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.

The influence of mussel restoration on coastal carbon cycling.

Increasing responsiveness to anthropogenic climate change and the loss of global shellfish ecosystems has heightened interest in the carbon storage and sequestration potential of bivalve-dominated systems. While coastal ecosystems are dynamic zones of carbon transformation and change, current uncertainties and notable heterogeneity in the benthic environment make it difficult to ascertain the climate change mitigation capacity of ongoing coastal restoration projects aimed at revitalizing benthic bivalve populations. In this study we sought to distinguish between direct and indirect effects of subtidal green-lipped mussels (Perna canaliculus) on carbon cycling, and combined published literature with in-situ experiments from restored beds to create a carbon budget for New Zealand's shellfish restoration efforts. A direct summation of biogenic calcification, community respiration, and sediment processes suggests a moderate carbon efflux (+100.1 to 179.6 g C m-2  year-1 ) occurs as a result of recent restoration efforts, largely reflective of the heterotrophic nature of bivalves. However, an examination of indirect effects of restoration on benthic community metabolism and sediment dynamics suggests that beds achieve greater carbon fixation rates and support enhanced carbon burial compared to nearby sediments devoid of mussels. We discuss limitations to our first-order approximation and postulate how the significance of mussel restoration to carbon-related outcomes likely increases over longer timescales. Coastal restoration is often conducted to support the provisioning of many ecosystem services, and we propose here that shellfish restoration not be used as a single measure to offset carbon dioxide emissions, but rather used in tandem with other initiatives to recover a bundle of valued ecosystem services.

Enhancing multiple scales of seafloor biodiversity with mussel restoration.

Restoration projects are underway internationally in response to global declines in shellfish beds. As diverse biological assemblages underpin a variety of ecosystem services, understanding broader changes in biodiversity associated with mussel restoration becomes increasingly valuable to scientists and restoration practitioners. Studies generally show bivalve beds increase species richness and abundance, but results are scale-dependent and conditional on the mobility of specific communities observed. We examined biodiversity at multiple scales to determine how communities with varying levels of mobility are influenced by subtidal mussel restoration. Significant changes in assemblage structure were observed in both mobile fish and epifaunal communities, with enhanced species richness and total abundance of associated individuals. In contrast, we observed site-dependent effects of bivalve restoration on macrofaunal community structure and composition, with sheltered, harbour mussel bed communities numerically dominated by detritivores accustomed to organically enriched, muddy sediments. Sediment organic matter significantly increased within mussel beds, and distance-based linear models showed that sediment organic matter was an important predictor of macrofaunal assemblage structure on mussel beds, highlighting the significance of benthic-pelagic coupling and biodeposition to soft-sediment communities. This study contributes novel methods and ecological insights on the role of species mobility and site selection in structuring restoration outcomes, better informing future mussel restoration efforts aimed at emphasising functionally-driven ecosystem services.

Predicting habitat suitability of filter-feeder communities in a shallow marine environment, New Zealand.

The distribution of benthic ecosystems, dominated by filter-feeding communities, is highly influenced by the seabed geomorphology. However, the spatial variation in settlement of these species is also affected by near-bottom currents and any changes in light, nutrient concentration and food quality often associated with increases of suspended sediment concentrations within the water column. Detailed predictions of the geographic distribution of filter-feeder species and a deeper understanding of the physical processes influencing their distribution patterns is key for effective management and conservation. To date, predictive distribution modelling has been derived essentially from geomorphological parameters, mainly using spatially limited observations. In this study, seabed mapping, oceanographic modelling, hydrographic records and biological observations are integrated to provide high-resolution prediction of filter-feeder habitat distribution within Queen Charlotte Sound/Totaranui and Tory Channel/Kura Te Au, South Island of New Zealand. The aim is to evaluate potential suitable habitat areas for filter-feeders to inform where habitat restoration management should focus efforts to recover communities such as the horse mussel (Atrina zelandica) or the green-lipped mussel (Perna canaliculus), both of which have high economic impact in New Zealand. To accomplish this, Maximum Entropy (MaxEnt) predictive modelling was used to produce Habitat Suitability (HS) maps, using geomorphological parameters and seafloor classification information. Final HS maps also incorporated oceanographic and sediment dynamic information, showing that filter-feeder habitat distribution is highly influenced by the hydrodynamics and sedimentary processes apart from the seafloor geomorphology. Filter-feeder communities inhabit quiescent areas, limited by depth, slope and sediment type; and coincide with regions presenting low near-bottom currents and low turbidity levels. Additionally, the obtained results reveal the effects of the coastal settlements and major marine traffic routes, limiting the suitable habitats to areas with less human impact. This study demonstrates that a multidisciplinary approach is crucial to better predict the spatial distribution of benthic communities, which is key to improve benthic habitat restoration and recovery assessments.

