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1. Mussels Repair Shell Damage despite Limitations Imposed by Ocean Acidification

   https://doi.org/10.3390/jmse10030359  

   George, Matthew N.; O’Donnell, Michael J.; Concodello, Michael; Carrington, Emily (March 2022, Journal of Marine Science and Engineering)

   Bivalves frequently withstand shell damage that must be quickly repaired to ensure survival. While the processes that underlie larval shell development have been extensively studied within the context of ocean acidification (OA), it remains unclear whether shell repair is impacted by elevated pCO2. To better understand the stereotypical shell repair process, we monitored mussels (Mytilus edulis) with sublethal shell damage that breached the mantle cavity within both field and laboratory conditions to characterize the deposition rate, composition, and integrity of repaired shell. Results were then compared with a laboratory experiment wherein mussels (Mytilus trossulus) repaired shell damage in one of seven pCO2 treatments (400–2500 µatm). Shell repair proceeded through distinct stages; an organic membrane first covered the damaged area (days 1–15), followed by the deposition of calcite crystals (days 22–43) and aragonite tablets (days 51–69). OA did not impact the ability of mussels to close drill holes, nor the microstructure, composition, or integrity of end-point repaired shell after 10 weeks, as measured by µCT and SEM imaging, energy-dispersive X-ray (EDX) analysis, and mechanical testing. However, significant interactions between pCO2, the length of exposure to treatment conditions, the strength and inorganic content of shell, and the physiological condition of mussels within OA treatments were observed. These results suggest that while OA does not prevent adult mussels from repairing or mineralizing shell, both OA and shell damage may elicit stress responses that impose energetic constraints on mussel physiology. 

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2. Freshwater mussels alter fish distributions through habitat modifications at fine spatial scales

   Hopper, G.W.; DuBose, T.P.; Gido, K.B; Vaughn, C.C. (December 2019, Freshwater science)

   Aggregations of freshwater mussels create patches that can benefit other organisms through direct habitat alterations or indirect stimulation of trophic resources via nutrient excretion and biodeposition. Spent shells and the shells of living mussels add complexity to benthic environments by providing shelter from predators and increasing habitat heterogeneity. Combined, these factors can increase primary productivity and macroinvertebrate abundance in patches where mussel biomass is high, providing valuable subsidies for some fishes and influencing their distributions. We performed a 12-wk field experiment to test whether fish distributions within mussel beds were most influenced by the presence of subsidies associated with live mussels or the biogenic habitat of shells. We used remote underwater video recordings to quantify fish occurrences at fifty 0.25-m2 experimental enclosures stocked with either live mussels (2-species assemblages), sham mussels (shells filled with sand), or sediment only. The biomass of algae and benthic macroinvertebrates increased over time but were uninfluenced by treatment. We detected more fish in live mussel and sham treatments than in the sediment-only treatment but found no difference between live mussel and sham treatments. Thus, habitat provided by mussel shells may be the primary benefit to fishes that co-occur with mussels. Increased spatiotemporal overlap between fish and mussels might strengthen ecosystem effects, such as nutrient cycling, and the role of both fish and mussels in freshwater ecosystems 

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3. Developmental plasticity of shell morphology of quagga mussels from shallow and deep-water habitats of the Great Lakes

   https://doi.org/10.1242/jeb.042549  

   Peyer, Suzanne M.; Hermanson, John C.; Lee, Carol Eunmi (August 2010, Journal of Experimental Biology)

   SUMMARY The invasive zebra mussel (Dreissena polymorpha) has quickly colonized shallow-water habitats in the North American Great Lakes since the 1980s but the quagga mussel (Dreissena bugensis) is becoming dominant in both shallow and deep-water habitats. While quagga mussel shell morphology differs between shallow and deep habitats, functional causes and consequences of such difference are unknown. We examined whether quagga mussel shell morphology could be induced by three environmental variables through developmental plasticity. We predicted that shallow-water conditions (high temperature, food quantity, water motion) would yield a morphotype typical of wild quagga mussels from shallow habitats, while deep-water conditions (low temperature, food quantity, water motion) would yield a morphotype present in deep habitats. We tested this prediction by examining shell morphology and growth rate of quagga mussels collected from shallow and deep habitats and reared under common-garden treatments that manipulated the three variables. Shell morphology was quantified using the polar moment of inertia. Of the variables tested, temperature had the greatest effect on shell morphology. Higher temperature (∼18–20°C) yielded a morphotype typical of wild shallow mussels regardless of the levels of food quantity or water motion. In contrast, lower temperature (∼6–8°C) yielded a morphotype approaching that of wild deep mussels. If shell morphology has functional consequences in particular habitats, a plastic response might confer quagga mussels with a greater ability than zebra mussels to colonize a wider range of habitats within the Great Lakes. 

