_Applied_  
_sciences_  
_Article_  
**Glyphosate-Based Herbicide Toxicophenomics in**  
**Marine Diatoms: Impacts on Primary Production**  
**and Physiological Fitness**  
**[PERSON] 1,2,*(r)**, [PERSON] 1, [PERSON] 3,4(r)**, [PERSON] 5,**  
**[PERSON] 6, [PERSON] 6(r)**, [PERSON] 1,4, [PERSON] 7,**  
**[PERSON] 1,8(r)**, [PERSON] 1,9(r)** and [PERSON] 1,4(r)  
1 MARE--Marine and Environmental Sciences Centre, Faculdade de Ciencias da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal; [EMAIL_ADDRESS] (E.F.); [EMAIL_ADDRESS] (I.C.); [EMAIL_ADDRESS] (P.R.-S.); [EMAIL_ADDRESS] (V.E.F.); [EMAIL_ADDRESS] (B.D.)
2 c3E, Centre for Ecology, Evolution and Environmental Changes, Faculty of Sciences, University of Lisbon, Campo Grande, Edificio C2, Piso 5, 1749-016 Lisbon, Portugal
3 BioIS--Biosystems and Integrative Sciences Institute, Plant Functional Genomics Group, Departamento de Biologia Vegetal, Faculdade de Ciencias da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal; [EMAIL_ADDRESS]
4 Departamento de Biologia Vegetal da Faculdade de Ciencias da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
5 Centro de Estudos Geograficos (CEG), Instituto de Geografia e Ordenamento do Territorio (IGOT) da Universidade de Lisboa, Rua Branca Edmee Marques, 1600-276 Lisboa, Portugal; t [EMAIL_ADDRESS]
6 MARE--Marine and Environmental Sciences Centre, ESTM, Polytechnic of Leiria, 2411-901 Leiria, Portugal; [EMAIL_ADDRESS] (S.C.N.); [EMAIL_ADDRESS] (M.F.L.L)
7 University of Coimbra, MARE--Marine and Environmental Sciences Centre, Department of Life Sciences, 3000 Coimbra, Portugal; [EMAIL_ADDRESS]
8 Southern Seas Ecology Laboratories, School of Biological Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
9 Departamento de Biologia Animal da Faculdade de Ciencias da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
* Correspondence: [EMAIL_ADDRESS]  
Received: 9 September 2020; Accepted: 19 October 2020; Published: 22 October 2020  
**Featured Application: Application of non-invasive bio-optical techniques to evaluate the ecotoxicity of glyphosate-based pesticide in marine diatoms with confirmation by classical biochemical tools.**  
**Abstract:** Glyphosate is the main active component of the commercial formulation Roundup(r), the most widely used chemical herbicide worldwide. However, its potential high toxicity to the environment and throughout trophic webs has come under increasing scrutiny. The present study aims to investigate the application of bio-optical techniques and their correlation to physiological and biochemical processes, including primary productivity, oxidative stress, energy balance, and alterations in pigment and lipid composition in _Phaeodactylum tricornutum_, a representative species of marine diatoms, using the case study of its response to the herbicide glyphosate-based Roundup(r) formulation, at environmentally relevant concentrations. Cultures were exposed to the herbicide formulation representing effective glyphosate concentrations of 0, 10, 50, 100, 250, and 500 \(\mu\)g L\({}^{-1}\). Results showed that high concentrations decreased cell density; furthermore, the inhibition of photosynthetic activity was not only caused by the impairment of electron transport in the thylakoids, but also by a decrease of antioxidant capacity and increased lipid peroxidation. Nevertheless, concentrations of one of the plastidial marker fatty acids had a positive correlation with the highest concentration as well as an increase in total protein. Cell energy allocation also increased with concentration, relative to control and the lowest concentration, although culture growth was inhibited. Pigment composition and fatty acid profiles proved to be efficient biomarkers for the highest glyphosate-based herbicide concentrations, while bio-optical data separated controls from intermediate concentrations and high concentrations.  
photobiology; energetic metabolism; pesticide; oxidative stress; glyphosate