Thin terrestrial sediment deposits on intertidal sandflats: effects on pore-water solutes and juvenile bivalve burial behaviour

Abstract

Abstract. Nearshore zones experience increased sedimentation due to coastal development and enhanced loads of fine terrestrial sediment (hereafter, TS) in river waters. Deposition of TS can alter seabed biogeochemical processes but the effects on benthic ecosystem functioning are unknown. The results of a past experiment with defaunated, intertidal sediment suggest that a decrease in the oxygenation of this sediment by a thin (mm) TS deposit causes substrate rejection (refusal to bury) by post-settlement juvenile recruits of the tellinid bivalve Macomona liliana. We further examined this behaviour, asking if such deposits negatively affect burial when applied to intertidal sediment that is oxygenated by bioturbation (C) or depleted of dead and living organic matter (D). We observed recruits on the surface of four treatments: C, D, and the same sediments to which we added a 1.7-1.9 mm layer of TS (CTS, DTS). The TS deposit decreased the oxygenation and the pH of the underlying intertidal sediment (CTS) confirming previous results, but significantly increased but not decreased the probability of burial, irrespectively of treatment. Juveniles more likely buried into C than into D. The mechanism that caused previously observed substrate rejection by post-settlement juvenile M. liliana remains unclear but our results suggest that contact of the recruits with the TS deposit does not cause substrate rejection. We now hypothesise that conditioning of sediment by bioturbation can mediate negative effects of TS deposits on the recruits' burial behaviour.

The scale‐dependent effect of environmental filters on species turnover and nestedness in an estuarine benthic community

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“…Contrary to the salinity gradient, which represents a transition along distinct but suitable conditions for life in aquatic systems, several factors make one end of the sedimentary gradient highly inhospitable for many species. In mud bottoms, superficial fine sediment acts as physical barrier that increases the contribution of anaerobic pathways to the overall decomposition and relocates the reoxidation of reduced solutes upwards (Hohaia et al 2014, Mestdagh et al 2018. Under this circumstance, oxygen penetration depth never exceeds a few centimeters and becomes a major limiting factor for sediment-dwelling organisms (Mestdagh et al 2018).…”

In situ soft sediment nutrient enrichment: A unified approach to eutrophication field experiments

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Resilience and Species Accumulation across Seafloor Habitat Transitions in a Northern New Zealand Harbour

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