Cottrell Richard S, Black Kenny D, Hutchison Zoë L, Last Kim S
Scottish Association for Marine Science, Oban, Argyll, Scotland, PA37 1QA.
School of Biology, University of St Andrews, St Andrews, Fife, KY16 9ST, Scotland.
PLoS One. 2016 Jan 25;11(1):e0147534. doi: 10.1371/journal.pone.0147534. eCollection 2016.
Aggregate dredging is a growing source of anthropogenic disturbance in coastal UK waters and has the potential to impact marine systems through the smothering of benthic fauna with organically loaded screening discards. This study investigates the tolerance of the blue mussel, Mytilus edulis to such episodic smothering events using a multi-factorial design, including organic matter concentration, temperature, sediment fraction size and duration of burial as important predictor variables.
Mussel mortality was significantly higher in organically loaded burials when compared to control sediments after just 2 days. Particularly, M. edulis specimens under burial in fine sediment with high (1%) concentrations of organic matter experienced a significantly higher mortality rate (p<0.01) than those under coarse control aggregates. Additionally, mussels exposed to the summer maximum temperature treatment (20°C) exhibited significantly increased mortality (p<0.01) compared to those in the ambient treatment group (15°C). Total Oxygen Uptake rates of experimental aggregates were greatest (112.7 mmol m-2 day-1) with 1% organic loadings in coarse sediment at 20°C. Elevated oxygen flux rates in porous coarse sediments are likely to be a function of increased vertical migration of anaerobically liberated sulphides to the sediment-water interface. However, survival of M. edulis under bacterial mats of Beggiatoa spp. indicates the species' resilience to sulphides and so we propose that the presence of reactive organic matter within the burial medium may facilitate bacterial growth and increase mortality through pathogenic infection. This may be exacerbated under the stable interstitial conditions in fine sediment and increased bacterial metabolism under high temperatures. Furthermore, increased temperature may impose metabolic demands upon the mussel that cannot be met during burial-induced anaerobiosis.
Lack of consideration for the role of organic matter and temperature during sedimentation events may lead to an overestimation of the tolerance of benthic species to smothering from dredged material.
在英国沿海水域，集料疏浚是人为干扰不断增加的一个来源，有可能通过用有机负荷较高的筛选弃料覆盖底栖动物，对海洋系统产生影响。本研究采用多因素设计，以有机物浓度、温度、沉积物颗粒大小和掩埋持续时间作为重要预测变量，研究紫贻贝对这类偶发性掩埋事件的耐受性。
仅2天后，与对照沉积物相比，在有机负荷较高的掩埋环境中，贻贝死亡率显著更高。特别是，被掩埋在含有高浓度（1%）有机物的细颗粒沉积物中的紫贻贝标本，其死亡率显著高于被掩埋在粗颗粒对照集料中的标本（p<0.01）。此外，与环境处理组（15°C）相比，暴露于夏季最高温度处理（20°C）的贻贝死亡率显著增加（p<0.01）。在20°C下，粗颗粒沉积物中有机负荷为1%时，实验集料的总摄氧率最高（112.7 mmol m-2 天-1）。多孔粗颗粒沉积物中较高的氧通量率可能是厌氧释放的硫化物垂直迁移至沉积物 - 水界面增加的结果。然而，在贝氏硫菌的细菌垫下紫贻贝的存活情况表明该物种对硫化物具有恢复力，因此我们认为掩埋介质中活性有机物的存在可能促进细菌生长，并通过致病性感染增加死亡率。在细颗粒沉积物稳定的间隙条件下以及高温下细菌代谢增加的情况下，这种情况可能会加剧。此外，温度升高可能会给贻贝带来代谢需求，而在掩埋导致的厌氧状态下这些需求无法得到满足。
在沉积事件中未考虑有机物和温度的作用，可能会导致高估底栖物种对疏浚物料掩埋的耐受性。
