A method for isolating an altered bioactive fraction from a stress-induced aquatic photosynthetic organism, said method comprising: providing an aquatic photosynthetic organism; cultivating the aquatic photosynthetic organism under stress-inducing cultivation conditions comprising subjecting the photosynthetic organism to a stress factor or to a plurality of stress factors to produce a stress-induced photosynthetic organism having an altered bioactive fraction and suitable for use in isolating the altered bioactive fraction therefrom; wherein the stress factor or plurality of stress factors is selected from the group consisting of: ultraviolet light stress by applying UVB irradiance of 1 or 2 mWatt/cm 2 during 3 to 12 hours a day; ozone stress by injecting ozone to obtain a redox potential from 200 to 400 and a concentration of dissolved O 2 from 7.0 to 9.0 mg/l; osmotic stress by applying osmolality of cultivation media from 600 to 1200 mOs/kg; reducing hydrostatic pressure compared to that in original conditions; and a combination thereof, and wherein the stress factor or plurality of stress factors alter at least one characteristic of at least one bioactive fraction isolated from the stress-induced photosynthetic organism compared to a corresponding bioactive fraction isolated from a non-stress-induced photosynthetic organism; separating the stress-induced photosynthetic organism into cell juice and a cell walls component; treating the cell juice under conditions effective to yield a bioactive fraction, wherein said bioactive fraction is selected from the group consisting of a cell serum fraction, a membrane fraction, a cell juice supernatant fraction, and a cell serum filtrate fraction; and isolating said bioactive fraction from the treated cell juice, wherein the isolated bioactive fraction has at least one altered characteristic compared to a corresponding bioactive fraction isolated from a non-stress-induced photosynthetic organism, wherein said aquatic photosynthetic organism is an aquatic photosynthetic organism of a class selected from the group consisting of Phaeophyceae and Chlorophyceae, or a Macrocystis spp., selected from the group consisting of Macrocystis angustifolia, Macrocystis integrifolia, Macrocystis laevis, and Macrocystis pyrifera, or a Chaetomorpha spp.selected from the group consisting of Chaetomorpha aerea, Chaetomorpha antennina, Chaetomorpha basiretorsa, Chaetomorpha brachygona, Chaetomorpha californica, Chaetomorpha cannabina, Chaetomorpha crassa, Chaetomorpha gracilis, Chaetomorpha linum, Chaetomorpha melagonium, Chaetomorpha natalensis, and Chaetomorpha spiralis. providing an aquatic photosynthetic organism; cultivating the aquatic photosynthetic organism under stress-inducing cultivation conditions comprising subjecting the photosynthetic organism to a stress factor or to a plurality of stress factors to produce a stress-induced photosynthetic organism having an altered bioactive fraction and suitable for use in isolating the altered bioactive fraction therefrom; wherein the stress factor or plurality of stress factors is selected from the group consisting of: ultraviolet light stress by applying UVB irradiance of 1 or 2 mWatt/cm 2 during 3 to 12 hours a day; ozone stress by injecting ozone to obtain a redox potential from 200 to 400 and a concentration of dissolved O 2 from 7.0 to 9.0 mg/l; osmotic stress by applying osmolality of cultivation media from 600 to 1200 mOs/kg; reducing hydrostatic pressure compared to that in original conditions; and a combination thereof, and wherein the stress factor or plurality of stress factors alter at least one characteristic of at least one bioactive fraction isolated from the stress-induced photosynthetic organism compared to a corresponding bioactive fraction isolated from a non-stress-induced photosynthetic organism; separating the stress-induced photosynthetic organism into cell juice and a cell walls component; treating the cell juice under conditions effective to yield a bioactive fraction, wherein said bioactive fraction is selected from the group consisting of a cell serum fraction, a membrane fraction, a cell juice supernatant fraction, and a cell serum filtrate fraction; and isolating said bioactive fraction from the treated cell juice, wherein the isolated bioactive fraction has at least one altered characteristic compared to a corresponding bioactive fraction isolated from a non-stress-induced photosynthetic organism, wherein said aquatic photosynthetic organism is an aquatic photosynthetic organism of a class selected from the group consisting of Phaeophyceae and Chlorophyceae, or a Macrocystis spp., selected from the group consisting of Macrocystis angustifolia, Macrocystis integrifolia, Macrocystis laevis, and Macrocystis pyrifera, or a Chaetomorpha spp.selected from the group consisting of Chaetomorpha aerea, Chaetomorpha antennina, Chaetomorpha basiretorsa, Chaetomorpha brachygona, Chaetomorpha californica, Chaetomorpha cannabina, Chaetomorpha crassa, Chaetomorpha gracilis, Chaetomorpha linum, Chaetomorpha melagonium, Chaetomorpha natalensis, and Chaetomorpha spiralis.