Mussel Abundance Research Articles

Baseline for the Northeast Atlantic (58-70°N) intertidal Mytilus species complex (Mytilus spp.).

Mussels (Mytilus spp.) are abundant in the North Atlantic, sessile, and sensitive to environmental change, and suitable as sentinels of environment and climate change of costal ecosystems. We aimed to determine the baseline for the Northeast Atlantic (58-70°N) Mytilus species complex, and to show the present distribution to surveys conducted 60 years ago. Baseline was obtained by investigating a total of 509 stations in the intertidal zone, in four regions comprising the environmental gradient from head of fjord to coast, and distributed over the latitudinal gradient from 58 to 70°N. The baseline shows a range in continuous abundance of mussels from 12% to 36%, patchy abundance from 26% to 57% and no or very limited mussel abundance from 26% to 46% between the four regions. The presence of mussels in the southeast and west region was visualized to previous surveys conducted 60 years ago. The data points to similar past and present presence of mussels in both regions, yet past major mussel fields in the inner section of region southeast was not detected in this study. The baseline of Mytilus spp. in the Northeast Atlantic (58-70°N) is now available for future reference. The baseline, plotted to surveys conducted 60 years ago, points to awareness of the population situated in the southeast section of the investigated region. Continued monitoring and modeling are needed to clarify drivers of temporal and spatial variation in the mussel populations along the Northeastern Atlantic coast.

Lateral connectivity maintains higher freshwater mussel biodiversity

Abstract The loss of lateral hydrological connectivity (LLHC) in freshwater ecosystems is increasingly threatening biodiversity; however, studies reporting this situation are limited, especially those assessing multi‐measure biodiversity features at large spatial scales. Here, and using one the most threatened taxonomic groups in freshwater ecosystems, we examined the possible influence of LLHC on the species diversity, density, and biomass of mussel assemblages and the genetic diversity and structure of Nodularia douglasiae (a common and widespread native species) in the Yangtze River floodplain. Results showed that the species diversity of freshwater mussels (α and β diversity) significantly differed between the connected and the disconnected areas, with higher α diversity and lower β diversity in the connected areas. At the same time, relative abundance, density, biomass, and genetic diversity of freshwater mussels were higher in the connected areas. High genetic differentiation and low gene flow were found among the 18 analysed N. douglasiae populations, indicating that LLHC is affecting genetic structure of this particular freshwater mussel species. Overall, results indicated that river–lake connectivity is affecting freshwater mussel biodiversity. In addition, this study highlights that multi‐measure biodiversity features provide distinct information about biodiversity dynamics, and are essential to evaluate the effects of floodplain disconnection. We advocate that an integrative approach to floodplain management embracing species and genetic diversity is needed for effective biodiversity conservation in large river ecosystems.

Adaptive stacked species distribution modelling: Novel approaches to large scale quantification of blue carbon to support marine management

This study introduces a novel concept of ‘Adaptively Stacked’ Species Distribution Models (AS-SDMs) to predict blue carbon habitat distribution, abundance, carbon stocks, and carbon sequestration potential in Orkney. AS-SDMs are built from Weighted Boosted Regression Trees (WBRTs) that adaptively stack blue carbon sediment thickness, sediment carbon content, and sequestration potential to predicted abundance. A novel method to describe substrate types by relative inputs of mud, sand, and gravel is detailed that better characterises the determining factors of seagrass, maerl, and horse mussel abundance. This study also introduces a novel use of indexes to mitigate double counting issues of mixed species distribution models.Seagrass, maerl, horse mussel, and mixed seagrass and maerl (SGM) habitats are estimated to cover a maximum area of 657 km2 in Orkney, have a total sediment carbon stock of 16 Mt. C, and sequester 6000 t C yr−1. Applying a conservative threshold of 50 % abundance to habitat predictions, six key potential areas of blue carbon offset projects are identified. These areas cover just over 9 km2, have a total carbon stock of 330,000 t C, and sequester 330 t C yr−1. When applied to UK carbon credit value, assuming integration with voluntary markets and compliance with accreditation criteria, the habitats in these areas have a potential value of £24.5 million. If applied as annual values, these areas have carbon stocks with a potential value of £0.93 million yr−1 and a carbon sequestration potential value of £24,000 yr−1.

