运用脂肪酸标志法分析刺参食物来源的季节变化

Seasonal variations of food sources in Apostichopus japonicus indicated by fatty acid biomarkers analysis

运用脂肪酸标志法分析了刺参的食物组成及季节变化。刺参饵料中含有硅藻、褐藻、多种异养细菌、大型绿藻、鞭毛藻或原生动物等,其中硅藻、褐藻和细菌在全年的食物贡献比较大,各种饵料来源比例具有显著的季节变化。实验期间,刺参体壁的硅藻脂肪酸标志22:5(n-3)相对含量很高(7.24%～14.45%),且16:1(n-7)/16:0比值全年在0.73～1.82之间(平均1.10),表现出典型的硅藻脂肪酸特征,表明硅藻是刺参主要的食物来源。褐藻脂肪酸标志20:4(n-6)在刺参体壁脂肪酸组成中相对含量较高(4.88%～8.16%),且在秋冬季节达到较高水平,表明秋冬季节褐藻类对刺参的食物贡献可能较大。噬纤维菌—黄杆菌类的脂肪酸标志奇数碳及支链脂肪酸(Odd&brFAs,5.31%～8.29%)和变形细菌的脂肪酸标志[18:1(n-7),5.85%～6.86%]相对含量比较高,表明细菌在全年都是刺参重要的食物来源。主成分分析发现,1月份刺参的主要食物来源是硅藻、鞭毛藻或原生动物、褐藻及细菌;3月份硅藻、鞭毛藻或原生动物、大型绿藻的食物贡献较大;6月份大型绿藻在刺参的食物来源中占较大比重;7月份细菌和大型绿藻的食物贡献较大,细菌在8、9月份的食物来源中占较大比重,褐藻和细菌在10、11月份的食物贡献较大。

Sea cucumber Apostichopus japonicus is a species of deposit feeders with abundant food sources. The analysis of fatty acid biomarkers provides an alternative method of investigating diets,which is not subject to the biases of stomach content analysis. In the present study,16：1（n - 7） /16：0 and EPA [20：5（n - 3）] were selected as diatom fatty acid biomarkers according to the fatty acid composition in body wall tissues of A. japonicus. DHA [22：6（n - 3）],∑[18：2（n - 6） ＋ 18：3（n - 3）]and 20：4（n - 6） were used as fatty acid biomarkers of flagellate or protozoan alga,Chlorophyta and brown alga respectively; Odd branched FAs and 18：1（n - 7） were the fatty acid biomarkers of heterotrophic bacteria. Seasonal variations of food sources in sea cucumber A. japonicus,sampled from a critical cofferdam aquaculture pond,were determined by fatty acid biomarkers analysis. The results showed the food sources consisted of diatoms,flagellate or protozoan, bacteria,brown alga and Chlorophyta originated organic matters. The sea cucumber A. japonicus was characterized by significant diatom markers such as high ratio of 16：1（n - 7） /16：0 （0. 73 - 1. 82） and EPA contents （7. 24% - 14. 45% ）,so diatoms were speculated as one of the main diets. And the two diatom markers showed significant variations during the period of the experiments （F = 8. 871,P 0. 001; F = 22. 882,P 0. 001; respectively）. The low content of DHA （2. 41% - 4. 45% ） and DHA/EPA ratio （0. 29 - 0. 40） showed the flagellate or protozoan provided low proportions of diets for A. japonicus in the year. The food contribution of Chlorophyta was also low with the biomarker [∑18：2（n - 6） ＋ 18：3（n - 3）]changing from 1. 51% to 2. 28% in the duration of the study. However,the relative contents of brown seaweed biomarker 20：4（n - 6） were also found high in the year （4. 88% - 8. 16% ） with the peak values appearing in autumn and winter. Fatty acid biomarkers specific to bacteria Cytophaga-Flavobacteria and Proteobacteria were also found in considerable amounts in the sea cucumber tissue,which suggested that there was substantial bacterial input into the food of the species. The principal component analysis showed the main food sources of A. japonicus changed with seasons. Diatoms,flagellate or protozoan,brown alga and bacteria were the main diets of the sea cucumber in January. The contributions of diatoms,flagellate or protozoan and Chlorophyta were comparatively high in March. Chlorophyta was the most important food for A. japonicus in June. The diets of sea cucumber were mainly bacteria and Chlorophyta in July. Bacteria were the most important food source of A. japonicus in August and September,and the brown alga and bacteria supplied considerable amounts of food for the sea cucumber from October to November. The present study provides alternative materials for feed research of sea cucumber A. japonicus.