Moore Thomas P, Clearwater Susan J, Duggan Ian C, Collier Kevin J
Environmental Research Institute, School of Science, The University of Waikato, Hamilton, New Zealand.
Department of Conservation, Hamilton, New Zealand.
Sci Total Environ. 2022 Dec 10;851(Pt 1):158124. doi: 10.1016/j.scitotenv.2022.158124. Epub 2022 Aug 19.
Globally-threatened freshwater mussels belonging to the order Unionida (Bivalvia) may be adversely affected by dense beds of submerged macrophytes that modify habitat at the sediment-water interface. Such effects can be particularly pronounced in modified lentic ecosystems such as reservoirs which are subject to hydrological regimes (e.g., hydropeaking) that can exacerbate macrophyte-mediated impacts, including anoxic or hypoxic conditions, the related release of toxic ions (e.g., ammonia), and silt accumulation that inhibits filter-feeding. Accordingly, we compared how population size-structure and biomass of the New Zealand mussel Echyridella menziesii varied inside and outside of dense beds of invasive macrophytes known to have similar impacts on water chemistry (e.g., anoxia) in two northern New Zealand hydroreservoir locations with contrasting hydrology (lacustrine location dominated by Ceratophyllum demersum; and riverine location dominated by Egeria densa). We found adverse sediment-water interface conditions were not always associated with dense submerged macrophyte beds in littoral zones. Nonetheless, where they occurred, adverse sediment-water interface conditions were related to reduced mussel density and adult skewed size-structure, inferring reduced recruitment. Disentangling direct and indirect effects with structural equation modelling indicated that increased pore-water ammonia did not impact these primarily adult populations of freshwater mussels. Increased sediment organic matter, silt, and previously recorded hypoxia and anoxia were exacerbated in the lacustrine section where variable flows promoting water mixing were not present. High densities of mussels <40 mm in length were associated with favourable sediment-water interface conditions of low silt and sediment organic matter, suggesting that enhanced water exchange in and around macrophyte beds may increase juvenile mussel survival in littoral zones of the riverine lake section. Our findings highlight a potential role for hydropeaking management in mitigating the development of adverse physicochemical conditions, and underscore the context-specific effects that dense non-native macrophyte beds can have on mussel populations.
属于蚌目（双壳纲）的全球受威胁淡水贻贝可能会受到水下大型植物密集床层的不利影响，这些大型植物会改变沉积物 - 水界面的栖息地。这种影响在经过改造的静水生态系统（如水库）中可能尤为明显，水库受到水文状况（如水位急剧变化）的影响，这会加剧大型植物介导的影响，包括缺氧或低氧状况、相关有毒离子（如氨）的释放以及抑制滤食的泥沙堆积。因此，我们比较了在新西兰北部两个水文特征不同的水库地点（以金鱼藻为主的湖泊区域；以伊乐藻为主的河流区域），已知对水化学（如缺氧）有类似影响的入侵大型植物密集床层内外，新西兰贻贝Echyridella menziesii的种群大小结构和生物量是如何变化的。我们发现，不利的沉积物 - 水界面条件并不总是与沿岸带的水下大型植物密集床层相关。尽管如此，在它们出现的地方，不利的沉积物 - 水界面条件与贻贝密度降低和成年个体大小结构偏向有关，这意味着补充率降低。用结构方程模型区分直接和间接影响表明，孔隙水中氨的增加并未影响这些主要由成年个体组成的淡水贻贝种群。在没有促进水混合的可变水流的湖泊区域，沉积物有机质、泥沙的增加以及先前记录的缺氧和低氧状况加剧。长度小于40毫米的贻贝高密度与低泥沙和沉积物有机质的有利沉积物 - 水界面条件相关，这表明大型植物床层内外水交换的增强可能会增加河流湖泊区域沿岸带幼体贻贝的存活率。我们的研究结果突出了水位急剧变化管理在减轻不利物理化学条件发展方面的潜在作用，并强调了密集的非本地大型植物床层对贻贝种群可能产生的特定环境影响。
