New scientific distribution records discovered
Unsurprisingly for a Park that counts biodiversity as one of its three outstanding universal values for which it was unilaterally inscribed as a UNESCO World Heritage Site, iSimangaliso has long been associated with a plethora of described species of fauna and flora. And that list continues to grow as new species are discovered by researchers undertaking a multitude of natural and social science projects in this fertile land.
“With 148 current registered research projects, our knowledge base of the Park is constantly expanding and reinforcing the wisdom of protecting this incredibly diverse mosaic of interlinking eco-systems,” says iSimangaliso’s Research Manager, Nerosha Govender.
One of these involves the study of predaceous water beetles (Coleoptera, Hydradephaga) of the Lake St Lucia system, led by Professor Renzo Perissinotto, who states: “Water beetles are one of the dominant macroinvertebrate groups in inland waters and are excellent ecological indicators, reflecting both the diversity and composition of the wider aquatic community. The predaceous water beetles (Hydradephaga) make up around one-third of known aquatic Coleoptera and, as predators, are a key group in the functioning of many aquatic habitats. Despite being relatively well-known taxonomically, ecological studies of these insects in tropical and subtropical systems remain rare”.
The study reveals that the Lake St Lucia system and its associated wetlands support at least 68 species of Hydradephaga. Says Perissinotto: “It is currently estimated that ca. 410 species of Hydradephaga occur in southern Africa as a whole, meaning that almost 20% of the known fauna of this biodiverse region occur in the wetlands of the St Lucia system. This is a very high level of diversity comparing favourably with other hotspots on the African continent and elsewhere in the world and a number of taxa are reported for South Africa for the first time”.
The study, which took place between 2013 and 2015 provided the first biodiversity census for this important aquatic group in the iSimangaliso Wetland Park, a UNESCO World Heritage Site within the Maputaland biodiversity hotspot.
Perissinotto says: “Our study is the first to highlight the importance of temporary depression wetlands and emphasises the need to maintain a variety of wetland habitats for aquatic conservation in this biodiverse region”.
Only three species (Cybister vulneratus Klug, 1834, Hydaticus servillianus Aubé, 1838 and Derovatellus cf. natalensis Omer-Cooper, 1965) were found in the margins of Lake St Lucia itself, the overwhelming majority of species being associated with small wetlands in the park. False Bay sites supported relatively distinctive beetle assemblages, including species which were not recorded elsewhere, whereas the fauna of the eastern and western shores largely overlapped.
The impact of drought
Due to unprecedented drought conditions in the region and past anthropogenic activities, there have been significant changes in the Lake St Lucia system in recent decades. The estuary mouth closed in 2002 and large-scale desiccation of the lake basins began in 2004. At the peak of these events, over 80% of the lake bottom sediments became exposed to the air and hypersaline conditions dominated the lake system, except in the Narrows and at the mouth. Alternation of dry and wet cycles are not new to this estuary, as can be seen for instance in historic records showing the regular occurrence of 4–10 year cycles of either droughts or anomalous wet conditions since at least the early 1900s. Projections of climate change for the next 50-100 years indicate that this situation will persist and possibly intensify, with the most likely scenario being an alternation of extreme droughts followed by floods. making iSimangaliso’s current GEF – World Bank restoration of Lake St Lucia hydrology by strengthening the flow of the Umfolozi river into the Lake St Lucia even more critical to ensure future resilience. Predaceous water beetle biodiversity in the at Lake St Lucia system is concentrated in small natural water bodies, rather than the main lake system. With the most likely scenario being an alternation of extreme droughts followed by floods, and the consequences of such changes for the beetles remain unclear, and may depend on the degree to which changes in the lake system cascade through the wider wetland complex.
To read the full report on the study, please visit http://zookeys.pensoft.net/articles.php?id=8614.
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