Benthic Ecosystems Research Articles

Tracing microplastic pollution in Mahi River estuary, Gulf of Khambhat, Gujarat, and their influence on functional traits of macrobenthos.

Most maritime habitats contain microplastic (MPs) contamination. The quality of the benthic ecosystem's habitat is declining as MPs accumulate in marine system. The contamination of MPs must therefore be investigated. We studied MPs pollution in the Mahi River, estuary, and macrobenthos. In the present study, the abundance of MPs fragments gradually decreased from the high tide zone to the low tide zone and muddy sediment has high MPsconcentrations due to sediment characteristics and particle size. The majority of sediment and biota MPs were fibrous and black. MPs in both silt and biota have identical chemical compositions (modified cellulose), shapes, and colors. A significant source of pollutants and MPs fluxing into the ocean is well within the river system. Perinereis aibuhitensis ingested the most MPs out of 11 species, whereas Amphipods did not show any presence of MPs. Our findings showed that functional characteristics are essential for macrobenthos MPs intake. MPs in macrobenthos are high due to biological functions such as feeding, ecological groups, feeding mechanisms, body size, and bioturbation. MPs in marine sediment and organisms aretracked down to the Mahi River exceeding 50km. The present work has investigated the idea that the macrobenthos that live in the sediment are ingesting the MPs that are building up there and this ingestion relies on the macrobenthos' functional characteristics.

“Quantifying the Impacts of Multiple Stressors” (QIMS)—a new experimental platform for robust multifactorial experiments in benthic ecosystems

AbstractTo predict the ecological consequences of expected global change, we need to understand the independent and combined effects of multiple stressors. Multiple experimental treatments are required to simultaneously test for effects of multiple stressors at different levels of intensity, independently and combined, and at different levels of biological organization. Most marine multiple stressors studies to date are conducted on assembled communities in mesocosms with a low number of treatments or low replication of treatments or both. These limitations prevent (1) robust data analyses, (2) characterization of single and combined effects of multiple stressors, and (3) identification of mechanisms underpinning biological responses. We present a new mesocosm‐based experimental platform for benthic communities: Quantifying the Impacts of Multiple Stressors (QIMS). Here, 96 independent mesocosms facilitate multifactorial and multilevel experimental designs with the high replication required for robust tests of multiple stressors and biological interactions. For example, three distinct pH levels are achieved by manipulating CO2 concentrations in the air supply, and three water temperature levels are provided by a cooling system in a fully crossed design that is required to identify all potential interactions, from which all combinations can be replicated 10 times (i.e., 90 experimental units). We demonstrate clearly how different levels of temperature and pCO2/pH can be manipulated precisely and maintained for at least 7 weeks. QIMS complements the limited number of permanently installed marine mesocosm facilities worldwide that simulate ocean warming and/or acidification and expedites multiple stressor research by providing an unprecedented level of replication for statistical robustness.

Resource utilisation and trophic niche overlap of coralline intertidal benthic amphipods: an isotopic perspective.

Benthic amphipod feeding groups are a well-established trophic classification that is mostly based on field observations and laboratory tests and are used in ecological studies to monitor the ecological state of benthic ecosystems. Globally, carbon and nitrogen stable isotope ratio investigations have provided confirmation of, and novel insights into, the trophic ecology of benthic animals, such as polychaetes. However, stable isotopic examinations of benthic amphipods have been limited. Here, we used microgram samples to compare the species-specific dietary sources, trophic positions, and isotopic niche overlap of selected benthic amphipods from the Gulf of Kachchh, Marine National Park, using elemental analyser-isotopic ratio mass spectrometry (EA-IRMS) of carbon and nitrogen. Overall, all primary carbon sources presented wide variation in the isotopic values of δ13C (6.3‰) and δ15N (greater than 13‰). Conversely, the amphipod taxa displayed relatively narrow range for δ13C (3.9‰) and wider range for δ15N (more than 10‰). The results of the Bayesian mixing model revealed that the benthic amphipods had species-specific feeding preferences. However, the predominant carbon source was organic matter in sediment which reinforced benthic pathways for energy flow for most species. According to the estimated trophic level values (1.62-3.39), these species play a significant role as primary and secondary consumers serving as crucial trophic intermediaries in the food chain, connecting the base to the top consumers. High overlapping ecological niche amongst species was detected by SIBER analysis which indicated co-existence of the benthic amphipods in their respective microhabitats. This signifies wider utilisation of resources and inter-specific feeding preferences with minimal competition amongst amphipod species.

