Mussel Beds Research Articles

Using multiple linear regression for estimating total mussel (Mytilus californianus) shell size to accommodate morphological variability related to diverse environments

Understanding variation in mollusk shell size through time can be useful for interpreting changes in past marine environments and human behavior related to subsistence. Recent studies have provided means to estimate total shell length for California mussel (Mytilus californianus) by using a single morphological measurement in a simple linear regression approach; however, shell morphology may differ between environmentally diverse areas and through time, in turn potentially influencing the reliability of single variable models generated from measurements of shells harvested from a different geographic region to predict total shell length for archaeological samples. In this study, we examined the performance of models built from three site specific samples from contemporary mussel beds from Santa Rosa Island, southern California and models built from a pooled sample. The data was split into training (80%) and testing (20%) subsets to construct and validate eight multivariable models using a best subset regression approach. We then examined the performance of our models on each subset, evaluating measures of bias, accuracy, coverage, and precision. We also evaluated the performance of our models using an archaeological sample (CA-SRI-138) as an additional external validation sample. For each sample, we consider a model with all measurements and a model using only those measurements likely observed in fragmentary assemblages. We also developed single variable models for comparison to the performance of multivariable models. Multivariable models consistently demonstrate better performance than single variable models. The models using the pooled sample were also more accurate, precise, and exhibited less bias than the site-specific models. Each site-specific model selected a different subset of variables and indicated a range of variable importance, which is captured in the increased generalizability of the multivariable, pooled sample models when estimating total shell length for both contemporary and archaeological samples.

Shedding light on variation in reproductive success through studies of population genetic structure in a Southeast Pacific Coast mussel.

Phylogeography often focuses on the spatial dimension of genetic diversity, rarely including the temporal dynamics occurring interannually among local populations, which can provide insight into past variations in reproductive success. Currently, there is an intense aquaculture industry of Mytilus spp. on the Southeast Pacific Coast which depends entirely on the spat released by natural populations forming a relevant and sensitive social-ecological system. Temporal and spatial spat variability from natural mussel beds could be related to interannual reproductive dynamics with variable reproductive success and recruitment, which leave genetic signatures. Temporal and spatial genetic structure was evaluated in six natural beds in the Southeast Pacific (from 39°25'S to 43°07'S) on the most abundant and widespread Mytilus lineage detected, Mytilus cf. chilensis, in 4 consecutive years. Analyses included data from >180 individuals per year, with a total of 751 (mitochondrial COI) and 747 (nuclear H1) individuals, respectively. Overall, both markers showed high haplotype diversity and low spatial and temporal genetic differentiation. Likely, the high dispersal capacity of Mytilus cf. chilensis maintains population homogeneity and prevents diversity erosion. The slight differences in genetic variance of COI were better explained by differences among sites (space), and conversely, the H1 genetic variance was better explained by interannual (temporal) comparisons, which could explain temporal variability in spat availability. This study highlights the important insights achieved with the evaluation of both temporal and spatial population genetic structures in marine species with high reproductive output, which can condition the success and sustainability of the relevant social-ecological system.

Assessing Potential Habitat for Freshwater Mussels by Transferring a Habitat Suitability Model within the Ozark Ecoregion, Missouri

Habitat suitability models for freshwater mussels can inform conservation of these imperiled animals. Riverscape-scale hydrogeomorphic variables were previously used to predict suitable mussel habitat in the Meramec River basin, Missouri. We evaluated transferability of the Meramec River habitat suitability model to the Gasconade and Little Black rivers, in the Ozark Highlands ecoregion, Missouri. The best-fit models relied on transferring and adapting the original modeling framework to better represent the unique habitat characteristics of each river. Mussel bed occurrence in both rivers was associated with reaches that were classified as pools. Mussel beds in the Gasconade River were also associated with laterally stable reaches adjacent to small bluffs, distant from gravel bars, and with higher stream power indices. Mussel beds in the Little Black River were associated with reaches with higher surface water availability during low-flow conditions, lower stream power indices, and bluffs located downstream. Our results show that existing habitat models can be transferred to other streams with similar environmental conditions, but differences in watershed characteristics can affect transferability.

