Methods of physiological energetics were applied to compare growth rates of mussels Mytilus galloprovincialis Lmk from 2 habitats: intertidal and raft cultures. Scope for growth was determined after l and 15 d under standard laboratory conditions Both groups of mussels improved their growth potential during maintenance in the laboratory due to a combination of increased ingestion rate and decreased metabol~c rate. Cultivated mussels presented h~g h e r weight-specific clearance rates, higher absorption efficiency and higher rates of ammonia excretion, w h~c h resulted in increased scope for growth with respect to ~ntertldal mussels. This finding is related to the differential characteristics of these 2 habitats in terms of cycles of food availability and air exposure. Differences between the groups of mussels persisted after 15 d of experimental treatment and were mainly accounted for by absorption efficiency.KEY WORDS: Mussel . Physiological energetics Clearance rate -Metabolic rate Absorption efficiency . A m m o n~a excretion rate . Scope for growth (SFG) . Net growth efficiency (K,)

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8The effect of spawning events of the mussel Mytilus galloprovincialis on both quantitative and 9 qualitative values of byssus secretion and its associated attachment force was investigated. 10Byssogenesis rates and absorption efficiency values were significantly reduced after spawning 11 of individuals. However, the maintenance of individuals under sub-optimal conditions (lack of 12 microalgae in the diet) for a week caused no effect on thread's number. Surprisingly, 13 attachment force varied within a narrow range of values (1.7-1.9 N) with the exception of a 14 significant drop in the experimental group spawned and kept unfed (1.0 N; P<0.001) most 15 likely due to a similar pattern of the thread's thickness variability. 16Qualitative analysis concerned to the amino acid composition of the byssus highlighted a 17 higher presence of the basic residues histidine and lysine in threads secreted by spawned 18 individuals. The presence of both histidine and lysine residues in the byssal collagen is 19 associated to the formation of cross-links and specifically histidine has a functionality with a 20 pronounced effect on metal chelation to stabilise the integrity of the byssus. Results reported 21here evidence the necessity to integrate all components that eventually determine the 22 attachment strength of the mussels to get more insight the plasticity of such secretion. 23Morphology of the byssus (thickness) secreted under different endogenous conditions of 24 2 mussels was the major parameter to explain variability in attachment force. Moreover, 1 aminoacidic composition as quality term of the byssus secreted may also contribute to 2 understand plasticity of this secretion and needs to be extended in further surveys. 3 4

The rapid, global spread of COVID-19, and the measures intended to limit or slow its propagation, are having major impacts on diverse sectors of society. Notably, these impacts are occurring in the context of other anthropogenic-driven threats including global climate change. Both anthropogenic stressors and the COVID-19 pandemic represent significant economic challenges to aquaculture systems across the globe, threatening the supply chain of one of the most important sources of animal protein, with potential disproportionate impacts on vulnerable communities. A web survey was conducted in 47 countries in the midst of the COVID-19 pandemic to assess how aquaculture activities have been affected by the pandemic, and to explore how these impacts compare to those from climate change. A positive correlation between the effects of the two categories of drivers was detected, but analysis suggests that the pandemic and the anthropogenic stressors affect different parts of the supply chain. The immediate measurable reported losses varied with aquaculture typology (land vs. marine, and intensive vs. extensive). A comparably lower impact on farmers reporting the use of integrated multitrophic aquaculture (IMTA) methods suggests that IMTA might enhance resilience to multiple stressors by providing different market options under the COVID-19 pandemic. Results emphasize the importance of assessing detrimental effects of COVID-19 under a multiple stressor lens, focusing on areas that have already locally experienced economic loss due to anthropogenic stressors in the last decade. Holistic policies that simultaneously address other ongoing anthropogenic stressors, rather than focusing solely on the acute impacts of COVID-19, are needed to maximize the long-term resilience of the aquaculture sector.

Secretion of byssal threads and attachment strength of Mytilus galloprovincialis: the influence of size and food availability jose m.f. babarro, mar ia jos e fern andez reiriz and ux io labarta Instituto de Investigaciones Marinas CSIC, Eduardo Cabello 6, 36208 Vigo, Spain Byssogenesis rate and attachment strength of the mussel Mytilus galloprovincialis were investigated in the laboratory considering different body sizes and feeding conditions. Byssal thread secretion was significantly higher in juveniles as compared to larger mussels of approximately 87 mm shell length. Asymptotic number of threads attached was obtained from approximately 72 hours onwards within a range of 42 -46 and 27-31 for juveniles and larger experimental mussels, respectively (P , 0.05 ANOVA). Absorption efficiency values of control fed individuals dropped significantly from 0.78 in juveniles to 0.70 in larger mussels (P , 0.001 ANOVA) which pointed out energetic constraints of mussels with regard to their size and its probable effect on byssus secretion rates. Attachment force was 2.8 times higher in larger mussels than in juveniles (2.21 versus 0.78 N for both sizes, respectively; P , 0.001 ANOVA) which in turn followed the same order of magnitude than differences in the thread's thickness values of both experimental mussel sizes. Tenacity followed a reverse pattern with juveniles presenting two-fold higher values than larger mussels (P , 0.001 ANOVA) based on a lower increment of attachment force (x2.8) as compared to shell area (x6) for the comparison larger versus juvenile mussel size, which in turn might suggest that larger specimens secreted weaker threads. When animals were maintained unfed for a week, a significant drop in both byssus secretion and attachment force were observed in juveniles but was not the case for larger mussels most likely as a consequence of a relatively short period of maintenance under food availability stress for the latter individuals that showed significantly higher initial condition and/or energetic store values. Accordingly, the use of energetic reserves in juveniles kept unfed for a week together with a significant drop in byssus secretion and attachment force might suggest a link, i.e. transfer of energy between soft tissues and byssus under stress. Quantitative values of byssal threads, based on the significance of the byssus versus attachment force relationship, together with its morphometric value, i.e. thread's thickness, represented a primary mechanism to explain variability in attachment strength of M. galloprovincialis of the different body sizes studied here.

