Benthic boundary layer macrofauna from the upper slope of the Chatham Rise (SW Pacific)

Abstract

Benthic boundary layer (BBL) communities are a taxonomically and functionally diverse but poorly known component of deep‐sea environments. We investigated macrofaunal assemblages across the upper slope of the Chatham Rise (CR) in the south‐western Pacific in relation to location, depth and sediment variables. Using data from the TAN1116 voyage to the CR in austral spring 2011, we assessed variation in abundance, faunal composition and diversity of three BBL compartments: fully suprabenthic taxa, taxa with suprabenthic affinities and fully epibenthic taxa across taxonomic levels (phylum, class, order, family, genus and species). In total, eight samples were taken using an epibenthic sledge across three areas on the CR (Mernoo Gap, CR North and CR South) and at two depth ranges (400–600 and 900–1,000 m) distributed along a north to south as well as east to west axis, crossing different productivity gradients. In contrast to previous studies from the CR, there was no significant correlation between macrofaunal densities and sediment variables or depth. Species diversity of isopods and tanaidaceans was average to high, compared to other geographic regions, but did not show any significant pattern with location or depth. Most species in these two groups (~82%) were new to science, probably reflecting the paucity of sampling and taxonomic study of these faunal components in New Zealand waters. Our results suggest employing finer‐scale investigations across a range of temporal and spatial scales and at finer taxonomic resolution would greatly further our knowledge and understanding of patterns and processes shaping deep‐sea BBL community structure.

Diversity and composition of benthic asellote Isopoda from two different New Zealand continental margin habitats - implications of habitat heterogeneity, productivity and depth

“…Depth-related patterns reflect, among others, changes in productivity, food supply, hydrostatic pressure and temperature, and are usually accompanied by marked declines in macrofaunal abundance and biomass with increasing depth (Rex et al, 2006). Depth ranges in our study, however, seemed to be too narrow (218-1239 m) to detect notable trends (see also Pilditch et al, 2015;Kaiser et al, 2018). On the Chatham Rise, productivity gradients occur along a north to south and east to west axis under the influence of the STF (Murphy et al, 2001;Chiswell et al, 2013), which is mirrored by higher benthic biomass and abundance on the southern flank of the rise and closer to the shore as seen in previous studies (Nodder et al, 2003;Berkenbusch et al, 2011;Pilditch et al, 2015).…”

“…Nevertheless, analyses of Australian and New Zealand macrofaunal data have revealed species diversity to be equal to or exceeding levels found at corresponding Northern Hemisphere latitudes (Poore et al, 1994(Poore et al, , 2015Kaiser et al, 2018). The high degree of previously undescribed species in these studies (polychaetes, >70%; crustaceans, 82-95%) further highlights the fragmentary knowledge of Southern Hemisphere bathyal diversity and related drivers (Poore et al, 1994(Poore et al, , 2015Brandt et al, 2007;Kaiser et al, 2011Kaiser et al, , 2018.…”

“…Significant results are shown in bold (p < 0.05). (Brandt, 1995), there was no indication in others (Meyer-Löbbecke et al, 2014;Kaiser et al, 2018). Likewise, water depth or related abiotic factors were not strong predictors of asellote isopod densities.…”

“…However, untangling patterns and processes of bathymetric diversity remains difficult; most data available have been derived from the North Atlantic, while equivalent species-level information from Southern Hemisphere continental slopes is sparse (Rex and Etter, 2010;O'Hara et al, 2011;Leduc et al, 2012a;McCallum et al, 2015;MacIntosh et al, 2018). Nevertheless, analyses of Australian and New Zealand macrofaunal data have revealed species diversity to be equal to or exceeding levels found at corresponding Northern Hemisphere latitudes (Poore et al, 1994(Poore et al, , 2015Kaiser et al, 2018). The high degree of previously undescribed species in these studies (polychaetes, >70%; crustaceans, 82-95%) further highlights the fragmentary knowledge of Southern Hemisphere bathyal diversity and related drivers (Poore et al, 1994(Poore et al, , 2015Brandt et al, 2007;Kaiser et al, 2011Kaiser et al, , 2018.…”

“…The present study focuses on asellote isopods from these collections and aims to explore the variation in its community structure (abundance, taxonomic diversity and composition) with changes in environmental variables and relative to location and depth. Isopoda of the suborder Asellota represent among the most dominant and diverse macrofaunal taxon in the deep sea, and due to their predominant reproductive mode, as obligate benthic brooders, they have been widely used to study broad-scale diversity and distributional patterns in a deep-sea context (e.g., Hessler and Wilson, 1983;Rex et al, 1993;Wilson, 1998;Brandt et al, 2007;Kaiser et al, 2007;Raupach et al, 2009;Janssen et al, 2015;Kaiser et al, 2018;Malyutina and Brandt, 2020).…”