Polychaetous annelids in the deep Nordic Seas: Strong bathymetric gradients, low diversity and underdeveloped taxonomy

Abstract

Not much is known on polychaete diversity in the deep Nordic Seas. Based on data from extensive sampling over three decades, new data on polychaetes covering depths from 550 m to 3,800 m are presently reported. On a depth gradient, the number of polychaete families gradually declined from 35 at the upper slope (500-750 m) to 11 at 3,800 m. Species diversity in eight polychaete families subjected to critical taxonomic studies showed a gradual decrease from a diverse group of slope species in the upper and middle slope (500-1,000 m) to a species poor fauna in the deepest areas (> 3,000 m), with a distinct break at about 2,000 m. Faunal changes were documented both at alpha (sample species richness) and gamma (large area species richness) scales, whereas the break at about 2,000 m was clearly from beta (turnover) species richness. Only six species (12%) in the examined families were found in the deepest areas. The slope and deep-water polychaete fauna differs substantially from west Norwegian shelf and costal fauna. Not more than 30% of the species in the examined families were recorded in coastal and shelf waters, and several presumably refer to species complexes. The strong faunal change coincides with the upper border of cold sub-zero temperature deep water at the shelf break and upper slope. Polychaete taxonomy of the deep-water fauna is generally underdeveloped, illustrated by a high proportion of recently described or undescribed species (about 40%) in the examined families. Based on the present results, we hypothesise that the cold Nordic Sea deep-water polychaete fauna differs significantly from the North Atlantic deep fauna and rather is more similar to the fauna of deep Arctic waters.

Relating Depth and Diversity of Bivalvia and Gastropoda in Two Contrasting Sub-Arctic Marine Regions

“…Notably, species richness estimates indicate an order of a magnitude decrease from the 501-1000 m depth range to the 1501-2000 m depth range in bivalves. These findings are in agreement with a decrease in α-diversity with increasing depth previously described in other benthic taxa in the Nordic Seas, including isopods (Svavarsson, 1997), amphipods (Stephensen, 1940;Weisshappel and Svavarsson, 1998), polychaetes (Narayanaswamy et al, 2005;Oug et al, 2017), foraminifera (Mackensen et al, 1985;Gudmundsson, 2002), and the overall macrofauna (Bett, 2001). In fact, studies on benthic diversity in the deep Nordic Sea basin have consistently described low species richness compared to deep zones in other seas and ocean basins, including the North Atlantic south of the GIF ridge (Bouchet and Warén, 1979;Dahl, 1979;Rex et al, 2000).…”

Spaghetti to a Tree: A Robust Phylogeny for Terebelliformia (Annelida) Based on Transcriptomes, Molecular and Morphological Data

“…With~1100 named species, Terebelliformia is one of the most speciose groups of annelids [1] and its species range from shallow coastal areas to the deep sea, occupying habitats ranging from mud flats, coralline reefs, whale falls to hydrothermal vents [2,3]. Their diversity is likely underestimated as new species are continually being discovered [4,5]. An illustration of the underappreciated biodiversity is the "cosmopolitan" species Terebellides stroemii that was recently shown to comprise 27 species in the northeast Atlantic alone [6].…”

Systematic re-structure and new species of Sphaerodoridae (Annelida) after morphological revision and molecular phylogenetic analyses of the North East Atlantic fauna

“…Some of the contemporary expeditions that have contributed with material to this project are: BIOICE project (1991–2004) and the IceAGE project (ongoing since 2011) around Iceland (Omarsdottir et al 2013), the MAREANO Programme (2005-present) in Norwegian waters (Buhl-Mortensen et al 2015), and the “Brattegard-Sneli” sampling programme (1980–87) (Oug et al 2017).…”