Soft-sediment Ecosystems Research Articles

Addition of mussel shells enhance marine benthic biodiversity in two degraded coastal soft sediment ecosystems

The decline in coastal shellfish populations, attributed to anthropogenic stressors such as harvesting via dredging, can deplete the seabed of vital biogenic habitat. This removal of shellfish significantly reduces habitat complexity, biodiversity, and the hard substrate required for the natural recovery of some key species. A common method for oyster restoration involves deploying oyster shell material to provide habitat and substrate for settling larval oysters. In contrast, hard substrate is not required for the mussel lifecycle and as a result the deployment of mussel shell for seabed restoration has received minimal attention, with the effects of reintroducing this material poorly understood. Deploying mussel shell material has the potential to aid in ecosystem recovery, including reviving seabed biodiversity, especially in areas that have been depleted of shellfish via damaging methods such as dredging. This study aimed to investigate the ecosystem effects of returning mussel shells onto two locations with differing soft sediment (sand and mud) in areas historically subjected to excessive dredging of mussel populations and sedimentation. Within 2 years 4 months the infaunal taxa richness was higher in the shell areas compared to the reference areas in both locations, while abundance of infauna was higher in only the sand location and infaunal diversity did not differ at either location. Epifaunal diversity was also higher in the shell area compared to the reference areas at both locations, while the abundance and richness did not differ. Few significant differences were seen in benthic biogeochemical variables between the reference and shell areas and those observed were likely the result of the addition of the shell material changing the sediment composition. These findings demonstrate that mussel shells are a restoration tool that can enhance epifaunal biodiversity and infaunal taxa richness in soft sediment ecosystems historically impacted by shellfish overharvesting and sedimentation.

Effects of sediment disturbance by the heart urchin <i>Echinocardium cordatum</i> on the sediment–seawater solute exchange: An exclusion experiment

<p>Spatangoid heart urchins are dominant bioturbators in marine soft-sediment ecosystems worldwide. Their repeated sediment reworking prevents biogeochemical sediment stratification and colonization by other species, with implications for sedimentary reaction processes that affect the local sediment–seawater solute exchange. Here, we used a simple exclusion experiment to investigate how a subtidal <italic>Echinocardium cordatum</italic> population (18.2 ± 6.7 individuals m<sup>−2</sup>), foraging at an individual speed of ~45 cm per day affects the sediment–seawater solute exchange. To do so, we removed all heart urchins from eight one-meter-diameter areas of the 10-m deep seafloor of Man O'War Bay, Hauraki Gulf, New Zealand, and prevented recolonization and thus sediment reworking for 56 days. Subsequently, we measured the sediment–seawater exchange of O<sub>2</sub>, NO<sub>3</sub><sup>–</sup>, NO<sub>2</sub><sup>–</sup>, NH<sub>4</sub><sup>+</sup>, and N<sub>2</sub> both within and outside the exclusion areas, under light or dark conditions, and found no difference. The absence of a legacy effect of foraging <italic>E. cordatum</italic> after their removal suggests that, at least in this habitat, their influence on the sediment–seawater solute exchange may be limited to sediment being displaced in the immediate surrounding of the urchin. This unexpected result underlines the importance of evaluating the influence of bioturbators on the sediment–seawater solute exchange in the context of local environmental conditions, animal behavior, and population characteristics.</p>

