鳑鲏对“蚌-草”关系的影响

重建沉水植物群落是修复浅水富营养化湖泊的关键.河蚌可改善水下光照条件、促进沉水植物生长，因此放养河蚌常被用于沉水植物群落恢复的并行手段.河蚌是鳑鲏产卵的重要基质，因此河蚌可能促进鳑鲏种群发展，而鳑鲏对水生态系统的影响还尚不清楚.本研究以密刺苦草、大鳍鱊和背角无齿蚌为研究对象，通过中宇宙试验研究河蚌和鳑鲏对附着藻的影响，以及鳑鲏对水质和沉水植物生长的影响及机理.结果发现：鳑鲏显著增加了水体总磷、总溶解性磷、总悬浮物和叶绿素a浓度，而对总氮和总溶解性氮浓度的影响不显著.河蚌对苦草的相对生长率、总株数、根冠比及苦草最大叶长均无显著影响，而显著增加了苦草的单株平均生物量，这可能与河蚌组较高的附着藻生物量有关.鳑鲏未显著影响河蚌与苦草间的关系，但鳑鲏的出现显著增加了附着藻类生物量；此外，鳑鲏还降低了苦草的根冠比，而增加了苦草的最大叶长，这可能与鳑鲏引起的营养盐和叶绿素a浓度升高，以及植物表面附着藻生物量显著升高有关.鳑鲏属于小型杂食性鱼类，在长江中下游地区分布广泛，与沉水植物关系密切，且易在修复后的湖泊中形成优势鱼类，因此在湖泊修复和管理中应加强此类小型杂食性鱼类的监测与管理.

Effects of bitterling fish on the relationships between submerged macrophytes and mussel

Submerged macrophytes play an important role in stabilizing the water environments, thus restoration of submerged macrophytes has been the key to the restoration of shallow eutrophic lakes. Meanwhile, mussel stocking has been conducted as a parallel measure for submerged macrophytes restoration, because the filter-feeding mussels can improve and maintain a higher water clarity which it will enhance the growth of macrophytes. However, mussels, acting as an important spawning substrate for bitterling, may also facilitate the population development of bitterling fish (the common name for cyprinid fishes from the subfamily Acheilognathinae). The effects of bitterling fish on aquatic ecosystems are not clear. In the present study, we conducted an outdoor mesocosm experiment to study the effects of bitterling fish on water quality, the growth of submerged macrophytes and the attached periphyton, and the relationship between mussel and macrophytes. Three treatments were set with 4 replicates for each group, they are control (without mussel and bitterlings), mussels (with Sinanodonta woodiana), and mussel-bitterlings treatment (with both A. woodiana and Acheilognathus macropterus), meanwhile all the mesocosms were planted with equal density and biomass of Vallisneria denseserrulata. The results showed that the presence of bitterlings significantly increased the concentrations of total phosphorus, total dissolved phosphorus, suspended solids (TSS, OSS and ISS) and Chl.a of phytoplankton, but not for total nitrogen and total dissolved nitrogen. At the end of the experiment, the growth rate (both RGR and total individual), root-shoot biomass ratio, and maximum leaf length of macrophytes did not differ significantly between the mussel and control mesocosms, while the mean individual biomass of macrophytes in the mussel group was significantly higher than that of the controls which may be related to the higher biomass of periphyton on the surface of macrophytes leaves, though not significant compared with the controls. However, the presence of bitterlings did not significantly affect the mussel-macrophytes relationships. In comparison with the mussel''s treatment, although bitterlings did not affect the RGR and total individuals of macrophytes, the maximum length of leaves was higher in the mussel-bitterling mesocosms than mesocosms with mussels, while the root-shoot biomass ratio was lower. These changes may be caused by the much higher concentrations of nutrients, suspended solids, Chl.a of phytoplankton and biomass of periphyton on the surface of leaves induced by the bitterlings which may boosted the growth of macrophytes leaves. Our results have important implications for lake management and restoration: bitterling is a small omnivorous fish which is widely distributed in lakes in the middle and lower reaches of Yangtze River. Moreover, they are highly correlated with submerged macrophytes and recovered quickly after lake restoration, so the monitoring and management of the small omnivorous fish, like bitterling in our study, should be strengthened when restoring and managing of shallow lakes.