| dc.description.abstract | Seamounts are important places in the ocean due to their ecological importance as hotspots of biodiversity harbouring extensive communities of fish. Saba Bank, the largest submarine Atoll in the Atlantic ocean, has been subject to many studies focusing on the shallow coral reefs located on top of the bank, whereas deeper parts are fairly unexplored. Here, results are presented of the first exploratory study of Saba Bank’s deep flanks, whereby patterns of distribution, abundance and diversity of organisms were investigated through the analysis of video transects (covering 94600 m) on the north and south flank of the bank. In addition, trophic interactions of the benthic deep-sea communities on both flanks were inferred using stable isotope analysis (SIA). Samples for SIA were collected during NICO expedition 64PE432 on February 2018, between 94-1300 m depth. SIA did not show major differences in food web structure between Saba Bank’s northern and southern flank. Both food webs counted four trophic levels, whereby the faunal communities in the shallow and deep waters were connected through trophic coupling. In addition, three main trophic guilds were identified: pelagic, bentho-pelagic and benthic feeders. Analysis of the video transects did show large differences in benthic community composition between Saba Bank’s northern and southern flank. On the southern flank the highest abundance of organisms, mainly suspension feeders, was found in the first 100-250 m. The high abundance was correlated to intensified mixing that increased nutrient concentrations and trapped migrating layers of zooplankton, which is proposed to form a major food source for Saba Bank’s deep-sea communities. On the northern flank, suspension feeders dominated the first 100-200 m, but only by half the amount compared to the southern flank. Sponges were almost absent on the northern flank, whereas on the southern flank a sponge belt was observed around 400 m. Below 250 m, the communities on both the northern and southern flanks were dominated by deposit feeders and scavengers. In addition, the north flank harboured higher amounts and a larger diversity of fish compared to the southern flank. This has been attributed to the highly abundant occurrence of Sargassum on the northern flank, which creates habitat forming structures for fishes, and might form a additional source of food for the deep-sea community on Saba Bank’s northern flank. | |