How climate-driven changes in disturbance frequency affect the recovery of intertidal mussel beds

Community and population recovery from disturbance depends on the intensity, spatial scales, and frequency of disturbance events. Moreover, foundation species, like bed-forming mussels in rocky intertidal shores, are especially prone to disturbance associated with extreme climatic events. The aim of the present study was to experimentally evaluate how the frequency of physical disturbances that generate gaps in beds of the mussel Brachidontes rodriguezii affects mussel recolonization and the succession process on two rocky shore sites of the Southwestern Atlantic. Experimental disturbances (removal of mussels and other forms of biotic cover) were applied to small plots (14 cm × 14 cm) at three different frequencies over two years: 1) only at the beginning of the experiment (i.e., 1× removal frequency), 2) at the beginning of the experiment and 12 months later (2× removal frequency) and, 3) at the beginning of the experiment and 6, 12, and 18 later (4× removal frequency). Unmanipulated areas were maintained as controls. Before applying the experimental disturbance, we measured the abundance of all organisms present in all plots, obtaining data every 6 months. The data were analyzed considering two factors associated with the disturbance frequency: the time since the last removal and the number of removals on the same plot. Our results indicate that increases in disturbance frequencies were sufficient to maintain mussel bed recovery below control levels and increased the cover of crustose algae at the end of the two-year experimental period in one of the rocky shores studied. The decreases observed in the mussel recovery rates under increased disturbance scenarios are expected to have cascading consequences on rocky shore biodiversity, such as reductions in the overall abundance of interstitial invertebrate species that depend on mussel bed habitats and increases in the abundance of sessile organisms that preferentially occur in gaps and are otherwise excluded by mussels, such as the non-native barnacle Balanus glandula.

Euendolithic Infestation of Mussel Shells Indirectly Improves the Thermal Buffering Offered by Mussel Beds to Associated Molluscs, but One Size Does Not Fit All

Mussel beds form important intertidal matrices that provide thermal buffering to associated invertebrate communities, especially under stressful environmental conditions. Mussel shells are often colonized by photoautotrophic euendoliths, which have indirect conditional beneficial thermoregulatory effects on both solitary and aggregated mussels by increasing the albedo of the shell. We investigated whether euendolithic infestation of artificial mussel beds (Perna perna) influences the body temperatures of four associated mollusc species during simulated periods of emersion, using shell temperature obtained via non-invasive infrared thermography as a proxy. Shell temperatures of the limpet Scutellastra granularis and the chiton Acanthochitona garnoti were higher in non-infested than infested mussel beds during simulated low tides under high solar irradiance and low wind speeds. However, this was not the case for the limpet Helcion pectunculus or the top shell Oxystele antoni. Morphological differences in mollusc shape and colour could, in part, explain this contrast between species. Our results indicated that endolith-induced improvements in humidity and temperature in mussel beds could benefit associated molluscs. The beneficial thermal buffering offered by euendolithic infestation of the mussel beds was effective only if the organism was under heat stress. With global climate change, the indirect beneficial effect of euendolithic infestation for invertebrate communities associated with mussel beds may mitigate intertidal local extinction events triggered by marine heatwaves.

Phase-separation physics underlies new theory for the resilience of patchy ecosystems.

Spatial self-organization of ecosystems into large-scale (from micron to meters) patterns is an important phenomenon in ecology, enabling organisms to cope with harsh environmental conditions and buffering ecosystem degradation. Scale-dependent feedbacks provide the predominant conceptual framework for self-organized spatial patterns, explaining regular patterns observed in, e.g., arid ecosystems or mussel beds. Here, we highlight an alternative mechanism for self-organized patterns, based on the aggregation of a biotic or abiotic species, such as herbivores, sediment, or nutrients. Using a generalized mathematical model, we demonstrate that ecosystems with aggregation-driven patterns have fundamentally different dynamics and resilience properties than ecosystems with patterns that formed through scale-dependent feedbacks. Building on the physics theory for phase-separation dynamics, we show that patchy ecosystems with aggregation patterns are more vulnerable than systems with patterns formed through scale-dependent feedbacks, especially at small spatial scales. This is because local disturbances can trigger large-scale redistribution of resources, amplifying local degradation. Finally, we show that insights from physics, by providing mechanistic understanding of the initiation of aggregation patterns and their tendency to coarsen, provide a new indicator framework to signal proximity to ecological tipping points and subsequent ecosystem degradation for this class of patchy ecosystems.

