Hydrothermal assemblages associated with different foundation species on the East Pacific Rise and Mid‐Atlantic Ridge, with a special focus on mytilids

Abstract

AbstractThis study was aimed at comparing the composition and structure of macrofauna assemblages living on mytilid foundations from different hydrothermal vent areas and depths and comparing their composition with that of other foundation species (alvinellids, siboglinids and alvinocaridid shrimps) from various ecotopes within the same vent field, attempting to identify unique features of mytilid assemblages. Areas investigated were located at different depths on the Mid‐Atlantic Ridge (MAR; Menez Gwen – 850 m, Lucky Strike – 1650 m, Rainbow – 2300 m, Broken Spur – 3000 m, Snake Pit – 3480 m, Logatchev – 3000 m) and at the depth of 2500 m on the East Pacific Rise (EPR; 9° N, 11° N, 17° S). Mussels occur at temperatures from 2 to 20 °C, whereas shrimps and alvinellids inhabit warmer zones with temperatures ranging from 20 to 40 °C. Siboglinids may occur together with mytilids, but more often they settle closer to hydrothermal vent emissions and live at temperatures exceeding 20 °C. Four main geographic groups of mytilid assemblages were distinguished: the northern EPR (9° N and 11° N) and southern EPR groups (17° S) and the more northern MAR (Lucky Strike and Rainbow) and more southern MAR groups (Broken Spur, Snake Pit and Logatchev). The most northern and shallow Atlantic area, Menez Gwen (850 m), differed from other Atlantic and Pacific areas by specific taxa composition and dominance of one taxon, the lepetodrilid gastropod, Lepetodrilus atlanticus (59%). Family richness was higher in mytilid assemblages than in shrimp and alvinellid assemblages: 2 and 2.5 times, respectively. Species composition in shrimp and alvinellid assemblages was poorer than in mytilid assemblages from the same field: 35% of species penetrated from mytilid to shrimp assemblages and 22% from mytilid to alvinellid assemblages. The percentage of species unique to shrimp or alvinellid assemblages was relatively low: 0% and 32%, respectively. On the MAR, similarity among assemblages of different foundation species within the same hydrothermal field was higher than among assemblages of the same foundation species from different fields and depths. On the EPR, similarity was higher among assemblages of the same foundation species from different fields at the same depth than among assemblages of different foundation species from the same field.