An RGB‐D framework for capturing soft‐sediment microtopography

Abstract Capturing sediment topography is one component in understanding how large animals in soft sediment ecosystems affect ecosystem processing. Traditional approaches for sampling soft‐sediment systems are too invasive and destructive for the fragile sediment structures. In contrast, non‐invasive approaches, such as LIDAR and monocular structure‐from‐motion (SfM) systems, can be expensive and cumbersome for data processing. We developed a low cost and practical framework for measuring morphological characteristics of soft sediment topography at the millimetre scale. Using an RGB‐D (red, green, blue and depth) device and a semi‐opaque container, the sediment surface can be imaged rapidly while operating in outdoor environments. The RGB‐D device imaged 0.3 m2 intertidal sediment surfaces, creating depth imagery over seven sites and 82 surfaces. First, using simulated surface data, we formulated and tested four variations of a geometrical detrending model to extract and measure the undulating surface microtopography. We then computed nine morphological characteristics, including arithmetic mean roughness, mean sediment peaks and rugosity, for the detrending models. We then used the two best performing models, linear and quadratic detrending models, to compare extracted morphological characteristics from the field data. We found a strong correlation between the models for extracted surface measures and similar extracted sediment trends. The results showed that RGB‐D real‐time imaging is a promising rapid scanning tool for collecting field data in intertidal regions and can be expanded to other fragile sediment surfaces outside the marine environment. The low costs and real‐time feedback makes it an attractive data collection tool for environments where data collection is challenging.

Multiple climate change-driven tipping points for coastal systems

As the climate evolves over the next century, the interaction of accelerating sea level rise (SLR) and storms, combined with confining development and infrastructure, will place greater stresses on physical, ecological, and human systems along the ocean-land margin. Many of these valued coastal systems could reach “tipping points,” at which hazard exposure substantially increases and threatens the present-day form, function, and viability of communities, infrastructure, and ecosystems. Determining the timing and nature of these tipping points is essential for effective climate adaptation planning. Here we present a multidisciplinary case study from Santa Barbara, California (USA), to identify potential climate change-related tipping points for various coastal systems. This study integrates numerical and statistical models of the climate, ocean water levels, beach and cliff evolution, and two soft sediment ecosystems, sandy beaches and tidal wetlands. We find that tipping points for beaches and wetlands could be reached with just 0.25 m or less of SLR (~ 2050), with > 50% subsequent habitat loss that would degrade overall biodiversity and ecosystem function. In contrast, the largest projected changes in socioeconomic exposure to flooding for five communities in this region are not anticipated until SLR exceeds 0.75 m for daily flooding and 1.5 m for storm-driven flooding (~ 2100 or later). These changes are less acute relative to community totals and do not qualify as tipping points given the adaptive capacity of communities. Nonetheless, the natural and human built systems are interconnected such that the loss of natural system function could negatively impact the quality of life of residents and disrupt the local economy, resulting in indirect socioeconomic impacts long before built infrastructure is directly impacted by flooding.

Biodiversity, community structure and ecosystem function on kelp and wood falls in the Norwegian deep sea

Fjordic systems in temperate and Arctic regions often feature extensive kelp forests at their shallow coastal margins as well as extensive terrestrial forests. Detrital export from these shallow-water and terrestrial ecosystems is an important source of carbon for deep-sea communities in the form of kelp and wood falls. Benthic landers with experimental substrates (wood blocks and kelp parcels) were deployed for 10 mo at a depth of 530 m in a deep Norwegian fjord to investigate and compare macro- and megabenthic community structure, biodiversity and ecosystem functioning on kelp and wood falls. Results revealed that while wood and kelp falls can support a similar number of species and abundance of fauna, they support significantly different faunal communities. Biomass and secondary production on both wood and kelp substrates were significantly greater than in the control samples. Secondary production estimates were similar or higher than those reported from soft-sediment ecosystems at shallower European marine sites. Biological trait analysis showed that macrofaunal assemblages were distinct between the kelp and wood, providing evidence for differences in ecosystem function between the substrates. This case study from a deep-sea fjord in Norway provides clear evidence that while wood and kelp organic falls can support similar abundances of fauna, the associated benthic biodiversity, community structure and ecosystem functioning can be dramatically different between these substrates. The work presented here aims to provide information that is useful in assessing the extent of anthropogenic impacts on deep fjord ecosystems with respect to informing future conservation and management strategies.