A revision of Rhombuniopsis Haas, 1920 (Unionida, Unionidae) endemic to the ancient lakes of Yunnan, China, with descriptions of two new species

Freshwater mussels are an important component of the macrobenthic fauna but due to modern environmental pollution and destruction, the abundance of freshwater mussels has declined rapidly, and this fauna is one of the most threatened animal groups in the world. China is the country with the second highest diversity of freshwater mussels in the world. Rhombuniopsis is a genus of freshwater mussels endemic to the ancient lakes and surrounding area in Yunnan Province, China. Species in this genus are threatened with extinction and have not been recorded alive for many years. We present a revision of Rhombuniopsis based on the morphological study of the museum materials and newly collected specimens, and propose two species new to science: Rhombuniopsis linan sp. nov. and Rhombuniopsis songmeng sp. nov. The two new species are considered extinct because the lakes they inhabited were completely dried up due to human activity. We compare our recent data with the historical studies to trace the population change of the Rhombuniopsis species in different lakes. We revise the distribution and assess the conservation status for each species. The present work confirms the importance of conservation of molluscs in the ancient lakes of Yunnan and suggest that several species are already extinct.

Impacts of seeding density on the abundance and size of juvenile mussels and biofouling accumulation in Greenshell™ mussel aquaculture

Growth of the Greenshell™ mussel (Perna canaliculus) industry, New Zealand's most significant aquaculture sector, is limited by spat abundance in the early stages of the aquaculture cycle. However, there are few management techniques to improve spat production. Here, we tested the effects of seeding density (low: 257, mid: 515, and high: 1030 mussels per 10 cm of culture rope) – a putative method to manage spat seeding efficiency and yield – on the abundance and size of P. canaliculus spat at four depths at two sites in the Marlborough Sounds. We also recorded the abundance and size of blue mussels, Mytilus galloprovincialis, which are a problematic biofouling species, as well as the biomass and composition of the biofouling accumulating on mussel culture ropes under the same experimental treatments. Although the abundance of P. canaliculus was greatest at the highest seeding density (∼200 mussels per 10 cm of rope at 87 days), this seeding density also experienced the greatest losses. However, while fewer spat were lost from the low-density seeding treatment, the overall number of spat per 10 cm was significantly reduced, resulting in few operational gains in terms of biofouling reduction or spat size. Overall, the seeding density of suggesting that seeding density of ∼1030 spat per 10 cm of rope was the optimal density tested in this study and could be a useful target density for mussel farmers.

An Initial Survey of Unionid Mussels in Lakes East of the Missouri River in South Dakota, USA

This study surveyed freshwater mussels (family Unionidae) in 116 lakes and reservoirs east of the Missouri River in South Dakota, USA, during 2017. Using two-person–hour/site timed searches, evidence of a total of 1789 mussels, including 1053 live mussels, was obtained from 50 waters. Nine species, from two different orders, were found in lakes and reservoirs throughout five of the six major river drainages east of the Missouri River. The native species observed included Giant Floater Pyganodon grandis, Fatmucket Lampsilis siliquoidea, Threeridge Amblema plicata, White Heelsplitter Lasmigona complanata, Wabash Pigtoe Fusconaia flava, Deertoe Truncilla truncata, and Pink Heelsplitter Potamilus alatus. Giant Floater was the most widespread and abundant species observed, representing 63.3% of the live mussels sampled. Two non-native species, Zebra Mussel Dreissena polymorpha and Chinese Basket Clam Corbicula fluminea, were also documented from three water bodies in the lower Missouri River drainage. Overall, mussel abundance was negatively correlated with lake water conductivity and positively correlated with turbidity. No significant correlations were observed between species abundance and water temperature, pH, dissolved oxygen, or substrate particle size.

