Diversity of meiofauna and free-living nematodes in hydrothermal vent mussel beds on the northern and southern East Pacific Rise

Abstract

The ecology and biogeography of meiofauna at deep-sea hydrothermal vents have historically received less attention than those of mega-and macrofauna. This study examines the composition of major meiofaunal taxa in beds of the mussel Bathymodiolus thermophilus at hydrothermal vents on the northern and southern East Pacific Rise (EPR) and presents the first comparison of species assemblages of the dominant taxon, the nematodes, among sites spanning 27 degrees of latitude. Meiofaunal samples were collected by submersible from three mussel beds at 9°N on the EPR and four mussel beds between 17 and 18°S in 1999. Estimated ages of the mussel beds at the time of sampling range from 4 to >20 years, enabling investigation of the influence of mussel bed age on meiofaunal assemblages. Overall, the meiofauna of the mussel beds was dominated by nematodes, with copepods constituting the second most abundant meiofaunal group. There was variation in the ratio of nematodes to copepods between sites, however, with copepods more abundant than nematodes in the youngest mussel beds. Apart from polychaete larvae, other meiofaunal groups were generally present at very low abundance (<1%) in the samples and restricted in diversity to gastropod larvae, acari, foraminifera, ostracoda and turbellaria. Seventeen nematode species from 14 genera and 11 families were found in the samples, with no evidence of endemicity to hydrothermal vents at the generic level. Four genera present were not previously recorded at hydrothermal vents. Nematode species richness, species:genus ratios and abundances were low compared with other deep-sea habitats, though the ecological relevance of comparisons with soft-sediment benthos is discussed. Nematode assemblages exhibited high dominance by a few species, with one species of Thalassomonhystera most abundant at five of the seven vent sites. Multivariate analysis of nematode assemblages reveals similarities among sites that do not match geographical proximity. The youngest mussel beds were most similar to each other and exhibited lower species richness than other sites, consistent with colonization of mussel bed habitat by nematodes over time. Similarity in the composition of nematode assemblages among sites separated by ∼3000 km indicates that they lie within a single biogeographic province, consistent with that proposed for mussel bed macrofauna. At a generic level, samples exhibited some overlap with nematode assemblages at vents elsewhere on the EPR, on the Mid Atlantic Ridge and in the North Fiji Basin.

Characteristics of meiofauna in extreme marine ecosystems: a review

“…In recent years, the deep-sea hydrothermal vent meiofauna has increasingly gained interest and several studies have been published (Vanreusel et al 1997;Tsurumi et al 2003;Zekely et al 2006a, b;Copley et al 2007;Gollner et al 2007Gollner et al , 2010bGollner et al , 2013Limén et al 2007;Degen et al 2012;Cuvelier et al 2014;Sarrazin et al 2015). Meiofauna is considered to contribute up to 20% of the total diversity known from deep-sea hydrothermal vents (Bright 2006).…”

“…In the vicinity of deep-sea vents, meiofauna can be associated with habitats ranging from inactive bare basalts (Gollner et al 2010b) and sediments (Vanreusel et al 1997) to diffuse vent flow areas colonised by macrofaunal assemblages (Zekely et al 2006a, c;Sarrazin et al 2015). Almost all studies that include meiofauna were conducted along the East Pacific Rise (EPR; Dinet et al 1988;Flint et al 2006;Gollner et al 2006Gollner et al , 2007Gollner et al , 2010bZekely et al 2006a, b, c;Copley et al 2007;Limén et al 2007Limén et al , 2008, with the exception of four studies: two in the West Pacific back-arc basins (Shirayama 1992;Vanreusel et al 1997) and three on the Mid-Atlantic Ridge (MAR; Zekely et al 2006a, b, c;Cuvelier et al 2014;Sarrazin et al 2015). The picture emerging from these studies points to a vent meiofauna with low abundance and diversity (Dinet et al 1988;Vanreusel et al 1997;Tsurumi et al 2003;Copley et al 2007;Limén et al 2007;Gollner et al 2010b) compared with other chemosynthetic ecosystems characterised by less extreme conditions.…”

“…Almost all studies that include meiofauna were conducted along the East Pacific Rise (EPR; Dinet et al 1988;Flint et al 2006;Gollner et al 2006Gollner et al , 2007Gollner et al , 2010bZekely et al 2006a, b, c;Copley et al 2007;Limén et al 2007Limén et al , 2008, with the exception of four studies: two in the West Pacific back-arc basins (Shirayama 1992;Vanreusel et al 1997) and three on the Mid-Atlantic Ridge (MAR; Zekely et al 2006a, b, c;Cuvelier et al 2014;Sarrazin et al 2015). The picture emerging from these studies points to a vent meiofauna with low abundance and diversity (Dinet et al 1988;Vanreusel et al 1997;Tsurumi et al 2003;Copley et al 2007;Limén et al 2007;Gollner et al 2010b) compared with other chemosynthetic ecosystems characterised by less extreme conditions. Their distributions vary with the abiotic conditions of the habitat (Gollner et al 2010b;Sarrazin et al 2015) and the presence of bacterial mats and large engineer species, such as mussels and tubeworms (Zekely et al 2006a, c;Gollner et al 2010b;Degen et al 2012).…”

Rapid colonisation by nematodes on organic and inorganic substrata deployed at the deep-sea Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge)

“…Whilst mega-and macrofauna in HVs have been studied since their discovery, the ecology of meiofaunal organisms has only recently been included in vent studies (Tsurumi et al 2003;Zekely et al 2006a, b;Limén et al 2007;Gollner et al 2007Gollner et al , 2010aCopley et al 2007;Sarrazin et al in press). Several HV habitats, from inactive bare basalts (Gollner et al 2010b) and sediments (Vanreusel et al 1997) to diffuse flow areas colonized by macrofaunal assemblages (Zekely et al 2006a, c), host meiofaunal communities characterized by low abundance and diversity, linked with the abiotic and biotic conditions of the habitat (Gollner et al 2010b;Zekely et al 2006a, c;Degen et al 2012).…”

“…A study on mussel beds of different ages (4 to >20 years) showed that nematodes were less abundant and diverse at younger sites (Copley et al 2007). Volcanic eruptions would negatively impact nematodes that may require long periods to colonize a newly lava-flooded area (Gollner et al 2013).…”