Mussel Growth Research Articles

Sulfate sensitivity of early life stages of freshwater mussels Unio crassus and Margaritifera margaritifera

Sulfate is increasingly found in elevated concentrations in freshwater ecosystems due to anthropogenic activities. Chronic exposure to sulfate has been reported to cause sublethal effects on freshwater invertebrates. Previous sulfate toxicity tests have mostly been conducted in hard or moderately hard waters, and research on species inhabiting soft water is needed, given that freshwater organisms face heightened sensitivity to toxicants in water of lower hardness. In the present study, we examined sulfate sensitivity of two endangered freshwater mussel species, Unio crassus, and Margaritifera margaritifera. Glochidia and juveniles of both species were subjected to acute and/or chronic sulfate exposures in soft water to compare sulfate sensitivity across age groups, and effective concentrations (EC)/lethal concentrations (LC) values were estimated. Mussels were individually exposed to allow relatively larger numbers of replicates per treatment. Chronic sulfate exposure significantly reduced growth, foot movement, and relative water content (RWC) in juvenile mussels of M. margaritifera. Mussels at younger stages were not necessarily more sensitive to sulfate. In the acute tests, LC50 of glochidia of M. margaritifera and U. crassus was 1301 and 857 mg/L, respectively. Chronic LC10 was 843 mg/L for 3-week-old U. crassus juveniles, 1051 mg/L for 7-week-old M. margaritifera juveniles, and 683 mg/L for 2-year-old M. margaritifera juveniles. True chronic Lowest Effective Concentration for 7-week-old M. margaritifera may be within the 95% interval of EC10 based on RWC (EC10 = 446 mg/L, 95%CI = 265–626 mg/L). Our study contributed to the understanding of sulfate toxicity to endangered freshwater mussel species in soft water.

Enhanced Satellite Analytics for Mussel Platform Census Using a Machine-Learning Based Approach

Mussel platforms are big floating structures made of wood (normally about 20 m × 20 m or even a bit larger) that are used for aquaculture. They are used for supporting the growth of mussels in suitable marine waters. These structures are very common near the Galician coastline. For their maintenance and tracking, it is quite convenient to be able to produce a periodic census of these structures, including their current count and position. Images from Earth observation satellites are, a priori, a convenient choice for this purpose. This paper describes an application capable of automatically supporting such a census using optical images taken at different wavelength intervals. The images are captured by the two Sentinel 2 satellites (Sentinel 2A and Sentinel 2B, both from the Copernicus Project). The Copernicus satellites are run by the European Space Agency, and the produced images are freely distributed on the Internet. Sentinel 2 images include thirteen frequency bands and are updated every five days. In our proposal, remote-sensing normalized (differential) indexes are used, and machine-learning techniques are applied to multiband data. Different methods are described and tested. The results obtained in this paper are satisfactory and prove the approach is suitable for the intended purpose. In conclusion, it is worth noting that artificial neural networks turn out to be particularly good for this problem, even with a moderate level of complexity in their design. The developed methodology can be easily re-used and adapted for similar marine environments.

Modelling and mapping carbon capture potential of farmed blue mussels in the Baltic Sea region

This study applies a regional Dynamic Energy Budget (DEB) model, enhanced to include biocalcification processes, to evaluate the carbon capture potential of farmed blue mussels (Mytilus edulis/trossulus) in the Baltic Sea. The research emphasises the long-term capture of carbon associated with shell formation, crucial for mitigating global warming effects. The model was built using a comprehensive pan-Baltic dataset that includes information on mussel growth, filtration and biodeposition rates, and nutrient content. The study also examined salinity, temperature, and chlorophyll a as key environmental factors influencing carbon capture in farmed mussels. Our findings revealed significant spatial and temporal variability in carbon dynamics under current and future environmental conditions. The tested future predictions are grounded in current scientific understanding and projections of climate change effects on the Baltic Sea. Notably, the outer Baltic Sea subbasins exhibited the highest carbon capture capacity with an average of 55 t (in the present scenario) and 65 t (under future environmental conditions) of carbon sequestrated per farm (0.25 ha) over a cultivation cycle – 17 months. Salinity was the main driver of predicted regional changes in carbon capture, while temperature and chlorophyll a had more pronounced local effects. This research advances our understanding of the role low trophic aquaculture plays in mitigating climate change. It highlights the importance of developing location-specific strategies for mussel farming that consider both local and regional environmental conditions. The results contribute to the wider discourse on sustainable aquaculture development and environmental conservation.

