Eklöf Johan, Austin Åsa, Bergström Ulf, Donadi Serena, Eriksson Britas D H K, Hansen Joakim, Sundblad Göran
Department of Ecology, Environment and Plant Sciences (DEEP), Stockholm University , Stockholm , Sweden.
Department of Aquatic Resources, Swedish University of Agricultural Sciences , Öregrund , Sweden.
PeerJ. 2017 Jan 25;5:e2906. doi: 10.7717/peerj.2906. eCollection 2017.
Organism biomass is one of the most important variables in ecological studies, making biomass estimations one of the most common laboratory tasks. Biomass of small macroinvertebrates is usually estimated as dry mass or ash-free dry mass (hereafter 'DM' vs. 'AFDM') per sample; a laborious and time consuming process, that often can be speeded up using easily measured and reliable proxy variables like body size or wet (fresh) mass. Another common way of estimating AFDM (one of the most accurate but also time-consuming estimates of biologically active tissue mass) is the use of AFDM/DM ratios as conversion factors. So far, however, these ratios typically ignore the possibility that the relative mass of biologically active vs. non-active support tissue (e.g., protective exoskeleton or shell)-and therefore, also AFDM/DM ratios-may change with body size, as previously shown for taxa like spiders, vertebrates and trees.
We collected aquatic, epibenthic macroinvertebrates (>1 mm) in 32 shallow bays along a 360 km stretch of the Swedish coast along the Baltic Sea; one of the largest brackish water bodies on Earth. We then estimated statistical relationships between the body size (length or height in mm), body dry mass and ash-free dry mass for 14 of the most common taxa; five gastropods, three bivalves, three crustaceans and three insect larvae. Finally, we statistically estimated the potential influence of body size on the AFDM/DM ratio per taxon.
For most taxa, non-linear regression models describing the power relationship between body size and (i) DM and (ii) AFDM fit the data well (as indicated by low SE and high ). Moreover, for more than half of the taxa studied (including the vast majority of the shelled molluscs), body size had a negative influence on organism AFDM/DM ratios.
The good fit of the modelled power relationships suggests that the constants reported here can be used to quickly estimate organism dry- and ash-free dry mass based on body size, thereby freeing up considerable work resources. However, the considerable differences in constants between taxa emphasize the need for taxon-specific relationships, and the potential dangers associated with ignoring body size. The negative influence of body size on the AFDM/DM ratio found in a majority of the molluscs could be caused by increasingly thicker shells with organism age, and/or spawning-induced loss of biologically active tissue in adults. Consequently, future studies utilizing AFDM/DM (and presumably also AFDM/wet mass) ratios should carefully assess the potential influence of body size to ensure more reliable estimates of organism body mass.
生物量是生态研究中最重要的变量之一，这使得生物量估计成为最常见的实验室任务之一。小型大型无脊椎动物的生物量通常以每个样本的干质量或无灰干质量（以下简称“DM”与“AFDM”）来估计；这是一个费力且耗时的过程，通常可以通过使用易于测量且可靠的替代变量（如体型或湿（鲜）质量）来加快速度。估计AFDM（生物活性组织质量最准确但也最耗时的估计之一）的另一种常见方法是使用AFDM/DM比率作为转换因子。然而，到目前为止，这些比率通常忽略了生物活性与非活性支持组织（如保护性外骨骼或外壳）的相对质量——因此，AFDM/DM比率——可能随体型变化的可能性，正如之前对蜘蛛、脊椎动物和树木等类群所显示的那样。
我们沿着波罗的海瑞典海岸360公里的一段区域，在32个浅湾收集了水生、底栖大型无脊椎动物（>1毫米）；波罗的海是地球上最大的半咸水体之一。然后，我们估计了14种最常见类群的体型（以毫米为单位的长度或高度）、身体干质量和无灰干质量之间的统计关系；五种腹足纲动物、三种双壳纲动物、三种甲壳纲动物和三种昆虫幼虫。最后，我们从统计学上估计了体型对每个类群的AFDM/DM比率的潜在影响。
对于大多数类群，描述体型与（i）DM和（ii）AFDM之间幂关系的非线性回归模型与数据拟合良好（低标准误差和高[相关指标值]表明了这一点）。此外，在超过一半的研究类群中（包括绝大多数有壳软体动物），体型对生物体的AFDM/DM比率有负面影响。
模拟的幂关系拟合良好，这表明这里报告的常数可用于根据体型快速估计生物体的干质量和无灰干质量，从而节省大量工作资源。然而，不同类群之间常数的显著差异强调了需要特定类群的关系，以及忽视体型所带来的潜在风险。在大多数软体动物中发现的体型对AFDM/DM比率的负面影响可能是由于随着生物体年龄增长外壳越来越厚，和/或成年个体产卵导致生物活性组织损失。因此，未来利用AFDM/DM（可能还有AFDM/湿质量）比率的研究应仔细评估体型的潜在影响，以确保对生物体质量的估计更可靠。