Long-term fluctuations and recent decline of mussel populations in an Irish sea lough

ABSTRACT Intertidal mussels (Mytilus spp.) and their benthic invertebrate predators were monitored annually for 25 years at 10 sites within Lough Hyne Marine Reserve in southwest Ireland. Mussel abundance was relatively low in the early 1990s but increased substantially after the cold winter of 1995/1996. High mussel abundance was maintained until 2014 after which there was an abrupt decline leading to low levels in 2015–2019, when populations were dominated by older size-classes. Recruitment on benthic rock surfaces in 2018 and 2019 was low in contrast to that on an isolated mooring rope in deep water, suggesting mortality of recruits (e.g. from predation or benthic hypoxia). The generalist predatory starfish, Marthasterias glacialis, increased substantially during the study, with population peaks in 2005 and 2009 that mirrored the peaks of mussel populations. Predatory dogwhelks were not abundant at the monitoring sites and were never seen associated with mussels. Predators or other physical factors may have reduced recruitment, but the decline of the mussel population probably reflected increasing age and removal by wave action combined with consistently sparse recruitment.

When rivers run dry: Perennial pools as ecological refuges for freshwater mussels during drought

Abstract As the intensity and frequency of drought and drying events are predicted to increase globally with climate warming and increasing human water usage, there is an urgent need to understand what kind of habitats may serve as refuges for organisms to withstand adverse effects. When flows decrease in rivers, disconnected pools may provide critical habitat for survival of aquatic organisms such as freshwater mussels, a highly imperilled group for which drought and dewatering pose a major threat. The objective of this study was to (1) examine whether pools serve as ecological refuges for freshwater mussels (Bivalvia: Unionidae) in drought‐stricken streams by surveying mussel distribution in an intermittent section (i.e., a section that regularly goes dry) of the San Saba River, Texas, and (2) examine the habitat characteristics that influence whether a pool functions as a refuge. We found that pool dimensions, thermal conditions, past dryness (number of years a pool was dry between 2004 and 2020), underlying geology, and aquatic and riparian vegetation influence the abundance and species richness of freshwater mussels in pools that may serve as important refuges for mussels to avoid desiccation and lethal high temperatures. Despite this, abundances and richness of mussels were low at all sites. Our results suggest that pools that retain water during drought conditions (i.e., perennial pools) may serve as ecological refuges for globally imperilled organisms such as freshwater mussels on shorter timescales (e.g., days to years). Protection and prioritisation of maintaining suitable conditions in refuge pools may help mussels persist as drought and drying issues become more pervasive in aquatic ecosystems. However, if there is a limited number of isolated pools that only allow the survival of a small number of mussels, then these pools cannot prevent overall declines of mussels in drying rivers. Better management of surface water and groundwater in anthropogenically impacted systems could ensure the flowing conditions that are needed to protect mussels in the face of climate change.

Survey of freshwater mussels using high‐resolution acoustic imaging sonar and deep learning‐based object detection in Lake Izunuma, Japan

Abstract The use of traditional in situ methods for underwater surveys to map freshwater mussel habitats is limited by challenges such as water transparency, depth and high labour demands. In this study, adaptive resolution imaging sonar (ARIS) was applied to monitor mussel distribution and abundance. In contrast to conventional quadrat surveys, this acoustic survey is non‐invasive and enables direct observation of mussels to allow their survival status to be determined in turbid water. ARIS produces high‐quality acoustic images that facilitate the creation of a distribution map for broader‐scale monitoring, especially if paired with deep learning methods such as the YOLOv4 algorithm for automatic mussel detection and classification. ARIS was successfully applied to surveying over 2000 m2 of Lake Izunuma in Miyagi, Japan. In one site, a high mussel abundance of ~0.6 individuals/m2 was detected, while other sites had low densities. The detection model achieved a mean average precision of 0.97. The survey results were used to generate a distribution map of living mussels. This study illustrates the feasibility of using an acoustic video camera with an open‐source deep learning algorithm to monitor mussels and other benthos in turbid water.

