Algae are at the base of the aquatic food chain, producing the food resources that fish are adapted to consume. Previous studies have proven that the inclusion of small amounts (<10% of the diet) of algae in fish feed (aquafeed) resulted in positive effects in growth performance and feed utilisation efficiency. Marine algae have also been shown to possess functional activities, helping in the mediation of lipid metabolism, and therefore are increasingly studied in human and animal nutrition. The aim of this study was to assess the potentials of two commercially available algae derived products (dry algae meal), Verdemin (derived from Ulva ohnoi) and Rosamin (derived from diatom Entomoneis spp.) for their possible inclusion into diet of Atlantic Salmon (Salmo salar). Fish performances, feed efficiency, lipid metabolism and final product quality were assessed to investigated the potential of the two algae products (in isolation at two inclusion levels, 2.5% and 5%, or in combination), in experimental diets specifically formulated with low fish meal and fish oil content. The results indicate that inclusion of algae product Verdemin and Rosamin at level of 2.5 and 5.0% did not cause any major positive, nor negative, effect in Atlantic Salmon growth and feed efficiency. An increase in the omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) content in whole body of fish fed 5% Rosamin was observed.

The depth distribution of reef-building corals exposes their photosynthetic symbionts of the genus Symbiodinium to extreme gradients in the intensity and spectral quality of the ambient light environment. Characterizing the mechanisms used by the coral holobiont to respond to the low intensity and reduced spectral composition of the light environment in deeper reefs (greater than 20 m) is fundamental to our understanding of the functioning and structure of reefs across depth gradients. Here, we demonstrate that host pigments, specifically photoconvertible red fluorescent proteins (pcRFPs), can promote coral adaptation/acclimatization to deeper-water light environments by transforming the prevalent blue light into orange-red light, which can penetrate deeper within zooxanthellae-containing tissues; this facilitates a more homogeneous distribution of photons across symbiont communities. The ecological importance of pcRFPs in deeper reefs is supported by the increasing proportion of red fluorescent corals with depth (measured down to 45 m) and increased survival of colour morphs with strong expression of pcRFPs in long-term light manipulation experiments. In addition to screening by host pigments from high light intensities in shallow water, the spectral transformation observed in deeper-water corals highlights the importance of GFP-like protein expression as an ecological mechanism to support the functioning of the coral–Symbiodinium association across steep environmental gradients.

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The seagrass Halophila stipulacea grows in the northern Red Sea from the intertidal to depths of , 50 m. Along that gradient, there is a . 1 order of magnitude difference in irradiance and the spectrum narrows from that of full sunlight to dim blue-green light. Based on these differences, we set out to estimate the molar ratios and potential contributions of photosystem II (PSII) and photosystem I (PSI) to light absorption, and photosynthetic electron transport rates (ETR), in plants growing at 1-m and 48-m depths. The amount of PsaC (a proxy for PSI) was three times higher in the deep-growing plants. On the other hand, the amount of PsbA (a proxy for PSII) did not differ significantly between the two depths. Thus, the PSII : (PSII + PSI) ratio (FII) was 0.62 in the shallowand 0.41 in the deep-growing plants. Similar results were obtained by 77K emission fluorescence. Because ETR is linearly dependent on FII, it follows that the ETR vs. irradiance curves differed significantly if calculated based on the commonly used FII value of 0.5 or the FII values we found. As a result, the photosynthetic parameters ETR max and a also differed when using the different FII values. Correct(ed) FII values should, therefore, be used in the calculation of photosynthetic ETRs. The ability of H. stipulacea to alter its amount of PSI relative to PSII according to the ambient irradiance and spectrum may be one reason why this organism can grow down to its exceptional depth limit in clear tropical waters.In aquatic systems, irradiance is attenuated with depth, and the light spectrum in clear waters shifts from that of full sunlight in the intertidal to a narrower band of bluish light at depth. Accordingly, plants growing along a depth gradient have to acclimate to these differences in the optical properties of the water that surrounds them. In addition to changes in plant morphology (Schwarz and Hellblom 2002) and meadow architecture (Dalla Via et al. 1998;Peralta et al. 2002), marine angiosperms, or seagrasses, may also enhance chlorophyll (Chl) concentrations and photosynthetic efficiencies at low irradiances (reviewed in Ralph et al. 2007). Also spectral changes can affect light absorption by altering the composition and ratio of the two photosystems (PSs) and, thus, photosynthetic rates and plant growth (Fujita 1997; Falkowski and Raven 2007). Among marine macrophytes, such spectral changes were shown to influence the functionality of the two PSs as found for the green macroalgae Ulva pertusa and Bryopsis maxima (Yamazaki et al. 2005). Regarding seagrasses, only two studies have reported on changes in the PS composition: one in shallow-growing plants during various seasons (Major and Dunton 2000) and another along a narrow depth gradient down to 1.6 m (Major and Dunton 2002). To our knowledge there are no studies on photosystems' acclimatory mechanism in seagrasses growing at greater depths where both the irradiance and light spectrum change drastically.In the Gulf of Aqaba (northern Red Sea), the seagrass Halophila stipul...