OCEAN CITIZEN’s pilot site in Tarragona: a mission for coral conservation

One of the pilot sites of OCEAN CITIZEN is located on the Mediterranean coast of Tarragona, Spain. This initiative, led by the University of Barcelona (UB), focuses on addressing the conservation challenges of coral populations in this region. Tarragona’s continental shelf, with its unique ecological characteristics, serves as a critical area for studying and restoring coral habitats. The work being conducted here aims to understand the current state of coral populations, mitigate threats, and develop strategies for their recovery.

The continental shelf off Tarragona stretches approximately 22.5 kilometres and has a gentle slope¹. The seabed is mainly composed of fine sediments, such as fine mud and muddy sand¹. In areas to the north and south of Tarragona, seagrass meadows host a diverse array of protected marine flora and fauna species². Among the most emblematic protected fauna are the seahorse^3,4,5,6,7 (Hippocampus genus), the bottlenose dolphin^3,4,5,6,7 (Tursiops truncatus), and fan mussels (Pinna nobilis and Pinna rudis)^3,6,7. As for flora, seagrass species like Posidonia oceanica^3,4,6,7 and Cymodocea nodosa^3,4,6,7, along with the red algae Lithophyllum byssoides^4,6,7, are key elements of the ecosystem. Furthermore, the area in front of Tarragona is part of the “Delta de l’Ebre – Illes columbretes” protected maritime space, an area covering over 9000 km² and including the entire continental shelf and slope influenced by the sedimentary input of the Ebro River Delta.

Despite its ecological richness, the marine environment of Tarragona faces significant challenges. Coral and gorgonian populations, in particular, are under growing pressure from both human activities and environmental changes. These challenges include fishing practices, such as trawling, which cause physical damage and habitat loss^8,9, and wastewater discharges from marine outfalls that may impact benthic communities¹⁰. In the “Delta de l’Ebre – Illes Columbretes” protected area – which also encompasses the OCEAN CITIZEN restoration sites – over 247 active fishing vessels, including 151 trawlers¹¹, contribute to these pressures, with a cumulative fishing effort in 2024 exceeding 100,000 hours¹¹.

Adding to these anthropogenic threats, climate change poses a major risk to Mediterranean gorgonian populations. Over recent decades, rising sea surface temperatures have led to extreme climate events, including recurrent marine heatwaves¹², which compromise the health and functionality of gorgonian populations^13,14 and can result in mass mortality events^15,16. These combined threats underline the urgency of implementing effective conservation and restoration efforts in the region.

OCEAN CITIZEN is undertaking essential work to characterise baseline coral populations in Tarragona and to carry out effective and targeted restoration efforts. The project’s restoration strategy in Tarragona involves transplanting gorgonians extracted from the port of Tarragona into Smart Enhanced Reefs (SERs). The goal is to restore gorgonian populations at two depths: a shallow site at 30 metres and a mesophotic site at 40 metres. To monitor the marine environment surrounding the restored gorgonians, oceanographic sensors will be installed in the restoration area to measure sea temperature, turbidity, and the direction and velocity of marine currents. Vertical sedimentation fluxes will also be quantified using a sediment trap. The ecological evolution of the restored populations will be closely monitored using divers and a Remotely Operated Vehicle (ROV).

To support these efforts, the project will leverage extremely valuable Local Ecological Knowledge by fostering meaningful collaborations and working closely with local stakeholder groups in the region. These combined approaches aim to enhance our understanding of Tarragona’s marine ecosystem and ensure the conservation and recovery of these habitats in the face of emerging threats.

References:

