Ecophysiological and biochemical variation of the surf zone diatom asterionellopsis glacialis sensu lato from Santa Catarina, Southern Brazil

Abstract Patches formed by dense accumulations of diatoms in the surf zone (surf diatoms) are common on sandy beaches with intermediate to dissipative morphodynamic states. Their appearances are correlated with environmental factors such as the passage of cold fronts when onshore winds increase beach hydrodynamics, resuspending epibenthic stocks and accumulating them through the inner surf zone. In Santa Catarina state, Southern Brazil, two beaches are known to have frequent occurrence of accumulations of the surf diatom Asterionellopsis glacialis sensu lato: Rincão Beach (28°50' S) and Navegantes Beach (26°52' S). The high biomass of this alga and its central importance in the trophic structure of the coastal ecosystems suggest studies about its potential applications. In the present study, strains of A. glacialis were isolated, cultured under different conditions and evaluated for ecophysiological aspects: growth rate under different conditions, potential biological activities of exudates, biomass and lipid content, and fatty acid profile. A. glacialis cells in culture showed deformation, which were ameliorated by using agitation and silicon and phosphorus enriched culture media. Exudates of the strains showed no allelopathic effects, although previous studies have indicated activity. Lipid content showed variation depending on the strain and culture media. Values ranged from 9% to 13.6% by dry weight. In all strains saturated fatty acids and polyunsaturated fatty acids were identified. Some hypotheses were proposed to explain the variation of the lipid contents, fatty acid profiles and physiological features between strains of the same species. We believe that the fatty acids profile of this primary producer has important consequences in the sandy beach ecology.

摘要：冲浪带内由硅藻密集聚集形成的藻斑（surf diatoms，冲浪带硅藻）常见于处于中等至消散型地貌动力状态的沙滩。其出现与诸多环境因素相关：例如冷锋过境时，向岸风增强沙滩水动力条件，使底栖硅藻种群重新悬浮，并通过内冲浪带将其富集聚集。
在巴西南部圣卡塔琳娜州，已知林孔海滩（Rincão Beach，南纬28°50′）与纳维甘特海滩（Navegantes Beach，南纬26°52′）这两处沙滩频繁出现冲浪带硅藻广义冰川星柄藻（Asterionellopsis glacialis sensu lato）的聚集现象。该藻类生物量颇高，且在沿岸生态系统的营养结构中占据核心地位，这提示开展其潜在应用价值研究的必要性。
本研究中，研究人员分离得到冰川星柄藻（Asterionellopsis glacialis，简称A. glacialis）菌株，在不同培养条件下进行培养，并从生理生态学维度开展评估：包括不同条件下的生长速率、藻体分泌物的潜在生物活性、生物量与脂质含量，以及脂肪酸谱。
培养过程中观察到冰川星柄藻细胞出现变形现象，通过施加搅拌以及添加硅、磷元素的富集培养基可缓解该变形问题。尽管前期研究表明该藻分泌物具有相关活性，但本研究中各菌株的分泌物未表现出化感效应。脂质含量因菌株和培养基不同而存在差异，干重占比范围为9%至13.6%。所有受试菌株中均检测到饱和脂肪酸与多不饱和脂肪酸。
研究人员提出若干假说，用以解释同一物种不同菌株间脂质含量、脂肪酸谱及生理特征的差异。我们认为，该初级生产者的脂肪酸谱对沙滩生态系统具有重要影响。