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Collapse of macrophytic communities in a eutrophicated coastal lagoon.

2019; Frontiers Media; Volume: 6; Linguagem: Inglês

10.3389/conf.fmars.2019.08.00192

2296-7745

Maria Dolores Torrente, Juan M. Ruíz, R. Velez Muñoz, Aranzazu Segura, Jaime Bernardeau Esteller, Judit Casero, Lázaro Guirao, Pedro A. Moreno, Ignacio Navarro, Eugenio Oliver Fraile Nuez, Jesús M. Mercado,

Marine and coastal plant biology

Event Abstract Back to Event Collapse of macrophytic communities in a eutrophicated coastal lagoon. Maria Dolores B. Torrente1, Juan M. Ruiz1*, Rocío G. Muñoz1, Aranzazu R. Segura1, Jaime B. Esteller1, Judit J. Casero1, Lázaro M. Guirao1, Pedro G. Moreno2, Ignacio F. Navarro1, Eugenio F. Nuez3 and Jesús M. Mercado4 1 Oceanographic Center of Murcia, Spanish Institute of Oceanography, Seagrass Ecology Group, Spain 2 Association of Naturalists of the Southeast (ANSE), Spain 3 Instituto Español de Oceanografía (IEO), Oceanographic Center of Canarias, Spain 4 Oceanographic Center of Málaga, Spanish Institute of Oceanography (IEO), Spain Marine ecosystems can experience sudden and unexpected catastrophic shifts to impoverished and undesirable states in response to environmental changes (Scheffer et al. 2001). Coastal habitats based on one or few engineer, foundation species such as those represented by macroalgae and seagrasses are particularly sensitive to these abrupt changes (Maxwell et al. 2016). In the present study we provide relevant information about the extensive and abrupt benthic macrophytes die-off recorded in one of the major Mediterranean coastal lagoons (Mar Menor; SE Spain) during an unprecedented period of turbid waters caused by a massive phytoplankton bloom (Figure 1). This relevant ecosystem remained in a clear-water state dominated by submerged vegetation during decades (Belando et al. 2019), despite the huge amounts of nutrients delivered into the lagoon from intensive agriculture practices (Velasco et al. 2006) and the limited water exchange of this semi-enclosed water body. The high resilience of this ecosystem to increased human pressures was likely associated to the existence of feedback mechanisms typically associated to benthic vegetation (e.g. high capacity to remove nutrients and particles from water column; Maxwell et al. 2016) and the phenotypic plasticity of the dominant species to buffer population responses to environmental changes (Marín-Guirao et al., 2019). However, the turbid-water period could have surpassed the environmental thresholds (i.e. light reduction) beyond which dampening mechanisms fail and vegetated seabed can rapidly shift to an unvegetated, bare state. Figure 1. Upper panel: evolution of chlorophyll a in the Mar Menor lagoon between 1980 and 2018, obtained by spectrophotometric determination from seawater samples; Central panel: evolution of chlorophyll a in the period 1998-2018 obtained from analysis of satellite images (the red line correspond to values obtained from water samples determinations); Lower panel: evolution of water turbidity (light attenuation coefficient k, m-1) and percentage of surface irradiance obtained at 3 m depth by direct measurement of PAR irradiance using a submergible photometer. Source: IEO-MMEM project, unpublished data. The aim of this study was to provide precise and robust evidence of the magnitude and dynamic of the apparent regime shift experienced by the Mar Menor lagoon, as well as to get some insights about factors that have driven such abrupt changes. We used standard methods of marine vegetation mapping (i.e. a combination of lineal transects using SCUBA diving and trawled underwater videocamera and satellite images; Short & Coles 2001) to obtain georeferenced and precise distribution limits of the main types of submerged vegetation (i.e monospecific and mixed meadows of the aquatic angiosperms Ruppia cirrhosa and Cymodocea nodosa and the chlorophyte Caulerpa prolifera). A first sampling approach was performed in autumm 2016 and a new sampling campaign was performed about one year before (summer 2017) using both direct and indirect visual methods. Georeferenced data was integrated in a Geographic Information System (© ArcGis 10.2) to obtain interpolated maps of macrophytes distribution and to estimate the surface area occupied by each vegetation type. The resulting maps were compared with data obtained by this research team using the same methodology in 2014, just before the turbidity event (Belando et al. 2019; Figure 2). Figure 2. Maps of macrophyte communities of the Mar Menor lagoon obtained in 2014 by Belando et al (2019) and in 2016 and 2017 in this study. The red line showed in the 2017 map correspond to the maximum depth limit of macrophytes on that year. Map leyend: C. nodosa (organge), C. prolifera (dark green), mixed meadow C. nodosa-C. prolifera (green), R. cirrhosa (pink) and silty unvegetated bottoms (yellow). Our results showed total absence of macrophytes beyond a depth limit between 1-2.5 m in autumm 2016 (Figure 2), evidencing that most areas in the lagoon have shifted to an unvegetated state characterized by muddy and silty sediments (Figure 3). This represents a massive total loss of 86.2% of the surface area covered by macrophytes in 2014,. The remaining vegetated bottoms were all concentrated in the very shallow areas of