Effects of key species mud snail Bullacta exarata (Gastropoda) on oxygen and nutrient fluxes at the sediment-water interface in the Huanghe River Delta, China

Since the mud snail Bullacta exarata was introduced for economic aquaculture in the Huanghe River(Yellow River) Delta in 2001, its quick population growth and expanded distribution make it a key-species in the intertidal zone of this area. This significantly contributed to the economic income of the local people, but its potential ecological impact on the benthic ecosystem remains unknown. A mesocosm study was conducted to test whether its bioturbation activities affect the microphytobenthos(MPBs;i.e., sedimentary microbes and unicellular algae)productivity and the nutrient exchange between the sediment-water interface. Our results show that the mud snail significantly impacted the dissolved oxygen(DO) flux across the sediment-water interface on the condition of normal sediment and light treatment, and significantly increased the ammonium efflux during recovery period in the defaunated sediment and dark treatment. The presence of micro-and meiofauna significantly increased the NH4-N flux in dark treatment. Whereas, in light treatment, these small animals had less effects on the DO and NH4-N flux between sediment-water interface. Our results provide better insight into the effect of the mud snail B.exarata on the ecosystem functioning via benthic fluxes.

The behavioral and antioxidant response of the bivalve Gomphina veneriformis to sediment burial effect

A laboratory-based microcosm experiment was carried out to examine both the behavioral and antioxidant response of the clam Gomphina veneriformis under the conditions of 3 types of burial material(sand,silt,silt-sand mixture)with 3 burial depths(5 cm,15 cm,30 cm).The concentration of dissolved oxygen decreased significantly after 3 d of burial in all experimental groups.In silt and sand-silt mixture groups,the interstitial water quality became worsened with lower pH,and higher NH4^(+)-N concentration,where clam mortality occurred simultaneously.However,clam samples in all sand groups and 5 cm,15 cm sand-silt mixture groups survived well for 8 d.Obviously fewer individuals left in the bottom sand in the 15 cm,30 cm silt groups and 30 cm sand-silt mixture groups than in the 5 cm groups.Therefore,it suggests that adding silt and increasing burial depth could stimulate the vertical movement of organisms and cause lethal effects.It was found that the burial depth was the key factor that influenced the activities of antioxidant enzymes,such as superoxide dismutase(SOD)and catalase(CAT).The SOD and CAT activities in the gills and hepatopancreases of organisms both showed significant upregulation in 30 cm burial depth after buried for 8 d.Higher enzyme activities were found in gills than in hepatopancreases,which indicated that the gills of the bivalve G.veneriformis were more susceptible to burial effects than hepatopancreases.Overall,this study shows that sediment burial could cause effects on the biological behavior and antioxidant enzyme activities.

烟台牟平海洋牧场季节性低氧对大型底栖动物群落的生态效应

由于气候变化和人类活动的影响,世界许多海区尤其是近岸海区发生了不同程度的低氧现象,导致海洋动物大量死亡,对海洋生态系统产生了不同程度的影响。为明确烟台牟平海洋牧场低氧对大型底栖动物的生态效应,我们于2016年夏季(6月、8月、9月共3个航次)在该海域进行现场调查,分析低氧对大型底栖动物群落时空变化的影响。结果表明:牟平海洋牧场8月低氧事件发生时,大型底栖动物群落的优势种为短叶索沙蚕(Lumbrinereis latreilli)、不倒翁虫(Sternaspis scutata)和内肋蛤(Endopleura lubrica)。低氧在一定程度上改变了大型底栖动物的群落结构,表现为物种组成和优势种变化上。例如,耐受低氧的机会种数量增加,如短叶索沙蚕;敏感种数量减少,如微小海螂(Leptomya minuta)、长吻沙蚕(Glycera chirori)、大蝼蛄虾(Upogebia major)、极地蚤钩虾(Pontocrates altamarimus)、塞切尔泥钩虾(Eriopisella sechellensis)等。同时,低氧也导致了物种多样性的降低,但丰度和生物量受其影响不明显,这主要是由于机会种短叶索沙蚕丰度和生物量的剧增所致。大型底栖动物不同物种耐受低氧的阈值不同。例如,短叶索沙蚕在溶解氧(DO)<1.0 mg/L受影响最大,在DO=2.0 mg/L时受到的影响不明显,而其他敏感种如微小海螂、大蝼蛄虾、极地蚤钩虾、塞切尔泥钩虾等在DO<2.5 mg/L时,已表现出明显的不适。低氧事件之后,大型底栖动物群落得到一定程度的恢复,其恢复程度和需要的时间长短与低氧发生的程度有关。