No escape from the mucilage impact: Even opportunistic hydroids were affected in the catastrophic mucilage of 2021 in the Sea of Marmara

This study examines the effects of sedimentation and mucilage events on the hydroid communities of the Prince Islands, Sea of Marmara. Sampling in October 2021 and April 2022 revealed significant declines in hydroid abundance post the 2021 mucilage event, contrasting with increases observed in 2015 after excessive sedimentation in the area. Statistical analyses demonstrate temporal variations in hydroid assemblages, underscoring the ecological consequences of mucilage events on benthic communities. The unprecedented scale and prolonged duration of the 2021 mucilage event accentuate the magnitude of its impact on marine ecosystems. The decline in hydroid abundance following the mucilage event suggests a significant ecological impact, with implications for the recovery and resilience of benthic ecosystems. These findings contribute to our understanding of the complex interactions between environmental stressors and benthic communities, emphasizing the importance of proactive management strategies that preserve marine biodiversity in the face of anthropogenic pressures and climate change.

Priapulid neoichnology, ecosystem engineering, and the Ediacaran–Cambrian transition

AbstractThe evolutionary rise of powerful new ecosystem engineering impacts is thought to have played an important role in driving waves of biospheric change across the Ediacaran–Cambrian transition (ECT; c. 574–538 Ma). Among the most heavily cited of these is bioturbation (organism‐driven sediment disturbance) as these activities have been shown to have critical downstream geobiological impacts. In this regard priapulid worms are crucial; trace fossils thought to have been left by priapulan‐grade animals are now recognized as appearing shortly before the base of the Cambrian and represent some of the earliest examples of bed‐penetrative bioturbation. Understanding the ecosystem engineering impacts of priapulids may thus be key to reconstructing drivers of the ECT. However, priapulids are rare in modern benthic ecosystems, and thus comparatively little is known about the behaviours and impacts associated with their burrowing. Here, we present the early results of neoichnological experiments focused on understanding the ecosystem engineering impacts of priapulid worms. We observe for the first time a variety of new burrowing behaviours (including the formation of linked burrow networks and long in‐burrow residence times) hinting at larger ecosystem engineering impacts in this group than previously thought. Finally, we identify means by which these results may contribute to our understanding of tracemakers across the ECT, and the role they may have had in shaping the latest Ediacaran and earliest Cambrian biosphere.

Carbon sequestration in coastal sediments via in situ capping with steel slag

A 4000 m2 steel slag (SS) bed was constructed in the brackish water area for water quality remediation in 2017. This study demonstrates the ability of SS to stimulate carbon sequestration based on one-year pilot and in situ SS beds. The pilot SS bed increased the soil organic matter (SOM) content by 5.1 wt %, sequestering sewage-derived organic carbon (Corg) as SOM. Notably, recalcitrant SOM increased by over 40 %, indicating long-term retention of Corg in the sediment. SS increased the Corg density in the sediment by approximately two times, exceeding that of the dense carbon ecosystems found in global seagrass meadows and peatlands. The complexation of the low-molecular-weight Corg with iron in SS was the main pathway for Corg fixation. Benthic animal investigations showed that SS capping fostered an anaerobic fauna ecosystem, aiding biotic Corg sequestration. Algae proliferation on the SS bed suggested complex benthic ecosystems with photosynthetic carbon fixation. Overall, SS beds offer a new abiotic carbon sequestration pathway with environmental restoration benefits; in situ capping with metal-containing material is potentially more economical and sustainable compared to traditional landfilling.

Seamounts generate efficient active transport loops to nourish the twilight ecosystem.

Seamounts are ecological oases nurturing abundant fisheries resources and epibenthic megafauna in the vast oligotrophic ocean. Despite their significance, the formation mechanisms underlying these seamount ecological oases remain uncertain. To shed light on this phenomenon, this study conducted interdisciplinary in situ observations focusing on a shallow seamount in the oligotrophic ocean. The findings show that the seamount's topography interferes with the oceanic current to generate lee waves, effectively enhancing the nutrient supply to the euphotic layer downstream of the seamount. This continuous supply enhances phytoplankton biomass and subsequently the grazing and diurnal vertical migration of zooplankton, rapidly transporting the augmented phytoplankton biomass to the aphotic layer. Unlike the cyclonic eddies that move in the upper ocean, seamounts stand at fixed locations creating a more efficient and steady active transport loop. This active transport loop connects the euphotic and twilight zones, potentially conveying nourishment to benthic ecosystems to create stereoscopic oases in the oligotrophic ocean.

