Demosponges from the Northern Mid-Atlantic Ridge shed more light on the diversity and biogeography of North Atlantic deep-sea sponges

Paco Cárdenas,Hans Tore Rapp

doi:10.1017/s0025315415000983

Abstract

In July–August 2004, the Mid-Atlantic Ridge Ecosystems (MAR-Eco) expedition collected Demospongiae (Porifera) from the Northern Mid-Atlantic Ridge (MAR) north of the Azores, between 41°N and 61°N. Demosponges were found at 10 stations, at depths ranging from 753 to 3046 m. Twenty-two species were identified: 17 Tetractinellida, one Polymastiida, one Suberitida, two Poecilosclerida and one Dendroceratida. The study of this material is an opportunity to revise the taxonomy and the North Atlantic distribution of each of these deep-sea species. Some species are particularly rare and poorly known (Tetilla longipilis, Tetilla sandalina, Craniella azorica, Polymastia corticata) and two are new to science:Forcepia(Forcepia)toxaferasp. nov. andIotroata paravaridenssp. nov. This study suggests that the MAR is not a longitudinal barrier for the dispersal of deep-sea demosponges while on the contrary, the Charlie-Gibbs Fracture Zone (CGFZ) may be a latitudinal border for the dispersal of deep-sea demosponges, due to great depths and currents.

Highlights

The Mid-Atlantic Ridge (MAR) between Iceland (638N) and the Azores (36– 398N) spans across 3000 km
We have found two other specimens belonging to this southern morphotype in the Bergen Museum (ZMBN 25668) and in Naturalis (RMNH 1458): both were collected in the Azores area at .2400 m depth
We re-examined sections of G. phlegraei ZMBN 77929 (Korsfjord, Norway) for crystalline structures, and we found many: small (27–37 mm) dirty sub-circular ones were very abundant below the cortex, larger ones were observed deeper in the choanosome

Summary

Introduction

The Mid-Atlantic Ridge (MAR) between Iceland (638N) and the Azores (36– 398N) spans across 3000 km. About mid-way between Iceland and the Azores (around 528N), the Charlie-Gibbs Fracture Zone (CGFZ) offsets the MAR about 300 km, with depths reaching 4500 m (Felley et al, 2008), thereby opening the deepest connection between North-East and North-West Atlantic waters (Figure 1). The CGFZ area is considered a major latitudinal transition zone in the environment and biodiversity of the MAR (Vecchione et al, 2010) and is part of the world’s first network of marine protected areas (MPAs) by both OSPAR (Oslo-Paris Convention) and the NEAFC (North-East Atlantic Fisheries Commission) (O’Leary et al, 2012).

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Conclusion