Body size is a master functional trait that can be used as a bioindicator to assess the impact of disturbance in natural communities. The community size structure responds to biotic and abiotic gradients, including anthropic perturbations across taxa and ecosystems. However, manual measurements of small-bodied organisms such as benthic macroinvertebrates can be time-consuming to carry out. Here, we develop a novel protocol to semi-automatically measure the body size of preserved river macroinvertebrates, which are one of the most used bioindicators to assess freshwater ecosystems. This protocol is adapted from the existing methodology developed to scan marine mesozooplankton with the ZooSCAN. We scanned 98 samples (fine and coarse size fractions) of river macroinvertebrates from 41 sites sampled in Ter, Segre and Besòs basins (NE Iberian Peninsula). The digitalised images were processed with the Zooprocess software to individualise each detected object and obtain several attributes related to size (e.g., ellipsoidal volume), shape, and opacity. A total of 377,410 individual images of the objects were obtained. In order to depict the size structure of macroinvertebrates, we semi-automatically separated the individual images of macroinvertebrates from detritus and artifacts present in the samples. This was achieved with the aid of a learning set through artificial intelligence. We tested the performance of several learning sets created with different subsets of these individual images and classified into different levels of categories attending to morphological aspects. Through cross-validation we selected the most efficient learning set according to recall and precision of macroinvertebrates and detritus and we manually validate it with a subset of 45 samples. Here, we show calibration results, enumerate several challenges in the procedure to take into consideration for further improvements and propose options to improve the method in terms of invested time reduction and accuracy. Overall, results support the use of the ZooSCAN for semi-automated body size measurements of river macroinvertebrates as a valuable tool for bioassessment of freshwater ecosystems

2nd Meeting of the Iberian Ecological Society (SIBECOL), 3-8 July 2022, Aveiro, Portugal

Peer reviewed