Cinderella effects in conservation assessment: Re-evaluating biodiversity merit in a South African estuarine system

Two adjacent estuaries in South Africa differ markedly in their assessed biodiversity, conservation status and management style: one, a flagship site, is considered to support the richest estuarine biodiversity in the country, receives the management and protection of a National Park, and attracts much research attention; the other is regarded as having an impoverished macrobenthic fauna, bears no formal conservation status, and is much less studied. To test whether these supposed contrasts in biodiversity are simply a reflection of differential levels of scientific attention, the biodiversity, abundance and nature of the macrobenthos in a representative habitat, beds of the endangered seagrass Nanozostera capensis that dominate both estuaries, were compared in apparently equivalent upstream (estuarine and lagoonal) locations of the two systems using identical field research effort and methodology. There the neglected and supposed impoverished estuary (the Keurbooms/Bitou) was found to support as great, if not greater, macrobenthic biodiversity, in greater abundance, and with more numerous rare endemics than the flagship conservation site (the Knysna estuarine bay). Its previously considered species poverty appears entirely due to inadequate earlier investigation, particularly in respect of its invertebrate fauna. Of the two, Keurbooms/Bitou also has the merit of being less accessible and less anthropogenically impacted. This study highlights the consequences of basing conservation assessments on incomplete biodiversity data, and stresses that a uniform programme of investigative fieldwork is critical for the meaningful ranking of sites. It also emphasises the extent to which non-bait species of invertebrate are often ignored in estuarine management protocols to the detriment of local and overall conservation management aims. • Seagrass biodiversity status of two estuaries compared using uniform methodology. • The biodiversity of one ranked ‘exceptionally rich’, the other ‘unexpectedly poor'. • Comparable investigation shows the ‘poor’ site equally rich if not the richer. • Biodiversity comparisons are critically dependent on equivalent and accurate data. • Insufficient attention is given to benthic invertebrates in estuarine assessments.