Faunal characteristics of the Nyegga/Storegga cold-seep, NE-Atlantic

Abstract:

Several studies at Arctic cold-seep locations have demonstrated a close link between geochemical signatures of seepage processes and biomass production. Especially in the Arctic, due to low temperature and light conditions, these processes result in enhanced infaunal abundance, diversity, and biomass, compared to inactive control regions. We here describe how an «oasis-effect» is expressed at the Nyegga/Storegga (N/S) seep location. These seeps represent Arctic conditions of -0.7 °C at ~750 m water depth. Based on ROV recorded videos, N/S is characterised by a remarkable macrofaunal composition located in a varied physical environment produced by seepage, hydrates, and carbonate precipitation.

Within this complex environment the following faunistic micro-environments are found: a) Sediment ‘hydrate pingo mounds’ characterized by carpets of tubeworms (siboglinids) with patches of bacterial mats; b) Cryptic ‘rooms’ surrounded by methane-derived carbonate rocks with giant pycnogonids (‘sea spiders’) and brittle stars; c) Protruding carbonate rocks with ‘lush’ oasis-like infaunal organisms (communities including cnidria, crinoids, basket stars and sea anemones); and d) Isolated sedimentary basins, ‘pools’ with various types of unusually idle fish, apparently resting? - The metabolism of some of these fish may, thus, be affected by the cold seawater temperature. Other reasons for the idleness may be: a stable food supply, a safe refugia (no predators), or low seawater oxygen level in the basins.

In addition, we present some new information on the occurrence of bacteria sampled in 1) the near-seafloor water at N/S, 2) the sediments, and 3) the inside body of a collected giant pycnogonid. The 16S rRNA gene fragments profiled and identified from the pycnogonid revealed, for example, 99% sequence identity with Gammaproteobacteria from hydrothermal fluids at the Okinawa Trough, a methylnaphthalene enrichment, but also cod larvae intestine. The cultured bacteria revealed isolates for example most closely related to Psycrobacter from seawater at 200 m depth near icebergs in Antarctica.

We further compare some of our observations with results from two other Arctic cold-seep locations (Haakon Mosby Mud Volcano and Vestnesa cold-seep), where we find similarities, but also some notable differences.