A Hotspot of TTX Contamination in the Adriatic Sea: Study on the Origin and Causative Factors.

Tetrodotoxins (TTXs), the pufferfish venom traditionally associated with Indo-Pacific area, has been reported during last decades in ever wider range of marine organisms and ever more geographical areas, including shellfish in Europe. Wild mussels (Mytilus galloprovincialis) grown in the Marche Region (N Adriatic Sea, Italy) were shown to be prone to TTX contamination during the warm season, with a suspected role of Vibrio alginolyticus characterized by non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS)-encoding genes. This work aimed to deepen the knowledge about the toxin's origin and the way through which it accumulates in mussels. A two-year study (spring-summer 2020-2021) confirmed the recurrent presence of TTX (11-68 µg kg-1) in the official monitored natural mussel beds of the Conero Riviera. During 2021, a supplementary nonroutine monitoring of a natural mussel bed in the same area was carried out weekly from June until August for TTXs and/or the presence of V. alginolyticus. Biotic (mussels, mesozooplankton, worms and phytoplankton); abiotic (water and sediment) matrices and phytoplankton assemblage characterizations were studied. Mussels showed relevant TTX contamination levels (9-296 µg kg-1) with extremely rapid TTX accumulation/depletion rates. The toxin presence in phytoplankton and its distribution in the different mussel tissues supports its possible exogenous origin. The V. alginolyticus count trend overlaps that of TTX contamination in mussels, and similar trends were reported also for some phytoplankton species. The role of V. alginolyticus carrying NRPS or PKS genes as a possible TTX source and of phytoplankton as a "potential vector" should therefore be further investigated.

Symbiont-induced phenotypic variation in an ecosystem engineer mediates thermal stress for the associated community

Microbial symbionts have strong potential to mediate responses to climate change. Such modulation may be particularly important in the case of hosts that modify the physical habitat structure. By transforming the habitats, ecosystem engineers alter resource availability and modulate environmental conditions which, in turn, indirectly shape the community associated with that habitat. Endolithic cyanobacteria are known to reduce the body temperatures of infested mussels and here, we assessed whether the thermal benefits of endoliths on the intertidal reef-building mussel Mytilus galloprovincialis extends to the invertebrate community utilising mussel beds as habitat. Artificial reefs of biomimetic mussels either colonised or not colonised by microbial endoliths were used to test whether infauna species (the limpet Patella vulgata, the snail Littorina littorea and mussel recruits) in a mussel bed with symbionts experience lower body temperatures than those within a bed composed of mussels without symbionts. We found that infaunal individuals benefitted from being surrounded by mussels with symbionts, an effect that may be particularly critical during intense heat stress. Indirect effects of biotic interactions, complicate our understanding of community and ecosystem responses to climate change, especially in cases involving ecosystem engineers, and accounting for them will improve our predictions.

Strategy of micro-environmental adaptation to cold seep among different brittle stars’ colonization

