The cell transformation from green motile cells to non-motile cells and astaxanthin accumulation can be induced in the green alga Haematococcus pluvialis cultured outdoors. In the initial 3 d of incubation (cell transformation phase), light absorption and photosynthetic electron transport became more efficient. After five days of incubation (astaxanthin accumulation phase), the light absorption per active reaction center (ABS/RC) increased, but the efficiency of electron transport (ψ_o) and the quantum yield of electron transport (φ_Eo) decreased with increased time, indicating that the capacity of photosynthetic energy utilization decreased significantly during astaxanthin accumulation, leading to an imbalance between photosynthetic light absorption and energy utilization. It would inevitably aggravate photoinhibition under high light, e.g., at midday. However, the level of photoinhibition in H. pluvialis decreased as the incubation time increased, which is reflected by the fact that F_v/F_m determined at midday decreased significantly in the initial 3 d of incubation, but was affected very little after seven days of incubation, compared with that determined at predawn. This might be because the non-photochemical quenching, plastid terminal oxidase, photosystem I cyclic electron transport, defensive enzymes and the accumulated astaxanthin can protect cells against photoinhibition.

We compared the carotenoids in tissues of various organs from four shrimps cultured in China, Penaeus monodon Fabricius, 1978, Fenneropenaeus chinensisOsbeck, 1765, Litopenaeus vannameiBoone,1931, and Exopalaemon carinicaudaHolthuis, 1950. The carotenoid levels vary greatly depending on the species and the tissues sampled, with the highest levels found in the cephalothorax of L. vannamei (295.20 mg kg^–1), and the lowest in the abdominal muscle of L. vannamei (2.12 mg kg^–1). Astaxanthin, mainly esterified (47.69–95.56%), but also unesterified (4.44–52.31%), was the predominant carotenoid and contributed 66.64–95.26% of the total carotenoids in all species. β-carotene, echinenone, canthaxanthin, astacene, zeaxanthin, and some unidentified carotenoids were also detected. All-trans-astaxanthin was the predominant geometrical isomer and 9-cis and 13-cis were the major cis isomers. Two other isomers, 15-cis and di-cis-astaxanthin, were also detected. The stereoisomers (3S, 3’S) and (3S, 3’R)-astaxanthin were only observed in E. carinicauda, where (3’S, 3’S)-astaxanthin contributed more than 96% to the total astaxanthin content. In contrast, all three possible stereoisomers were detected in P. monodon, F. chinensis, and L. vannamei and the relative levels of these stereoisomers were similar, 25.37–39.11% of (3S, 3’S)-astaxanthin, 38.85–52.01% of (3S, 3’R)-astaxanthin, and 14.07–29.89 % of (3R, 3’R)-astaxanthin. The astaxanthin-enriched waste, particularly the cephalothorax generated from L. vannamei, is suggested as a good source of natural astaxanthin available by further processing. These results provide some valuable information on carotenoid characteristics of cultured shrimps, especially the specific configurations of astaxanthin.

Arthrospira (Spirulina) is widely used as human health food and animal feed. In cultures grown outdoors in open ponds, Arthrospira cells are subjected to various environmental stresses, such as high temperature. A better understanding of the effects of high temperature on photosynthesis may help optimize the productivity of Arthrospira cultures. In this study, the effects of heat stress on photosynthetic rate, chlorophyll a fluorescence transients, and photosystem (PS) II, PSI activities in a marine cyanobacterium Arthrospira sp. were examined. Arthrospira cells grown at 25 °C were treated for 30 min at 25 (control), 30, 34, 37, or 40 °C in the dark. Heat stress (30–37 °C) enhanced net photosynthetic O₂ evolution rate. Heat stress caused over-reduction PSII acceptor side, damage of donor side of PSII, decrease in the energetic connectivity of PSII units, and decrease in the performance of PSII. When the temperature changed from 25 to 37 °C, PSII activity decreased, while PSI activity increased, the enhancement of photosynthetic O₂ evolution was synchronized with the increase in PSI activity. When temperature was further increased to 40 °C, it induced a decrease in photosynthetic O₂ evolution rate and a more severe decrease in PSII activity, but an increase in PSI activity. These results suggest that PSI activity was the decisive factor determining the change of photosynthetic O₂ evolution when Arthrospira was exposed to a temperature from 25 to 37 °C, but then, PSII activity became the decisive factor adjusting the change of photosynthetic O₂ evolution when the temperature was increased to 40 °C.