Early stage of invasion of the quagga mussel (Dreissena rostriformis bugensis) within the interconnected lakes Lough Ree and Lough Derg of the Shannon River system, Ireland

Quagga and zebra mussels of the genus Dreissena are two of the most impactful freshwater invasive alien species that have spread widely across the globe. These species attach to natural and artificial substrates, form dense populations and filter large volumes of water causing ecological and economic damage. Following the quagga mussel’s discovery in the Shannon River system in Ireland, this study assesses its local distribution, population density, relative abundance, and population structure in the interconnected lakes Lough Ree and Lough Derg in order to determine the likely year and location of its introduction. Polymodal length-frequency analysis was used to distinguish between year cohorts and estimate growth rates. The quagga mussel is established widely across both lakes and is settling on a range of artificial surfaces, natural substrates, dead shells, plant material, and other invasive bivalves. High densities of quagga mussels exceeding 20 000 individuals per m2 were present on artificial surfaces in Lough Ree with total dreissenid densities reaching 26 758 per m2. The relative abundance of quagga mussels to zebra mussels on natural substrates is high in Lough Ree (up to 94.7%) and low in Lough Derg (up to 16.8%). Two to four year cohorts were present at all sites, with quagga mussels attaining large shell sizes over 34 mm in length. Growth varied between sites with a maximum estimated yearly growth rate of 16.8 mm. The time and place of the quagga mussel’s initial introduction in Ireland is still uncertain, but its widespread distribution, population structure, and high population density and relative abundance suggest it was first introduced to Lough Ree in 2016 or 2017.

Habitat aging and degradation in terrestrialized floodplains: a need to rejuvenate processes for sustaining freshwater mussel populations

Progressive floodplain terrestrialization leads to the deterioration of floodplain ecosystems. Although the importance of hydrological connectivity between floodplain habitats and river channels for floodplain‐dependent organisms has been emphasized, less attention has been paid to the temporal relationship between habitat degradation and aquatic organisms. In this study, we examined temporal changes in mussel population structures and the hydrological connectivity of pond‐like floodplain water bodies (FWBs) in the terrestrialized floodplains of a lowland river in Japan. We tested the hypothesis that FWB habitats for mussels degrade over time, while newly formed FWBs contribute to providing recruitment sites for mussels. The habitat age for 53 FWBs was determined as of 2018, using historical aerial photographs. Inundation frequency, mussel abundance, and size structures (shell length) were also investigated in the FWBs in 2007 and 2018. Mussel abundance decreased with FWB aging (6–36 years), which coincided with a decrease in inundation frequency. In most existing FWBs, mussel abundance in all size classes decreased over the decade (2007–2018). In contrast, small individuals occurred in the newly formed FWBs at age 6, and in the existing FWBs where inundation frequency slightly increased over the decade (2007–2018), such FWBs were rare. In conclusion, the “young” and “rejuvenated” FWBs were found to be critically important for the recruitment and persistence of mussel populations. This suggests that the floodplain management strategy of “cyclic floodplain rejuvenation” could be applicable for mussel conservation in terrestrialized floodplains of lowland rivers.