Diffusing fluid from methane seepage in cold seep field creates zones with physicochemical gradients and divergent ecosystems like the mussel beds and clam beds. Three species of brittle stars (Ophiuroidea) were discovered in the Haima cold seep fields, of which Ophiophthalmus serratus and Histampica haimaensis were found on top of or within mussel beds and clam beds, whereas Amphiura sp. was only collected from muds in the clam bed assemblage. Here, we evaluated the genetic signatures of micro-environmental adaptation of brittle stars to cold seep through the comparison of mitogenomes. This study provided two complete mitogenome sequences of O. serratus and Amphiura sp. and compared with those of H. haimaensis and other non-seep species. We found that the split events of the seep and non-seep species were as ancient as the Cretaceous period (∼148–98 Mya). O. serratus and H. haimaensis display rapid residue mutation and mitogenome rearrangements compared to their shallow or deep-sea relatives, in contrast, Amphiura sp. only show medium, regardless of nucleotide mutation rate or mitogenome rearrangement, which may correlate with their adaptation to one or two micro-ecosystems. Furthermore, we identified 10 positively selected residues in ND4 in the Amphiura sp. lineage, suggesting important roles of the dehydrogenase complex in Amphiura sp. adaptive to the cold seep environment. Our results shed light on the different evolutionary strategies during colonization in different micro-environments.

Community composition of mussel associates at deep-sea methane seeps in the Gulf of Mexico and the US Atlantic Margin

Efforts to understand and preserve the methane seep communities of the Gulf of Mexico and the US western Atlantic margin begin with an understanding of biodiversity and community composition. In this study, 10,143 individuals representing 63 different taxa were sampled from mussel-beds surrounding methane seeps at various depths within two different ocean basins. Diversity in mussel beds was highest at Baltimore Canyon, the shallowest site sampled in the Atlantic. Although only four species were sampled at more than one site, species composition was most alike among sites found at similar depths; the two deepest sites sampled, Florida Escarpment and Blake Ridge, showed a 9.6% similarity. However, depth is not the only predictor of similarity: Baltimore Canyon and Chincoteague are both located in the Atlantic Ocean at different depths but had a 5.3% similarity in species composition. The high diversity of individuals sampled among these sites emphasizes the importance of preserving seep communities, which provide essential nursery habitats and primary production that establish a food source for many migratory species within the deep-sea ecosystem. Not only is the diversity of seep communities unique and important to the deep sea, but seeps may be beneficial to the overall health of our Earth’s ecosystem through the support of commercial fisheries and the sequestering of methane.

Variety in responses of wintering oystercatchers Haematopus ostralegus to near-collapse of their prey in the Exe Estuary, UK.

Globally, habitat loss or degradation is a major threat to many species, and those with specific habitat requirements are particularly vulnerable. Many species of wading birds (Charadrii) are dependent upon intertidal sites to feed, but, as a result of anthropogenic pressures, the prey landscape has changed at many estuaries. Behavioral adaptations may be able to buffer these changes. In this study over multiple seasons, we aimed to investigate the foraging behaviors of wintering Eurasian oystercatchers in the Exe Estuary where mussel beds, the preferred prey at this site, have almost disappeared in the last decade. From 2018 to 2021, GPS tracking devices were deployed on 24 oystercatchers, and the foraging locations of adults, sub-adults, and juveniles were determined. Of the 12 birds tracked over multiple winter periods, 10 used the same foraging home ranges but a juvenile and sub-adult changed locations interannually. The dominant prey species at key foraging sites were assessed, and we found that younger birds were more likely to visit sites with lower quality prey, likely due to being at a competitive disadvantage, and also to explore sites further away. Individuals were generally consistent in the areas of the estuary used in early and late winter, and over 90% of locations were recorded in the protected area boundary, which covers the sand and mudflats of the Exe. These findings suggest high specificity of the current protected area for oystercatchers in the Exe Estuary, although, if the prey landscape continues to decline, younger individuals may provide the potential for adaptation by finding and foraging at additional sites. Continued monitoring of individual behavior within populations that are facing dramatic changes to their prey is essential to understand how they may adapt and to develop suitable management plans to conserve threatened species.