Effect of temperature and body size on anterior and posterior regeneration in Hermodice carunculata (Polychaeta, Amphinomidae)

In recent years, population outbreaks of the annelid Hermodice carunculata (Polychaeta, Amphinomidae) are recurrently detected along the coastal zone of the Salento peninsula (Southern Italy), with impacts on marine benthic ecosystems. Annelida are renowned for their remarkable regeneration potential, enabling them to reform lost body parts. A handful of studies have reported posterior regeneration of H. carunculata, but anterior regeneration has not been fully explored. In this study, we investigated the capacity of H. carunculata collected in shallow coastal areas (Ionian Sea, 40°08’26.9” N 17°58’44.1” E) to regenerate anterior body parts under different temperature conditions (22 and 14 °C) and considering two different body sizes (∼ 4 g and 25 g). In addition, histological analysis and lipid analyses were carried out to detect changes in the reproductive cycle and lipid storage during ongoing regeneration. The results suggest that small and large-sized specimens of H. carunculata can regenerate efficiently anterior body parts in 12–20 weeks post amputation when kept at 22 °C. Small-sized worms kept at 14 °C regenerated slower but died in 24 weeks post amputation before regenerating a mouth, while large-sized worms kept at 14 °C were affected by a 100% mortality during blastema formation. In addition, lipid extraction analyses show that H. carunculata can regenerate during extended periods of starvation by de novo synthesizing lipid reserves and regeneration in H. carunculata does not negatively impact the reproductive cycle, as gametogenesis occurs also during the regenerative processes.

Food web attributes to assess spatial–temporal dynamics in estuarine benthic ecosystem

Threatened benthic ecosystems need urgent tools for effective bioassessment and relevant management. EU Marine Strategy Framework Directive (MSFD) obligates member states to achieve GES (Good Environmental Status) for 11 descriptors of environmental state (MSFD; 2008/56/EC). From all of the descriptors, D4 that focuses on Food Webs is the most functional-oriented indicator, but also the most challenging to implement due to our limited knowledge on benthic interactions. Particularly, it is still unclear how spatially and temporally regulated abiotic variables determine the entire benthic food webs, and which benthic food web attributes best respond to these spatially and temporally derived environmental variations. To fill this gap, we measured the natural isotopic ratios (δ13C and δ15N) of macrobenthic organisms and their food sources and build twelve food web topologies across three distinct sites (Navigator, Gambia, Tróia) in summer and winter during two consecutive years. To assess these food web topologies, we applied isotopic metrics, further integrated with univariate and multivariate analysis to find food web-based indicators that best respond to these spatial and temporal variability.We found clear spatial patterns associated to an increase in primary production and quantity and quality of organic matter (OM). Sites with higher organic load and less quality OM (Navigator and Gambia) had simpler food webs, likely associated to high abundance of opportunistic meiobenthic species. Site located inside protected area (Tróia) with high quality OM had the most complex food web characterized by high diversity of specialist consumers that used more efficiently available resources. Similarity metrics were valuable complementary tool that helped to further disentangle the causes of spatial variability, in this case distinguishing between two food webs (Navigator and Gambia) that had similar structures but different resource utilization.The temporal patterns were not so evident than the spatial patterns, although significant differences were reported between sampling occasions for the same metrics (maximum trophic position and the percentage of carnivores and omnivores, p < 0.05). The most complex Tróiás food web demonstrated greater responsiveness in capturing temporal differences in resource use, suggesting that more complex food webs are better equipped to reflect temporal variability. The integration of isotopic metrics complemented with multivariate and univariate analyses proved to be an important tool for the analysis of different aspects of the benthic food web complexity in a spatial–temporal context providing a promising approach to assess the functional integrity of the estuarine ecosystems, especially in the context of the descriptor 4 within MSFD.

