The Rias Baixas are four flooded tectonic valleys located on the northwest Iberian

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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

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.

Isochrysis galbana clone T‐ISO was cultured in 5‐L vessels with continuous light at 100 µmol photons m−2 s−1 at temperature room (22 °C) and harvested at early exponential phase. Dry weight (dw), ash content, biochemical composition and fatty acid profile were determined in fresh biomass and after storage for 7 days and 3 months at −76 °C for both freeze‐dried and frozen biomasses. Both freezing and freeze‐drying caused significant losses in dry weight (range 13.67–19.74%) when compared with fresh microalgae (40.17 pg cell−1), irrespective of storage time. Ash content increased significantly (P < 0.05) from 21.15% in the case of fresh T‐ISO up to a range of 24.13–26.26% when different treatments were used. Both freezing and freeze‐drying techniques caused a significant protein loss of a similar magnitude from 13.60 to 11.74 and 11.40 pg organic weight (OW) cell−1, respectively, only when long‐term storage was used (3 months). Carbohydrate content was only affected by the preservation technique (P < 0.01). Freeze‐drying caused significant loss of the latter component after both 7 days (4.53 pg OW cell−1) and 3 months (4.24 pg OW cell−1) when compared with fresh T‐ISO (6.15 pg OW cell−1). Lipid content remained constant when subjected to either microalgal treatment or storage time (P > 0.05). However, the relative percentage of polyunsaturated fatty acids underwent a significant loss after 3 months when T‐ISO was freeze‐dried. Our results suggest that freezing is a more appropriate long‐term preservation technique (3 months) than freeze‐drying. Both carbohydrate and polyunsaturated fatty acids contents, important components in the determination of the nutritional value of food in aquaculture (i.e. for bivalves), remain unchanged when frozen. The processes responsible for the observed loss of biochemical compounds when samples are freeze‐dried is most probably as a result of a physical altering of the cell wall.