As part of the New Zealand government Ocean Survey 20/20 programme (OS 20/20, 2006–2013), samples from the Chatham Rise and Challenger Plateau collected in 2007 were analysed to determine the effects of key environmental parameters, in particular sediment and water mass properties, on spatial changes in the community structure (abundance, diversity and community composition) of bathyal asellotan isopods. Benthic collections were obtained in austral autumn (May/June 2007) and included a total of 21 epibenthic sledge samples taken from the upper slope between 218 and 1239 m. Due to the contrasting environmental settings between the Chatham Rise and Challenger Plateau, in terms of surface productivity and habitat heterogeneity, we expected the abundance, regional (or gamma-) diversity and community composition of benthic isopods to significantly differ between the two regions, and furthermore local (or alpha-) diversity and abundance (density) to decrease with increasing depth. Consistent with our assumptions, multivariate PERMANOVA analysis revealed a clear distinction in species composition between the Chatham Rise and Challenger Plateau with satellite surface chlorophyll (Chl) a and bottom temperature being the main environmental drivers. In contrast to previous benthic studies from the same sampling campaign, however, differences in isopod density and diversity between the two regions were not significant, either at species, or generic and family level. In addition, no depth-related changes in abundance and diversity could be observed at any hierarchical level. Instead, isopod densities at species and generic level were positively correlated with satellite surface Chl a and %silt, whilst species and generic diversity could be positively linked to the amount of total organic matter (TOM) in surficial sediments. In total, 97 asellote species in 54 genera and 15 families could be identified from both regions, of which 90.7% were likely new species. Species diversity was average to high when compared to other regions in the Northern and Southern hemispheres. However, neither for Chatham Rise nor for the Challenger Plateau did the species accumulation curves reach an asymptote, indicating that additional samples are required to provide more robust diversity estimates. |
