|Distribution of net-collected planktonic cnidarians along the northern Mid-Atlantic Ridge and their associations with the main water masses|
|Hosia, A.; Stemmann, L.; Youngbluth, M. (2008). Distribution of net-collected planktonic cnidarians along the northern Mid-Atlantic Ridge and their associations with the main water masses. Deep-Sea Res., Part 2, Top. Stud. Oceanogr. 55(1-2): 106-118. dx.doi.org/10.1016/j.dsr2.2007.09.007|
|In: Deep-Sea Research, Part II. Topical Studies in Oceanography. Pergamon: Oxford. ISSN 0967-0645, more|
Plankton surveys; Biogeography; Gelatinous zooplankton; Cnidaria; North Atlantic; Mid-Atlantic Ridge
Planktonic cnidarians and ctenophores were sampled with a multiple opening–closing net (Multinet) as well as a non-quantitative plankton net along the northern Mid-Atlantic Ridge (MAR) between Iceland and the Azores. Sixty-four species or genera of planktonic cnidarians (38 siphonophora, 21 hydromedusae, 5 scyphomedusae) and one genus of ctenophore were collected. Of these, Leuckartiara adnata and Clausophyes laetmata were new records for the area. Multinet samples collected from depths of 0–100, 100–500, 500–1000, 1000–1500 and 1500–2500 m at 11 stations were compared. Multivariate analysis of the data indicated that species composition and abundance along the ridge varied with the dominant water masses, with changes in the cnidarian zooplankton assemblage observed with regard to geographic location as well as depth. The surface waters of the two northernmost stations characterized by modified North Atlantic Water (MNAW) as well as the three southernmost stations characterized by North Atlantic Central Water (NACW) exhibited relatively high abundances (3284–13,915 individuals·1000 m-3) in the upper 100 m. No such peak was evident at the middle stations characterized by Subarctic Intermediate Water (SAIW), where the abundances in the upper three depth strata were consistently lower (57–863 individuals·1000 m-3). Across the study area, the lowest abundances were found in the 1500–2500 m stratum (0–56 ind.·1000 m-3). The main divergence in the species composition and abundance of planktonic cnidarians was observed at the Subpolar Front (SPF), which marked the boundary for the distribution of many species. The divergence at the SPF was strongest in the upper 500 m but observable down to 1500 m. Profoundly different epipelagic species assemblages were observed in SAIW and NACW on opposite sides of the SPF, with the distribution of several species of calycophoran siphonophores confined to the southern NACW. At mid-water depths, the species composition north of the SPF was possibly influenced by Labrador Sea Water (LSW). The highest diversity of planktonic cnidarians was observed in the surface waters south of the SPF and in the 100–1000 m range north of the SPF.