AbstractsBiology & Animal Science

The use of brown algae in numerous commercial and industrial applications has resulted in extensive research into the ecology and ecophysiology of these macrophytes. Brown algae are cultivated for human consumption, feed supplement in aquaculture, and extraction of commercially-relevant chemical compounds, and have been identified as a potentially effective means of bioremediation of nutrient-polluted waters. Saccharina latissima (formerly Laminaria saccharina), a common coastal kelp in polar and temperate waters, is of particular interest to researchers due to its wide distribution along arctic and temperate coastlines, suggestive of robust traits. Ecotypic diversity in S. latissima is associated with a broad tolerance to various abiotic stressors, including salinity, the fluctuation of which has the effect of imposing osmotic stress on aquatic organisms. Besides the osmoregulatory function of inorganic ions, it has been shown that mannitol, a simple monosaccharide polyol, may fulfil a similar role in osmotic adustment, albeit more effectively as a compatible solute. In this study, juvenile sporophytes of S. latissima were removed from a line cultivation site in the Danish Limfjord and treated at variable levels of steady-state salinity (5-30 ppt) over a month-long period in order to determine optimal salinity for growth as well as to investigate the role of mannitol as a possible osmoprotectant. In addition to growth and survivorship, various parameters related to photosynthetic efficiency were measured using pulse-amplitude modulated (PAM) fluorometry. Exposure to low-salinity treatment resulted in total mortality within a week at the 5 ppt level; survivorship at the 10 ppt level was 20% by the end of the study. Elongation and relative growth rates were significantly impacted at lower salinities compared with the optimal range (25-30 ppt). Mannitol concentrations showed little variation across lower salinity levels, with the highest concentrations found at 25 and 30 ppt, which also differed significantly from the baseline (pre-treatment) concentration. However, all levels tended to show non-significantly higher concentrations of mannitol compared with that found in baseline measuements for the sampled population. PAM fluorometry revealed a drop in FvFm across all levels compared with the baseline; overall, FvFm values were found to be much lower than expected, both prior to the experimental phase and at its conclusion, suggesting a stressed starting condition. Pigment content also showed a significant drop at lower salinities when compared with baseline levels.