Application of eDNA methods to evaluate abundance and reproduction of winter-breeding freshwater mussels (Buldowskia iwakawai) in the Ishikari River floodplain

Application of eDNA methods to evaluate abundance and reproduction of winter-breeding freshwater mussels (Buldowskia iwakawai) in the Ishikari River floodplain

The silent extinction of freshwater mussels in Portugal

Freshwater mussels are one of the most threatened animal groups in the world. In the European Union, threatened and protected mussel species are not adequately monitored, while species considered to be common and widespread receive even less attention. This is particularly worrying in the Mediterranean region, where species endemism is high and freshwater habitats are severely affected by water scarcity. In the absence of hard data on population trends, we report here a long-term comparison of freshwater mussel assemblages at 132 sites covering 15 different hydrological basins in Portugal. This study reveals a widespread decline of 60 % in the number of sites and 67 % in the overall abundance of freshwater mussels across Portugal over the last 20 years, indicating that all species are rapidly declining and threatened with extinction. These results show that current legislation and conservation measures are largely ineffective and highlight the importance of updating the Habitats Directive to enforce standard monitoring protocols for threatened species in the European Union and to extend monitoring to other freshwater species thought to be common and widespread. Efficient water management, restrictions on irrigation expansion in important biodiversity areas, mitigation of hydrological changes and loss of aquatic habitat connectivity caused by physical alterations are urgently needed to reverse these declining population trends. For the severely endangered species Margaritifera margaritifera, Potomida littoralis, and Unio tumidiformis, where populations are now critically low, more urgent action is needed, such as ex-situ conservation, protection of remaining populations and large-scale habitat restoration.

Functional non‐equivalence in ecosystem engineers? Different freshwater mussels (Bivalvia: Unionidae) are associated with different macroinvertebrate communities in a subtropical lake

Abstract Freshwater mussels (Bivalvia: Unionidae) are often described as ecosystem engineers, with the capacity to alter abiotic habitats; this can facilitate certain macroinvertebrate taxa, increasing biodiversity and potentially altering community composition. Mussel species are often implicitly considered to be broad ecological equivalents, with similar impacts on abiotic environments and benthic communities. This assumption of redundancy is important in conservation approaches that aim to preserve ecosystem functioning, rather than species identity. We tested this assumption of equivalence in two species of subtropical freshwater mussels, Lamellidens marginalis and Parreysia caerulea, studying the associations between these mussel species and macroinvertebrate communities. We measured mussel density and abundance of macroinvertebrates, identified to family level, at 50 sites within Dhanmondi Lake, a heavily polluted sub‐tropical urban lake in Dhaka, Bangladesh. We investigated the associations of mussel density on different macroinvertebrate families, which we further classified into functional feeding groups (predators, scrapers, collectors and shredders). We found that densities of the two mussel species were negatively correlated in the 1–3‐m nearshore zone; average density of Lamellidens was 46.4 ± SE 3.6 individuals/0.25 m2, and average density of Parreysia was 6.4 ± SE 1.4 individuals/0.25 m2. In total, 2319 Lamellidens and 320 Parreysia specimens were recorded. Sites containing higher densities of Lamellidens had greater similarity in macroinvertebrate community composition, while there was no effect for Parreysia. Particular macroinvertebrate families and functional feeding groups were also associated with mussels; the majority of significant associations were with Lamellidens but not Parreysia. The clearest associations were with predators and scrapers, which increased in abundance with Lamellidens density. This provides support for a possible role for mussels in structuring freshwater invertebrate communities and emphasises the importance of species identity in these effects, with one possible keystone species (Lamellidens) largely accounting for mussel–invertebrate associations. While microhabitat variables (shading and sediment type) were poor predictors of abundance in any invertebrate taxa (including mussels), manipulative studies are needed to disentangle the direct effects of mussels from the role of overlapping habitat preference between mussels and other invertebrates. Our results highlight the importance of species identity in patterns of community composition, particularly for ecosystem engineer species. We also reinforce the need to test the assumption of ecological redundancy within communities.

