EXAMINING CATCHMENTS AS FUNCTIONAL UNITS FOR THE CONSERVATION OF RIVERINE BIOTA AND MAINTENANCE OF BIODIVERSITY
Report No: 975/1/02
Motivation and Research Objectives
This project has arisen from a number of developments in the conservation and management of water resources. These include the shift toward catchment management philosophies and practices, articulated and reflected in the development of the new South African Water Act of 1998, and the findings and concerns raised by WRC project K665/1/00 reported in Snaddon and Davies (1999). In the first instance, the new Water Act of 1998 gives full powers to the Minister of Water Affairs and Forestry to transfer water from river basins with perceived surpluses to basins and human populations with perceived water deficits. Such transfers can only be achieved by means of a wide variety of inter-basin water transfers (IBTs), a rapidly expanding technology in South Africa. Concerns about the impacts of IBTs on river basin integrity, in terms of faunal and floral biodiversity, were first raised by Petitjean & Davies in 1988. The concerns were subsequently pursued by Davies et al. (1992) and finally, through the research of Snaddon & Davies (1998, 1999) and Snaddon et al. (1998, 1999), the problems surrounding the genetic integrity of historically isolated river basins and populations and the maintenance of biological processes were first quantified. It was clearly demonstrated that a wide variety of viable organisms could unwittingly be transferred across natural catchment divides via IBTs. In order to address the findings of these researchers and the implications of IBTs for catchment management, and the ultimate conservation of riverine biodiversity, research was initiated to assess the genetic integrity of catchments as management units. The primary object of the research was to quantify the degree of congruence between catchments as management units and natural populations of a variety of riverine organisms.
Following recommendations arising from the first steering committee advising the project reported here, the original aims and objectives were modified in order to broaden the scope of the research and the relevance of the results for management action. The modified objectives of the programme are:
Achievement of Objectives
The results allowed all of the objectives to be suitably addressed, whilst also providing a large amount of additional information on the distribution of genetic and organismal biodiversity in the aquatic fauna of the south-western Cape region.
Considering the management implications and the development of a protocol for assessing the effects of IBTs (Chapter 8) the results highlight the suitability of two species for use as target species in future assessments of the degree of genetic separation of historically isolated catchments -the net-winged midge, Elporia barnardi (Chapter 5) and the Cape galaxiid, Galaxias zebratus (Chapter 4).
For some organisms, catchments represent the primary unit within which movement and dispersal is confined (Chapters 4 and 5). For other more mobile organisms, populations effectively cover a wide geographic area that encompasses a number of different catchment units (Chapter 7).
With regard to the last of the specific objectives, collaboration and work was undertaken at each of the institutions. In addition, the project was officially listed as an associated project (B803) within the Restoration Ecology Programme of the Co-operative Research Centre for Freshwater Ecology (CRC FE) in Australia.Capacity Building and Collaboration
The Water Research Commission has recognised the need to incorporate the development of South Africa's capacity as a part of its research projects. Whilst not part of the initially aims or objectives of this project, we feel that we have undertaken a number of activities that have contributed to the development of personnel and information that will enable South Africa to develop and enable future conservation and management strategies within a sustainable framework. As such we have been involved in:
Our hypothesis was that catchments as biogeographically distinct units would isolate riverine populations, depending upon the dispersal characteristics of each species within a particular community of riverine organisms. Those species with poor powers of dispersal would thus tend to be genetically different from related populations in other catchments, whilst those species with robust dispersal characteristics (strongly flying insects, for instance) would show little genetic differentiation in separate catchments. Quantification of such divergences or similarities would then allow us to establish:
The four organisms selected reflected a wide range of dispersal characteristics. They are:
Samples of these organisms were taken from two discontinuous regions -three streams on the Table Mountain massif, and a number of streams in the 10nkershoek catchment of the Hottentots Holland mountain range north of Stellenbosch -based on the assumption that the movement or organisms between catchments will be reflected in the genetic structure of their populations. In order to ascertain degrees of genetic similarity or divergence, some 30 to 50 organisms were genetically analysed using allozyme electrophoresis and direct sequencing of a targeted section of mitochondrial DNA (mtDNA).