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

Coastal marine soft-sediment ecosystems profoundly influence nutrient cycling, carbon flows and primary productivity; both the resident animal communities and environmental characteristics can drive the direction and magnitude of fluxes across the sediment–water interface. Coastal and estuarine sedimentary ecosystems are spatially heterogeneous, and many are degrading due to environmental change. How ecosystem function is affected by spatial variation in both habitats and associated animals is critical for understanding the role of specific habitats in ecosystem function and defining the consequence of the functional extinction of species and changes in habitat spatial distributions. In a multi-site field experiment, we tested the effects of spatial variation in benthic communities and environmental characteristics along natural gradients in sediment grain size. We experimentally simulated the depletion of large benthic macrofauna to assess the impact of these functionally important taxa on key ecosystem functions through ammonium and oxygen solute fluxes across the sediment–water interface. The magnitude of change in solute fluxes varied across sites and depletion treatments and was explained by changes in both sediment physico-chemical characteristics and the functional attributes of the benthic community. Quantifying variation in fluxes across multiple habitats provides insight into the trajectory of change and the consequences for ecosystem function at broad spatial scales.

Historic and contemporary anthropogenic effects on granulometry and species composition detected from sediment cores and death assemblages, Nelson Bays, Aotearoa-New Zealand

To effectively manage anthropogenic stressors causing widespread and pervasive habitat change, resource managers and policy makers require advice on priority stressors to optimally target conservation and restoration outcomes. This is difficult in soft sediment ecosystems affected by multiple stressors operating across centuries with possible legacy interactions. Using tools from the emerging discipline of conservation paleobiology, we attempted to disentangle the effects of two stressors: i) changes to sediments (sedimentation rate, composition) and ii) fishing disturbance across pre-human to contemporary timescales by analysing death assemblages (DA) at a rare location protected from power fishing methods for ca. 30 yr in Nelson Bays, Aotearoa-New Zealand. Replicate sediment cores and surface grab samples were collected at paired stations, spread across three depth profiles (25, 30, 35 m), split inside and outside the fishing exclusion zone. Sediment core geochronologies were established using radioisotope dating and analysis of terrestrial plant palynomorphs (spores, pollen, starch) associated with Māori and European introduction to Aotearoa-New Zealand. Results unearthed a complex of brachiopods, molluscs, crustacea, bryozoan, and Māori-introduced pollen and starch remains – the latter a marine first. Following human arrival in the region (ca.1500AD) statistical models revealed separation of DAs between time periods were correlated with a 10–15% increase in sediment silt content following a ca.11-fold increase in Sediment Accumulation Rates (SAR). In contrast, separation of recent surface DAs (ca. 60yr) are now more strongly correlated with sediment mixing, detected by discordance in radioisotope profiles, consistent with exposure to homogenising effects of fishing disturbance outside the exclusion zone. We conclude that historic legacy effects, ongoing sedimentation and fishing disturbance have synergistically modified the sediment characteristics from “natural” baseline conditions. Those changes have likely contributed to the collapse and lack of recovery of Nelson Bays shellfish fisheries.

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.

Biodiversity breakpoints along stress gradients in estuaries and associated shifts in ecosystem interactions

Denitrification in coastal sediments can provide resilience to eutrophication in estuarine ecosystems, but this key ecosystem function is impacted directly and indirectly by increasing stressors. The erosion and loading of fine sediments from land, resulting in sedimentation and elevated sediment muddiness, presents a significant threat to coastal ecosystems worldwide. Impacts on biodiversity with increasing sediment mud content are relatively well understood, but corresponding impacts on denitrification are uncharacterised. Soft sediment ecosystems have a network of interrelated biotic and abiotic ecosystem components that contribute to microbial nitrogen cycling, but these components (especially biodiversity measures) and their relationships with ecosystem functions are sensitive to stress. With a large dataset spanning broad environmental gradients this study uses interaction network analysis to present a mechanistic view of the ecological interactions that contribute to microbial nitrogen cycling, showing significant changes above and below a stressor (mud) threshold. Our models demonstrate that positive biodiversity effects become more critical with a higher level of sedimentation stress, and show that effective ecosystem management for resilience requires different action under different scenarios.

