Fecal pellet and egg production rates of copepod species at varying suspended sediment concentrations

We investigated the effect of suspended sediments on the vital rates of the copepods Calanus finmarchicus, Pseudocalanus sp. and Metridia longa in a Greenland sub-Arctic fjord. The fjord had a gradient of suspended particulate matter (SPM) with high concentrations (>50 mg/L) in the inner fjord due to glacial melt water runoff. Laboratory experiments showed that when feeding on the diatom Thalassiosira weissflogii specific ingestion rates were low at high concentrations of suspended sediment for C. finmarchicus (>20 mg/L) and Pseudocalanus sp. (>50 mg/L), while no effect was found for M. longa. For C. finmarchicus, a relatively constant fecal pellet production (FPP) and fecal pellet volume suggested ingestion of sediment, which probably led to reduction in egg production rates (EPRs) at high sediment concentrations. For Pseudocalanus sp., FPP decreased with increasing sediment concentrations, while no effect was observed on EPR. No significant difference was observed in FPP for M. longa feeding on the diatom T. weissflogii compared to the ciliate Strombidium sulcatum. The study shows that high sediment concentrations influence the capability of carbon turnover in C. finmarchicus and Pseudocalanus sp., while M. longa appears to be more tolerant to high sediment loads. Therefore, high concentrations of SPM could potentially influence the species composition of glacially influenced fjords.

本研究针对格陵兰亚北极峡湾内3种桡足类（copepods）——菲玛哲水蚤（Calanus finmarchicus）、假哲水蚤属物种（Pseudocalanus sp.）及长脚足哲水蚤（Metridia longa）——的生命速率受悬浮沉积物（suspended sediments）的影响展开了探究。该峡湾存在悬浮颗粒物（suspended particulate matter, SPM）浓度梯度：受冰川融水径流影响，峡湾内湾的悬浮颗粒物浓度较高（>50 mg/L）。室内实验结果显示，当以硅藻（diatom）威氏海链藻（Thalassiosira weissflogii）为摄食基质时，高悬浮沉积物浓度会使菲玛哲水蚤（>20 mg/L）与假哲水蚤属物种（>50 mg/L）的特定摄食率显著降低，而长脚足哲水蚤未表现出此类响应。对于菲玛哲水蚤，其粪粒产量（fecal pellet production, FPP）与粪粒体积相对恒定，提示其摄入了沉积物，这大概率是高沉积物浓度下其产卵率（egg production rates, EPRs）下降的诱因。对于假哲水蚤属物种，其粪粒产量随沉积物浓度升高而下降，但产卵率未受显著影响。相较于以纤毛虫（ciliate）Strombidium sulcatum为食的对照组，长脚足哲水蚤的粪粒产量无显著差异。本研究表明，高浓度悬浮颗粒物会干扰菲玛哲水蚤与假哲水蚤属物种的碳周转能力，而长脚足哲水蚤对高沉积物负荷的耐受性更强。因此，高浓度悬浮颗粒物或可改变受冰川影响的峡湾内的物种组成。