniformes, the family Unionidae is the

largest, comprising nearly 80% of both the genera and species within the order (Bogan and

Roe, 2008). Other important families include Hyriidae (17 genera, 83 species),

Mycetopodidae (12 genera, 39 species), Sphaeriidae (8 genera, 196 species) (Bogan and Roe,

2008). As the order Unionidae is the most diverse, and has had the most research dedicated

to it, we shall from here on out refer to freshwater mussels simply as Unionids, or unionid

mussels.

Biodiversity Loss in a Changing Planet

140

2.2 Freshwater mussel distribution

Freshwater mussels are found on every continent with the exception of Antarctica, but reach

their highest level of diversity in the Nearctic geographic region, with one-third of all

species (297 recognized taxa) being found there (Bogan, 2008). The Neotropical region has

179 described species, the Oriental has 121, the Palaearctic 92, the Afrotropical 74, and the

Australasian region has 29 (Bogan, 2008). Data on the conservation status of freshwater

mussels globally is incomplete, with relatively strong data from only a few areas (North

America, Europe, and Australia). In other areas (Africa and South America), detailed

taxonomic information including the total number of species currently or historically

present is lacking, which makes determining changes in species abundance and richness

difficult (Bogan, 2008). There has been increased interest in the biodiversity of freshwater

mussels worldwide over the last few decades, though, as scientists have realized just how

rapidly this group is declining (Graf and Cummings, 2007). Hopefully this increased

awareness will lead to more surveys in these understudied areas to fill in the gaps in basic

knowledge that currently exist.

Family Genera Species

Order Arcoida

Order Mytiloida

Order Unioniformes

Order Veneroida

Order Myoida

Order Anomalodesmata

Arcidae

Mytilidae

Etheriidae

Hyriidae

Iridinidae

Margaritiferidae

Mycetopodidae

Unionidae

Cardiidae

Corbiculidae

Sphaeriidae

Dreissenidae

Solenidae

Donacidae

Navaculidae

Corbulidae

Erodonidae

Teridinidae

Lyonsiidae

142

620

196

Total 209 1026

Table 2. Classification of freshwater mussels (6 orders and 19 families), including number of

genera and species for each family (after Bogan, 2008).

2.3 Endemism and conservation

One of the major reasons for the high proportion of extinct and endangered freshwater

mussels is the high degree of endemism found in this group, which is characteristic of many

freshwater organisms. Endemic species have a limited geographical range, often limited to a

single drainage basin or lake, and often have unique characteristics suited to that particular

locale (Strayer and Dudgeon, 2010). Local rarity also puts a species at a much higher risk of