No abstract

Cuttlebone, the sophisticated buoyancy device of cuttlefish, is made of extensive superposed chambers that have a complex internal arrangement of calcified pillars and organic membranes. It has not been clear how this structure is assembled. We find that the membranes result from a myriad of minor membranes initially filling the whole chamber, made of nanofibres evenly oriented within each membrane and slightly rotated with respect to those of adjacent membranes, producing a helical arrangement. We propose that the organism secretes a chitin–protein complex, which self-organizes layer-by-layer as a cholesteric liquid crystal, whereas the pillars are made by viscous fingering. The liquid crystallization mechanism permits us to homologize the elements of the cuttlebone with those of other coleoids and with the nacreous septa and the shells of nautiloids. These results challenge our view of this ultra-light natural material possessing desirable mechanical, structural and biological properties, suggesting that two self-organizing physical principles suffice to understand its formation.

In this study, two new alternative preys: Grapsus adscensionis zoeae (as sole prey) and Palaemon elegans zoeae (in cofeeding with Artemia sp.), as well as, Artemia sp. juveniles were used as feed for octopus paralarvae, as a way to understand its lipid requirements. Total lipid (TL) content, lipid class (LC) and fatty acid (FA) profiles of preys, octopus hatchlings and 9-day-old paralarvae were analysed. Growth and survival of the paralarvae were also determined. Regardless the prey provided, a notable shift in the lipid profile of paralarvae was registered after 9 days of rearing. The highest index of growth rate (IGR) recorded when decapod crustacean zoeae were supplied might have some relation with levels of 20:4n-6 (ARA) and DHA/EPA ratio observed. In this sense, Grapsus adscensionis zoeae leaded to a higher content of ARA and a lower content of EPA, which may indicate a possible competition between these two FA. For that a balanced EPA/ARA ratio might be significant in this species nutrition without disconsidering DHA levels as an essential fatty acid. Finally, the changes observed in paralarvae FA profile might not only be related to prey FA profile, but also with changes occurring in the lipid classes contents.

25The high mortalities observed during Octopus vulgaris paralarvae culture have been 18:2n-6, 18:3n-3, 20:4n-6 (ARA), 20:5n-3 (EPA) or 22:6n-3 (DHA), which were added 33 directly to the seawater as their potassium salts bound to bovine serum albumin (BSA). 34A control treatment without [ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 3 50 Introduction 51The common octopus (Octopus vulgaris) is a cephalopod species that has been 52 suggested as a candidate for large scale culture (Vaz-Pires et al., 2004), not only due to 53 its high nutritional value and demand in several countries, but also due to biological 54 characteristics such as short life cycle, rapid growth, high fecundity rate, easy 55 adaptability to rearing conditions, high food conversion rates and acceptance of non-56 living natural foods during the juvenile and adult stages (Estefanell et al., 2011; Iglesias 57 et al., 2007; Vaz-Pires et al., 2004). 58Currently this species is being cultured in NW Spain by ongrowing wild-captured sub-59 adults in land-based tanks or sea cages until they reach 2-3 Kg (Iglesias et al., 2007). Iglesias et al., 2007; Moxica et al., 2002; Viciano et al., 2011; Villanueva and Norman, 73 2008). A recent study was able to determine a predominance of crustacean zoeae in wild 74O. vulgaris paralarvae diet (Roura et al., 2012 Miliou et al., 2006; Navarro and Villanueva 2003; Okumura et al., 2005). 81Among those, polyunsaturated fatty acids (PUFA), and particularly 20:5n-3 (EPA) and 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 8 220 ± 1.5 %) and phosphatidylcholine (PC, 19.6 ± 0.6 %) as the main PL classes (Table 1). 221Cholesterol was the most abundant lipid class of octopus hatchlings, corresponding to 222 30.1 ± 2.9 %, and TAG and sterol esters (SE) accounted for 1.2 ± 0.4 and 2.1 ± 0.8 % of 223 TL, respectively (Table 1). 224The O. vulgaris hatchlings were particularly rich in the n-3 LC-PUFA, DHA and EPA, might be related to the energy-generating FA oxidation systems (Sargent et al., 1989). 321In marine fish larvae, NL and more specifically TAG are presumably used to satisfy 64 65 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 11 322 energy demands (Rainuzzo et al., 1997, Sargent et al., 1989, with SFA and MUFA 323 being the main substrates. In contrast, LC-PUFA are preferentially esterified into PL, 324revealing their important structural role in cell membranes (Sargent et al., 1989). FA was suggested (García-Garrid...

Comparisons of three sets of surveys in the Ria Formosa Lagoon, Portugal, over a 13 year period (2001-2002, 2008-2009 and 2010-2013) revealed significant population fluctuations in at least one of the two seahorse (Hippocampinae) species living there, and that those fluctuations were potentially associated with habitat changes in the lagoon. After a significant decline between the first two survey periods (2001-2002 v. 2008-2009), long-snouted seahorse Hippocampus guttulatus populations increased significantly between 2008-2009 surveys and new 2010-2013 surveys. There were no significant differences in H. guttulatus populations between the 2001-2002 and 2010-2013 surveys. In contrast, there were no significant differences in short-snouted seahorse Hippocampus hippocampus densities among the 16 sites surveyed throughout the three sampling periods, although the ability to detect any change was hampered by the low densities of this species in all time periods. Fluctuations in H. guttulatus densities were positively correlated with the percentage of holdfast coverage, but with none of the other environmental variables tested. These results highlight the importance of holdfast availability in maintaining stable seahorse populations. While population fluctuations are certainly more promising than a consistent downward decline, such extreme fluctuations observed for seahorses in the Ria Formosa Lagoon could still leave these two species vulnerable to any additional stressors, particularly during low density periods.