Passive reclamation of soft-sediment ecosystems on the North Coast of British Columbia, Canada

Estuarine ecosystems are degraded through anthropogenic development, leading to reduced habitat suitability for biological communities. The Skeena River estuary (British Columbia, Canada) is undergoing passive reclamation from historical salmon canneries and pulp mills, while localized disturbances continue at present. To reveal both current impacts and the trajectory of passive reclamation from historical activities, the intertidal mudflat surrounding the longest operating salmon cannery, Cassiar Cannery, within the Skeena estuary was surveyed. Nutrient availability (chlorophyll a concentration/organic matter content), sediment variables (particle size, water content, penetrability, woody debris/macroalgae cover, apparent redox potential discontinuity depth), and infaunal community composition varied spatiotemporally, and suggest that an old dock may be influencing the infaunal community given the abundance of disturbance indicating taxa below the dock. However, with populations of amphipods, mobile polychaetes, and a complex community structure, the mudflat as a whole appears to be relatively healthy. Therefore, cessation of historic activities has allowed for passive reclamation to a reasonably unstressed state, though a threshold of recovery may exist for intertidal mudflats beyond which passive reclamation will not be effective.

Quantitatively characterizing benthic community-habitat relationships in soft-sediment, nearshore environments to yield useful results for management

Effective management of benthic habitats is important for maintaining heathy and functional aquatic ecosystems. To provide managers with the best possible information, characterizing benthic habitats at the community level is essential; yet, acquiring the data sets needed to achieve this task is resource intensive and, at times, prohibitively expensive. Thus, thoughtful assessments of which data to collect and utilize in benthic habitat characterization studies are needed. Environmental data sets commonly used to characterize benthic habitats include a range of variables from water depth and sediment grain size to seabed features identified by sonar backscatter. The objective of this study was to identify the most useful environmental variables for characterizing infaunal benthic habitats and to determine how to best utilize these variables in analyses (e.g., by comparing continuous vs. categorical explanatory variables). The modeling approach used multivariate regression tree and redundancy analysis along with a critical cross-validation step for model evaluation. Results indicated that models with more than ~7 environmental predictors overfitted the data sets analyzed and that categorizing continuous predictors into categorical ones influenced the proportion of infaunal community variation explained by each model. Habitats identified and characterized on the basis of sonar backscatter explained more of the infaunal community variation than any model that used a combination of other environmental variables (e.g., water depth & sediment grain size) or those constructed using categorical habitat classes from existing classification schemes. We therefore recommend maximizing the potential of sonar-derived variables for characterizing infaunal benthic habitats in nearshore, soft-sediment ecosystems.

Impact of an artificial structure on the benthic community composition in the southern North Sea: assessed by a morphological and molecular approach

Abstract Man-made structures in the North Sea are known to act as artificial reefs by providing a habitat for sessile epifauna in a predominantly soft sediment environment. This epifauna is hypothesized to cast a so-called “shadow” over the soft sediment ecosystem by altering the nutrient composition in the overlying water column. In addition, the structure itself could alter currents and thereby influence the deposition and erosion of the sediments in the wake of the platform. This study aims to assess the long-term effects of a gas platform in the southern North Sea on the surrounding benthic community by both morphological and molecular identification of benthic species. The species composition and a set of abiotic factors of the sediment around a gas platform were assessed along four transects. Differences for the abiotic factors were found in the closer vicinity of the platform in the direction corresponding to the predominant currents. The number of benthic fauna families found in the molecular approach were on average three times higher than for the morphological approach. Both approaches showed that small differences occurred primarily due to changes in sedimentary organic matter content. Differences in species composition were more pronounced between transects rather than between distances from the platform.

Has Phytodetritus Processing by an Abyssal Soft-Sediment Community Recovered 26 Years after an Experimental Disturbance?