Mytilus galloprovincialis shell growth – Insights from shell geochemistry

Despite the wide geographic distribution of mussels and their importance in fisheries and aquaculture, understanding of temporal and spatial variations of their growth is still limited. This can be, at least partly, attributed to the lack of distinct growth lines in their shells. Our study uses geochemical properties of shells, particularly oxygen (δ18Oshell) and carbon (δ13Cshell) stable isotope values, to reconstruct mussel growth. Mytilus galloprovincialis specimens were collected from two of the most important bivalve aquaculture sites in the eastern Adriatic - Krka River estuary and Mali Ston Bay. The first site has variable environmental conditions, influenced mainly by the Krka River, resulting in a strong temperature and salinity gradient along the estuary. In contrast, Mali Ston Bay is a relatively shallow enclosed bay with more stable conditions. Samples for δ18Oshell and δ13Cshell analysis were acquired by manual microdrilling cross-sectioned shells from three similar sized shells from each site. In addition, analysis of elemental profiles (Mg/Ca, Sr/Ca, and Ba/Ca) in shells from the Krka River estuary was conducted using laser ablation ICPMS. Temperature and salinity values were obtained for each site through research and monitoring projects and used to calculate predicted δ18Oshell values. By aligning the measured δ18Oshell data along the predicted δ18Oshell curve, it was possible to reconstruct the timing and rate of seasonal shell growth. Results show that M. galloprovincialis shell deposition slows down and/or ceases during high temperature and low salinity periods. Specimens from the Krka River estuary had faster shell growth rates and were characterised by higher δ13Cshell values. Mg/Ca profiles of M. galloprovincialis specimens from the Krka River estuary, confirm growth periodicity data obtained by δ18O analysis. Ba/Ca peaks were also discussed by comparison with δ13C time-series and environmental data. Results have potential applications in fisheries studies as well as in palaeoecology and palaeoceanography research.

Effects of different culture methods on growth, meat yield, and nutritional composition of Mediterranean mussels (Mytilus galloprovincialis), south side of Marmara Sea, Türkiye

This study, conducted between February 2016 and October 2017 on the coast of Erdek in the Marmara Sea, established two longline systems (buoy and pipe). Monthly growth rates of juvenile mussels placed in polyethylene and polyamide nets within these systems were monitored. The monthly chemical composition and meat yield of mussels that reached harvest size were analyzed in both systems. Environmental parameters were measured monthly to assess environmental conditions. The highest meat yield of harvested mussels was recorded in January, with values of 36.99 ± 0.72% for mussels cultured in the pipe system and 31.43 ± 1.82% for those cultured in the buoy system. The highest growth in mussels was achieved in the group cultured in the pipe system within polyamide nets. The December sample showed the highest moisture content of 83.98% and the highest ash content of 2.34%. The highest crude fat content was found in the September sample. The June sample had the highest protein content. The Black Sea, Sea of Marmara, and Aegean Sea offer suitable areas for mussel cultivation. Currently, mussel farming is conducted in these areas, producing tens of thousands of tons annually. This publication contributes to the expansion of the production process.

Relative Importance of Macroalgae and Phytoplankton to Nearshore Consumers and Growth Across Climatic Conditions in the Northern Gulf of Alaska

Macroalgae and phytoplankton support the base of highly productive nearshore ecosystems in cold-temperate regions. To better understand their relative importance to nearshore food webs, this study considered four regions in the northern Gulf of Alaska where three indicator consumers were collected, filter-feeding mussels (Mytilus trossulus), pelagic-feeding Black Rockfish (Sebastes melanops), and benthic-feeding Kelp Greenling (Hexagrammos decagrammus). The study objectives were to (1) estimate the proportional contributions of macroalgal and phytoplankton organic matter using carbon and nitrogen stable isotopes, (2) determine if macroalgal use affected consumer growth using annual growth rings in shells or otoliths, and (3) describe changes in organic matter use and growth during the Pacific Marine Heatwave (PMH; 2014–2016) in one consumer, mussels. Macroalgae were the major organic matter source (> 60%) to the diet for all three consumers. The relationships between macroalgal contribution and growth were neutral for both fish species and significantly positive for mussels. During the PMH, mussels had a drop (> 10%) in macroalgal contributions and grew 45% less than in other time periods. Simultaneously, the relationship between macroalgal contribution and mussel growth was strongest during the PMH, explaining 48% variation compared to 3–12% before or after the PMH. Collectively, the results suggest that macroalgae is likely more important to cold-temperate nearshore food webs than phytoplankton. Management actions aimed at conserving and expanding macroalgae are likely to benefit nearshore food webs under all climate scenarios and especially during marine heatwaves.

