Habitat modification mediated by motile surface stirrers versus semi-motile burrowers: potential for a positive feedback mechanism in a eutrophied ecosystem

Abstract

We performed a 4 wk laboratory experiment with the semi-motile burrowers Macoma balthica and Marenzelleria spp. and the motile surface sediment stirrers Monoporeia affinis and Mysis mixta to study their effects on the transport of tracer particles (mean diameter [л] 1 µm) in the sediment, sediment parameters (depth of the oxidized layer, water content, organic matter content), water turbidity, and nutrient fluxes across the sediment-water interface , NO 2 -+ NO 3 -, NH 4 + ; measured weekly). Two densities were included for each taxon, representing a low and a high field density. M. balthica significantly increased particle mixing, the rates being 59.6 and 61.9 × 10 -3 cm 2 d -1. While all taxa increased turbidity in the overlying water, the strongest effects were caused by M. affinis and M. mixta, resulting in 112-and 45-fold increases, respectively. In addition, these 2 motile species increased oxidation of the sediment surface layers. A distinctive difference in the nutrient fluxes was observed between the semi-motile (M. balthica, Marenzelleria spp.) and the motile taxa (M. affinis, M. mixta). The former increased the efflux of both PO 4 3 -and NH 4 + , while the latter suppressed the efflux of NH 4 + and decreased the sediment uptake of NO x , indicating enhanced N removal. Higher nutrient exchange rates were observed at the higher animal densities. We conclude that a shift in the benthic communities from the 2 motile to the 2 semi-motile taxa, observed throughout the northern Baltic Sea, may notably alter the regime of benthic nutrient cycling and thereby the performance of the entire ecosystem.KEY WORDS: Bioturbation · Motile · Semi-motile · Nutrient cycling · Particle mixing · Turbidity Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 376: [21][22][23][24][25][26][27][28][29][30][31][32] 2009 The macrozoobenthos of the northern Baltic Sea is characterized by a low number of species, with the amphipod Monoporeia affinis Lindström, the bivalve Macoma balthica (L.) and the invasive polychaetes Marenzelleria spp. being some of the few key organisms (Laine et al. 1997, Karlson et al. 2002. In addition to sediment-dwelling taxa, the nectobenthic mysid Mysis mixta Lilljeborg is an important, although frequently neglected, component of the benthic biota (e.g. Lindström & Sandberg-Kilpi 2008). These taxa, hereafter referred to as Monoporeia, Macoma, Marenzelleria, and Mysis, differ in terms of their degree of motility and their burrowing depth: Mysis is epibenthic, while the others belong to the infauna, Marenzelleria being the only deep-burrowing (>10 cm) taxon. Monoporeia and Mysis are motile detritivores and carnivores, stirring the sediment surface (Lopez & Elmgren 1989, Viherluoto et al. 2000, while Macoma and Marenzelleria are semi-motile detritivores, capable of switching between deposit-and suspension-feeding modes (Dauer et al. 1981, Lin & Hines 1994.Large-scale changes in the relative abundance of these 4 taxa have occurred in the northern Balt...

Nutrient fluxes from reduced Baltic Sea sediment: effects of oxygenation and macrobenthos

“…In the present study, no resuspension was observed, and small fluxes of particulate nutrients unrelated to bioturbation were recorded. As resuspension by M. affinis is positively related to animal abundance (Viitasalo-Frösén et al 2009), the relatively low animal abundance in the present study is a plausible explanation for the insignificant effect of M. affinis on benthic DOP and PP fluxes.…”

“…The lack of species identification in this and most related previous studies, therefore, introduces uncertainty in the comparison of results and may explain diverging experimental findings on the effects of Marenzelleria bioturbation on benthic DIP exchange rates (Viitasalo-Frösén et al 2009, Bonaglia et al 2013). Our results are most likely representative for M. arctia (see 'Sampling and introduction of animals').…”

Are similar worms different? A comparative tracer study on bioturbation in the three sibling species Marenzelleria arctia, M. viridis, and M. neglecta from the Baltic Sea

“…These differences could in part be due to the choice of models, fitness of organisms, or sediment characteristics not measured here. The particle transport of M. arctia was investigated in a study by Viitasalo-Frö sen et al (2009). The high diffusion coefficients (3.76-5.11 cm 2 yr 21 ) originate most likely from the initial burrowing effect included in the investigation, while the different tracer used may also influence the results.…”

“…The spreading of M. viridis is accompanied by decreasing populations of H. diversicolor , whereas M. neglecta is known for their competitive interactions with M. affinis (Kotta et al 2006). The invasion of the polychaetes has complex effects on nutrient dynamics (Hietanen et al 2007;Norkko et al 2011;Quintana et al in press) and eutrophication (Karlson et al 2007;Viitasalo-Frö sen et al 2009). In the Baltic Sea, where deep-burrowing species are naturally absent, the burrowing activity of Marenzelleria spp.…”

Contrasting effects of the polychaetes Marenzelleria viridis and Nereis diversicolor on benthic metabolism and solute transport in sandy coastal sediment

“…Effects of Marenzelleria viridis on sediment biogeochemistry are poorly known and the only studies available on Marenzelleria effects are from the central and northern Baltic Sea (Karlson et al 2005, Hietanen et al 2007, Viitasalo-Frösén et al 2009), where primarily the sibling species M. neglecta or M. arctia occur in finegrained muddy sediments. However, Quintana et al (2007) found that M. viridis in Danish waters prefers shallow sandy sediment.…”