The potential harvest of polymetallic nodules will heavily impact the abyssal, soft sediment ecosystem by removing sediment, hard substrate, and associated fauna inside mined areas. It is therefore important to know whether the ecosystem can recover from this disturbance and if so at which rate. The first objective of this study was to measure recovery of phytodetritus processing by the benthic food web from a sediment disturbance experiment in 1989. The second objective was to determine the role of holothurians in the uptake of fresh phytodetritus by the benthic food web. To meet both objectives, large benthic incubation chambers (CUBEs; 50 × 50 × 50 cm) were deployed inside plow tracks (with and without holothurian presence) and at a reference site (holothurian presence, only) at 4100 m water depth. Shortly after deployment, 13C- and 15N-labeled phytodetritus was injected in the incubation chambers and during the subsequent 3-day incubation period, water samples were taken five times to measure the production of 13C-dissolved inorganic carbon over time. At the end of the incubation, holothurians and sediment samples were taken to determine biomass, densities and incorporation of 13C and 15N into bacteria, nematodes, macrofauna, and holothurians. For the first objective, the results showed that biomass of bacteria, nematodes and macrofauna did not differ between reference sites and plow track sites when holothurians were present. Additionally, meiofauna and macrofauna taxonomic composition was not significantly different between the sites. In contrast, total 13C uptake by bacteria, nematodes and holothurians was significantly lower at plow track sites compared to reference sites, though the number of replicates was low. This result suggests that important ecosystem functions such as organic matter processing have not fully recovered from the disturbance that occurred 26 years prior to our study. For the second objective, the analysis indicated that holothurians incorporated 2.16 × 10−3 mmol labile phytodetritus C m−2 d−1 into their biomass, which is one order of magnitude less as compared to bacteria, but 1.3 times higher than macrofauna and one order of magnitude higher than nematodes. Additionally, holothurians incorporated more phytodetritus carbon per unit biomass than macrofauna and meiofauna, suggesting a size-dependence in phytodetritus carbon uptake.

Generalizing Ecological Effects of Shoreline Armoring Across Soft Sediment Environments

Despite its widespread use, the ecological effects of shoreline armoring are poorly synthesized and difficult to generalize across soft sediment environments and structure types. We developed a conceptual model that scales predicted ecological effects of shore-parallel armoring based on two axes: engineering purpose of structure (reduce/slow velocities or prevent/stop flow of waves and currents) and hydrodynamic energy (e.g., tides, currents, waves) of soft sediment environments. We predicted greater ecological impacts for structures intended to stop as opposed to slow water flow and with increasing hydrodynamic energy of the environment. We evaluated our predictions with a literature review of effects of shoreline armoring for six possible ecological responses (habitat distribution, species assemblages, trophic structure, nutrient cycling, productivity, and connectivity). The majority of studies were in low-energy environments (51 of 88), and a preponderance addressed changes in two ecological responses associated with armoring: habitat distribution and species assemblages. Across the 207 armoring effects studied, 71% were significantly negative, 22% were significantly positive, and 7% reported no significant difference. Ecological responses varied with engineering purpose of structures, with a higher frequency of negative responses for structures designed to stop water flow within a given hydrodynamic energy level. Comparisons across the hydrodynamic energy axis were less clear-cut, but negative responses prevailed (>78%) in high-energy environments. These results suggest that generalizations of ecological responses to armoring across a range of environmental contexts are possible and that the proposed conceptual model is useful for generating predictions of the direction and relative ecological impacts of shoreline armoring in soft sediment ecosystems.

Site-dependent effects of bioturbator-detritus interactions alter soft-sediment ecosystem function