Cumulative stressors reduce the self-regulating capacity of coastal ecosystems.

Marine ecosystems are prone to tipping points, particularly in coastal zones where dramatic changes are associated with interactions between cumulative stressors (e.g., shellfish harvesting, eutrophication and sediment inputs) and ecosystem functions. A common feature of many degraded estuaries is elevated turbidity that reduces incident light to the seafloor, resulting from multiple factors including changes in sediment loading, sea-level rise and increased water column algal biomass. To determine whether cumulative effects of elevated turbidity may result in marked changes in the interactions between ecosystem components driving nutrient processing, we conducted a large-scale experiment manipulating sediment nitrogen concentrations in 15 estuaries across a national-scale gradient in incident light at the seafloor. We identified a threshold in incident light that was related to distinct changes in the ecosystem interaction networks (EIN) that drive nutrient processing. Above this threshold, network connectivity was high with clear mechanistic links to denitrification and the role of large shellfish in nitrogen processing. The EIN analyses revealed interacting stressors resulting in a decoupling of ecosystem processes in turbid estuaries with a lower capacity to denitrify and process nitrogen. This suggests that, as turbidity increases with sediment load, coastal areas can be more vulnerable to eutrophication. The identified interactions between light, nutrient processing and the abundance of large shellfish emphasizes the importance of actions that seek to manage multiple stressors and conserve or enhance shellfish abundance, rather than actions focusing on limiting a single stressor.

Investigating changes in estuarine ecosystem functioning under future scenarios.

Estuaries are subject to disturbance by land-based sediment and nutrient inputs, resulting in changes to the ecosystems and the functions and services that they support. Spatial mapping tools that identify how functional hotspots in the estuary may shift in location and intensity under different disturbance scenarios highlight to managers the trajectory of change and the value of active management and restoration, but to date these tools are only available in the most intensively researched ecosystems. Using empirical data derived from long-term monitoring and multi-habitat field experiments we developed future scenarios representing different impacts of environmental degradation on estuarine ecosystem functions that are important for supporting ecosystem services. We used the spatial prioritization software Zonation in a novel fashion to assess effects of different disturbance scenarios on critical soft-sediment ecosystem processes (nutrient fluxes and sediment erodibility measures) that are influenced by macrofaunal communities and local environment conditions. We compared estimates of current conditions with three scenarios linked to changes in land-use and resulting downstream impacts on estuarine ecosystems to determine how disturbance influences the distribution of high value areas for ecosystem function. Scenarios investigated the implications of habitat degradation associated with sediment deposition and declines in large sediment-dwelling animal abundance whose behavior has important influences on ecosystem function. Our analyses demonstrate decreases in the majority of ecosystem processes under scenarios associated with disturbances. These results suggest that it is important to restore biodiversity and ecosystem function and that the application of Zonation in this context offers a simple, rapid and cost-effective way of identifying priority actions and locations for restoration, and how these shift due to multiple impacts.

Rising tides, cumulative impacts and cascading changes to estuarine ecosystem functions.

In coastal ecosystems, climate change affects multiple environmental factors, yet most predictive models are based on simple cause-and-effect relationships. Multiple stressor scenarios are difficult to predict because they can create a ripple effect through networked ecosystem functions. Estuarine ecosystem function relies on an interconnected network of physical and biological processes. Estuarine habitats play critical roles in service provision and represent global hotspots for organic matter processing, nutrient cycling and primary production. Within these systems, we predicted functional changes in the impacts of land-based stressors, mediated by changing light climate and sediment permeability. Our in-situ field experiment manipulated sea level, nutrient supply, and mud content. We used these stressors to determine how interacting environmental stressors influence ecosystem function and compared results with data collected along elevation gradients to substitute space for time. We show non-linear, multi-stressor effects deconstruct networks governing ecosystem function. Sea level rise altered nutrient processing and impacted broader estuarine services ameliorating nutrient and sediment pollution. Our experiment demonstrates how the relationships between nutrient processing and biological/physical controls degrade with environmental stress. Our results emphasise the importance of moving beyond simple physically-forced relationships to assess consequences of climate change in the context of ecosystem interactions and multiple stressors.