by: Dr Ferdy de Moor
The Freshwater Invertebrates Department at the Makana Biodiversity Centre, Albany Museum has been involved in conducting ongoing research on rivers in the Tsitsikamma mountains since 2000.
In August and December 2000 surveys of the aquatic macroinvertebrates in the Salt River (Nature’s Valley) were conducted by Mrs Helen Barber-James and Dr Ferdy de Moor from the Albany Museum to assess the diversity of species in this river. The aim was to report if special conservation measures to protect any rare or endemic species were needed, following a request to introduce trout for recreational fishing into this river. Although the Salt River naturally has no freshwater fish the macroinvertebrate fauna collected proved to be so special, recording 13 undescribed species, that a permit for introducing this alien fish into the Salt River was denied.
In April 2004 Nature’s Valley Trust requested a follow-up survey of the macroinvertebrates of the Salt River in order to obtain a more complete coverage of species of macroinvertebrates throughout the annual cycle. A second reason was to assess whether any changes in the macroinvertebrate communities had occurred since the surveys conducted in 2000 because of several developments that had taken place in the catchment and along the riparian zone in the interim period. Of particular concern was the possible impact of a devastating silt discharge down the river late in 2002 that occurred following land clearing operations in the catchment preceding the development of a polo-field.
The findings of the study revealed that the reported large sediment discharge had no discernable long-term impact on the macroinvertebrate community structure and that the fauna of the Salt River can in time recover from infrequent massive sedimentation events. Continuous and regular inputs of sediment would, however, result in significant deterioration of the conservation status of the Salt River. Further concerns regarding water quality deterioration were however raised during this study. The most serious threat to the continued existence of the rich macroinvertebrate communities was excessive water abstraction. Reduced flow volumes can result in a multitude of detrimental impacts (such as pH changes, eutrophication and temperature increases), due to reduced dilution effects. The high number of unplaceable species and the diversity and abundance of certain species considered rare, resulted in recommendations that the Salt River should be given special conservation status with no introduction of any fish in the system and the eradication of alien fish in surrounding farm dams in its catchment.
THE LARGER PICTURE
On a broader scale, surveys of all the rivers in the southern Cape should be carried out to assess the status of indigenous and endemic fish and invertebrate fauna in these rivers in order to evaluate their conservation importance. It was suggested that, special measures should be taken to preserve the Salt and Wit Rivers as an aquatic insect sanctuary or nature reserve. Educational posters depicting some of the research findings are on display along the main Garden Route Road through Natures Valley and along the beach at Nature’s Valley.
From these recommendations a two-year study of eleven selected rivers in the Tsitsikamma mountains was proposed and this has been undertaken by a team of researchers from the Albany Museum, Rhodes University and Stellenbosch University between January 2008 and February 2010. The research is being written up for an MSc thesis by Mr Terence Bellingan and is also being drafted as a number of scientific papers and a special report for SANParks, WWF, Nature’s Valley Trust and Cape Nature who are the funding bodies of this research.
The aquatic invertebrate fauna of the southern and south-western Cape is unique when compared to the rest of Africa, being adapted to the cool, low nutrient, fast-flowing acidic waters typical of this region. The distribution of many of these species and genera is restricted to the southern and south-western Cape and they are considered to be endemic to that region. The rivers in the southern Cape are all headwater streams plunging straight from mountainous catchments to the sea without any of the slow, meandering lowland river and floodplain attributes characteristic of most other South African rivers. The large diversity of species can be partially attributed to the fact that there has been no major catastrophic event such as glaciation, flooding by epicontinental seas or total aridity since the middle Cretaceous (over 100 million years ago). These cold, acidic waters house the remnant of the cold-adapted, temperate Gondwanana fauna that was common to the southern land-mass during the Permian to the Jurassic periods, before the splitting of Gondwanaland in the Cretaceous. The nearest modern-day relatives are found in South America, Australia, Madagascar and India rather than in the rest of Africa. This has resulted in a high degree of endemism in this region.
Some of the main findings of the research are a discovery of more that 30 undescribed species. The recording of large, healthy populations of Cape endemic species of macroinvertebrates. The identification and selection of certain rivers that require special conservation protection. Other outcomes of the research project were, that we worked with teams of researchers from DWAE and were able to help train them in the identification of the endemic Cape freshwater invertebrates. SANParks rangers also joined us on surveys and helped find sites and learnt all about invertebrate life in the rivers. With Nature’s Valley Trust involvement, the development of a strong outreach with information posters and displays being made along National Roads and at Nature’s Valley.