Limitations of beta diversity in conservation site selection

Preservation of diversity is a key issue in many conservation efforts. It has recently been suggested that beta diversity should be considered in conservation planning and that sites with high local contribution to beta diversity (LCBD) may be valuable for conservation. Yet, such an approach has not been applied to freshwater mussels, a highly imperiled group of organisms. We used a dataset on freshwater mussel from the five largest rivers of southwestern Ontario, Canada to examine whether LCBD would be an efficient approach for assessing the conservation value of sites and compared it to more traditional conservation approaches (biomonitoring, high richness, high abundance). Sites with high LCBD value were associated with low mussel richness and were often characterized by mussels that are regionally widespread and usually abundant in lentic systems or smaller streams, limiting site selection based on beta diversity. Species at risk (including IUCN categories of Critically Endangered through Near Threatened) were more likely to occur in communities with high richness and abundance at sites chosen by the more traditional approaches. Thus, protecting sites with higher alpha diversity of mussels would also support higher gamma diversity of mussels. The provision of important ecosystem services by higher abundances of mussels which was also correlated with local richness should be considered as well. Our study suggests that there likely is an important link between high richness and abundance of mussels and the presence of species at risk which we argue is driven by facilitation (i.e., positive species interaction), an important, yet understudied, process that deserves more attention in conservation.

Enigmatic freshwater mussel declines could be explained by the biodiversity‐disease relationship

AbstractThe biodiversity‐disease relationship states that increased species richness leads to lower pathogen pressure (i.e. the dilution effect), an effect that erodes with biodiversity loss. However, whether losses of the dilution effect can trigger extinction cascades remains largely unexplored.To explore this idea, we consider declines in freshwater mussels, on average the most threatened non‐marine group of organisms in the world. We argue that anthropogenically stimulated declines in mussel richness amplify pathogens in remaining species. Pathogen amplification triggers further local losses in both mussel abundance and richness, explaining the observed so‐called “enigmatic” declines in freshwater mussels.Vulnerable communities could become trapped in cycles of pathogen amplification and host decline. We highlight knowledge gaps and provide key steps to assess the likelihood of this occurring; these key steps are applicable to any host group.Policy implications. Our argument constitutes a testable hypothesis that may explain richness or abundance declines in previously intact communities. We provide further impetus for the consideration and preservation of diversity at a local scale and show that effective conservation requires integration of both host and parasite ecology.

Feeding behavior and species interactions increase the bioavailability of microplastics to benthic food webs

Plastics are pervasive in aquatic ecosystems, in which they circulate in the water column, accumulate in sediments, and are taken up, retained, and exchanged with their biotic environment via trophic and non-trophic activities. Identifying and comparing organismal interactions are a necessary step to improve monitoring and risk assessments of microplastics. We use a community module to test how abiotic and biotic interactions determine the fate of microplastics in a benthic food web. Using single-exposure trials on a trio of interacting freshwater animals (the quagga mussel Dreissena bugensis, a filter feeder; the gammarid amphipod Gammarus fasciatus, a deposit feeder; and the round goby Neogobius melanostomus, a benthivorous fish), we quantify the (1) uptake of microplastics from environmental routes (water, sediment) under six exposure concentrations, (2) the depuration capacities over 72 h, and (3) the transfer of microbeads via trophic (predator-prey) and behavioral interactions (commensalism, intraspecific facilitation). Under 24 h exposures, each animal of our module acquired beads from both environmental routes. The body burden of filter-feeders was higher when they were exposed to particles in suspension, whereas detritivores had similar uptake from either route. Mussels transferred microbeads to amphipods, and both invertebrates transferred beads to their mutual predator, the round goby. Round gobies generally displayed low contamination from all routes (suspension, sedimented, trophic transfer) with a higher microbead load from preying on contaminated mussels. Higher mussel abundance (10–15 mussel per aquaria, i.e., ~200–300 mussels·m2) did not increase individual mussel burdens during exposure, and neither did it increase the transfer of beads from mussels to gammarids via biodeposition. Our community module approach revealed that the feeding behavior of animals allows microplastic uptake from multiple environmental routes, whereas trophic and non-trophic species interactions increased their burden within their food web community.

