Assessment of wet mass, dry mass, ash mass, ash free dry mass, carbon content and nitrogen content of selected coastal bird species and harbor seal tissues

Top predators are relevant indicators of the ecological status of a system and can have a high impact on food webs. But top predators are difficult to include in network analyses because their biomass in ash free dry weight or carbon content is missing. Regression equations were determined for the relationships between fresh weight and dry weight, ash free dry weight, carbon and nitrogen contents respectively for six of the most abundant bird species in the Wadden Sea (Calidris canutus, Limosa lapponica, Haematopus ostralegus, Chroicocephalus ridibundus, Larus canus, Anas penelope) and harbor seals (Phoca vitulina). The relationships for all species were interpreted as linear through the origin. Carbon content vs. fresh weight ratios for birds ranged from 0.16 ± 0.01 to 0.22 ± 0.02. Carbon content vs. fresh weight ratio was 0.17 ± 0.02 on average for harbor seals. This work highlights that the biomass of top predators was often over- or underestimated in previous studies. The determined conversion factors will be useful for future studies to generate more realistic food web models.

顶级捕食者是生态系统状况的重要指示指标，对食物网具有显著调控作用。但由于其无灰干重（ash free dry weight）或碳含量数据缺失，顶级捕食者难以被纳入食物网分析。本研究针对瓦登海（Wadden Sea）6种优势鸟类——红腹滨鹬（Calidris canutus）、黑尾塍鹬（Limosa lapponica）、蛎鹬（Haematopus ostralegus）、棕头鸥（Chroicocephalus ridibundus）、银鸥（Larus canus）、赤颈鸭（Anas penelope）——以及港海豹（Phoca vitulina），分别建立了鲜重与干重、无灰干重、碳含量及氮含量之间的回归方程。所有物种的相关关系均被拟合为过原点的线性模型。鸟类的碳含量与鲜重比值范围为0.16±0.01至0.22±0.02；港海豹的碳含量与鲜重比值平均为0.17±0.02。本研究指出，过往研究中对顶级捕食者生物量的估算常存在高估或低估的问题；本次得到的转换因子可为未来研究构建更贴合实际的食物网模型提供有力支撑。