光裸方格星虫(Sipunculus nudus)生物扰动对混养系统沉积物及间隙水中营养物质的影响

摘要

To study the effects of bioturbation of Sipunculus nudus on the sediment and the pore water, we established a polyculture ecosystem consisting of S. nudus and Mugil cephlus in the laboratory conditions. The experiment was conducted in 20 breeding tanks (diameter 1 m, height 0.8 m, water volumn 550 L). S. nudus [mean weight (1.2±0.1) g] was stocked at four different densities in the sandy sediment at the bottom of the tank: 0 (control), 50, 100 and 150 individuals per tank. In each tank 3 juvenile M. cephlus [mean weight (24.5±0.5) g] were cultured with normal ration supply in a net cage (diameter of 0.8 m, height of 0.6 m). The sediment was prepared in layers: the bottom layer was 6 cm thick medium sand (grain size 0.40–1.10 mm), and the top layer was 1 cm thick fine sand (grain size 0.10–0.28 mm). The results showed that the organic content in the bottom sediment (6–8 cm) in the experimental groups was slightly but insignificantly higher than that in the control group (P>0.05). The contents of nitrate nitrogen (NO3-N), ammonia nitrogen (NH4-N) and soluble reactive phosphorus (SRP) in the pore water increased gradually as the experiment lasted. At the end of the experiment, it was found that the NO3-N content in the bottom pore water was negatively correlated with the density of S. nudus, and it was lower in pore water of the T100 and T150 groups than in the T0 group (P<0.05). The NH4-N content of the pore water in the surface layer was the highest in the T0 group. The TN content in the water column rose along with the increase in the density of S. nudus. During the experiment, the NH4-N content of the bottom pore water in the T100 and T150 groups was significantly higher than that in the T0 group (P<0.05). The lowest NH4-N content was observed in all layers of the pore water in the T50 group. These results suggested that the bioturbation of S. nudus could partly boost the downward transportation of organic content across the sediment, and consequently affect the nutrients content in the pore water.%采用养殖水化学测定方法分析沉积物中有机质和营养盐含量变化，研究方格星虫生物扰动对混养系统中沉积物的生态效应。混养试验在20个养殖桶内(水体积550 L)进行，方格星虫(1.2±0.1 g)养殖在桶底沙层中，其放养密度为0、50、100和150条/桶；鲻(24.5±0.5 g)的放养密度为3尾/桶，养殖在水体中的网箱中(直径0.8 m、高度0.6 m)。试验共分4个处理组(T0、T50、T100和 T150)，每个处理组各设5个重复。结果显示，与对照组(T0)相比，方格星虫组底层(6–8 cm)沙中有机质含量有所增加，但未达到统计学显著差异(P>0.05)。随着试验的进行，4个试验组的间隙水中硝态氮(NO3-N)、氨氮(NH4-N)以及活性磷(SRP)浓度均呈现出升高的趋势。试验结束时，T100和 T150组各层间隙水的 NO3-N 浓度均低于T0组(P<0.05)，且底层间隙水的 NO3-N 浓度随方格星虫密度的增加而降低；T0组表层 NH4-N 浓度高于方格星虫组，而底层氨氮却显著低于高密度方格星虫组(T100和 T150)(P<0.05)。结果表明，方格星虫的生物扰动在一定程度上可以促进沉积物表层的有机质向底层转移，从而影响间隙水中氮、磷营养盐的转化和释放。方格星虫的生物扰动在精养池塘中的底质修复作用仍需进一步研究。