Habitat properties and invertebrate composition in mussel-dominated rocky shores: A test of edge effects

Mussels form dense three-dimensional beds that serve as habitat to other species. In rocky shores, these beds are often interspersed by gaps due to patchy dislodgement/mortality caused by the action of waves, predators, and/or extreme temperatures. Although mussel beds and gaps are known to support distinctive invertebrate communities, variations in invertebrate habitat function between the interior and edges of mussel beds and gaps were not yet examined. Here, we evaluated variations in habitat properties and invertebrate composition between the edge and interior of mussel (Brachidontes rodriguezii) beds and gaps at three rocky shore sites in the Southwestern Atlantic. Our results indicate that the interior and edge of mussel-covered areas differ in terms of mussel size, density and orientation relative to the rock surface (all surrogates of habitat structure), and in the quantity of sediments they accumulate. However, this does not directly translated into differences in temperature, desiccation, and invertebrate composition within the mussel bed. As it concerns to gaps, we generally observed increased limpet (Siphonaria lesonii) densities at their edges, which suggests that they encounter favourable conditions by the perimeter of mussel beds. The general lack of edge effects on the invertebrates inhabiting mussel beds suggests that their species composition would remain largely unaffected by expected increases in gap and edge habitat formation due to ongoing increases in the frequency and magnitude of storms and heat waves. Yet, if increased availability of edge habitats leads to increased overall density of limpets in these rocky shores, then changes could be expected in algal production, composition, and dynamics.

Community Characteristics and Genetic Diversity of Macrobenthos in Haima Cold Seep

Knowledge about community structure and genetic diversity can help assess the potential for change in the loss and restoration of biodiversity, thereby facilitating effective management and ecosystem protection. Macroinvertebrate communities are an important biotic component of deep sea cold seep ecosystems. As Haima cold seep is increasingly being assessed for its potential gas hydrate mineral wealth, knowledge of community characteristics and genetic diversity of macrobenthos is needed to anticipate the potential impacts on biodiversity. In this study, we examined species diversity and community structure at five sites in the Haima cold seep using a remote-operated vehicle (ROV) for in situ surveying. The results identified 12 macrobenthic species from 5 phyla and 12 families. The macrobenthos community could be divided into two communities (H1 and H2=mussel bed community, and H3 and H4= vesicomyid clams community) based on CLUSTER and NMDS analyses. Gigantidas haimaensis (Mollusca), Branchipolynoe pettiboneae (Annelida), and Histampica haimaensis (Echinodermata) were most dominant within their respective phyla, with values of the dominance of 0.160, 0.021 and 0.114, respectively. The genetic diversity of these three typical macrobenthic species in the Haima cold seep was evaluated using the mitochondrial cytochrome c oxidase subunit I (COI) gene, haplotype, and nucleotide diversity values were 0.651 to 0.912 and 0.00148 to 0.00812, respectively, representing high haplotype diversity but low nucleotide diversity. Finally, mitochondrial concatenated dataset (MCD) sequences from three mitochondrial genes (ATP6, COI, and NAD4) and 294,734 genome-wide single nucleotide polymorphisms (SNPs) from restriction site-associated DNA-sequencing (RAD-seq) data were obtained from 60 individuals from two sites (H1 and H2), providing deep insight into the genetic diversity and structure of G. haimaensis, the engineer species in Haima cold seep. No significant genetic differentiation between G. haimaensis in H1 and H2 was detected based on MCD sequences. Nevertheless, when using SNP datasets, a small but clear genetic subdivision between G. haimaensis in the two sites as revealed by STRUCTURE and principal component analysis (PCA). The results comprehensively illuminate macrobenthos biodiversity in the Haima cold seep ecosystem and provide a baseline against which population dynamics may be assessed in the future.

Evidence of increased mussel abundance related to the Pacific marine heatwave and sea star wasting

