The biodiversity of the deep Southern Ocean benthos

Abstract

Our knowledge of the biodiversity of the Southern Ocean (SO) deep benthos is scarce. In this review, we describe the general biodiversity patterns of meio-, macro- and megafaunal taxa, based on historical and recent expeditions, and against the background of the geological events and phylogenetic relationships that have influenced the biodiversity and evolution of the investigated taxa. The relationship of the fauna to environmental parameters, such as water depth, sediment type, food availability and carbonate solubility, as well as species interrelationships, probably have shaped present-day biodiversity patterns as much as evolution. However, different taxa exhibit different large-scale biodiversity and biogeographic patterns. Moreover, there is rarely any clear relationship of biodiversity pattern with depth, latitude or environmental parameters, such as sediment composition or grain size. Similarities and differences between the SO biodiversity and biodiversity of global oceans are outlined. The high percentage (often more than 90%) of new species in almost all taxa, as well as the high degree of endemism of many groups, may reflect undersampling of the area, and it is likely to decrease as more information is gathered about SO deep-sea biodiversity by future expeditions. Indeed, among certain taxa such as the Foraminifera, close links at the species level are already apparent between deep Weddell Sea faunas and those from similar depths in the North Atlantic and Arctic. With regard to the vertical zonation from the shelf edge into deep water, biodiversity patterns among some taxa in the SO might differ from those in other deep-sea areas, due to the deep Antarctic shelf and the evolution of eurybathy in many species, as well as to deep-water production that can fuel the SO deep sea with freshly produced organic matter derived not only from phytoplankton, but also from ice algae.

Brooding and Species Diversity in the Southern Ocean: Selection for Brooders or Speciation within Brooding Clades?

“…Nonpelagic development could have developed well before the Southern Ocean cooled, or even elsewhere altogether, but spread via a founding species to the Southern Ocean and then undergone radiation. Regardless of where or how nonpelagic development originated, if this is the case, we have not only an explanation of the unusually high number of species with nonpelagic development but also, perhaps, an explanation for the unexpected high species diversity in the Southern Ocean (Brandt et al, 2007a(Brandt et al, , 2007bRogers, 2007). At least two different scenarios about how this might occur are specifi c to the Southern Ocean.…”

“…That is, nonpelagic development in the Southern Ocean might not refl ect adaptation scattered among several clades, as it does elsewhere (e.g., Byrne et al, 2003;Collin, 2003), but rather, it may occur mainly in relatively few clades in which species proliferated. Moreover, some of these species-rich, brooding clades could contribute substantially to the unexpected high species diversity found in the Southern Ocean (Brandt et al, 2007a(Brandt et al, , 2007bRogers, 2007). Indeed, in some taxa, species-rich clades of brooders constitute most of the species (e.g., echinoids: Poulin and Féral, 1996;David et al, 2003David et al, , 2005crustaceans: Brandt, 2000;Brandt et al, 2007aBrandt et al, , 2007b.…”

“…Moreover, some of these species-rich, brooding clades could contribute substantially to the unexpected high species diversity found in the Southern Ocean (Brandt et al, 2007a(Brandt et al, , 2007bRogers, 2007). Indeed, in some taxa, species-rich clades of brooders constitute most of the species (e.g., echinoids: Poulin and Féral, 1996;David et al, 2003David et al, , 2005crustaceans: Brandt, 2000;Brandt et al, 2007aBrandt et al, , 2007b. Consequently, the occurrence of many species with nonpelagic development may not be due to specifi c adaptations to conditions in the Antarctic but, instead, may be a consequence of isolation after vicariant events that now or in the past led to their proliferation.…”

Assemblages and habitat preferences of soft bottom Antarctic Amphipoda: Admiralty Bay case study

“…It has been relatively short time since more intense deep-sea sampling started and the results showed the existence of very diverse bathyal and abyssal crustacean fauna (e.g. Brandt et al 2007). Fig.…”

“…Last years have brought new investigations where the bathyal and abyssal Antarctic fauna was studied, confirming high abundance and diversity of amphipod crustaceans and consequently their importance also in deep-sea communities (e.g. De Broyer et al 2004;Brandt et al 2007;Brökeland et al 2007). However, the amphipod fauna of middle and deep sublittoral of the Antarctic region is still poorly recognized.…”