Variable food absorption by Antarctic krill: Relationships between diet, egestion rate and the composition and sinking rates of their fecal pellets
Variable food absorption by Antarctic krill: Relationships between diet, egestion rate and the composition and sinking rates of their fecal pellets
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DOI：
10.1016/j.dsr2.2011.06.008
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发表时间：
2012-01-01
影响因子：
3
通讯作者：
Geissler, P. A.
中科院分区：
文献类型：
--
作者：
Atkinson, A.;Schmidt, K.;Geissler, P. A.
浮游动物处理食物的动力学既影响它们的能量平衡，也影响它们粪便颗粒的生物地球化学命运。我们在春季、夏季和秋季对斯科舍海对岸的40只磷虾进行了采样，发现在所有三个季节，它们的吸收和排出的各个方面都有很大的差异。粪便颗粒的C含量从其干质量的0.85%到29%不等(中位数9.8%)，C排泄率变化75倍。颗粒的C：N质量比为4.9~13.2(中位数7.8)，高于磷虾的3.9和食物中的5.4，表明颗粒对N的吸收增强，颗粒沉降率为2 7~1218md(-1)(中位数304md(-1))，主要受颗粒直径(80~6 0 0 mm，平均183 mm)和密度(1.038~1.391 g cm(-3)，平均1.121 g cm(-3))控制。在头两天，颗粒滤料在过滤后的海水中几乎没有碳或氮的损失，并且物理上很坚固。当喂食率低时，肠道通过时间慢，吸收效率高，导致C、N含量低的颗粒排泄率低。这些颗粒致密、致密、下沉快。相反，在良好的饲养条件下，许多食物往往会快速通过肠道，不能被有效吸收，产生富含C和N的缓慢下沉的颗粒。这种“过量摄食”可能会最大限度地提高营养物质的绝对吸收速度。食物组成也很重要：富含硅藻的饮食降低了球团的C含量，但增加了它们的沉降率，这可能是由于二氧化硅的压载。因此，根据磷虾处理食物的方式，它们的颗粒可能既是快速出口的工具，也是缓慢下沉的工具，是远洋食腐动物富含C和N的食物来源。磷虾的摄食率平均为夏季初级生产量的3.4%(摄食率将比这个数字高出2-10倍)，所以无论颗粒的命运如何，磷虾都是食物链中重要的重新包装器。虽然咸水球的下沉速度往往比磷虾快，但后者往往在沉积物圈闭中占优势。我们认为，这是因为磷虾种群更加紧凑，产生的球状颗粒“阵雨”超过了远洋食腐动物对它们进行再加工的能力。(C)2011爱思唯尔有限公司。保留所有权利。
The kinetics of food processing by zooplankton affects both their energy budgets and the biogeochemical fate of their fecal pellets. We sampled 40 schools of krill across the Scotia Sea during spring, summer and autumn and found that in all 3 seasons, every aspect of their absorption and defecation varied greatly. The C content of fecal pellets varied from 0.85% to 29% of their dry mass (median 9.8%) and C egestion rates varied 75-fold. C:N mass ratios of pellets ranged from 4.9 to 13.2 (median 7.8), higher than values of 3.9 in the krill and 5.4 in their food, pointing to enhanced uptake of N. Pellet sinking rates equated to 27-1218 m d(-1) (median 304 m d(-1)), being governed mainly by pellet diameter (80-600 mu m, mean 183 mu m) and density (1.038-1.391 g cm(-3), mean 1.121 g cm(-3)). Pellets showed little loss of C or N in filtered seawater over the first 2 days and were physically robust. When feeding rates were low, slow gut passage time and high absorption efficiency resulted in low egestion rates of pellets that were low in C and N content. These pellets were compact, dense and fast-sinking. Conversely, in good feeding conditions much food tended to pass quickly through the gut and was not efficiently absorbed, producing C and N-rich, slow-sinking pellets. Such "superfluous feeding" probably maximises the absolute rates of nutrient absorption. Food composition was also important: diatom-rich diets depressed the C content of the pellets but increased their sinking rates, likely due to silica ballasting. So depending on how krill process food, their pellets could represent both vehicles for rapid export and slow sinking, C and N-rich food sources for pelagic scavengers. C egestion rates by krill averaged 3.4% of summer primary production (and ingestion rates would be 2-10-fold higher than this) so whatever the fate of the pellets, krill are an important re-packager within the food web. While salp pellets tend to sink faster than those of krill, it is the latter that tend to prevail in sediment traps. We suggest that this is because krill schools are more compact, producing "rain showers" of pellets that exceed the capacity of pelagic scavengers to reprocess them. (C) 2011 Elsevier Ltd. All rights reserved.