Nematode species distribution patterns at the Håkon Mosby Mud Volcano (Norwegian Sea)

Abstract

The Håkon Mosby Mud Volcano (HMMV) is a methane seep that is densely populated by the bacteria Beggiatoa spp. as well as by tubeworms of the Family Siboglinidae. Analyses of samples from seven stations located in five different habitats (bare sediments, bacterial mats, siboglinid fields, sediments with small patches of siboglinids and areas of ‘normal’ sea floor) revealed differences in the density and species‐level diversity of nematode communities. Total densities increased from stations inside the mud volcano and on its rim towards the ‘normal’ areas outside the volcano. Nematode species diversity was similar in samples from the siboglinid fields and the bare HMMV sediments. However, the sediment with patches of siboglinids collected outside the volcano was characterised by a diverse nematode community comprising 47 species, whereas the control sediments without siboglinids yielded only 27 species. The nematode assemblage at the bacterial mat site included only two identified species, Halomonhystera disjuncta and Sabatieria ornata, with H. disjuncta being strongly dominant. Terschellingia distlamphida, S. ornata and Aponema ninae dominated nematode communities at the siboglinid fields and in bare HMMV sediments. Species dominating at stations inside the caldera were found in comparable low densities in the sediment with siboglinid patches collected outside the volcano, but were missing in the background samples, where species of Endeolophos, Acantholaimus and Desmoscolex were dominant. Species diversity generally decreased with sediment depth. A subsurface‐dwelling nematode community was observed in the siboglinid fields and the bare sediments. Background sediments showed a sharp decline with 18–20 species at 0–2 cm versus three species at 3–5 cm sediment depth. The trophic composition of the nematode fauna at the HMMV showed a prevalence of deposit feeders at almost all stations, whereas background sediments exhibited a uniform distribution of non‐selective and selective deposit feeders and epistrate feeders. The high percentage of deposit feeders inside the mud volcano could be related to the grain‐size distribution and the significantly higher bacterial biomass compared to the control sediments.

Meiobenthos and nematode assemblages from different deep-sea habitats of the Strait of Sicily (Central Mediterranean Sea)

“…Low Δ+ measurement in PS and low diversity indices in two pockmark samples are in accordance with the established notion that nematode assemblages from extreme ecosystems imprinted by reduced conditions, like cold seeps and hot vents, often show a low diversity (Shirayama and Ohta, 1990;Dando et al, 1991;Van Gaever et al, 2010;Copley et al, 2007;Portnova et al, 2010b;De Groote and Vanreusel, 2011;Hauquier et al, 2011). Thus, low diversity indices might indicate that samples PS77 and PS82 are influenced by more stressing environmental conditions, such as those closer to seepage (De Groote and Vanreusel, 2011;Van Gaever et al, 2010).…”

“…Nematode assemblages from two PS samples (stations #77 and #82) had significantly lower diversity indices, possibly as a consequence of their proximity to the seep fluid emission (cf. Van Gaever et al, 2006;Portnova, 2010b). On the other hand, the fact that most samples (Group A) share similar assemblage structure may indicate a resemblance of habitats at these two sites.…”

“…Deep-water coral and cold seeps habitats are characterized by very different environments, and it is not reasonable to assume that the observed resemblance of nematode assemblages from these two sites reflects identical feeding conditions, as the total meiobenthos density at CS and MS was much higher than at PS. A possible explanation for this resemblance could be that PS samples were collected rather far from the seep fluid emission points, as also shown by the quite high redox potential in 0-2 cm sediment layer; moreover, the diversity of nematode assemblages within the samples of Group A was also high, in comparison to nematode assemblages living close to the seep fluid emission (Van Gaever et al, 2006;Portnova, 2010b).…”

“…The genus Sabatieria strongly dominated in the reduced sediments of several deep-sea cold seeps in the Mediterranean (De Groote and Vanreusel, 2011;Pape et al, 2011;Lampadariou et al, 2013). Halomonhystera were noted as a strong dominant in several studies on cold seeps from polar regions; other dominants from these regions included Terschellingia, Sabatieria, Tricoma and Laimella (Van Gaever et al, 2006;Portnova et al, 2010b;Hauquier et al, 2011; for review see Vanreusel et al, 2010a). Daptonema prevailed in the cold-seep nematode assemblage off Hatsushima, Central Japan followed in order of abundance by Chromadorita (Shirayama and Ohta, 1990).…”

“…Previous studies on nematode assemblages from cold seeps revealed high variability in their density, taxonomic composition, and assemblage structures, as a function of the geographic region, depth, macrobenthic communities, remoteness from the centre of seepages (Shirayama and Ohta, 1990;Olu et al, 1997;Van Gaever et al, 2006Portnova et al, 2010a, b;Vanreusel et al, 2010a, b;Zeppilli et al, 2011). They can exhibit high densities and, at the same time, a very low diversity (Van Gaever et al, 2006;Portnova et al, 2010b).…”