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

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

Coupling marine ecosystem state with environmental management and conservation: A risk-based approach

\ua9 2024 The Author(s)The sustainability of marine ecosystems demands a focus on ecological improvement, necessitating managers and conservationists to consider a range of actions from those that limit stressors to those that actively restore. Deciding the most appropriate action should be informed by environmental context, which includes assessing information on both degradation and recovery potential. Here, we provide an analysis of how the degree of ecological degradation coupled with the stressor regime can inform environmental management and conservation actions (e.g., stressor reductions, adaptive management, assisted recovery/restoration). With this analysis we design a risk framework combining principles that define ecosystem resilience and recovery times with those that characterize stressor regimes (i.e., the number, type, and impact). The combination of these principles defines where an ecosystem is placed along sliding scales of degradation and recovery and likely response to protective and restorative interventions. It is designed to facilitate place-based conversations regarding the risks of different management actions informed by the temporal dynamics of ecosystem degradation and recovery

Barriers to coastal planning and policy use of environmental research in Aotearoa-New Zealand

Identifying barriers to the effective use of science in coastal management of Aotearoa-New Zealand is easy, due to the present lack of complicated governance and management structures, coupled with an emphasis on funding science that includes pathways to implementation. This opinion piece discusses four areas that still hinder effective use of science, all of which are likely to be problematic for other countries. We initially focus on why the science may not be used related to: misunderstandings (linguistic and conceptual differences including indigenous world views); timing of information delivery; uncertainty surrounding the information (knowledge limitations and funding); and top-down constraints (legal systems, politics and institutional objectives). We use Aotearoa-New Zealand examples to demonstrate the barriers operating within each area and discuss three potential solutions. Importantly our analysis indicates that researchers alone cannot transcend these barriers; rather, we need to work as part of an ecosystem, requiring commitment from all society, extending beyond the usual suspects (management agencies). We believe that ecological and systems education from junior school levels through to universities have an important role to play in setting the context to overcome current barriers

Calcium carbonate alters the functional response of coastal sediments to eutrophication-induced acidification

Coastal ocean acidification research is dominated by laboratory-based studies that cannot necessarily predict real-world ecosystem response given its complexity. We enriched coastal sediments with increasing quantities of organic matter in the field to identify the effects of eutrophication-induced acidification on benthic structure and function, and assess whether biogenic calcium carbonate (CaCO₃) would alter the response. Along the eutrophication gradient we observed declines in macrofauna biodiversity and impaired benthic net primary productivity and sediment nutrient cycling. CaCO₃ addition did not alter the macrofauna community response, but significantly dampened negative effects on function (e.g. net autotrophy occurred at higher levels of organic matter enrichment in +CaCO₃ treatments than −CaCO₃ (1400 vs 950 g dw m‾²)). By identifying the links between eutrophication, sediment biogeochemistry and benthic ecosystem structure and function in situ, our study represents a crucial step forward in understanding the ecological effects of coastal acidification and the role of biogenic CaCO₃ in moderating responses