Small-scale effect of intertidal seagrass (Zostera muelleri) on meiofaunal abundance, biomass, and nematode community structure

Abstract

Seagrass beds are common features of coastal ecosystems worldwide, and their associated infauna are often more productive and diverse than in unvegetated habitats. Little is known, however, about the ecology of meiofaunal communities living in seagrass sediments. We compared the abundance and biomass of sediment meiofauna inside and outside an intertidalZostera muelleribed in southern New Zealand to assess the impact of seagrass cover on meiofaunal distribution. Nematode community structure, diversity, and feeding groups were also compared between habitats and sediment depths (0–2, 2–5 and 5–10 cm) to evaluate the effect of seagrass on nematode communities. Meiofaunal biomass was significantly higher inside than outside theZ. muelleribed, but secondary productivity inside the bed is likely to have been limited by the availability of labile organic matter. There were significant differences in nematode community structure between unvegetated, sparsely vegetated, and densely vegetated sites (102 m scale), as well as between sediment depths (cm scale). No significant differences were found in depth-integrated (0–10 cm) nematode diversity between sites, but vertical gradients in diversity differed between vegetated and unvegetated sites. Epistrate feeders were the most common feeding group in unvegetated sediments whereas most feeding groups were common inside the seagrass bed. Findings from this study indicate that seagrass beds can have a marked impact on infaunal structure and function over small spatial scales through their effect on sediment characteristics and organic matter input. Some unexpected trends observed in the present study, i.e. low meiofaunal biomass at the vegetated sites, and lower abundance of copepods inside than outside the seagrass bed, suggest that the nature of seagrass–invertebrate interactions may depend on habitat characteristics and the identity and ecology of species considered.

Meiofaunal communities in a tropical seagrass bed and adjacent unvegetated sediments with note on sufficient sample size for determining local diversity indices

“…According to the multivariate analyses, the nematode abundance and diversity recorded in the seagrass bed being higher than those in the adjacent unvegetated sediments are consistent with previous studies (Castel et al 1989;Hourston et al 2005;Monthum and Aryuthaka 2006;Leduc and Probert 2011). However, an unexpected pattern was observed in this study where copepods display a reverse trend to nematodes, i.e., the abundance of copepods inside the seagrass bed is lower than that in the unvegetated area.…”

“…However, an unexpected pattern was observed in this study where copepods display a reverse trend to nematodes, i.e., the abundance of copepods inside the seagrass bed is lower than that in the unvegetated area. Most surveys have mentioned that copepod densities are higher in seagrass beds (e.g., Hicks 1986;Ansari and Parulekar 1994;Ndaro and Ólafsson 1999;De Troch et al 2001), but a contrary result has also been reported (Leduc and Probert 2011). Shallow seagrass beds may not substantially influence the abundance of copepods as the deeper ones do (De Troch et al 2001).…”

“…The abundance of copepods is positively related to the coarser sediments (Coull 1985), whereas sediments underneath seagrass are commonly finer than those of unvegetated areas. In addition, the dense canopies of seagrasses prevent the growth of microphytobenthos, which are the main diet of copepods (Leduc et al 2009;Leduc and Probert 2011). The epibenthic and interstitial Figure 3 Scatterplots by correspondence analysis of (a) higher meiofaunal taxa and (b) nematode genera.…”

“…Water flows or bioturbated activities improve oxygen penetration in sandy habitats and then induce vertical migration of nematodes to a deeper (beneath 5 cm) sediment layer (Steyaert et al 2003;Giere 2009). The seagrass bed in Shihlang possesses a large amount of coarse sands, where nematodes tend to distribute more deeply (McLachlan et al 1977;Heip et al 1985), and thus, the vertical profile of the nematode community can be clarified by sampling deeper than 5-or 10-cm depths (Steyaert et al 2003;Leduc and Probert 2011).…”

“…The abundance and community structure of nematodes show substantial differences between vegetated and peripheral unvegetated sites (Fisher and Sheaves 2003;Hourston et al 2005;Monthum and Aryuthaka 2006;Fonseca et al 2011;Leduc and Probert 2011), although no difference between both habitats has also been reported (Ndaro and Ólafsson 1999). The variability in nematode populations on a small spatial scale (centimeter scale) accounts for 30% and 43% in intertidal and shallow subtidal sediments, respectively (Hodda 1990;Li et al 1997).…”