13Marine organisms adapt to a wide variety of environments, often altering their morphology and behaviour in 14 response to local habitat. This study addressed the effects of habitat (wave exposure) and body size on the 15 morphology and byssal attachment of mussels within the same estuary. Tenacity of the mussel Mytilus 16 galloprovincialis was higher at the exposed site, particularly for the smaller size classes. This was largely 17 due to differences in thread thickness; mussels from the exposed site produced thicker and stronger byssal 18 threads. For a given shell length, exposed mussels also produced thicker and smaller shells and had lower 19 gonadal condition. In laboratory flume experiments, both thread production and mechanical performance 20 (strength and extensibility) decreased with increased flow, suggesting flow alone does not explain tenacity 21 differences between sites. Altogether, these analyses suggest that mussels at exposed sites allocate resources 22 to reducing risk of dislodgment (smaller and thicker shell, stronger byssal threads) instead of growth and 23 reproduction, and these allocation differences between sites are less apparent in larger size classes. The lack 24 2 of the largest size class (8 cm) at the exposed site may reflect an upper limit to size imposed by wave 25 induced mortality, where attachment strength does not keep pace with hydrodynamic loading. 26 27 28 Introduction 29

Mussel seed Mytilus galloprovincialis (Bivalvia: Mytilidae) from two origins (rocky shore and collector ropes) was cultivated on a raft in the Ría de Arousa (north-west Spain), from seeding to thinning out, for 226 d (November 1995–July 1996) and two aspects of metabolism, oxygen consumption rate (VO2) and ammonia excretion rate (VNH4-N) were studied in situ.The model derived from multiple analysis of oxygen consumption accounted for 91.9% of the variance, based on dry weight of the mussels and the environmental factors quality of food (organic content) and mainly chlorophyll-a. Seed origin also showed significant influence. The seasonal pattern of the oxygen consumption can be attributed mainly to the variation of chlorophyll-a, which showed a higher range of values in the spring months.Origin of seed did not show a homogeneous effect on oxygen consumption throughout the cultivation period. Collector rope mussels showed higher oxygen consumption values at the beginning of the cultivation period and after the first 15 d, but the rocky shore mussels showed a higher oxygen consumption between days 22 and 110. Energy-conserving patterns and lower condition index at the onset of the experiment for rocky shore mussels could explain these initial differences.Multiple analysis on the variation of ammonia excretion rate provided a model that accounted for 72.6% of the variance based on dry weight of mussels, seed origin and the environmental parameters chlorophyll-a and total particulate matter. The rocky shore mussels showed a significantly higher excretion values for most of the cultivation period, although there was no constant tendency throughout. High excretion values were recorded between January and March, whilst for the rest of the cultivation period values were low.The O:N index was higher in collector rope mussels for most of the cultivation period, which may suggest a more favourable energy metabolism and/or a more appropriate nutritional state for these specimens.

The effect of the abiotic environment on byssus tenacity and associated features was investigated for Mytilus galloprovincialis in the Ría de Vigo (NW Spain). The effect of site was examined at macro-geographical (outer exposed Cabo Estay vs. inner sheltered San Simón Ensenada sites) and micro-geographical (intertidal vs. subtidal locations) scales. Site significantly influenced byssus tenacity, shape and byssus thread diameter, whereas location did not. Qualitative analysis of the byssus corroborated the importance of site; mussels inhabiting the rougher outer Ría secreted stronger and stiffer threads regardless of location and had a higher potential to form cross-links or metal chelation in the byssal collagen to gain structural integrity when needed. When mussels were transplanted between exposed and sheltered sites, asymmetrical changes were observed in tenacity, endogenous indices, byssus morphology and mechanical properties after 3 mo. Individuals transferred from the sheltered to the exposed site shifted all variables, suggesting that mussels have a plastic response to rougher environments by increasing byssus size and mechanical integrity. In contrast, mussels transplanted from the exposed to the sheltered site shifted tenacity, endogenous indices and thread length but not thread diameter nor mechanical properties. In summary, we report the highly dynamic nature of the mussel ability to modify byssus tenacity when subjected to abrupt environmental changes. Mussels have the potential to change byssus diameter and mechanical properties to increase strength in stressful abiotic conditions, and can re-allocate energy for vital structures such as gonadal and soft tissue growth in more benign environments.