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The effects of increased photosynthetic active radiation (PAR), UV radiation (UVR), and nutrient supply on photosynthetic activity, pigment content, C:N ratio and biomass yield were studied in tank cultivated Gracilaria conferta (Rhodophyta). Electron transport rate (ETR) and biliprotein content were higher under high nutrient supply (HNS), obtained from fishpond effluents, compared to low nutrient supply (LNS), in contrast to mycosporine-like amino acids (MAAs) dynamic. The high MAA content in LNS-algae could be explained by higher UVR penetration in the thallus and by the competition for the use of nutrients with other processes. Effective quantum yield decreased after short-term exposure to high irradiance whereas full recovery in shade was produced only under slightly heat shock. UVA radiation provoked an additional decrease in photosynthesis under high water temperature. UVB radiation reversed UVA's negative effect mainly with HNS. Results support that nutrient-sufficiency help G. conferta to resist environmental changes as short-term temperature increase.

In order to test their usability in vertical structured, integrated aquaculture approaches, the light acclimation characteristics of three commercially important red algal species of southern Chile were investigated. Light affinity, maximum photosynthesis and respiration rate were measured. Analyses of the non-photochemical quenching and pigment contents were conducted. This work is focused on the differences between field-grown algae exposed to the full range of irradiance variability in the field caused by tidal changes, and algae grown in buoyant long-line aquacultures at different depths (1, 3, 5 and 7 m). The acclimation patterns of the respective species were clearly related to the irradiance regime of their natural habitat. However, all species were also able to acclimate their photosynthesis characteristics to conditions exceeding the irradiance ranges of their natural habitat. The results revealed that the three species followed different acclimation strategies: Gracilaria chilensis was almost completely lacking physiological acclimation. Sarcothalia crispata exhibited a combination of both morphological as well as physiological acclimation processes, while Mazzaella laminarioides exclusively used physiological acclimation mechanisms. Further differences were found with respect to their ability to survive periods of supersaturating irradiation. As expected, the subtidal S. crispata was unable to acclimate to large irradiance fluctuations in shallow water, whereas the other two species adjusted their capability for dynamic photoinhibition to the respective irradiance climate. The implications of these acclimation patterns for aquaculture purposes are discussed and recommendations for appropriate positioning of these species in vertical structured aquaculture are given.