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.

The need for innovations to secure the future of artisanal mussel farming in the coastal sea of the Gulf of Trieste (Slovenia)

Mariculture along the Slovene coastline is mainly mussel culture operated as a family business; in one case, it is combined with sea bass farming. It started in the early 70 s with cultivation of Mediterranean mussels, while today, the two largest producers incorporate the cultivation of Venus clams and oysters as species with higher economic value on the market. Currently, all mussels and clams produced in Slovenia are sold in the Slovenian, Italian, Croatian and French markets. The production of Mediterranean mussels (Mytilus galloprovincialis) has increased steadily, with the main obstacles being a limited area for cultivation, occasional harmful algal blooms, predation by gilthead seabream and flatworms. In addition, more recent summer heatwaves negatively affected mussel production when seawater reached high temperatures at the thermal limits unsuitable for mussel growth. This study aimed to collect first-hand information about the current mussel production technology, processes and needs to identify opportunities for innovations that could benefit the entire sector (increased knowledge, production yield, reduced workload and effort with administrative issues). The study was based on a semi-structured questionnaire with the owners of mussel farms. Analysis of the questionnaire was supplemented with current knowledge from the field and provided comprehensive insight into a small sector of mussel farming along the Slovenian coast and its possible development in the future.

Genotype by environment interactions for growth and inner shell color disparity in Hyriopsis cumingii under different light conditions

The light plays a pivotal role in influencing the growth and body color for aquaculture animals. The freshwater pearl mussel Hyriopsis cumingii, inhabiting benthic environments naturally, is predominantly cultivated by hanging methods. This aquaculture method altersmutiple environmental factors, with light being one of the maximum variationfactor. In order to comprehend the impact of light change on the growth and inner shell color of H. cumingii, a total of 14 full-sibling families were established and cultivated separately under natural light and dim light conditions for a period of 13 months in this study. The results revealed that under natural light conditions, juvenile mussel exhibited accelerated growth rates, while dim light conditions expedited purple pigmentation in the inner shell. Genetic analysis indicated general heritability range for the entire experimental population falls between 0.07 and 0.28. heritability estimates for all traits under natural light conditions (NL) ranged from 0.33 to 0.72, indicating consistently high heritability. However, heritability estimates for all traits under dim light conditions (DL) ranged from 0.05 to 0.16. The growth and inner shell color traits showed significant G × E interactions under different light conditions. The anal angle radial rib length (AARRL) trait exhibited a significantly higher correlation with body weight (BW) compared to shell height (SH) and total shell height (TSH). Furthermore, the growth and inner shell color traits of different families were compared and evaluated under the two environmental conditions in this study. Families 1 and 6 excelled in various traits under both conditions, making them promising candidates for genetic improvement breeding. In this study, pronounced influences of light exposure on the growth of pearl mussels were identified, emphasizing the need for tailored breeding strategies for both bottom seeding and suspended cultivation methods.

Optimising seafood nutritional value and environmental sustainability in aquaculture through a novel integrated modelling tool applicable to IMTA and monoculture

Aquaculture policies that decrease the reliance on wild-caught fish and promote integrated multi-trophic aquaculture (IMTA) both aim to lessen the environmental footprint but often overlook economic-environmental trade-offs and neglect social, health, and broad-scale sustainability considerations. Here we present a new bio-physical model (FYNE) that bridges some of these gaps, by linking farm operational choices, such as feed choices and farm siting, with the nutritional value of the farm-gate seafood products and the resulting environmental eutrophication footprint at the farm level. The FYNE model operates both in conditions of monoculture or of IMTA production, and estimates feed composition effects on growth and omega-3 fatty acid content of Atlantic salmon (Salmo salar) and blue mussel (Mytilus edulis), and nitrogen and carbon concentrations, the latter being a measure of the environmental eutrophication footprint of the farm. The model here developed integrates for the first time (i) an ecosystem model of an IMTA and (ii) a fatty acid dynamics model, with new models for salmon feed digestibility and mussel ingestion. The outputs span (i) production analysis for simulation of biomass; (ii) farm mass-balance analysis on deposition analysis and environmental eutrophication footprint; and (iii) product nutritional quality, in terms of fatty acid content. An application of the model to an IMTA farm in Scotland (UK) demonstrates how fatty acid and environmental changes can be modelled in tandem and could be used to support the industry to optimize the nutritional value of cultured species and manage aquatic environmental eutrophication footprint at farm level, informing feed and siting decisions. The model effectively predicts changes in omega-3 fatty acids, particularly DHA and EPA, in response to variations in feed composition. Notably, our results confirm that salmon waste has limited influence on mussel growth due to the spatial separation within the IMTA system, which emphasizes the need for strategic siting to enhance system productivity through effective waste recycling. Additionally, results show that while increasing fishmeal in diets enhances environmental outcomes, it reduces levels of critical fatty acids like DHA and EPA, underscoring the need for balanced feed formulations. The method developed in this study described a novel integrated model (FYNE) that extend previous modelling work by incorporating the influence of farmed species feed composition on fatty acid dynamics as well as the farming environmental factors.

