北部湾日本金线鱼摄食生态

Feeding ecology of Nemipterus japonicus in Beibu Gulf

中文关键词: 北部湾  日本金线鱼  摄食习性  碳氮稳定同位素  营养级

英文关键词: Beibu Gulf  Nemipterus japonicus  Feeding habit  Stable carbon and nitrogen isotopes  Trophic level

中文摘要:

      根据2018年1—4月和8—12月在北部湾采集的248尾日本金线鱼(Nemipterus japonicus)样品，采用传统胃含物分析法和碳氮稳定同位素技术研究其摄食生态。结果显示，日本金线鱼为广食性底栖肉食性动物，摄食饵料生物包括8个类群，鱼类和虾类是优势饵料类群，相对重要指数占比为92.92%。日本金线鱼四季均大量摄食鱼类，另外，在春季兼食虾类，夏季兼食蟹类，秋季兼食虾类和多毛类，冬季兼食虾类和星虫类；随着体长增加，日本金线鱼由摄食虾类和鱼类为主逐渐转变为摄食鱼类为主，摄食转变体长节点为130 mm。摄食强度存在明显的季节变化，秋季最高，春季和夏季次之，冬季最低。日本金线鱼摄食饵料种类多样性较高，Shannon-Wiener多样性指数(H')为1.77，Pielou均匀度指数(Jʹ)为0.64，从春季到冬季，H'值和Jʹ值随季节先升高后降低，秋季最高；Hʹ和Jʹ随体长呈增加趋势，体长≥160 mm群体的摄食生态位宽度最大。在同位素分析方面，δ13C值范围为–18.25‰ ~ –15.39‰，极差为2.86‰；δ15N值范围为13.01‰~17.24‰，极差为4.23‰；北部湾日本金线鱼的营养级范围为3.21~4.46，平均营养级为3.97，随着体长的增加，营养级逐渐升高。核心生态位(SEA)在4个季节虽有不同程度的重叠，但总生态位(TA)存在明显季节差异，表明对饵料的利用存在一定的相似，也存在特定的差异，有利于缓解该鱼种对优势饵料的季节性压力。不同大小的群体间SEA的重叠率较高，表明不同生长阶段营养来源成分相似，但不同大小的群体间TA差异较为明显，推测日本金线鱼通过生态位分化减轻种内的食物竞争压力。

英文摘要:

      The Beibu Gulf is the fourth largest Chinese fishing ground, with rich fishery resources and a significant role in marine fishery production. The feeding ecology of fish is important to explain the structure and function of marine ecosystems. As one of the most important fish species in the Beibu Gulf, Nemipterus japonicus plays an essential role in energy flow and other aspects of the marine ecosystem. Understanding its feeding ecology could provide a basic theoretical basis for the rational utilization and protection of this resource. A total of 248 N. japonicus specimens were collected from Beibu Gulf from January to April and August to December in 2018. The food content composition, feeding intensity, and feeding niche of N. japonicus were analyzed using stomach contents to reflect feeding habits. Combined with carbon and nitrogen stable isotopes, the food source and trophic structure characteristics were analyzed, the trophic level was determined, and the feeding ecology of N. japonicus in the Beibu Gulf was discussed. The stomach content analysis revealed that N. japonicus is a broad-feeding benthic carnivore, which feeds on a large number of species, including eight prey groups, including fish, shrimp, and crab, among which fish and shrimp are the dominant food groups, with a relative importance index of 92.92%. The proportion of food species varied with the season and growth. Fish were an important prey group across all seasons. Moreover, N. japonicus preyed on shrimp in spring, crab in summer, shrimp and polychaetes in autumn, and shrimp and sipunculoidea in winter. With an increase in body length, the feeding habits of N. japonicus gradually change from primarily feeding on shrimp and fish to mainly feeding on fish, and the body length node of feeding transition was approximately 130 mm. There were clear seasonal variations in feeding intensity, with the highest intensity in autumn, followed by that in spring and summer, and the lowest in winter. N. japonicus had a high prey diversity; the Shannon-Wiener diversity index (H') was 1.77, and the Pielou evenness index (Jʹ) was 0.64. From spring to winter, the H' and Jʹ values tended to increase and then decrease, and the highest value occurred in autumn, which meant that the feeding niche was the highest in autumn. The number of prey species increased with individual growth, and Hʹ and Jʹ showed an increasing trend with body length. The group with a body length ≥ 160 mm had the largest niche width, which suggested that the food diversity increased with individual growth, and the diet changed to broad-feeding. Based on stable isotope analysis, δ13C was positively correlated with the body length of N. japonicus (P<0.05), indicating that the trophic source changed with growth. The span of the δ13C (CR) range was 2.86%, indicating extensive basic food sources. The span of the δ15N (NR) range was 4.23%, and the trophic span was more than one trophic level, indicating considerable differences in feeding among individuals. A significant positive correlation was found between body length and δ15N (P<0.01), which indicated that the trophic level increased with an increasing body length. The trophic level of N. japonicus ranged from 3.21 to 4.46, with an average value of 3.97, indicating that N. japonicus species were middle-high carnivorous animals, and were at a high trophic level in the fish food web of the Beibu Gulf. The trophic level obtained in this study is higher than that obtained in other studies, which may be related to the changes in the composition of the prey, N. japonicus has shifted from feeding mainly on the low trophic level (crustaceans) to the high trophic levels (fish). In terms of trophic structure, the CR value of N. japonicus in the Beibu Gulf in spring and winter was lower than that in summer and autumn, indicating that the basic food source diversity in spring and winter is lower than that in summer and autumn, however, there are fewer prey species in summer, which might be caused by the feeding preference of N. japonicus. Simultaneously, the NR values in spring and summer were greater than those in summer and autumn, indicating that the span of the main trophic sources in the feed was higher than that in summer and autumn, consistent with the seasonal variation of dominant prey. Although the standard ellipse area (SEA) overlaps to different degrees among seasons, the total niche (TA) had clear seasonal differences, signifying that there were certain similarities and specific differences in prey resource utilization, which is beneficial for alleviating the seasonal pressure on the dominant prey. Furthermore, the CR value in different body length groups of N. japonicus showed an overall upward trend with individual growth, indicating that the food source diversity increased with growth. The NR value decreased when body length was greater than 130 mm, which indicates that the average trophic level of the population was concentrated when individuals grew to a certain stage. The SEA overlap rate was higher among length groups, implying that the trophic source components were similar at different growth stages; however, TA tended to increase and then decrease with body length, which may reduce food competition within species by niche differentiation.