Benthic fauna associated with mussel beds and shrimp swarms within hydrothermal fields on the Mid-Atlantic Ridge

Macrofaunal assemblages with prevalence of Bresiliidae shrimps and Mytilidae mussels are abundant in at hydrothermal vents along the Mid-Atlantic Ridge. Mussels inhabit zones of diffuse seeps of hydrothermal fluids with temperature abnormalities up to several degrees. Shrimps inhabit an extreme biotope in a mixed interface between seawater and hydrothermal fluids at temperature up to 20-30°C. We studied the mussel and shrimp assemblages in three hydrothermal vent fields: Rainbow, Broken Spur, and Snake Pit. Species richness of the mussel assemblages within at least two fields (Broken Spur and Snake Pit) is higher as compared with shrimps from the same hydrothermal vent fields. Fauna inhibiting shrimp swarms lack almost any taxa specific for particular assemblages: almost all the taxa are also present in the mussel beds. Structure of the shrimp assemblage is less homogeneous as compared with that of the mussel assemblage. Population prevalence of one taxon (Copepoda) in the shrimp assemblage is most likely connected with extreme and unstable conditions of the biotope occupied by the shrimps in a hydrothermal field. Taxonomic similarity between the mussel and shrimp assemblages within one hydrothermal vent field is higher as compared with similarity between the mussel (or shrimp) assemblages from different fields.

Literature review of elasmobranch bycatch and retention rate

To address growing concern over the effects of fisheries non-target catch on elasmobranchs worldwide, the accurate reporting of elasmobranch catch is essential. This requires data on a combination of measures, including reported landings, retained and discarded non-target catch, and post-discard survival. Identification of the factors influencing discard vs. retention is needed to improve catch estimates and to determine wasteful fishing practices. To do this we compared retention rates of elasmobranch non-target catch in a broad subset of fisheries throughout the world by taxon, fishing country, and gear. A regression tree and random forest analysis indicated that taxon was the most important determinant of retention in this dataset, but all three factors together explained 59% of the variance. Estimates of total elasmobranch removals were calculated by dividing the FAO global elasmobranch landings by average retention rates and suggest that total elasmobranch removals may exceed FAO reported landings by as much as 400%. This analysis is the first effort to directly characterize global drivers of discards for elasmobranch non-target catch. Our results highlight the importance of accurate quantification of retention and discard rates to improve assessments of the potential impacts of fisheries on these species.

Stations data for crustacean at Juan de Nova Island during BIORECIE fieldwork in 2013

Field stations where Crustacea (Decapoda, Stomatopoda) have been collected during BIORECIE campaign at Juan de Nova Island (December 3-9, 2013). Station 20, in front of the camp, has been visited each day. Station 31 is arbitrarily chosen for a few samples collected in shallow waters of the outer reef.

SHRIMP U-Pb zircon data from Gjelsvikfjella, Dronning Maud Land, East Antarctica

The Maud Belt in Dronning Maud Land (western East Antarctic Craton) preserves a high-grade polyphase tectono-thermal history with two orogenic episodes of Mesoproterozoic (1.2-1.0 Ga) and Neoproterozoic (0.6-0.5 Ga) age. New SHRIMP U-Pb zircon data from southern Gjelsvikfjella in the northeastern part of the belt make it possible to differentiate between a series of magmatic and metamorphic events. The oldest event recorded is the formation of an extensive 1140-1130 Ma volcanic arc. This was followed by 1104 ± 8 Ma granitoids that might represent, together with so far undated mafic dykes, part of a decompression melting-related bimodal suite that reflects the sub-continental Umkondo igneous event. The first high-grade metamorphism is constrained at 1070 Ma. The metamorphic age data are similar to those obtained from other parts of the Maud Belt, but also from the Namaqua-Natal Belt in South Africa, but the preceding arc formation was diachronous in the two belts. This indicates that the two belts did not form a continuous volcanic arc unit as suggested in previous models, but became connected only at the end of the Mesoproterozoic. Intense reworking during the Neoproterozoic, probably as a result of continent-continent collision between components of Gondwana, is indicated by ductile refliation, further high-grade metamorphic recrystallisation and metamorphic zircon overgrowths at approximately 530 Ma. This was followed by late- to post-tectonic magmatism, reflected by 500 Ma granite bodies and 490 Ma aplite dykes as well as a 480 Ma gabbro body.