Plankton organisms, biogenic particles, inorganic mineral particles, and microplastics are the four main components of particulate organic matter in aquatic ecosystems. We propose a new index, the Relative Microplastics Concentration (RMC, in %), considering that microplastics are more deleterious when food is scarce. A total of 112 plankton net samples were collected in estuarine, coastal and shelf environments of Tamandaré, Brazil. Particles were identified by image analysis (ZooScan) and FTIR. Higher concentrations of total microplastics, PP (Polypropylene) and PE (Polyethylene) in the estuary indicate an oceanward decreasing gradient from terrestrial sources. Higher concentrations of nylon fibres were found offshore. Yet, RMC indicated that the Bay had the most severely impacted ecosystems (RMC: 2.4% in the estuary, 5.1% in the Bay, and 2.0% on the shelf), for total microplastics and PP & PE. Shelf ecosystems were most severely impacted with nylon fibres. RMC analysis provided a new perspective into the impact of microplastics on tropical coastal food webs.

浮游生物，生物颗粒，无机矿物颗粒和微塑料是水生生态系统中颗粒有机物的四个主要成分。考虑到食物短缺时微塑料的有害性更高，我们提出了一个新的指标，即相对微塑料浓度（RMC，以％为单位）。在巴西塔马达雷的河口，沿海和陆架环境中，总共收集了112个浮游生物网样本。通过图像分析（ZooScan）和FTIR鉴定颗粒。河口中的总微塑料，PP（聚丙烯）和PE（聚乙烯）浓度较高，表明陆地来源的海洋梯度逐渐减小。在海上发现较高浓度的尼龙纤维。然而，RMC指出海湾对生态系统的影响最严重（RMC：河口为2.4％，海湾为5.1％，而2。货架上为0％），用于全部微塑料以及PP和PE。货架生态系统受尼龙纤维的影响最大。RMC分析为微塑料对热带沿海食物网的影响提供了新的视角。