Estimating growth using an ecophysiological and scope for growth model for the mussel Perna perna grown under suspended culture in Santa Catarina, Brazil

We present a dynamic simulation ecophysiological model for an important aquaculture mussel, Perna perna, grown under suspended culture in Santa Catarina, Brazil. The ecophysiological model was divided in four sectors; driving variables, feeding, energy reserve, and growth. This generated descriptions and explanations of the functions controlling feeding and metabolic responses to changing food availability and seawater temperature. The driving variables sector included time-series of seston variables likely to influence food and energy acquisition in mussels. It included relationships among seston variables to estimate the energy content of phytoplankton, the main component of mussel diet. The feeding sector described mussel suspension-feeding behavior measured using natural seston. Rates of filtration, rejection, ingestion, and absorption were directly related to the quantity and quality of available food. In the energy reserve sector, absorbed matter was transformed to absorbed energy using estimates of energy content of food provided in the driving variables sector. After accounting for the maintenance requirements of the mussels (heat loss and excretion), surplus energy, or the scope for growth, was directed to the growth sector. The growth sector included byssus, organic shell, and soft tissue production based on energy partitioning estimated from monthly measurements of somatic and reproductive tissue and shell growth. The model successfully predicted mussel growth during the study and provided estimates of the response to food acquisition, energy expenditure and allocation to growth. This was the first attempt to model the ecophysiology of this fast growing sub-tropical mussel. Given the capacity of this ecophysiological model to estimate growth of mussels, it has significant economic and environmental value in estimating carrying capacity to support sustainable management of shellfish farming in Brazil.

Food, water quality, and the growth of a freshwater mussel: Implications for population restoration

Food, water quality, and the growth of a freshwater mussel: Implications for population restoration

Assessing the mechanical properties of biobased versus fossil-based ropes and their impact on the productivity and quality of mussel (Mytilus galloprovincialis) in longline aquaculture: Toward decarbonization

The expansion of offshore mussel aquaculture is intertwined with the rising demand for mussel grow-out ropes. Currently, these ropes are manufactured using fossil-fuel based or fossil-based plastics. In response to concerns about plastic pollution and sustainable aquaculture practices, biobased materials have emerged as more sustainable alternatives. Yet, the importance of the choice of raw materials, as well as the methods used in their production and sourcing, is key in determining the performance of materials in sea conditions within the context of aquaculture. This study evaluated the functionality of biobased ropes in terms of productivity and durability, comparing them to fossil-based counterparts during a one-year mussel culture in offshore conditions. Across one-year culture, noteworthy mussel losses were observed in the fossil-based (65%) ropes compared to the biobased B1 (53%) and B2 (18%) prototype ropes, B2 and B1 ropes yielding 85% and 23% more mussel (kg/ m rope) than the fossil-based ropes. Moreover, the higher correlations of shell length and body weight over time suggesting that biobased ropes may be more suitable substrates for mussel growth compared to fossil-based ropes. The structural distinction between the round and more uniform fine multifilaments in biobased ropes, as opposed to the clustered structure of flat fibres in fossil-based ropes, may have contributed to a more effective surface area for the initial attachment and growth of seeded mussels, avoiding subsequent losses. The use of biobased ropes contributed positively to the interplay between substrate structure, biofouling, and mussel attachment, which may be used for guiding further designs of aquaculture biobased gears. Despite seasonal variations, the final condition, proximate and fatty acid composition of mussel indicated their marketability and high nutritional quality. Higher shell length and mussel yields observed, indicating a potential for mussels cultivated on biobased ropes, especially in B2, to reach a higher market value. Regarding durability, linear density of biobased ropes remained unaltered after one-year offshore mussel culture. The biobased B2 rope prototype showed the highest ratio between the retention of mechanical properties (Load at Break and elongation) and the total mussel weight held for one year. The findings of this study validate the biobased B2 prototype as the most promising alternative to fossil-based ropes. It significantly boosted production yields of high-quality mussels while maintaining rope durability throughout one year in offshore culture. These results hold promise for reducing the reliance on fossil-based plastic ropes in mussel aquaculture, thereby contributing to decarbonization efforts.

