Abstract:Mollusk shells protect against diverse environmental and predatory physical threats, from one-time impacts to chronic, low-magnitude stresses. The effectiveness of shells as armor is often quantified with a test of shell strength: increasing force is applied until catastrophic fracture. This test does not capture the potential role of fatigue, a process by which chronic or repeated, low-magnitude forces weaken and break a structure. We quantified the strength and fatigue resistance of California mussel (Mytilu… Show more
“…At the start of the study, we measured the length, width and height of each live mussel ( Crane and Denny, 2020 ). The animals were then patted dry and weighed.…”
Section: Methodsmentioning
confidence: 99%
“…For mussels whose shells did not break during fatigue loading, the applied force can be described according to the linear regression equation: applied force (N)=64.6+29.7×wet weight (g) ( F 1,162 =2284, P <0.0001, R 2 =0.93). The range of forces was determined based on previous work to cause critical damage to approximately half of shells ( Crane and Denny, 2020 ) and the resulting range resembled the range of crushing forces from many shell-crushing crabs in the Pacific Northwest, USA ( Taylor, 2000 ), which the California mussel could encounter. Fig.…”
Section: Methodsmentioning
confidence: 99%
“…Mussels were compressed for 15 cycles between two flat plastic plates. The materials testing device applied a compressive force from above with a hydraulic ram, with the mussel resting on a force plate with its aperture parallel to both plates (details about force sensor and materials testing device in Crane and Denny, 2020 ). The valve (left or right) in contact with the force plate was randomly determined.…”
Section: Methodsmentioning
confidence: 99%
“…The shells possess an external proteinaceous layer, the periostracum, covering layers of crystals of calcium carbonate in organic matrix: an outer prismatic layer, a middle layer of bricklike nacre and a thin, innermost prismatic layer (Dodd, 1964;Taylor et al, 1969). Mussel shells experience fatigue on potentially biologically relevant timescales (Crane and Denny, 2020), although repair in response to fatigue has not been directly studied.…”
Section: Introductionmentioning
confidence: 99%
“…This positive feedback can progressively weaken a structure. In this way, subcritical forces applied repeatedly or for an extended duration can ultimately break a shell ( Boulding and LaBarbera, 1986 ; Crane and Denny, 2020 ; Currey and Brear, 1984 ; LaBarbera and Merz, 1992 ).…”
Hard external armors have to defend against a lifetime of threats yet are traditionally understood by their ability to withstand a single attack. Survival of bivalve mollusks thus can depend on the ability to repair shell damage between encounters. We studied the capacity for repair in the intertidal mussel Mytilus californianus by compressing live mussels for 15 cycles at ∼79% of their predicted strength (critically fracturing 46% of shells), then allowing the survivors 0, 1, 2 or 4 weeks to repair. Immediately after fatigue loading, mussel shells were 20% weaker than control shells that had not experienced repetitive loading. However, mussels restored full shell strength within 1 week, and after 4 weeks shells that had experienced greater fatiguing forces were stronger than those repetitively loaded at lower forces. Microscopy supported the hypothesis that crack propagation is a mechanism of fatigue-caused weakening. However, the mechanism of repair was only partially explained, as epifluorescence microscopy of calcein staining for shell deposition showed that only half of the mussels that experienced repetitive loading had initiated direct repair via shell growth around fractures. Our findings document repair weeks to months faster than demonstrated in other mollusks. This rapid repair may be important for the mussels’ success contending with predatory and environmental threats in the harsh environment of wave-swept rocky coasts, allowing them to address non-critical but weakening damage and to initiate plastic changes to shell strength. We highlight the significant insight gained by studying biological armors not as static structures but, instead, as dynamic systems that accumulate, repair and respond to damage.
