Article Ants as Bioindicators of Riparian Ecological Health in Catalonian Rivers Vera Zina 1 , Marc Ordeix 2 , José Carlos Franco 1 , Maria Teresa Ferreira 1 and Maria Rosário Fernandes 1, *   Citation: Zina, V.; Ordeix, M.; Franco, J.C.; Ferreira, M.T.; Fernandes, M.R. Ants as Bioindicators of Riparian Ecological Health in Catalonian Rivers. Forests 2021, 12, 625. https://doi.org/10.3390/ f12050625 Academic Editor: Young-Seuk Park Received: 20 March 2021 Accepted: 11 May 2021 Published: 14 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal; verazina@isa.ulisboa.pt (V.Z.); jsantossilva@isa.ulisboa.pt (J.C.F.); terferreira@isa.ulisboa.pt (M.T.F.) 2 Centre d’Estudis dels Rius Mediterranis, Universitat de Vic-Universitat Central de Catalunya, Museu del Ter, Passeig del Ter, 2 08560 Manlleu, Spain; marc.ordeix@uvic.cat * Correspondence: mrfernandes@isa.ulisboa.pt Abstract: In this study, we assess the potential of ants as bioindicators of riparian ecological health in two river types (upland and lowland type) located in the Catalonian region. We proposed to understand to what extent do metrics based on ant responses provide useful information that cannot be presented by traditional biophysical assessments while attempting an approach to creating an ant-based multimetric index (ant-based MMI) of the riparian ecological health. A total of 22 ant species were identified, and 42 metrics related to ant foraging activity, species richness, and functional traits were evaluated as potential core metrics of the index. Riparian features and proximal land use land cover (LULC) were used to distinguish disturbed from less disturbed sites. We found that ant communities strongly responded to human disturbance. When compared with an exclusively physical-based index for the assessment of the riparian health, the ant-based MMI was more sensitive to human disturbance, by also reacting to the effects of the surrounding LULC pressure. This study provides a preliminary approach for an ant-based assessment tool to evaluate the health of riparian corridors although additional research is required to include other river types and a wider stressor gradient before a wider application. Keywords: ant metrics; biodiversity; Formicidae; functional index; Iberian Peninsula; integrity; riverscapes 1. Introduction Riparian zones are complex multidimensional systems, responsible for many ecolog- ical functions considered crucial to the preservation of river well-being [1,2]. Different ecosystem services are also provided by riparian systems, at different spatial scales [3]. These highly dynamic ecosystems are driven by environmental factors and human dis- turbance that shape their structural and compositional attributes [4,5]. In particular, land use land cover (LULC) pressure, such as urban and agricultural intensification within the vicinity, has been pointed out as the main cause of riparian ecological degradation in the Mediterranean region [6–9]. Therefore, the monitoring and management of riparian areas are increasingly important [3]. A key component of any riparian monitoring and management program, whether for habitat preservation or restoration, is the assessment of their ecological health and/or integrity. Ecological integrity implies the capacity to support and maintain a balanced, integrated and adaptive biological system whereas ecological health also includes the notion of what society values in the ecosystem [10–12]. There is an urgent need to develop methodologies for evaluating riparian ecological health from a multiple and integrated perspective. Most of the methods are based on phys- ical aspects (e.g., channel and riverbank alterations), vegetation composition (e.g., exotic vs. native species) or structural indicators (e.g., vegetation cover, width, connectivity) [13–16], lacking a biological-based assessment [17]. Forests 2021, 12, 625. https://doi.org/10.3390/f12050625 https://www.mdpi.com/journal/forests