The results of the research revealed the following:
Over and above these findings we discovered a high degree of diversity and genetic divergence within species - the Cape galaxiid, the net-winged midges and the stoneflies - all of which had been thought to be single species. This begs further research and illustrates the fact that the Western Cape is not simply a botanical biodiversity "hotspot", but that in-stream faunas are also rich in endemics. The long period of geological and climatic stability and the isolation of individual catchments has resulted in a unique assemblage of aquatic organisms, many of which remain undescribed and/or undetected. This has obvious implications for management as individual catchments seem to be exhibiting unique signatures in terms of their species complements and genetic structure. In addition:
Recommendations for IBT Planning and Management
In light of the results, and South Africa's national and international obligations, the following recommendations are made with reference to the design of a conservation strategy for riverine biodiversity and specific consideration of the implications of inter-basin water transfers. Further to this, the report serves as a statement of consequence, providing an iteration of the facts and the implications of certain actions, or non-actions, on future conservation strategies. The onus of responsibility for incorporating such considerations into practical management decisions lies with the decision makers and will invariably need to incorporate compromises between conservation considerations and the practical constraints of meeting supply requirements. As such we recommend that:
Statement of Consequence
The information contained within this report suggests that the development of water resources could have very serious effects on the future conservation of aquatic biodiversity. Obviously such concerns need to be carefully weighed against national needs for water. The final decisions and onus of responsibility clearly lie with water resources planners and decision makers; specifically the ministers and departments of Water Affairs and Forestry, Environmental Affairs and Tourism and Mines and Energy Affairs. Therefore, in addition to the specific recommendation, the information contained in this report serves as a statement of consequence.
For some species, the development of IBTs will provide a conduit for the transfer of individuals between geologically separated catchment units and historically isolated populations. The transfer of individuals from such historically isolated populations has the potential to undermine the evolutionary processes important in species formation and thus the generation of biodiversity by providing an avenue for gene flow between genetically discrete populations. As a signatory to a number of international treaties addressing the conservation and management of biodiversity, there is a framework and obligation to take necessary mitigatory measures to ensure the protection of such components of biodiversity for the long-term sustainable utilisation and protection of the countrys' natural heritage.
For other, more mobile species, the distribution of genetic variation and pattern of population sub-division indicates that the effective population covers a wide geographic range. As such IBTs between adjacent catchments would not have an impact on these species. However, it should be noted that there are a number of existing IBTs that transfer water over huge distances from catchments far removed from each other. While beyond the scope of this project, such IBTs may have implications for conservation with the transfer of individuals across different biogeographical zones. Such lack of genetic population structure does have other conservation and management implications. An interbreeding, homogeneous population structure across a wide geographic area would suggest that catchment units may not represent the appropriate scale for conservation of the aquatic fauna.
From the distribution and patterns of genetic variation reflected among these organisms, efforts at conserving the fauna of riverine ecosystems should move beyond individual catchment considerations to incorporate the design of protected areas and management strategies that cover and incorporate a number of adjacent catchments. Such areas or management plans should be replicated and spread through identified biogeographic regions.
The idea of the Precautionary Principle is being afforded increasing recognition, having already been incorporated into many international conventions and national legislations. It would therefore seem prudent to incorporate such considerations into the development of conservation strategies. From the distribution and patterns of genetic variation reflected among the taxa examined, efforts at conserving the fauna of riverine ecosystems should move beyond individual catchment considerations to incorporate protected areas and management strategies that cover and incorporate a adjacent catchments. Such areas or management plans should be replicated and distributed across identified biogeographic regions. Further consideration should be afforded to the influence of water resources developments on the genetic population structure of aquatic organisms and on the long-term sustainable conservation of aquatic ecosystems and processes therein. As a signatory to a number of international treaties and conventions addressing the conservation and management of biodiversity, South Africa has an obligation to take necessary mitagatory measure to ensure the protection of such components of biodiversity for the long-term sustainable utilisation and protection of the countries natural heritage.
Further Research Needs
Despite careful selection of taxonomically well resolved species, the results of this work have revealed a number of unresolved taxonomic considerations, highlighting the need for more detailed systematic revisions and genetic surveys. Such surveys should be undertaken before further genetic mixing can take place via the transfer of individuals through the new IBTs.
In order to properly assess the implications of future water resources developments such genetic surveys should be extended over a very broad geographic range using carefully selected organisms. Such a wide-scale genetic survey using obligate freshwater species, such as the net-winged midges or freshwater fish, could provide the basis for identifying phylogeographic regions within which to manage future water resource planning. Such information will also allow for taxonomic assessments as well the elucidation and definition of important historical, landscape and evolutionary processes that ultimately underlie the faunal and ecological properties of a system or a bioregion.
Given the climatic characteristics of South Africa, along with the demographic and socio-economic constraints, there is a growing need to provide water. Such provision will continue to involve its redistribution through the development of IBTs. Accordingly, emphasis should be placed on developing techniques and protocols to prevent the transfer of living organisms or their seeds or eggs.
Given the age and antiquity of the south-western Cape region, where the research presented here was undertaken, there is a clear need to expand this type of research to other distinct biogeographical regions. For instance, we regard it as an imperative that similar research be undertaken Mpumalanga tropical low-veld rivers, high-veld rivers and systems within ranges such as the Drakensberg in KwaZululNatal. This in order to establish whether or not there are similar patterns of genetic distinction elsewhere in the country and, hence, the implications for future IBTs in those regions.