Rapport de Campagne - Station Biologique de Roscoff
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Rapport de Campagne - Station Biologique de Roscoff

Rapport de Campagne - Station Biologique de Roscoff Rapport de Campagne - Station Biologique de Roscoff

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11.02.2014 Views

COMPTE RENDU DE CAMPAGNE A LA MER SUR UN NAVIRE Ifremer H OP E 99 URM 7 Nom : HERRING Prénom : Peter Campagne : HOPE 99 Navire : L'ATALANTE - Submersible: NAUTILE Organisme maître d'oeuvre : URM 7 Chef de mission : F. LALLIER Première partie: du 9 au 26 avril 1999 Participants associés: Ben BOORMAN Institution : SOUTHAMPTON OCEANOGRAPHY David EDGE CENTRE, UK Rappel des Objectifs The programme of trawling with the RMT system was aimed at identifing the fauna in the water column immediately above the 13° N active sites. This would show whether any of the mobile fauna seen at the sites during the submersible dives, or their larvae, extended upwards into the overlying water column. Travaux réalisés Twelve nighttime trawls were achieved, each with three sets of nets. Ten trawls were along the ridge axis over the active sites: 2 of these covered the depths from the surface to 1500m, 2 were between 2000and 2400m, 3 sampled at 2400-2500m, 1 at 2500-2550m and 2 were fished ~50m above the bottom. Net 2 was always open as the trawl passed over the main region of active sites. Two samples were lost through technical problems but 28 were successfully achieved. Two off-axis trawls were made, for comparison with the tows down the ridge. One was fished across the ridge and the other was in deeper water several km to the west of the ridge. Both were fished at the same depth as the main trawls along the ridge axis (2400- 2500m). Exploitation à terre The RMT8 samples will be sorted and the major faunal components identified. The catches of net 2 and of nets 1 and 3 will be compared to see if there is any clear influence of the active sites on the respective samples. Biomass determinations will be made on the basis of displacement volume. The RMT1 samples will be examined for the larger larval forms. The pelagic fauna over the EPR will then be compared with that over the MAR sites, sampled in 1997 during the MARVEL and FLAME cruises. Commentaires The first impressions of the trawl samples are that they comprise a typical bathypelagic fauna, and that the active hydrothermal sites have little influence on the fauna above them. Even the two trawls fished perilously close to the bottom (closest approach was ~25m) lacked any obvious components derived from the vent fauna. Despite the presence of many Lebbeus at some locations, none were taken in any of the nets. However, 2 specimens of Nematocarcinus sp. were taken, superficially similar to the species observed during several dives. Juveniles of vent-associated animals included several postlarval macrurids and three very young specimens of a cirrate octopod. HOPE 99 Page 189 RAPPORTS SCIENTIFIQUES

COMPTE RENDU DE CAMPAGNE A LA MER SUR UN NAVIRE Ifremer The catches close to the bottom were consistently very small, with very few fish or pelagic decapods. Nemertine worms are a feature of both the EPR and MAR samples, and some exceptionally large specimens were taken in the trawls. The overall indication is that the near-bottom biomass levels over the EPR are much lower than at Lucky Strike or Rainbow. The off-axis trawls made at similar depths but over deeper water produced somewhat larger samples and it is possible that the intrusion of the ridge into the water column actively reduces the bathypelagic fauna immediately above it. HOPE 99 Page 190 RAPPORTS SCIENTIFIQUES

COMPTE RENDU DE CAMPAGNE A LA MER SUR UN NAVIRE Ifremer<br />

The catches close to the bottom were consistently very small, with very few fish or<br />

pelagic <strong>de</strong>capods. Nemertine worms are a feature of both the EPR and MAR samples, and<br />

some exceptionally large specimens were taken in the trawls. The overall indication is that the<br />

near-bottom biomass levels over the EPR are much lower than at Lucky Strike or Rainbow.<br />

The off-axis trawls ma<strong>de</strong> at similar <strong>de</strong>pths but over <strong>de</strong>eper water produced somewhat larger<br />

samples and it is possible that the intrusion of the ridge into the water column actively<br />

reduces the bathypelagic fauna immediately above it.<br />

HOPE 99 Page 190 RAPPORTS SCIENTIFIQUES

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