Evidence of size-dependent toxicity of polystyrene nano- and microplastics in sea cucumber Apostichopus japonicus (Selenka, 1867) during the intestinal regeneration

Microplastics are ubiquitous pollutants in the global marine environment. However, few studies have adequately explored the different toxic mechanisms of microplastics (MPs) and nanoplastics (NPs) in aquatic organisms. The sea cucumber, Apostichopus japonicus, is a key organism in the marine benthic ecosystem due to its crucial roles in biogeochemical cycles and food web. This study investigated the bioaccumulation and adverse effects of polystyrene micro- and nanoplastics (PS-M/NPs) of different sizes (20 μm, 1 μm and 80 nm) in the regenerated intestine of A. japonicus using multi-omics analysis. The results showed that after 30-day exposure at the concentration of 0.1 mg L−1, PS-MPs and PS-NPs accumulated to 155.41–175.04 μg g−1 and 337.95 μg g−1, respectively. This excessive accumulation led to increased levels of antioxidases (SOD, CAT, GPx and T-AOC) and reduced activities of immune enzymes (AKP, ACP and T-NOS), indicating oxidative damage and compromised immunity in the regenerated intestine. PS-NPs had more profound negative impacts on cell proliferation and differentiation compared to PS-MPs. Transcriptomic analysis revealed that PS-NPs primarily affected pathways related to cellular components, e.g., ribosome, and oxidative phosphorylation. In comparison, PS-MPs had greater influences on actin-related organization and organic compound metabolism. In the PS-M/NPs-treated groups, differentially expressed metabolites were mainly amino acids, fatty acids, glycerol phospholipid, and purine nucleosides. Additionally, microbial community reconstruction in the regenerated intestine was severely disrupted by the presence of PS-M/NPs. In the PS-NPs group, Burkholderiaceae abundance significantly increased while Rhodobacteraceae abundance decreased. Correlation analyses demonstrated that intestinal regeneration of A. japonicus was closely linked to its enteric microorganisms. These microbiota-host interactions were notably affected by different PS-M/NPs, with PS-NPs exposure causing the most remarkable disruption of mutual symbiosis. The multi-omic approaches used here provide novel insights into the size-dependent toxicity of PS-M/NPs and highlight their detrimental effects on invertebrates in M/NPs-polluted marine benthic ecosystems.

Diverse inorganic carbon uptake strategies in Antarctic seaweeds: Revealing species-specific responses and implications for Ocean Acidification

Seaweeds are important components of coastal benthic ecosystems along the Western Antarctic Peninsula (WAP), providing refuge, food, and habitat for numerous associated species. Despite their crucial role, the WAP is among the regions most affected by global climate change, potentially impacting the ecology and physiology of seaweeds. Elevated atmospheric CO2 concentrations have led to increased dissolved inorganic carbon (Ci) with consequent declines in oceanic pH and alterations in seawater carbonate chemistry, known as Ocean Acidification (OA). Seaweeds possess diverse strategies for Ci uptake, including CO2 concentrating mechanisms (CCMs), which may distinctly respond to changes in Ci concentrations. Conversely, some seaweeds do not operate CCMs (non-CCM species) and rely solely on CO2. Nevertheless, our understanding of the status and functionality of Ci uptake strategies in Antarctic seaweeds remains limited. Here, we investigated the Ci uptake strategies of seaweeds along a depth gradient in the WAP. Carbon isotope signatures (δ13C) and pH drift assays were used as indicators of the presence or absence of CCMs. Our results reveal variability in CCM occurrence among algal phyla and depths ranging from 0 to 20 m. However, this response was species specific. Among red seaweeds, the majority relied solely on CO2 as an exogenous Ci source, with a high percentage of non-CCM species. Green seaweeds exhibited depth-dependent variations in CCM status, with the proportion of non-CCM species increasing at greater depths. Conversely, brown seaweeds exhibited a higher prevalence of CCM species, even in deep waters, indicating the use of CO2 and HCO3−. Our results are similar to those observed in temperate and tropical regions, indicating that the potential impacts of OA on Antarctic seaweeds will be species specific. Additionally, OA may potentially increase the abundance of non-CCM species relative to those with CCMs.