Clumped isotopes reveal relationship between mussel growth and river discharge

Freshwater mussels preserve valuable information about hydrology, climate, and population dynamics, but developing seasonal chronologies can be problematic. Using clumped isotope thermometry, we produced high-resolution reconstructions of modern and historic (~ 1900) temperatures and δ18Owater from mussel shells collected from an impounded river, the Brazos in Texas, before and after damming. We also performed high-resolution growth band analyses to investigate relationships between mussel growth rate, rainfall, and seasonal temperature. Reconstructed δ18Owater and temperature vary little between the modern (3R5) and historic shell (H3R). However, a positive relationship between reconstructed δ18Owater and growth rate in H3R indicates that aside from diminished growth in winter, precipitation and flow rate are the strongest controls on mussel growth in both modern and pre-dam times. Overall, our results demonstrate (1) the impact, both positive and negative, of environmental factors such as flow alteration and temperature on mussel growth and (2) the potential for clumped isotopes in freshwater mussels as a paleohydrology and paleoclimate proxies in terrestrial environments.

Effects of microalgae diets on growth, proximate, and fatty acid composition of black mussel, Mytilus galloprovincialis

AbstractThis study evaluates the growth, proximate, and fatty acid composition of black mussel, Mytilus galloprovincialis fed four marine microalgae (Pavlova lutheri, Nannochloropsis oculata, Diacronema vlkianum and Rhinomonas reticulata) diets for 21 days. Black mussel is a common bivalve species that has been recognized as important for marine aquaculture with increasing production in the last two decades. The mussel group fed N. oculata showed a significantly lower survival rate than the other groups (p < 0.05). Shell height, length, and width of mussels were measured. The height and length of the mussel group fed N. oculata were statistically higher than other experimental groups (p < 0.05). Shell width did not show any significant differences among groups (p > 0.05). The microalgae N. oculata showed the highest protein content whereas P. lutheri had the highest crude lipid content among dietary treatments. The group fed P. lutheri showed significantly higher protein, lipid, and ash contents among experimental groups (p < 0.05). The D. vlkianum diet enhanced the highest docosahexaenoic acid level in black mussels. Black mussel fed P. lutheri showed the highest eicosapentaenoic acid and polyunsaturated fatty acid levels. Arachidonic acid was found to be similar among experimental groups. In our study, P. lutheri and D. vlkianum had outstanding results on survival, growth, and essential fatty acid accumulation in mussel culture.

Growth rate and survival of green shells (perna viridis l.) In ponds, alue naga village, banda aceh

Alue Naga is one of the coastal and marine areas in the city of Banda Aceh which has the potential for aquaculture and high economic value, namely green mussels (Perna viridis L). This research aims to determine the growth and survival rate of green mussels with different stocking densities in Alue Naga ponds which are still influenced by the tides of seawater. The layout of the green mussel cultivation container is at the pond water gate. The method used is an experimental test method using a Completely Randomized Design (CRD) model with 3 treatments, each treatment 3 times repeated. Research shows that the best average growth and survival rate for green mussels are found in treatment A with a stocking density of 20 seeds/basket, absolute length growth with an average value of 45.52 ± 0.42 mm, weekly length growth rate with an average value -an average of 3.79 ± 0.03 mm/week and an average weight of 25.92 ± 0.19 grams, while the survival rate reached 91.66%. Differences in green mussel stocking density had a significant effect on absolute length growth (PM), absolute weight (BM), and weekly length growth rate (LPPM), while survival (SR) had no significant effect.