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 569:145-161 (2017) - DOI: https://doi.org/10.3354/meps12086 Site-dependent effects of bioturbator-detritus interactions alter soft-sediment ecosystem function Rebecca V. Gladstone-Gallagher1,*, Hazel R. Needham1, Andrew M. Lohrer2, Carolyn J. Lundquist2,3, Conrad A. Pilditch1 1School of Science, University of Waikato, Hamilton 3240, New Zealand 2National Institute of Water and Atmospheric Research Ltd. (NIWA), Hamilton 3216, New Zealand 3Institute of Marine Science, University of Auckland, Auckland 1142, New Zealand *Corresponding author: rgladstonegallagher@gmail.com ABSTRACT: In coastal sediments, macrofauna can trap macrophyte detritus in their burrows, modifying organic matter retention/export. However, the resulting effects on ecosystem function are unclear. We conducted a field experiment to assess how detrital processing by a common bioturbating crab Austrohelice crassa influences benthic metabolism, primary production, and ammonium regeneration at a sand and muddy-sand site. Since the functional role of crabs and detrital decay rates vary with mud content, we hypothesised their interactive effects on ecosystem function would also vary. Sixteen cages (0.36 m2) were established at each intertidal site, and cages were allocated a crab (0 or 35 ind. cage-1) and seagrass detritus (0 or 120 g dry weight [DW] cage-1) treatment. Ten days later, sediment-water solute fluxes were measured. Treatment effects on ecosystem function were site-specific: detritus stimulated benthic metabolism in muddy-sand (by 12 to 29%, p = 0.01), but in sand, effects were dominated by crabs. Metabolism increased by 12 to 21% (p = 0.04), of which 24 to 52% could be attributed to crab respiration. Crabs enhanced ammonium regeneration in sand (p < 0.003), of which <26% could be attributed to crab excretion, but in muddy-sand, the presence of detritus masked this positive effect (dark ammonium flux, crab × detritus interaction: p = 0.03). Crabs and detritus had negative effects on primary production in sand, where crabs reduced primary production by 57% and detritus by 73%. In muddy-sand, variable light conditions made primary production estimates unreliable. Our results emphasise that context is paramount when understanding the effects of reductions in the densities of key species or changes in detrital inputs on soft-sediment ecosystem function. KEY WORDS: Bioturbation · Austrohelice crassa · Detrital decay · Primary production · Nutrient flux · Grapsid · Seagrass · Benthic community metabolism Full text in pdf format PreviousNextCite this article as: Gladstone-Gallagher RV, Needham HR, Lohrer AM, Lundquist CJ, Pilditch CA (2017) Site-dependent effects of bioturbator-detritus interactions alter soft-sediment ecosystem function. Mar Ecol Prog Ser 569:145-161. https://doi.org/10.3354/meps12086 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 569. Online publication date: April 07, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Cross shelf benthic biodiversity patterns in the Southern Red Sea

The diversity of coral reef and soft sediment ecosystems in the Red Sea has to date received limited scientific attention. This study investigates changes in the community composition of both reef and macrobenthic communities along a cross shelf gradient. Coral reef assemblages differed significantly in species composition and structure with location and depth. Inner shelf reefs harbored less abundant and less diverse coral assemblages with higher percentage macroalgae cover. Nutrient availability and distance from the shoreline were significantly related to changes in coral composition and structure. This study also observed a clear inshore offshore pattern for soft sediment communities. In contrast to the coral reef patterns the highest diversity and abundance of soft sediment communities were recorded at the inshore sites, which were characterized by a higher number of opportunistic polychaete species and bivalves indicative of mild disturbance. Sediment grain size and nutrient enrichment were important variables explaining the variability. This study aims to contribute to our understanding of ecosystem processes and biodiversity in the Red Sea region in an area that also has the potential to provide insight into pressing topics, such as the capacity of reef systems and benthic macrofaunal organisms to adapt to global climate change.

Challenges for the conservation of marine small natural features

Seascapes contain a mosaic of ecosystem types, including ‘small natural features’ that support a diverse fauna and flora, and provide ecosystem services disproportionate to their size. These include tropical coral reefs, seagrass meadows, rhodolith beds, kelp and mangrove forests as well as deep-sea coral reefs, sponge gardens and hydrothermal vents. The contributions of coral reefs, mangrove forests and seagrass meadows are well recognised as important components of tropical marine seascapes. In temperate regions, hotspots of primary productivity such as kelp forests, and vegetation-based ecosystems found at coastal margins play significant roles in nutrient and sediment trapping and coastal protection. Biogenic features in coastal regions can also play important roles, including shellfish reefs, sponge gardens and macroalgal mats that provide physical structure within soft sediment ecosystems. Similar biogenic features are found in the deep sea, which often occur associated with seamounts, canyon features, cold seeps and hydrothermal vents. Many marine small natural features are globally threatened as they are found at the interface with human-influenced landscapes (coastal ecosystems) or are the focus of resource exploitation (e.g., trawling for fish associated with seamounts and canyons). Challenges in management are, however, consistent across depths, and highlight the restricted spatial extent of such features, and the limited information typically available on their distributions, and the ecosystem services they provide. Numerous strategies can be utilized to sustainably manage, protect, create and restore these marine small natural features and their associated biodiversity.