Dissimilarity of megabenthic community structure between deep-water seamounts with cobalt-rich crusts: Case study in the northwestern Pacific Ocean

As anthropogenic disturbance on deep-sea seamount ecosystems grows, there is an urgent need for a better understanding of the biodiversity and community structure in benthic ecosystems, which can vary at local and regional scales. A survey of the benthic megafauna on two adjacent deep-water seamounts in the northwestern Pacific Ocean was conducted, which are covered by cobalt-rich crusts, to assess the biodiversity patterns and dissimilarity of assemblage composition. Based on a multidisciplinary dataset generated from video recordings, multibeam bathymetry data, and near-bottom currents, environmental and spatial factors impacting the megabenthic communities were explored. Results showed that these two deep-water seamounts were dominated by hexactinellids, crinoids, and octocorals. The seamounts were able to support diverse and moderately abundant megafauna, with a total of 6436 individuals classified into 94 morphospecies. The survey covered a distance of 52.2 km across a depth range of 1421–3335 m, revealing multiple distinct megabenthic assemblages. The megabenthic communities of the two deep-water seamounts, with comparable environmental conditions, exhibited similarities in overall density, richness, and faunal lists, while dissimilarities in the relative abundance of taxa and assemblage composition. No gradual depth-related change in terms of abundance, richness, or species turnover was observed across the two seamounts, despite the statistical significance of depth in structuring the overall communities. The spatial distribution of megabenthic communities displayed a discontinuous and patchy pattern throughout the two deep-water seamounts. This patchiness was driven by the interactive effects of multiple environmental factors. Near-bottom currents and microhabitat features were the primary drivers influencing their dissimilarities in megabenthic community structure. This case study on the megabenthic community structure of two adjacent seamounts with cobalt-rich crusts can serve as an environmental baseline, providing a reference status for the conservation and management of seamount ecosystems, particularly valuable for areas being considered for deep-sea mining.

In Vitro Toxicity and Modeling Reveal Nanoplastic Effects on Marine Bivalves.

Nanoplastics (NPs) represent a growing concern for global environmental health, particularly in marine ecosystems where they predominantly accumulate. The impact of NPs on marine benthic organisms, such as bivalves, raises critical questions regarding ecological integrity and food safety. Traditional methods for assessing NP toxicity are often limited by their time-intensive nature and ethical considerations. Herein, we explore the toxicological effects of NPs on the marine bivalve Ruditapes philippinarum, employing a combination of in vitro cellular assays and advanced modeling techniques. Results indicate a range of adverse effects at the organismal level, including growth inhibition (69.5-108%), oxidative stress, lipid peroxidation, and DNA damage in bivalves, following exposure to NPs at concentrations in the range of 1.6 × 109-1.6 × 1011 particles/mL (p/mL). Interestingly, the growth inhibition predicted by models (54.7-104%), based on in vitro cellular proliferation assays, shows strong agreement with the in vivo outcomes of NP exposure. Furthermore, we establish a clear correlation between cytotoxicity observed in vitro and the toxicological responses at the organismal level. Taken together, this work suggests that the integration of computational modeling with in vitro toxicity assays can predict the detrimental effects of NPs on bivalves, offering insightful references for assessing the environmental risk assessment of NPs in marine benthic ecosystems.

Are physiological and ecosystem-level tipping points caused by ocean acidification? A critical evaluation

Abstract. Ocean acidification (OA) is predicted to cause profound shifts in many marine ecosystems by impairing the ability of calcareous taxa to calcify and grow and by influencing the physiology of many others. In both calcifying and non-calcifying taxa, ocean acidification could further impair the ability of marine life to regulate internal pH and thus metabolic function and/or behaviour. Identifying tipping points at which these effects will occur for different taxa due to the direct impacts of ocean acidification on organism physiology is difficult because they have not adequately been determined for most taxa nor for ecosystems at higher levels. This is due to the presence of both resistant and sensitive species within most taxa. However, calcifying taxa such as coralline algae, corals, molluscs, and sea urchins appear to be most sensitive to ocean acidification. Conversely, non-calcareous seaweeds, seagrasses, diatoms, cephalopods, and fish tend to be more resistant or even benefit from the direct effects of ocean acidification, though the effects of ocean acidification are more subtle for these taxa. While physiological tipping points of the effects of ocean acidification either do not exist or are not well defined, their direct effects on organism physiology will have flow-on indirect effects. These indirect effects will cause ecological tipping points in the future through changes in competition, herbivory, and predation. Evidence for indirect effects and ecological change is mostly taken from benthic ecosystems in warm temperate–tropical locations in situ that have elevated CO2. Species abundances at these locations indicate a shift away from calcifying taxa and towards non-calcareous taxa at high-CO2 concentrations. For example, lower abundance of corals and coralline algae and higher covers of non-calcareous macroalgae, often turfing species, are often found at elevated CO2. However, there are some locations where only minor changes or no detectable changes occur. Where ecological tipping points do occur, it is usually at locations with naturally elevated mean pCO2 concentrations of 500 µatm or more, which also corresponds to just under that concentration where the direct physiological impacts of ocean acidification are detectable in the most sensitive taxa in laboratory research (coralline algae and corals). Collectively, the available data support the concern that ocean acidification will most likely cause ecological change in the near future in most benthic marine ecosystems, with tipping points in some ecosystems as low as 500 µatm pCO2. However, further research is required to more adequately quantify and model the extent of these impacts in order to accurately project future marine ecosystem tipping points under ocean acidification.

