Abstract:
Over the past decade, several clustered, multispecies, wildlife mortality events occurred in the
vicinity of two man-made earthen dams in the southern and south central regions of the
Kruger National Park, South Africa. On field investigation, heavy cyanobacterial blooms were
visible in these impoundments and analysis of water samples showed the dominance of
Microcystis spp. (probably Microcystis aeruginosa). Macroscopic lesions seen at necropsy and
histopathological lesions were compatible with a diagnosis of cyanobacterial intoxication.
Laboratory toxicity tests and assays also confirmed the presence of significant levels of
microcystins in water from the two dams. These outbreaks occurred during the dry autumn
and early winter seasons when water levels in these dams were dropping, and a common
feature was that all the affected dams were supporting a large number of hippopotamuses
(Hippopotamus amphibius). It is hypothesised that hippopotamus’ urine and faeces, together
with agitation of the sediments, significantly contributed to internal loading of phosphates
and nitrogen – leading to eutrophication of the water in these impoundments and subsequent
cyanobacterial blooms. A major cause for concern was that a number of white rhinoceros
(Ceratotherium simum) were amongst the victims of these bio-intoxication events. This
publication discusses the eco-epidemiology and pathology of these clustered mortalities, as
well as the management options considered and eventually used to address the problem.
