Benthic macrofauna from the abyssal equatorial and South Atlantic  collected during the DIVA 1&amp;3 expeditions (2000, 2009) using an  epibenthic sledge

Keywords: South Atlantic; Argentine Basin; Brazil Basin, Benthic, Macrofauna, Guinea Basin; Cape Basin; Angola Basin; epibenthic sledge; DIVA 1-3
Temporal coverage: 2000/2009

Project information
Benthic sampling was conducted during the DIVA 1-3 expeditions on board RV Meteor between 2000 and 2009: DIVA 1 (Me 48/1), 06.07.2000-02.08.2000, Walvis Bay – Walvis Bay; DIVA 2 Me 63/2, 25.02.2005 – 30.03.2005, Cape Town (South Africa) – Mindelo (Cape Verdes); DIVA 3 Me 79/1, 10.07.2009 – 23.08.2009, Montevideo (Uruguay – Ponta Delgada (Azores).

Study area
The study area encompasses five abyssal basins of the equatorial and South Atlantic, including the Argentine and Brazil basins located in the SW Atlantic, the Guinea basin in the equatorial Atlantic, as well as the Angola and Cape basins in the SE Atlantic. The hydrography of South Atlantic surface waters is dominated by the South Atlantic subtropical gyre, which is clockwise bounded by the Benguela current system in the East, the Antarctic circumpolar current in the South, the Brazil current in the West and the South Equatorial Current in the North (Rhein et al., 1996; Palma &amp; Matano 2017). Deep water masses consist of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). The southernmost basins, i.e. the Argentine and Cape basins, are mainly bathed in cold and dense AABW. In the eastern basins, the Walvis ridge separates the Cape from the Angola basin. While the abyssal seabed of the Cape basin is dominated by AABW, the Walvis ridge obstructs the AABW flow into the Angola basin, the latter being dominated by NADW and the inflow of Antarctic Intermediate Water (AAIW) that can cross the ridge (Taley, 1996).  The investigated abyssal areas differ greatly in terms of food availability, which is supposed to be significantly lower in the Cape and southern Angola basins and increases towards the north in the northern Angola and eastern Guinea basins (Kröncke &amp; Türkay 2003; Kröncke et al. 2013). In contrast, almost the opposite pattern is seen in the south-western basins, i.e. high oceanic productivity over the Argentine basin, a decline in entry the subtropical gyre and then again an increase towards the equator (Mollenhauer et al. 2004).

Sampling
Macrofauna was obtained by means of an EBS equipped with an epinet (below) and a supranet (above). The mesh size of the nets is 500 µm. The cod ends are equipped with net-buckets containing a 300 µm mesh window (Brenke, 2005). In addition, a box was developed for sampling in warm, tropical waters, which covers the code ends and keeps the samples cool on their way through the water column. The EBS was towed on the seabed for 10 minutes each time. The trawl distance was calculated according to equation (d) in Brenke (2005), where the trawl distance varied between 1368 and 5781.5 m.
Sample processing
Sample processing has changed slightly over the course of the expeditions. During DIVA 2, a cold chain was introduced to keep the samples at a constant temperature throughout the sampling, sieving and sorting process, and this protocol was followed from then on (cf. Riehl et al. 2014). After retrieval of the cod-ends and sieving of the sediment samples through a 300 µm mesh using pre-cooled seawater, samples were fixed in 80% denatured (DIVA 1), 96% denatured (DIVA 2) or 96% non-denatured EtOH (DIVA 3) (e.g., Brandt et al. 2005, S. Brix pers. communication). During DIVA 3, three replicate EBS with 1 nautical cable length (~180 m) between deployments were taken at each site. On board two replicates were sieved with cold (+2°C) sea water and immediately transferred into pre-cooled (-20°) non-denatured 96% EtOH. These samples were stored in -20° for at least 48 h for later DNA extractions (Riehl et al. 2014). For the first 12 hours samples were gently moved every two hours, to avoid freezing of the samples. After 48 hours these samples were refixed with 96% EtOH and kept at -20° until further sample processing. The third replicate was sieved in warm sea water and fixed with 4% buffered formalin. After (at least) 48 hours the formalin sample was washed with sea water and then transferred to 96% EtOH. 

Taxonomy
The material was sorted into individual taxa (phyla, class, order level) on board and in the laboratories of the DZMB and the Zoological Museum Hamburg (today LIB) using a stereo microscope. The systematic classification followed the World Register of Marine Species (WoRMS; Horton et al. 2021). For the DIVA-2 dataset, the echinoderms were not further classified. Arthropods were counted only when the head was present, ophiuroids only when the disc was present.

References
Brandt A, Brenke N, Andres HG, Brix S, Guerrero-Kommritz J, Mühlenhardt-Siegel U, Wägele JW (2005) Diversity of peracarid crustaceans (Malacostraca) from the abyssal plain of the Angola Basin. Organisms Diversity &amp; Evolution 5:105–112.
Brenke, N. (2005). An epibenthic sledge for operations on marine soft bottom and bedrock. Marine Technology Society Journal, 39(2), 10-21.
Horton T and WoRMS editors (2021) World Register of Marine Species. Available from https://www.marinespecies.org at VLIZ. Accessed 2021-05-12. doi:10.14284/170
Kröncke I, Türkay M (2003) Structural and functional aspects of the benthic communities in the deep Angola Basin. Marine Ecology Progress Series 260:43–53.
Kröncke I, Reiss H, Türkay M (2013) Macro-and megafauna communities in three deep basins of the South-East Atlantic. Deep Sea Research Part I: Oceanographic Research Papers 81:25–35.
Mollenhauer G, Schneider RR, Jennerjahn T, Müller PJ, Wefer G (2004) Organic carbon accumulation in the South Atlantic Ocean: its modern, mid-Holocene and last glacial distribution. Global and Planetary Change 40(3-4):249–266.
Palma ED, Matano RP (2017) South Atlantic circulation and variability from a data assimilating model. In: Marine pollution and climate change (pp. 39-65). CRC Press.
Rhein M, Schott F, Fischer J, Send U, Stramma L (1996) The deep water regime in the Equatorial Atlantic. In Wefer G, Berger WH, Siedler G, Webb DJ (Eds) The South Atlantic. Present and past circulation. Springer, Berlin, Heidelberg. 1996, pp. 261–271.
Riehl, T., Brenke, N., Brix, S., Driskell, A., Kaiser, S., &amp; Brandt, A. (2014). Field and laboratory methods for DNA studies on deep-sea isopod crustaceans. Polish Polar Research, 203-224. 
Taley LD (1996) Antarctic Intermediate Water in the South Atlantic. In Wefer G, Berger WH, Siedler G, Webb DJ (Eds) The South Atlantic. Present and past circulation.  Springer, Berlin, Heidelberg. 1996, pp. 219–238.