Combining three-dimensional acoustic coring and a convolutional neural network to quantify species contributions to benthic ecosystems.

The seafloor is inhabited by a large number of benthic invertebrates, and their importance in mediating carbon mineralization and biogeochemical cycles is recognized. However, the majority of fauna live below the sediment surface, so most means of survey rely on destructive sampling methods that are limited to documenting species presence rather than event driven activity and functionally important aspects of species behaviour. We have developed and tested a laboratory-based three-dimensional acoustic coring system that is capable of non-invasively visualizing the presence and activity of invertebrates within the sediment matrix. Here, we present reconstructed three-dimensional acoustic images of the sediment profile, with strong backscatter revealing the presence and position of individual benthic organisms. These data were used to train a three-dimensional convolutional neural network model and, using a combination of data augmentation and data correction techniques, we were able to identify individual species with an 88% accuracy. Combining three-dimensional acoustic coring with deep learning forms an effective and non-invasive means of providing detailed mechanistic information of in situ species-sediment interactions, opening new opportunities to quantify species-specific contributions to ecosystems.

Ecosystem functioning during biodiversity loss and recovery

Anthropogenic biodiversity loss can impair ecosystem functioning. Human activities are often managed with the aim of reversing biodiversity loss and its associated functional impacts. However, it is currently unknown whether biodiversity–ecosystem function (BEF) relationships observed during biodiversity recovery are the same as those observed during biodiversity loss. This will depend on how species extirpation and recolonisation sequences compare and how different species influence ecosystem functioning. Using data from a marine benthic invertebrate community, we modelled how bioturbation potential – a proxy for benthic ecosystem functioning – changes along biodiversity loss and recovery sequences governed by species' sensitivity to physical disturbance and recolonisation capability, respectively. BEF relationships for biodiversity loss and recovery were largely the same despite species extirpation and recolonisation sequences being different. This held true irrespective of whether populations were assumed to exhibit compensatory responses as species were removed or added. These findings suggest that the functional consequences of local biodiversity loss can be reversed by alleviating its drivers, as different species present at comparable levels of species richness during biodiversity loss and recovery phases have similar functional effects. Empirically verifying and determining the generality of our model‐based results are potential next steps for future research.

Freshwater mussels prefer a diet of stramenopiles and fungi over bacteria

Freshwater mussels (Mollusca: Unionidae) play a crucial role in freshwater river environments where they live in multi-species aggregations and often serve as long-lived benthic ecosystem engineers. Many of these species are imperiled and it is imperative that we understand their basic needs to aid in the reestablishment and maintenance of mussel beds in rivers. In an effort to expand our knowledge of the diet of these organisms, five species of mussel were introduced into enclosed systems in two experiments. In the first, mussels were incubated in water from the Clinch River (Virginia, USA) and in the second, water from a manmade pond at the Commonwealth of Virginia’s Aquatic Wildlife Conservation Center in Marion, VA. Quantitative PCR and eDNA metabarcoding were used to determine which planktonic microbes were present before and after the introduction of mussels into each experimental system. It was found that all five species preferentially consumed microeukaryotes over bacteria. Most microeukaryotic taxa, including Stramenopiles and Chlorophytes were quickly consumed by all five mussel species. We also found that they consumed fungi but not as quickly as the microalgae, and that one species of mussel, Ortmanniana pectorosa, consumed bacteria but only after preferred food sources were depleted. Our results provide evidence that siphon feeding Unionid mussels can select preferred microbes from mixed plankton, and mussel species exhibit dietary niche differentiation.

