Loss of Large Animals Differentially Influences Nutrient Fluxes Across a Heterogeneous Marine Intertidal Soft-Sediment Ecosystem

Benthic ecosystem function responses to plasticizer content in polyester and PVC

Plastics are ubiquitous contaminants in marine systems with a diverse set of chemical components. While eco-toxicological effects of plastic chemicals provide insights on how marine species respond to plastic exposure, there is lack in ecological understanding of such impacts. In a mesocosm experiment, we measured benthic fluxes to determine ecosystem function responses to polyester netting (low plasticizer concentration) and PVC netting (high plasticizer concentration). Gross primary production rates and ammonium efflux were higher in both plastic treatments compared to the control, but responses were stronger in the polyester treatment. In the PVC treatment we additionally observed a strong response in nitrate fluxes which suggests a disturbance of the benthic N cycle. Our results imply that the concentration of chemical additives in new plastics can be a driver for ecological responses and reduction of plastic emissions needs to remain at the forefront of environmental plastic pollution regulations.

Razor clam (Pinna bicolor) structural mimics as drivers of epibenthic biodiversity; a manipulative experiment

Shellfish ecosystems facilitate important ecological functions and communities, but overexploitation and mismanagement have contributed to their decline worldwide. Within recent decades, coastal management efforts have increasingly sought to understand and reinstate valuable ecological functions provided by habitat-forming bivalves including oysters, mussels and pinnids. However, many bivalve species are critically understudied, limiting restoration and ecological engineering opportunities. Pinnids, specifically, are an underappreciated bivalve group, with razor clams (Pinna bicolor) forming dense aggregations, and potentially supporting important ecological functions. This study, conducted in an urban Australian estuary, was a manipulative experiment that investigated whether artificial razor clam shells could facilitate beneficial ecological functions through the provision of structural habitat. Specifically, we investigated the influence of intertidal benthic structures, including the micro-habitat influences of surface structure associated with mortality status (open or closed shell), and the short-term response of the benthic and epifaunal communities. Within 12 weeks, the structural razor clam mimics rapidly changed the aboveground ecological community, relative to the bare habitat controls. Both open and closed artificial shells provided a settlement surface for epiphytic organisms and supported enhanced epifaunal biodiversity. Contrastingly, the artificial structures did not significantly alter sediment characteristics or infaunal macroinvertebrate composition in the surrounding benthos. These results provide important insights into the rapid ecological response to the installation of intertidal pinnid structures in dynamic estuarine ecosystems. Furthermore, we provide a case study for understanding the ecological functions of an understudied habitat-forming species, which could be used to inform future restoration and management efforts.

Polyester microfiber impacts on coastal sediment organic matter consumption

As plastic pollution continues to accumulate at the seafloor, concerns around benthic ecosystem functionality heightens. This research demonstrates the systematic effects of polyester microfibers on seafloor organic matter consumption rates, an important benthic ecosystem function connected to multiple reactions and processes. We used a field-based assay to measure the loss of organic matter, both with and without polyester microfiber contamination. We identified sediment organic matter content, mud content, and mean grain size as the main drivers of organic matter consumption, however, polyester microfiber contamination decoupled ecosystem relationships and altered observed organic matter cycling dynamics. Organic matter consumption rates varied across horizontal and vertical spaces, highlighting that consumption and associated plastic effects are dependent on environmental heterogeneity at both small (within sites) and larger (between sites) scales. Our results emphasize the important role habitat heterogeneity plays in seafloor organic matter consumption and the associated effects of plastic pollution on ecosystem function.

Modelled broad-scale shifts on seafloor ecosystem functioning due to microplastic impacts on bioturbation

Bioturbating species play an essential role in regulating nutrient cycling in marine sediments, but their interaction with microplastics (MP) remains poorly understood. Here we investigated the linkage between MP and ecosystem functioning using experimental observations of luminophore distribution in the sediment to parametrize bioturbation coefficients (Db). this information as fed into a simplified transport-reaction model, allowing us to upscale our experimental results. We found that the composition of bioturbators modulated shifts in the ecosystem functioning under microplastic stress. Maldanid worms (Macroclymenella stewartensis), functionally deep burrowing and upward-conveyor belt feeders, became less active. The Db of M. stewartensis reduced by 25% with the addition of 0.002 g MP cm-2 at surface sediment, causing accumulation of organic matter in the oxic sediment zone and stimulating aerobic respiration by 18%. In contract, the tellinid bivalve Macomona liliana, functionally a surface -deposit feeder that excretes at depth, maintained particle mixing behaviour in MP-contaminated systems. This study provides a mechanistic insight into the impacts of MP and indicates that the functional role of bioturbating species should be involved in assessing the global impact of MP. The model allowed us to understand the broad-scale impact of MP on seafloor habitat.

