Abstract
Marine invasive species may modify their host environment by altering ecosystem biogeochemistry. We hypothesized that the invasive polychaete Marenzelleria viridis in Baltic Sea areas increases sulfate reduction (SR) in sediment micro-zones surrounding its burrow. Consequently, higher free porewater sulfide (H2S) is expected in sediments dominated by M. viridis than in corresponding sediments inhabited by the native polychaete Hediste diversicolor. In a thin-aquaria experiment, we found high SR rates (220 to 539 nmol cm−3 d−1) around the burrow walls of M. viridis as well as in surface and subsurface sediments with overall rates 2-fold higher than in defaunated control sediment. Similarly, an in situ survey revealed subsurface porewater H2S peaks moving upward towards the sediment surface in M. viridis inhabited areas. Accordingly, 50–85% higher porewater H2S was found almost year-round in these areas compared with H. diversicolor inhabited areas, suggesting that the invasion of M. viridis probably led to a substantial change in sediment biogeochemistry. In conclusion, M. viridis stimulates SR in sediment micro-zones and increases H2S in coastal sediments. Such change to more reducing conditions after the invasion may have critical environmental implications on, e.g., the distribution of H2S intolerant flora and fauna species.
Highlights
Major impacts of invasive species in host environments are often related to biodiversity loss, predation and competition for space or food [1]
Hotspots of sulfate reduction (SR) ranging from 220 to 539 nmol cm−3 d−1 were identified in the center along the burrow walls of the two aquaria with M. viridis down to 16 cm depth (Figure 1A,B)
The AVS pool showed in Aq. 1 a pattern that was inverse of SR with lowest concentrations immediately around the burrow followed by 2–4-fold increased levels in zones 2–6 cm away from the burrow walls, while Aq. 2 had highest concentrations on the left side of M. viridis burrow (Figure 1D,E)
Summary
Major impacts of invasive species in host environments are often related to biodiversity loss, predation and competition for space or food [1]. M. viridis is the only Marenzelleria species found in high salinity coastal areas of Denmark with current abundances ranging from 200 to 1200 ind m−2 in sandy sediments [4]. The invasion of this species has shifted the dominance of benthic infauna and introduced a new functional niche through the formation of narrow (3 mm), but deep (up to 40 cm) “J”-shaped and blind-ended burrows [4,5]. Bioturbation by M. viridis is known to increase sulfate reduction (SR) in contrast to native species, such as Hediste diversicolor that increase aerobic processes in the sediment [6] This ability of M. viridis is explained by its burrow ventilation behavior. There is limited knowledge on the exact spatial pattern of SR stimulation by M. viridis in sediment micro-zones and to which extent high porewater H2S levels prevail in sediments where this species occurs
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