Survival and Growth of Juvenile Mussels in an Outdoor Pond after 28-Day Laboratory Exposure to Aqueous Zinc

Survival and Growth of Juvenile Mussels in an Outdoor Pond after 28-Day Laboratory Exposure to Aqueous Zinc

Impacts of acute and chronic suspended solids exposure on juvenile freshwater mussels

Construction activities may affect adjacent water systems by introducing increased levels of suspended solids into the water body and may subsequently affect the survival and growth of freshwater mussels. We tested three sediment types from sites in Missouri, including Spring River sediment (SRS), Osage River bank clay soil (ORC), and quarried limestone from Columbia (LMT). We prepared series of suspensions of each sediment with total suspended solids concentrations ranging from 0 to 5000 mg/L. Juveniles from three mussel species, Fatmucket (Lampsilis siliquoidea), Arkansas Brokenray (Lampsilis reeveiana), and Washboard (Megalonaias nervosa) were exposed to these suspensions in both acute (96-h) and chronic (28-d) tests. No clear impact on survival was observed from the acute or chronic exposures, but chronic test showed that juvenile mussels' growth was strongly affected. Interestingly, growth was enhanced at lower levels of SRS and ORC (≤500 mg/L, p < 0.05), and the juvenile mussels exposed to 500 mg/L SRS exhibited approximately 60 % more dry weight than those reared in the control. LMT did not enhance growth. Growth was slowed by high concentrations (>1000 mg/L) of all three sediments, implying that high suspended solids levels could reduce survival in the long term. Our findings may help to inform regulations and guidelines for construction activities to minimize adverse effects on juvenile mussels.

Western Lake Erie Quagga Mussel growth estimates and evidence of barriers to local population growth

Abstract Invasive Quagga Mussels (Dreissena rostriformis bugensis) and Zebra Mussels (D. polymorpha) have been present in the Great Lakes for almost four decades and have caused substantial economic and environmental impacts. Factors that influence dreissenid mussel growth and population dynamics warrant more study, particularly for Quagga Mussels. We conducted a five-month field experiment in western Lake Erie to measure multiple growth metrics for Quagga Mussels at two sites with different conditions using mussels contained in cages on instrumented moorings. We also quantified dreissenid mussels that colonized into the cages and surveyed dreissenid mussels in the sediments at each site. By multiple measures of growth except for one, growth rates were similar between the two sites despite different chlorophyll a and turbidity levels as well as notable differences in the density and size distribution of mussels found in the sediments at these sites. The growth rates were approximately 0.03 mm d-1 for 12-mm Quagga Mussels and these rates declined with increasing initial shell length. Specific growth rate did not differ between shell and tissue measures or between sites, but both shell and tissue specific growth rates were much higher for smaller mussels. Site WE2, which is closer to Maumee River, had very few dreissenid mussels present in the sediments surrounding the mooring despite having a potential for growth comparable to that at WE4. The high level of colonization on the mooring at WE2 indicated that conditions at the sediment surface inhibit mussel settlement; adjacent benthic surveys indicated that very few mussels survive beyond the juvenile stage. Ultimately, the results from this study provide useful mussel growth parameters and indicate substrate or other limitations for dreissenid mussel populations in western Lake Erie.

Impacts of dreissenid mussel growth and activity on phytoplankton and nutrients in Lake Erie's western basin

Abstract To examine the potential impact of invasive dreissenid mussels on in situ populations of phytoplankton and nutrients in western Lake Erie, we combined mussel population estimates from a 2018 survey, results from mussel excretion, grazing, and in situ growth experiments, along with nutrient measurements on collected lake water. We calculated the proportion of the water column filtered per day, based on both clearance rates from grazing experiments and mussel biomass. In most cases the water column was filtered less than once per day. Based on mussel densities from nearby survey sites, we found that mussels could be expected to clear less than 5% of phytoplankton from the water column each day. We combined measurements of nitrogen and phosphorus excretion by mussels with survey densities and found that concentrations of nitrogen and phosphorus from excretion were much less than the ambient inorganic nitrogen and phosphorus measured throughout the season. Despite the modest potential impact that we measured, spatial variability in mussel density and temporal variability in nutrients and seston suggest that more substantial impact likely occurs in some conditions. Lastly, we used a mass balance approach to compare flows of nitrogen and phosphorus attributable to mussel assimilation, growth, and excretion. The proportion of assimilated nitrogen (0.01-0.21) and phosphorus (0.007-0.08) due to growth changed markedly throughout the season, but the excretion rate sometimes exceeded the apparent assimilation rate. These differences in growth:assimilation suggest changes in food quantity or quality, fluctuations in growth rates over time, or other physiological effects can lead to short-term imbalance in nutrient cycling by mussels, which could lead to locally important impacts on phytoplankton and algal blooms. Moreover, this work underscores the importance of mapping mussel densities at fine spatial scales and across interannual variation.