Factors influencing biodeposit production by the New Zealand freshwater mussel Echyridella menziesii

Laboratory experiments on the New Zealand freshwater mussel Echyridella menziesii were used to investigate the short-term effects (7–8 days) of food type on rates of biodeposition and benthic substrate respiration. Post-feeding biodeposition rates ranged from 0.34 to 1.52 mg g−1 h−1 (mean = 0.50 mg g−1 h−1) and were unaffected by the addition of toxin-producing Microcystis. Addition of suspended sediment (30 mg L−1) visibly altered substrate composition, and increased total and inorganic biodeposit production rates by 24–33% compared to mussels fed commercial phytoplankton stock. Biodeposition rates of mussels in lake bed substrates were 38% higher than those in silica sand for identical feeding regimes, suggesting that a significant proportion of material produced in this experiment could have been derived from feeding on organic matter in the lake bed sediments. Respiration rates were higher in treatments with Microcystis but were unaffected by the presence of mussels. This laboratory study suggests that biodeposition by E. menziesii is resilient to short-term exposure to Microcystis, and highlights the ability of mussels to alter benthic substrate composition by incorporating suspended sediment into substrates.

本研究以新西兰淡水贻贝（Echyridella menziesii）为对象开展室内实验室实验，旨在探究食物类型对生物沉积（biodeposition）速率及底栖基质（benthic substrate）呼吸作用的短期影响（实验时长为7~8天）。实验结果显示，摄食后的生物沉积速率介于0.34~1.52 mg g⁻¹ h⁻¹之间，平均值为0.50 mg g⁻¹ h⁻¹，且添加产毒微囊藻（Microcystis）对该速率无显著影响。添加浓度为30 mg L⁻¹的悬浮沉积物（suspended sediment）可显著改变底质组成；相较于投喂商用浮游植物饵料（commercial phytoplankton stock）的贻贝组，该组的总生物沉积量与无机生物沉积量分别提升24%~33%。在相同投喂方案下，湖床基质组贻贝的生物沉积速率较石英砂（silica sand）组高出38%，这表明本实验中产生的大部分生物沉积物可能源自对湖床沉积物中有机质的摄食。此外，添加微囊藻的实验组呼吸速率更高，但贻贝的存在与否对呼吸速率无显著影响。本室内实验证实，E. menziesii的生物沉积作用对短期暴露于微囊藻的环境具备耐受能力，同时揭示了贻贝可通过将悬浮沉积物整合到底质中，进而改变底栖基质组成的能力。