Valorization of Seaweed Wracks: Inclusion as Additive in Diets for Grass Carp (Ctenopharyngodon idella).

Macroalgae have been recently described as a potential ingredient for aquafeeds, exerting several physiological benefits. Grass carp (Ctenopharyngodon idella) is a freshwater species, which has been the major fish species produced in the world in the last years. In order to determine the potential use of macroalgal wracks in fish feeding, C. idella juveniles were fed with an extruded commercial diet (CD) or the CD supplemented with 7% of a wind dried-powder (1 mm) from either a multispecific macroalgal wrack (CD + MU7) or a monospecific macroalgal wrack (CD + MO7) obtained from Gran Canaria island (Spain) coasts. After 100 days of feeding, survival, fish weight, and body indexes were determined, and muscle, liver, and digestive tract samples were collected. The total antioxidant capacity of macroalgal wracks was analyzed by assesing the antioxidant defense response and digestive enzymes activity in fish. Finally, muscle proximate composition, lipid classes (LC), and fatty acid (FA) profiles were also studied. Our results suggest that dietary inclusion of macroalgal wracks does not have negative effects on growth, proximate, and lipid composition, antioxidative status, or digestive capacity of C. idella. In fact, both macroalgal wracks caused a general lower fat deposition, and the multispecific wrack enhanced catalase activity in the liver.

Different Nutritional Histories Affect the Susceptibility of Algae to Grazing.

We hypothesize that algae with different cell compositions are differently perceived by their predators and consequently subjected to selective grazing. Five populations of the diatom Phaeodactylum tricornutum that differed in organic and elemental composition, but were otherwise identical, were generated by acclimation to distinct growth regimes. The different populations were then mixed in pairs and subjected to predation by either the rotifer Brachionus plicatilis or the copepod Acartia tonsa. The presence of rotifers had no impact on the ratio between any two algal populations. The presence of copepods, however, affected the ratio between algae previously acclimated to a medium containing 1 mM NH4+ and algae acclimated to 0.5 mM NO3- , and to either a lower irradiance or a higher CO2 concentration. We discuss the possible reason for the influence of different nutritional histories on the vulnerability of algae to predators. The differential impact of grazers on the growth of algae with different nutritional histories may result from direct selective grazing (i.e., grazers can detect algae with the most palatable cell composition), alone or combined to an asymmetric utilization of the nutrients regenerated after predation by co-existing algal populations. Our results strongly suggest that the nutritional history of algae can influence the relationships between phytoplankton and grazers and hint at the possibility that algal cell composition is potentially subject to natural selection, because it influences the probability that algae survive predation.

Intraspecific interactions between algae with different nutritional histories.

The diatom Phaeodactylum tricornutum was cultured in five different growth regimes to obtain cells with different composition. Pairs of populations subjected to different treatments were then mixed in a communal culture regime that differed from those of origin. After 6 h, the ratio between the two populations was verified by flow cytometry. Alterations in this ratio were found when cells previously grown at 1 mM NH4+ were mixed with GeO2 - and 0.5 mM NH4+ -grown cells. The nutritional background may thus make cells differently suited to new environmental conditions and afford advantages in terms of reproductive potential. Competitive interactions between populations may result from the differences in the expressed proteome and/or in the availability of tools for regulatory responses. This may have relevance to the persistence of phenotypically neutral variants present in the population best suited to the new condition, after the interaction of the conspecifics with different nutritional histories.

Intraspecific chemical communication in microalgae.

Contents 516 I. 516 II. 518 III. 518 IV. 521 V. 523 VI. 523 VII. 526 526 References 526 SUMMARY: The relevance of infochemicals in the relationships between organisms is emerging as a fundamental aspect of aquatic ecology. Exchanges of chemical cues are likely to occur not only between organisms of different species, but also between conspecific individuals. Especially intriguing is the investigation of chemical communication in microalgae, because of the relevance of these organisms for global primary production and their key role in trophic webs. Intraspecific communication between algae has been investigated mostly in relation to sexuality and mating. The literature also contains information on other types of intraspecific chemical communication that have not always been explicitly tagged as ways to communicate to conspecifics. However, the proposed role of certain compounds as intraspecific infochemicals appears questionable. In this article, we make use of this plethora of information to describe the various instances of intraspecific chemical communication between conspecific microalgae and to identify the common traits and ecological significance of intraspecific communication. We also discuss the evolutionary implications of intraspecific chemical communication and the mechanisms by which it can be inherited. A special focus is the genetic diversity among conspecific algae, including the possibility that genetic diversity is an absolute requirement for intraspecific chemical communication.

Characterization of Microalgae Biomass-Based Composites Obtained through Rotational Molding.

The wide range of applications and the numerous advantages of plastics have led to their excessive use, with subsequent damage to ecosystems. As an environmentally friendly alternative, biocomposites have gained much attention, and microalgae have become a potential source for their production. In this study, the use of washed and unwashed Spirulina in polyethylene-based composites has been evaluated as a way to prevent the thermooxidation of polyethylene, while at the same time, reducing the amount of virgin plastic used. Biocomposites were produced by rotomolding, testing different biomass contents and determining their mechanical and thermal performances as well as their water uptake level. Composites with up to 15% of biomass (by weight), a particularly high ratio for rotomolding, were satisfactorily produced. Using 5% of both biomasses did not significantly modify the behavior when compared with the neat PE samples' properties. For higher loadings, the use of non-washed biomass allowed us to obtain better properties, with added benefits related to using an unwashed biomass (less water consumption, lower costs and fewer environmental impacts). On the other hand, this study showed a promising beneficial effect on the thermooxidative resistance of composites, as the oxidation induction times were notably increased with biomass addition.