AbstractMussels occupy a key middle trophic position in nearshore food webs linking primary producers to predators. Climate‐related environmental changes may synergistically combine with changes in predator abundance to affect intertidal ecosystems. We examined the influence of two major events on mussel (Mytilus trossulus) abundance in the northern Gulf of Alaska: the recent Pacific marine heatwave (PMH, 2014–2016) and an outbreak of sea star wasting (SSW). We investigated how mussel abundance changed since the onset of SSW and whether the density of predatory sea stars or PMH‐related temperature metrics explain variation in mussel abundance. Sea stars and mussels were surveyed since 2005 approximately annually in four regions of the northern Gulf of Alaska: Katmai (KATM), Kachemak Bay (KBAY), Kenai Fjords (KEFJ) and western Prince William Sound (WPWS). Mussel percent cover in the mid‐intertidal increased 1–3 years after declines in sea stars at all regions and in the low‐intertidal at KATM, KBAY, and KEFJ, but not at WPWS. After the onset of SSW, large (≥20 mm length) mussel density and mussel bed width increased at KATM but not the other regions. Total mussel densities, including recruits, did not differ before and after the onset of SSW. The total number of sea stars significantly explained variation in mussel metrics, but the proportions of the three sea star species examined did not. We did not find strong evidence for direct effects of temperature on mussels. The effects of the PMH and the SSW outbreak appear to have combined, with increased temperatures indirectly benefiting mussels in concert with relaxed top‐down pressure from sea stars, allowing for increased mussel abundance. Changing mussel abundance may affect intertidal local productivity and the abundance or performance of other nearshore consumers of mussels.

Recolonization behavior of rapa whelk (Rapana venosa) and common starfish (Asterias rubens) eradicated from mussel bed

ABSTRACT This study aimed to investigate the recolonization behaviour of the rapa whelk (Rapana venosa) and the common starfish (Asterias rubens) on the mussel beds in their natural habitat. The monitoring studies were carried out seasonally on an island covered by a complete mussel bed in the Sea of Marmara (Turkey) between 19 October 2020 and 9 August 2021. Inhabitant rapa whelk and common starfish on the experimental study island (ESI) were tagged, then moved 10 m away from ESI. The recolonization potential of tagged invaders was monitored for 14 days with underwater surveys after their local eradication each season. The percentage of returned rapa whelk to the ESI was higher than common starfish end of the monitoring period. Rapa whelk moved non-stop towards the mussel bed, reaching the ESI at the latest 6th hour. Common starfish reached the mussel bed much later (at the 15th hour) than rapa whelk. The common starfish began to leave the ESI at the end of the 7th day, while the rapa whelk addicted to the ESI for 14 days. Re-invasion behaviour varied significantly seasonally, and both invaders reached the ESI much later in winter. During the monitoring periods, the highest invader densities were seen in the patches with the most abundant mussels, indicating continued uninterrupted feeding. The re-invasion duration and daily feeding activities support the spread of these invaders and could be considered a threat to marine resources.

Species- and site-specific circulating bacterial DNA in Subantarctic sentinel mussels Aulacomya atra and Mytilus platensis

Impacts of climate changes are particularly severe in polar regions where warmer temperatures and reductions in sea-ice covers threaten the ecological integrity of marine coastal ecosystems. Because of their wide distribution and their ecological importance, mussels are currently used as sentinel organisms in monitoring programs of coastal ecosystems around the world. In the present study, we exploited the concept of liquid biopsy combined to a logistically friendly sampling method to study the hemolymphatic bacterial microbiome in two mussel species (Aulacomya atra and Mytilus platensis) in Kerguelen Islands, a remote Subantarctic volcanic archipelago. We found that the circulating microbiome signatures of both species differ significantly even though their share the same mussel beds. We also found that the microbiome differs significantly between sampling sites, often correlating with the particularity of the ecosystem. Predictive models also revealed that both species have distinct functional microbiota, and that the circulating microbiome of Aulacomya atra was more sensitive to changes induced by acute thermal stress when compared to Mytilus platensis. Taken together, our study suggests that defining circulating microbiome is a useful tool to assess the health status of marine ecosystems and to better understand the interactions between the sentinel species and their habitat.

Effects of habitat homogenisation on assemblages associated with mussel clumps.

