Salinity drives meiofaunal community structure dynamics across the Baltic ecosystem

Abstract

Coastal benthic biodiversity is under increased pressure from climate change, eutrophication, hypoxia, and changes in salinity due to increase in river runoff. The Baltic Sea is a large brackish system characterized by steep environmental gradients that experiences all of the mentioned stressors. As such it provides an ideal model system for studying the impact of on‐going and future climate change on biodiversity and function of benthic ecosystems. Meiofauna (animals < 1 mm) are abundant in sediment and are still largely unexplored even though they are known to regulate organic matter degradation and nutrient cycling. In this study, benthic meiofaunal community structure was analysed along a salinity gradient in the Baltic Sea proper using high‐throughput sequencing. Our results demonstrate that areas with higher salinity have a higher biodiversity, and salinity is probably the main driver influencing meiofauna diversity and community composition. Furthermore, in the more diverse and saline environments a larger amount of nematode genera classified as predators prevailed, and meiofauna‐macrofauna associations were more prominent. These findings show that in the Baltic Sea, a decrease in salinity resulting from accelerated climate change will probably lead to decreased benthic biodiversity, and cause profound changes in benthic communities, with potential consequences for ecosystem stability, functions and services.

Animals, protists and bacteria share marine biogeographic patterns

“…In contrast to temperature, salinity had a minor role in structuring the studied communities (Fig. 2), an observation previously reported for the global ocean 12 , with exceptions found in microbial 63 and meiofaunal 64 life in regions with unusually strong salinity gradients (e.g. Baltic Sea).…”

Meiofauna improve oxygenation and accelerate sulfide removal in the seasonally hypoxic seabed

“…However, we cannot exclude that in our sediments nematodes were also oxidizing sulfide thanks to their microbial ecto- and endosymbionts ( Giere et al, 1995 ; Hentschel et al, 1999 ; Ott et al, 1991 ; Polz et al, 1992 ). Bacterivory is the most abundant feeding type among nematodes collected in the same area ( Broman et al, 2019 ; Olafsson and Elmgren, 1997 ). These nematodes can migrate several times per day between the oxic and sulfidic layers to promote the activity of their symbionts from which they receive food ( Ott et al, 1991 ).…”

High throughput shotgun sequencing of eRNA reveals taxonomic and derived functional shifts across a benthic productivity gradient

“…Potentially this could be a beneficial feeding strategy at the deeper stations where the sediment consists mainly of decayed organic particles and bacteria as food (and is reflected in the nematode feeding type analysis; Figure 7). Sabatieria are typical nematodes found in organic rich sediments, and have been identified in sediments also containing other nonselective deposit feeders such as Daptonema (Armenteros et al., 2009; Broman et al., 2019; Montagna & Harper, 1996; Schratzberger, Warr, & Rogers, 2006). Interestingly, the genera Daptonema and Desmolaimus (also a nonselective deposit feeder (Schratzberger et al., 2007)) had a higher relative abundance at the Low OC stations.…”