1. European Commission: Directorate-General for Maritime Affairs and Fisheries, Bruyckere, L., Wrona, K., Vonck, I., Viool, V., Walser, B., & Ludden, V. (2020). Evaluation of the European Marine Observation and Data Network (EMODnet): final report, Publications Office. https://data.europa.eu/doi/10.2771/3245
2. Escudier, R., Clementi, E., Omar, M., Cipollone, A., Pistoia, J., Aydogdu, A., Drudi, M., Grandi, A., Lyubartsev, V., Lecci, R., Cretí, S., Masina, S., Coppini, G., & Pinardi, N. (2020). Mediterranean Sea Physical Reanalysis (CMEMS MED-Currents) (Version 1) [Data set]. Copernicus Monitoring Environment Marine Service (CMEMS). https://doi.org/10.25423/CMCC/MEDSEA_MULTIYEAR_PHY_006_004_E3R1
3. Real Decreto 139/2011, de 4 de febrero, para el desarrollo del Listado de Especies Silvestres en Régimen de Protección Especial y del Catálogo Español de Especies Amenazadas. Boletín Oficial del Estado, 46, de 23 de febrero de 2011. https://www.boe.es/eli/es/rd/2011/02/04/139 
4. Espanya. Ministerio de Medio Ambiente & Programa de les Nacions Unides per a la Defensa del Medi. (1996). Convenio de Barcelona para la protección del Mediterráneo : Programa de las Naciones Unidas para el Medio Ambiente (PNUMA). Ministerio de Medio Ambiente. Secretaría General de Medio Ambiente.
5. Instrumento de ratificación del Convenio relativo a la conservación de la vida silvestre y del medio natural en Europa, hecho en Berna el 19 de septiembre de 1979. Boletín Oficial del Estado, 235, de 1 de octubre de 1986. https://www.boe.es/eli/es/ai/1979/09/19/(1)
6. Corbera, J., Abelló, P., y Gual I. (2009) Peixos i altra vida marina de la platja de Torredembarra. Centre d’Estudis Sinibald de Mas 9: 1-18. ISBN: 978-84-922136-1-0.
7. Folch, J. (2013) El litoral de Tarragona més enllà de la platja: una mirada naturalista al món submarí de la Costa Daurada. Impremta Virgili, Tarragona. DLT-499-13.
8. Lastras, G., Canals, M., Ballesteros, E., Gili, J. M., & Sanchez-Vidal, A. (2016). Cold-water corals and anthropogenic impacts in La Fonera submarine canyon head, Northwestern Mediterranean Sea. PloS one, 11(5), e0155729. https://doi.org/10.1371/journal.pone.0155729
9. González-Irusta, J. M., Cartes, J. E., Punzón, A., Díaz, D., de Sola, L. G., & Serrano, A. (2022). Mapping habitat loss in the deep-sea using current and past presences of Isidella elongata (Cnidaria: Alcyonacea). ICES Journal of Marine Science, 79(6), 1888-1901. https://doi.org/10.1093/icesjms/fsac123
10. Puente, A., & Diaz, R. J. (2015). Response of benthos to ocean outfall discharges: does a general pattern exist?. Marine pollution bulletin, 101(1), 174-181. https://doi.org/10.1016/j.marpolbul.2015.11.002
11. Global Fishing Watch. (2024). Global Fishing Watch. Accessed on December 2024. [dataset]. https://globalfishingwatch.org/map
12. Pisano, A., Marullo, S., Artale, V., Falcini, F., Yang, C., Leonelli, F. E., … & Buongiorno Nardelli, B. (2020). New evidence of Mediterranean climate change and variability from sea surface temperature observations. Remote Sensing, 12(1), 132. https://doi.org/10.3390/rs12010132
13. Gómez‐Gras, D., Linares, C., Dornelas, M., Madin, J. S., Brambilla, V., Ledoux, J. B., … & Garrabou, J. (2021). Climate change transforms the functional identity of Mediterranean coralligenous assemblages. Ecology Letters, 24(5), 1038-1051. https://doi.org/10.1111/ele.13718
14. Sarda, J., Gori, A., Doñate-Ordóñez, R., Viladrich, N., Costantini, F., Garrabou, J., & Linares, C. (2024). Recurrent marine heatwaves compromise the reproduction success and long-term viability of shallow populations of the Mediterranean gorgonian Eunicella singularis. Marine Environmental Research, 106822. https://doi.org/10.1016/j.marenvres.2024.106822
15. Garrabou, J., Coma, R., Bensoussan, N., Bally, M., Chevaldonné, P., Cigliano, M., … & Cerrano, C. (2009). Mass mortality in Northwestern Mediterranean rocky benthic communities: effects of the 2003 heat wave. Global change biology, 15(5), 1090-1103. https://doi.org/10.1111/j.1365-2486.2008.01823.x
16. Garrabou, J., Go ́mez-Gras, D., Medrano, A., Cerrano, C., Ponti, M., Schlegel, R., Bensoussan, N., Turicchia, E., Sini, M., Gerovasileiou, V., Teixido, N., Mirasole, A., Tamburello, L., Cebrian, E., Rilov, G., et al., (2022). Marine heatwaves drive recurrent mass mortalities in the Mediterranean Sea. Global Change Biol. 28 (19), 5708–5725. https://doi.org/10.1111/gcb.16301.
17. Institut Cartogràfic i Geològic de Catalunya. Ortofoto Territorial. Generalitat de Catalunya. https://www.icgc.cat/ca