Biodiversity loss is considered one of the main threats to marine ecosystems. In this framework of biodiversity decline, organisms that provide biogenic habitat play a relevant role by their capacity to structure assemblages and influence ecological processes. The Mediterranean mussel Mytilus galloprovincialis is considered an ecosystem engineer because it alters local environmental conditions maintaining habitat suitability for other organisms, and enhancing local biodiversity. Although it is widely recognized that mussel beds increase diversity, the drivers shaping these assemblages are poorly explored. We investigate whether mussel size homogenisation shapes the abundance, richness and structure of macrobenthic assemblages associated with mussel beds in two shores of the Galician coast (NW Spain). At each shore, two sites, 10 m apart, were selected and at each site, faunal assemblages were compared between mussel clumps showing shells of various sizes (control), and mussel clumps with closely similar-sized mussels, considered as homogenised. Homogenised clumps showed, in general, higher values in total number of individuals and species than control clumps. Regarding the effect of mussel size homogenisation on the multivariate structure of the assemblages, significant differences between control and homogenised clumps were found in three out of the four sites. Most relevant associated species usually reached higher abundances in homogenised clumps than control ones. Therefore, mussel size homogenisation influenced the structure of the macrofaunal assemblages associated with mussel beds but, its effect was context dependent (i.e., varied with sites). Information about the species contribution to dissimilarities among homogenised and control clumps was provided and the potential influence of sediment and algae on mussel clumps was discussed.

A Review of Coastal Anthropogenic Impacts on Mytilid Mussel Beds: Effects on Mussels and Their Associated Assemblages

Mussel beds are an important habitat in many coastal systems, harboring a high diversity of biota. They are threatened by anthropogenic impacts that affect mussels and their associated assemblages. Pollution, harvesting, trampling, dredging and trawling are major threats faced by these communities. Most of the studies on the effects of such impacts on the mussel beds overlook the associated fauna. Since mussels are very resilient, especially to pollution, the associated fauna can provide a better footprint of the impacts’ effects. In this review, we looked into the main remarks regarding the effects of anthropogenic impacts in mussel bed communities. Organic pollution was the best studied impact and the Atlantic region was the best studied zone. Low values of abundance, biomass, diversity, evenness and species richness were reported for all categories of impacts, with some studies describing declines in at least three of these descriptors. Among the associated fauna, some tolerant species benefited from the impacts, particularly organic enrichment, and became more abundant, but sensitive species suffered considerable declines in density, mainly in dredging and trawling impacts. Therefore, fauna associated with mussel beds is a suitable indicator of anthropogenic disturbances.

A preliminary study of macrofaunal communities and their carbon and nitrogen stable isotopes in the Haima cold seeps, South China Sea

The macrofaunal community in the Haima cold seeps of the South China Sea was investigated, and trophic relationships were evaluated using carbon and nitrogen stable isotope signatures (δ13C and δ15N). A total of 30 macrofaunal species were identified in this study, most of which were collected from the Gigantidas haimaensis mussel beds. Only four macrofaunal species were collected from the Calyptogena marissinica clam beds, where the environment may not be suitable for the survival of most macrofauna. The bush of slim tubeworms (Sclerolinum sp.) might be an important nursery ground for mussels. G. haimaensis was the predominant species, and its average δ13C and δ15N values were −52.7‰ and 0.6‰, respectively. Compared with the stable isotope signatures of particulate organic matter (POM), it suggested that the food source of macrofauna in the Haima cold seeps was mainly originated from chemosynthetic autotrophs. In the mussel bed, most of the macrofauna had a large δ13C isotopic distance compared with G. haimaensis, suggesting that G. haimaensis was not a direct food source for most cold-seep macrofauna in the mussel bed. The variation in stable isotope signatures of macrofauna might be attributed to different proportions of methanotrophic and thiotrophic endosymbionts. Neolithodes brodiei and Bathynomus jamesi showed the highest δ13C and δ15N values. However, the large isotopic distance indicated that N. brodiei and B. jamesi might just occasionally visit the cold-seep ecosystem and their food sources were mainly from the upper ecosystem relying on photosynthesis. Overall, our results suggested that there was no significant predator-prey relationship among these macrofaunal species in the Haima cold seeps. This study provided important baseline data of stable isotope signatures for further studies to elucidate the trophic interaction among seep organisms.

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.