Reversing functional extinction: successful restoration of eradicated oyster reefs

Functionally extinct ecosystems, those that have been locally eradicated save for remnant individuals, are unlikely to naturally recover over meaningful human time frames. However, ecosystem restoration provides opportunities to reverse functional extinction by rapidly addressing the physical and/or biological barriers that prevent natural recovery. Here, we assess the restoration progress of a native Flat oyster (Ostrea angasi) reef ecosystem in South Australia that was eradicated from the Australian mainland approximately 100 years ago. In the absence of any reference Flat oyster ecosystems in the region, restoration progress was assessed relative to ecological targets informed by a combination of local rocky reef ecosystems and an interim Flat oyster reference model informed by Australia's sole remaining O. angasi reef, in Tasmania. Two and half a years after the restoration was initiated via the construction of 14 boulder reefs, we observed densities of restored native adult O. angasi (192 ± 19 m−2; mean ± 1 SE) that exceeded oyster densities observed on the sole remaining natural reef. Communities of macroinvertebrates on the reef restoration represented approximately 60% of the biodiversity observed on healthy rocky reef reference systems, while ecological functions (e.g. filter feeding) are demonstrably increasing. The rate of recovery of this benthic ecosystem, from functionally extinct to a restored Flat oyster reef ecosystem within several years, demonstrates the latent resilience of degraded oyster communities and the capacity for effective marine restorations to achieve rapid ecological recoveries.

Experimental seabed disturbance effects on Chatham Rise deep-sea meiofaunal communities, Southwest Pacific

ABSTRACT Growing global demand for deep-sea resources may lead to increased pressure on benthic ecosystems. Here we examined changes in meiofaunal communities following an in situ physical disturbance experiment. A significant change in meiofaunal community structure in surface (0-1 cm) and subsurface (1-5 cm) sediments was observed immediately following the disturbance at both the directly and indirectly disturbed sites and adjacent potentially undisturbed/indirectly disturbed sites, reflecting a decrease in the abundance of several meiofaunal taxa. Abundance, taxon richness and diversity also decreased immediately following disturbance across all sites. Surface community parameters returned to pre-disturbance values one year post-disturbance, but only a partial recovery was observed for the subsurface community over the same period. The accumulation of recently resuspended and deposited sediment could have led to lower meiofaunal density and shifts in community structure. Passive dispersal and recolonisation from outside the study area may explain why the surface community recovered more fully than the subsurface community. We show that meiofauna were negatively affected by a relatively minor disturbance compared to proposed commercial seabed mining operations, but the finding that communities had largely recovered one year after disturbance has implications for resilience of fauna to much more pronounced impacts of potential large-scale mining.

Adverse effects of crushed seafloor massive sulphide deposits on the boreal deep-sea sponge Geodia barretti Bowerbank, 1858 and its associated fauna

Abundant mineral resources in the deep sea are prospected for mining for the global metal market. Seafloor massive sulphide (SMS) deposits along the Mid-Atlantic Ridge are one of the potential sources for these metals. The extraction of SMS deposits will expose adjacent marine ecosystems to suspended particle plumes charged with elevated concentrations of heavy metals and other potentially toxic compounds. Up to date there is no information about the impact of mining activities on deep-sea benthic ecosystems such as abundant deep-sea sponge grounds in the North Atlantic Ocean. Sponge grounds play a major role in benthic-pelagic coupling and represent an important habitat for a diversity of vertebrates, invertebrates and microorganisms. To simulate the effects of mining plumes on benthic life in the deep sea, we exposed Geodia barretti, a dominant sponge species in the North Atlantic Ocean, and an associated brittle star species from the genus Ophiura spp. to a field-relevant concentration of 30 mg L−1 suspended particles of crushed SMS deposits. Three weeks of exposure to suspended particles of crushed SMS resulted in a tenfold higher rate of tissue necrosis in sponges. All brittle stars in the experiment perished within ten days of exposure. SMS particles were evidently accumulated in the sponge's mesohyl and concentrations of iron and copper were 10 times elevated in SMS exposed individuals. Oxygen consumption and clearance rates were significantly retarded after the exposure to SMS particles, hampering the physiological performance of G. barretti. These adverse effects of crushed SMS deposits on G. barretti and its associated brittle star species potentially cascade in disruptions of benthic-pelagic coupling processes in the deep sea. More elaborate studies are advisable to identify threshold levels, management concepts and mitigation measures to minimize the impact of deep-sea mining plumes on benthic life.