Spatio-temporal trends in diversity of demersal fish species in the Benguela current large marine ecosystem region

Biodiversity is changing at an unprecedented rate on a global scale as a complex response to several anthropogenic changes, in addition to the background natural environmental variability and cycles. In the Benguela Current Large Marine Ecosystem region (BCLME), aspects of demersal fish species diversity were studied between 1985 and 2010 in three countries (Angola, Namibia, and South Africa) using scientific survey data (depending on country). The study was aimed to address multi-tiered objectives: to document patterns of diversity (as measured by the different indices of diversity) in the three countries; to relate these patterns to various explanatory variables (depth, latitude, longitude, bottom temperature, and total catch) using a generalized additive model; and to compare the patterns of diversity and importance of potential drivers of biodiversity across the BCLME region. Results showed contrasting diversity patterns between the three countries in terms of both the form and strength of the relationship with different sets of predictors. Species richness S, Pielou's evenness index J', and Shannon-Wiener index H' were shown to increase with increasing depth in all three countries. In addition, both the overall and depth-dependent latitudinal pattern in S showed local and regional level bottlenecks in biodiversity, and the latitudinal pattern of S was similar to the pattern of bottom temperature. Overall, the species richness of demersal fish species (S) was found to increase as one moved towards the equator, in line with similar studies that reported an increase in richness with latitude.