Hard science is essential to restoring soft-sediment intertidal habitats in burgeoning East Asia

Intertidal soft-sediment ecosystems such as mangrove, saltmarsh, and tidal flats face multiple stresses along the burgeoning East Asia coastline. In addition to direct habitat loss, ecosystem structure, function, and capacity for ecosystem services of these habitats are significantly affected by anthropogenic loss of hydrologic connectivity, introduction of invasive exotic species, and chemical pollution. These dramatic changes to ecosystem structure and function are illustrated by four case studies along the East Asian coast: the Mai Po Marshes in Hong Kong, the Yunxiao wetlands in Fujian, China, and the Lake Sihwa and Saemangeum tidal flats in Korea. While investment in restoration is increasing significantly in the region, the lack of key basic knowledge on aspects of the behaviour of intertidal soft-sediment ecosystems, particularly those in Asia, impairs the effectiveness of these efforts. The relationship between biodiversity and ecosystem function for relatively species-poor mangrove, seagrass, and saltmarsh systems has implications for restoration targeting monospecific plantations. The trajectory of recovery and return of ecosystem function and services is also poorly known, and may deviate from simple expectations. As many introduced species have become established along the East Asian coast, their long-term impact on ecosystem function as well as the socio-economics of coastal communities demand a multidisciplinary approach to assessing options for restoration and management. These knowledge gaps require urgent attention in order to inform future restoration and management of intertidal soft-sediment ecosystems in fast-developing East Asia.

Behavioral Response of Corophium volutator to Shorebird Predation in the Upper Bay of Fundy, Canada

Predator avoidance is an important component of predator-prey relationships and can affect prey availability for foraging animals. Each summer, the burrow-dwelling amphipod Corophium volutator is heavily preyed upon by Semipalmated Sandpipers (Calidris pusilla) on mudflats in the upper Bay of Fundy, Canada. We conducted three complementary studies to determine if adult C. volutator exhibit predator avoidance behavior in the presence of sandpipers. In a field experiment, we monitored vertical distribution of C. volutator adults in bird exclosures and adjacent control plots before sandpipers arrived and during their stopover. We also made polymer resin casts of C. volutator burrows in the field throughout the summer. Finally, we simulated shorebird pecking in a lab experiment and observed C. volutator behavior in their burrows. C. volutator adults were generally distributed deeper in the sediment later in the summer (after sandpipers arrived). In August, this response was detectably stronger in areas exposed to bird predation than in bird exclosures. During peak predator abundance, many C. volutator adults were beyond the reach of feeding sandpipers (>1.5 cm deep). However, burrow depth did not change significantly throughout the summer. Detailed behavioral observations indicated that C. volutator spent more time at the bottom of their burrow when exposed to a simulated predator compared to controls. This observed redistribution suggests that C. volutator adults move deeper into their burrows as an anti-predator response to the presence of sandpipers. This work has implications for predators that feed on burrow-dwelling invertebrates in soft-sediment ecosystems, as density may not accurately estimate prey availability.

Meiofauna increases bacterial denitrification in marine sediments.

Denitrification is a critical process that can alleviate the effects of excessive nitrogen availability in aquatic ecosystems subject to eutrophication. An important part of denitrification occurs in benthic systems where bioturbation by meiofauna (invertebrates <1 mm) and its effect on element cycling are still not well understood. Here we study the quantitative impact of meiofauna populations of different abundance and diversity, in the presence and absence of macrofauna, on nitrate reduction, carbon mineralization and methane fluxes. In sediments with abundant and diverse meiofauna, denitrification is double that in sediments with low meiofauna, suggesting that meiofauna bioturbation has a stimulating effect on nitrifying and denitrifying bacteria. However, high meiofauna densities in the presence of bivalves do not stimulate denitrification, while dissimilatory nitrate reduction to ammonium rate and methane efflux are significantly enhanced. We demonstrate that the ecological interactions between meio-, macrofauna and bacteria are important in regulating nitrogen cycling in soft-sediment ecosystems.