Nematodes as indicators of environmental quality in seagrass (Posidonia oceanica) meadows of the NW Mediterranean Sea

Abstract

Meiofauna in sediments colonized by Posidonia oceanica in the Ligurian Sea (NW Mediterranean) was investigated to evaluate its use as an early warning indicator of environmental disturbance. Descriptors commonly used in seagrass health assessment are mainly related to the plant (e.g., phenological parameters) and/or to the meadow (e.g., structural parameters) and are subjected to long-term response times. Conversely, meiofauna is considered a good bioindicator with a rapid response to environmental variations, due to its main features (e.g., short life cycle, scarce mobility, presence/absence of tolerant/sensitive species). Meiofaunal community, sediment characteristics and organic matter descriptors in three meadows located in urbanized coastal areas were contrasted with those observed in three meadows located within Marine Protected Areas. Samplings were carried out in two distinct periods, at the beginning and at the end of the summer season, in order to individuate early changes in the meiofaunal assemblages. The meiofauna and, particularly, the nematode assemblage composition and diversity, highlighted differences among meadows at the end of the summer not detectable by organic matter descriptors and structural parameters of the meadow (e.g. shoot density). Nematodes are, thus, proposed as appropriate biological quality elements (BQEs) able to show early responses to environmental disturbance.

Meiofauna and harpacticoid copepods in different habitats of a Mediterranean seagrass meadow

“…This is in contrast with most studies on meiofauna in seagrass meadows sediments (e.g. Fonseca et al, 2011;Losi et al, 2012) where nematodes dominate numerically. Nevertheless, dominance of copepods is often documented for seagrass meadow canopy leaves (Hall & Bell, 1993;De Troch et al, 2001;Hooper & Davenport, 2006).…”

Contribution to the knowledge of meiobenthic Copepoda (Crustacea) from the Sardinian coast, Italy

“…Most sediments of the study area are coarse sands rich in vegetal detritus from seaweeds and P. oceanica. Copepods become typically more abundant with the increase in grain size (Losi et al, 2012; and are often associated with algal or seagrass detritus (Ceccherelli and Mistri, 1990;Mascart et al, 2013Mascart et al, , 2015. As reported in the cited literature, the presence of macrophytal detritus may play an important role as a refuge and food source for these animals, increasing their abundance and diversity (e.g.…”

Meiofauna is an important, yet neglected, component of biodiversity ofPosidonia oceanica

“…At the same time, densely aggregated leaves foster many epiphytes, offering new and more abundant food sources to the meiofauna (Velimirov & Walenta-Simon, 1993;Mascart et al, 2018; but see Lebreton et al, 2012 on Zostera noltii). Indeed, all studies addressing temporal variation in P. oceanica found substantial differences over time, not only in taxa composition and abundance (Novak, 1989;Villora-Moreno et al, 1991;Losi et al, 2012;Cvitković et al, 2017;Polese et al, 2018), but also in species' dietary preferences (Mascart et al, 2018). These studies collectively showed that abundances of most meiofaunal taxa peaked between spring and summer (Novak, 1982(Novak, , 1989Villora-Moreno et al 1991;Sánchez-Jerez et al 1999a;Losi et al, 2012;Cvitković et al, 2017;Polese et al, 2018), in accordance with the apogee of P. oceanica.…”

“…Such sheltering effect is stronger in the matte, which also shows a higher diversity than that in the leaves, both in meiofaunal (Novak, 1982(Novak, , 1989Guilini et al, 2017; see Figure 2A and 2D) and macrofaunal species (Gambi et al, 1995;Borg et al 2006;Piazzi et al 2016). Food availability within each habitat, finally, drives the presence of different species not only depending on the amount of food (Mirto et al, 2010(Mirto et al, , 2014Castejón Silvo, 2011;Losi et al, 2012;Mascart et al, 2013;Cvitković et al, 2017;Polese et al, 2018) but also upon the presence of specific food sources. In fact, it has been shown that even closely related meiofaunal species may prefer different food sources (Mascart et al, 2018).…”