A multi-spatial analysis and the balanced requirements of freshwater mussels (Bivalvia: Unionidae) and urban inhabitants in the Cuyahoga River watershed

Water quality in the Cuyahoga River, a national heritage river of the United States, has improved greatly since the infamous river fire of 1969, but much of the watershed faces combined demands of a state scenic river valued for nature and the primary water source for surrounding cities. A comparative analysis of mussel abundance was applied to test success between water improvements and mussel assemblages in two similarly sized sub-watersheds, the upper reaches of the Cuyahoga River and an isolated tributary stream, Tinkers Creek. Multivariate GIS/remote sensing tools and government data resources were applied to contrast variation in lands use, soil types, and potential impacts from impoundments. Mussel populations declined in much of the Upper Cuyahoga River from 1990 to present, while in Tinkers Creek and the West Branch Cuyahoga River, both areas surrounded by residential lands, mussel species changed from a slow water species to species associated with flowing streams. Major structural differences among these stream reaches included regulated flow from reservoirs and consequentially poor soil drainage type in much of the Upper Cuyahoga River, while extensive improvements in Tinkers Creek enhanced flow dynamics and produced well-draining soils. Thus, the mussel assemblages appeared sustained despite a trend towards more human use where water flowed free.

A comparative study on CNN-based semantic segmentation of intertidal mussel beds

Mussels are globally distributed and abundant species on intertidal habitats such as rocky shores where they form dense beds and provide a variety of ecosystem services. The ability to measure mussel abundance on shores with high efficiency and accuracy will enhance assessment of their facilitative services to intertidal ecosystems. Traditional sampling methods, however, are labour intensive and consequently limited in spatial and temporal coverage. To advance such monitoring and quantification processes, four state-of-the-art convolutional neural networks (CNN); namely U-Net, FastSCNN, DeepLab v3+, and HRNet, were compared in their performance to segment mussels at the pixel level either with or without Cityscapes pre-trained weights. All proposed CNN were trained on a photographic dataset of 1455 images generated from field images of mussel beds. CNN trained with the Cityscapes pre-trained weights showed an overall increased model performance as illustrated by mean intersection-over-union (mIoU), loss, overall accuracy (oAcc), and Cohen's kappa coefficient. DeepLab v3+ and HRNet with the combination of Cityscapes pre-trained weights achieved over 95% mIoU and 97% oAcc for assessing distribution and abundance of these important intertidal species. Such combination of approaches is, therefore, recommended for ecologists who wish to conduct image-driven surveys of intertidal ecosystems and the code for this study is available at: https://github.com/Vicellken/CNN-SS-mussel.

Predators regulate the taxonomic structure of mixed Mytilus edulis L. and M.trossulus Gould settlements in the shallow waters of the White Sea

Cryptic mussel species Mytilus edulis (Me) and M.trossulus (Mt) form mixed settlements in shallow waters of the White Sea. The proportion of Mt and Me in local settlements varies in broad limits but the factors regulating taxonomic composition of mixed populations are poorly understood. Present study focuses on the assessment of the sea star (Asterias rubens) predation influence on the Mt-Me ratio in natural habitats. For this purpose, we’ve conducted a series of field experiments. For mussels placed on experimental units (ceramic plates submerged in starfish-infested habitats), we’ve estimated a probability of being eaten by starfish. We’ve constructed a linear model that includes several predictors which may influence the probability of being eaten (starfish biomass, mussel size, mussel species, prey abundance, Mt-Me ratio on experimental units and abundance of conspecifics). The analysis has revealed that the probability of being eaten expectedly increases with sea stars’ biomass increasing, but it is higher for Mt in comparison with Me. This indicates Mt as a preferable prey. Negative correlations between the probability of being eaten and shell size, number of conspecifics and mussel abundance were also revealed. No significant dependence on Mt-Me ratio was found. Additionally, we’ve taken field samples which revealed a significant decrease in the proportion of Mt in mussel patches after a massive starfish attack. This indicates that starfish ate out Mt as its preferable prey. These results show that predators can contribute to the regulation of taxonomic composition of mixed Mt-Me settlements in the White Sea.