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4. River Flow 2020 Proceedings of the 10th Conference on Fluvial Hydraulics (Delft, Netherlands, 7-10 July 2020)

   https://doi.org/https://doi.org/10.1201/b22619  

   Wu, H.; Constantinescu, G (August 2020, River Flow 2020)

   Wim Uijttewaal, Mário J. (Ed.)

   Freshwater mussels are bivalve mollusks that inhabit the substrates of rivers. Fully three-dimensional large eddy simulations are used to investigate flow, turbulence and the capacity of the flow to dislocate an isolated, partially-buried, isolated freshwater mussel placed in a ful-ly-developed incoming turbulent open channel flow. The mussel is aligned with the flow di-rection, which corresponds to normal conditions in rivers containing mussel beds. Its sub-mergence depth is about 60% of the mussel height. The paper focuses on quantifying the ef-fect of the active filtering flow through the incurring and excurring siphons. Simulation re-sults are discussed for two limiting cases with no active filtering and with a filtering flow dis-charge that is close to the maximum value recorded for the investigated freshwater mussel species. It is shown that the active filtering increases the turbulent kinetic energy in the wake and slightly decreases the mean streamwise drag acting on the mussel shell. The paper also discusses the main types of large-scale coherent structures generated by partially-burrowed mussels aligned with the flow, how they are affected by the filtered flow and the effects of these eddies on the bed shear stress, sediment entrainment/deposition phenomena and nutri-ent transport 

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5. Biogeography of ocean acidification: Differential field performance of transplanted mussels to upwelling-driven variation in carbonate chemistry.

   https://doi.org/10.1371/journal.pone.0234075  

   Rose, Jeremy M.; Blanchette, Carol A.; Chan, Francis; Gouhier, Tarik C.; Raimondi, Peter T.; Sanford, Eric; Menge, Bruce A. (July 2020, PloS one)

   Griffen, Blaine D. (Ed.)

   Ocean acidification (OA) represents a serious challenge to marine ecosystems. Laboratory studies addressing OA indicate broadly negative effects for marine organisms, particularly those relying on calcification processes. Growing evidence also suggests OA combined with other environmental stressors may be even more deleterious. Scaling these laboratory studies to ecological performance in the field, where environmental heterogeneity may mediate responses, is a critical next step toward understanding OA impacts on natural communities. We leveraged an upwelling-driven pH mosaic along the California Current System to deconstruct the relative influences of pH, ocean temperature, and food availability on seasonal growth, condition and shell thickness of the ecologically dominant intertidal mussel Mytilus californianus. In 2011 and 2012, ecological performance of adult mussels from local and commonly sourced populations was measured at 8 rocky intertidal sites between central Oregon and southern California. Sites coincided with a large-scale network of intertidal pH sensors, allowing comparisons among pH and other environmental stressors. Adult California mussel growth and size varied latitudinally among sites and inter-annually, and mean shell thickness index and shell weight growth were reduced with low pH. Surprisingly, shell length growth and the ratio of tissue to shell weight were enhanced, not diminished as expected, by low pH. In contrast, and as expected, shell weight growth and shell thickness were both diminished by low pH, consistent with the idea that OA exposure can compromise shell-dependent defenses against predators or wave forces. We also found that adult mussel shell weight growth and relative tissue mass were negatively associated with increased pH variability. Including local pH conditions with previously documented influences of ocean temperature, food availability, aerial exposure, and origin site enhanced the explanatory power of models describing observed performance differences. Responses of local mussel populations differed from those of a common source population suggesting mussel performance partially depended on genetic or persistent phenotypic differences. In light of prior research showing deleterious effects of low pH on larval mussels, our results suggest a life history transition leading to greater resilience in at least some performance metrics to ocean acidification by adult California mussels. Our data also demonstrate “hot” (more extreme) and “cold” (less extreme) spots in both mussel responses and environmental conditions, a pattern that may enable mitigation approaches in response to future changes in climate. 

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