Real-world impacts of microplastic pollution on seafloor ecosystem function

Emerging research shows that microplastic pollution could be impacting seafloor ecosystem function, but this has been primarily demonstrated without environmental and ecological context. This causes uncertainty in the real-world effects of microplastic pollution and leaves out essential information guiding policy and mitigation. In this study, we take a well-supported sampling design and statistical approach commonly employed in benthic ecology to evaluate real-world effects of microplastic pollution on coastal, benthic ecosystem function. We utilised environmental gradients in the Waitemata Harbour of Auckland, New Zealand to evaluate the importance of commonly assessed biological, chemical, and geological sediment variables and the characteristics of microplastic contaminants in driving essential ecosystem functions. Our results showed that models including microplastic terms were more accurate and explained more variability than those without microplastic terms, highlighting that microplastics impact real-world seafloor ecosystem function. Specifically, microplastic fibers significantly influenced oxygen flux (p < 0.03) and the diverse forms of microplastics (i.e., richness) significantly influenced ammonium flux (p < 0.02). Additionally, interactions between microplastic fiber concentrations and mollusc abundances significantly contributed to oxygen flux (p < 0.02). These results provide the first evaluation of in situ relationships between microplastics and ecosystem function. Even more importantly, this study suggests the value of environmental and ecological context for addressing microplastic impacts on benthic ecosystems and argues for further field examination.

Estimating Effects of Sea Level Rise on Benthic Biodiversity and Ecosystem Functioning in a Large Meso-Tidal Coastal Lagoon

Estuaries are among the world's most productive ecosystems, but due to their geographic location, they are at the forefront of anthropogenic pressures. Sea level rise (SLR) is one major consequence of climate change that poses a threat to estuaries with extensive intertidal habitats. The ecological implications of intertidal habitat loss have been largely overlooked despite their likely significance. We aimed to address this knowledge gap by investigating how benthic macroinvertebrate communities and their contributions to ecosystem function are likely to respond to SLR. Based on a spatially extensive dataset (119 sites) from a large coastal lagoon, depth, sediment chlorophyll concentrations, mud content, and average current speed were identified as the main drivers of community compositional turnover. Shifts in benthic community structure and associated functional implications were then evaluated using depth as a proxy for SLR. Three main macrofaunal groups representing intertidal, shallow subtidal, and deep subtidal habitats were identified. Functional trait analysis indicated low functional redundancy for a key intertidal suspension-feeding bivalve (Austrovenus stutchburyi) and the lack of a shallow subtidal functional replacement should intertidal habitats become inundated. These findings strongly suggest SLR and the associated environmental changes will alter estuarine macroinvertebrate communities, with implications for future ecosystem function and resilience.

Loss of benthic macrofauna functional traits correlates with changes in sediment biogeochemistry along an extreme salinity gradient in the Coorong lagoon, Australia

Estuarine ecosystems are considered hotspots for productivity, biogeochemical cycling and biodiversity, however, their functions and services are threatened by several anthropogenic pressures. We investigated how abundance and diversity of benthic macrofauna, and their functional traits, correlate to sediment biogeochemistry and nutrient concentrations throughout an estuarine-to-hypersaline lagoon. Benthic communities and functional traits were significantly different across the sites analysed, with higher abundance and more traits expressed in the estuarine region. The results revealed that the benthic trait differences correlated with sediment biogeochemistry and nutrient concentrations in the system. The estuarine regions were dominated by high abundance of large burrowing and bioturbating macrofauna, promoting nutrient cycling and organic matter mineralisation, while these organisms were absent in the hypersaline lagoon, favouring accumulation of organic matter and nutrients in the sediment. The results highlight the importance of preserving healthy benthic communities to maintain ecosystem functioning and mitigate the potential impacts of eutrophication in estuarine ecosystems.