“…At the start of the study, we measured the length, width and height of each live mussel ( Crane and Denny, 2020 ). The animals were then patted dry and weighed.…”
Section: Methodsmentioning
confidence: 99%
“…For mussels whose shells did not break during fatigue loading, the applied force can be described according to the linear regression equation: applied force (N)=64.6+29.7×wet weight (g) ( F 1,162 =2284, P <0.0001, R 2 =0.93). The range of forces was determined based on previous work to cause critical damage to approximately half of shells ( Crane and Denny, 2020 ) and the resulting range resembled the range of crushing forces from many shell-crushing crabs in the Pacific Northwest, USA ( Taylor, 2000 ), which the California mussel could encounter. Fig.…”
Section: Methodsmentioning
confidence: 99%
“…Mussels were compressed for 15 cycles between two flat plastic plates. The materials testing device applied a compressive force from above with a hydraulic ram, with the mussel resting on a force plate with its aperture parallel to both plates (details about force sensor and materials testing device in Crane and Denny, 2020 ). The valve (left or right) in contact with the force plate was randomly determined.…”
Section: Methodsmentioning
confidence: 99%
“…The shells possess an external proteinaceous layer, the periostracum, covering layers of crystals of calcium carbonate in organic matrix: an outer prismatic layer, a middle layer of bricklike nacre and a thin, innermost prismatic layer (Dodd, 1964;Taylor et al, 1969). Mussel shells experience fatigue on potentially biologically relevant timescales (Crane and Denny, 2020), although repair in response to fatigue has not been directly studied.…”
Section: Introductionmentioning
confidence: 99%
“…This positive feedback can progressively weaken a structure. In this way, subcritical forces applied repeatedly or for an extended duration can ultimately break a shell ( Boulding and LaBarbera, 1986 ; Crane and Denny, 2020 ; Currey and Brear, 1984 ; LaBarbera and Merz, 1992 ).…”
Hard external armors have to defend against a lifetime of threats yet are traditionally understood by their ability to withstand a single attack. Survival of bivalve mollusks thus can depend on the ability to repair shell damage between encounters. We studied the capacity for repair in the intertidal mussel Mytilus californianus by compressing live mussels for 15 cycles at ∼79% of their predicted strength (critically fracturing 46% of shells), then allowing the survivors 0, 1, 2 or 4 weeks to repair. Immediately after fatigue loading, mussel shells were 20% weaker than control shells that had not experienced repetitive loading. However, mussels restored full shell strength within 1 week, and after 4 weeks shells that had experienced greater fatiguing forces were stronger than those repetitively loaded at lower forces. Microscopy supported the hypothesis that crack propagation is a mechanism of fatigue-caused weakening. However, the mechanism of repair was only partially explained, as epifluorescence microscopy of calcein staining for shell deposition showed that only half of the mussels that experienced repetitive loading had initiated direct repair via shell growth around fractures. Our findings document repair weeks to months faster than demonstrated in other mollusks. This rapid repair may be important for the mussels’ success contending with predatory and environmental threats in the harsh environment of wave-swept rocky coasts, allowing them to address non-critical but weakening damage and to initiate plastic changes to shell strength. We highlight the significant insight gained by studying biological armors not as static structures but, instead, as dynamic systems that accumulate, repair and respond to damage.
Pismo clam extraction is currently banned in Mexico to help the recovery of natural populations. Thus, the primary objective of this study was to gain insight on its basic biology and husbandry protocols. Growth and clearance rate (CR) of sand-burrowed and sediment-free, laterally pressed adult Pismo clams were quantified in the laboratory as a function of burrowing condition, flow, temperature, and microalgal concentration using open-flow chambers. After 40 days clams remained healthy regardless of burrowing condition and showed a hyperbolic CR response pattern to increased flow, with CR directly proportional to flows lower than 1000 ml min−1. Maximal asymptotic CR values (300 to 400 ml min−1 org−1) were observed from 1000 to 2000 ml min−1. No significant CR differences were observed between burrowed and laterally pressed clams, yet microalgal concentration effects were detected, with constant maximal CRs of ca. 250 ml min−1 in the range of 50 to 200 cells µl−1 and decline at higher concentrations. Maintenance protocols of laterally pressed organisms were validated in the laboratory with both weight and CR data. To our knowledge this is the first study providing whole-body physiological data that translated into effective husbandry protocols for Pismo clams. This approach represents a fresh perspective to traditional research areas, opening the possibility for continued experimentation under controlled conditions.
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