the lagoon, suggesting that the light limitation favored by turbid waters could be a primary factor involved in this sudden, catastrophic shift. This is consistent with the drastic reduction of PAR irradiance recorded during at least 9 months in 2016 (i.e. less than 5% of subsurface downward irradiance; Figure 1), when light levels were far bellow the minimum requirements for the dominant macrophytes C. nodosa and C. prolifera. Despite this evidence, other environmental factors such as the temperature anomaly recorded in 2015 , which could have favored the phytoplankton bloom initiation, may have also contributed to the subsequent loss of submerged vegetation. Figure 3. Comparison of images obtained in a fixed sampling site at 4-5 m depth showing the macrophyte-dominated state documented in 2014 (left) and the shift to an unvegetated state dominated by highly anoxic silty sediments in 2016 (right). In the period 2016-2017 the total vegetated area increased by 4,421 hectares, which represent a recovery of 38.9% of the area lost in the precedent period. Most of this recolonized area corresponded to monospecific meadows of C. prolifera between the vegetation depth limit recorded in 2016 and the 4.5 m isobaths (Figure 2). This rapid recolonization can be explained by the recovery of water transparency during the macrophytes growing season (from March to July 2017; Figure 1) and the very fast growing rates of this opportunistic alga. By contrary, the seagrass C. nodosa, with considerably lower growth rates ,only recolonized 0.87% of the lost area during the same period. This work has evidenced that macrophyte-dominated marine ecosystems can follow a non-lineal dynamic response to sustained eutrophication, experiencing a sudden collapse after a long period of apparent stability. The ecosystem shifted to an unvegetated state once a critical environmental threshold has been surpassed, even in a single disturbance event (phytoplankton bloom). After collapse, our results suggest that the rate and fate of the recovery path up to the former vegetated state will depend on a complex interplay between the inherent characteristics of the species, recovery of water-column conditions and climatic variability. Therefore, the patterns of macrophyte community recovery could be complex with the potential to follow nonlineal dynamics or “hysteresis”thatcan lead to bistability in the ecosystem (Scheffer et al. 2001). Moreover, the rapid recolonization rate showed by C. prolifera could represent a positive feedback mechanism favoring the recovery process, but the lack of such response by the seagrass C. nodosa means that ecosystem could remain in a state with lowered resilience and hence more vulnerable to future disturbance events. Figure 1 Figure 2 Figure 3 Acknowledgements This study has been funded by the Biodiversity Foundation of the Spanish Ministry of Ecological Transition (projects FBCC2019 and G30072540). This project is also part of the UMBRAL project (Ref. CTM2017-86695-C3-2-R) funded by the National Research Programme of the Spanish Ministry of Science, Innovation and University. References Belando M, Bernardeau-Esteller J, Paradinas I, Marín-Guirao L, Ramos-Segura A, Garcia-Muñoz R, García-Moreno P and Ruiz JM. 2019. Assessment of long-term interaction between an opportunistic macroalga and a native seagrass in a Mediterranean coastal lagoon . Front. Vet. Sci. Conference Abstract: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) . Marín-Guirao L, Bernardeau-Esteller J, Belando M, Cerezo I, Pérez E, Ramos A, Muñoz RG and Ruiz JM. 2019. Physiological tipping points to light reduction underlie seagrass population collapse and abrupt shift in a shallow coastal lagoon. Front. Vet. Sci. Conference Abstract: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) . Maxwell PS, Eklöf JS, van Katwijk MM, O’Brien R, de la Torre-Castro M., Böstrom M, Bouma J, Krause-Jensen D, Unsworth RFK, van Tussenbroek BI and van der Heide. 2016. The fundamental role of ecological feedback mechanisms for the adative management of seagrass ecosystems –a review. Biological Reviews. https//doi: 10.1111/brv.12294. Short F. & R.G. Coles (Eds.) 2001. Global seagrass research methods. Elsevier, 482 pp. Scheffer M, Carpenter S, Foley JA, Folke C, Walker B. 2001. Catastrophic shifts in ecosystems. Nature, 413, 591–596. https://doi.org/10.1038/35098000 Velasco J, Lloret J, Millan A, Marín A, Barahona J, Abellán P & Sánchez-Fernández D. 2006. Nutrient and particulate inputs into the Mar Menor lagoon (SE Spain) from an intensive agricultural watershed. Water, Air and Soil Pollution 176: 37-56. https://doi: 10.1007/s11270-006-2859-8. Keywords: Eutrophication, Ecosystem shift, Nonlineal responses, Cymodocea nodosa, Caulerpa prolifera Conference: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019. Presentation Type: Oral Presentation Topic: Ecology, Biodiversity and Vulnerable Ecosystems Citation: Torrente MB, Ruiz J, Muñoz RG, Segura AR, Esteller JB, Casero JJ, Guirao LM, Moreno PG, Navarro IF, Nuez EF and Mercado JM (2019). Collapse of macrophytic communities in a eutrophicated coastal lagoon.. Front. Mar. Sci. Conference Abstract: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) . doi: 10.3389/conf.fmars.2019.08.00192 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 May 2019; Published Online: 27 Sep 2019. * Correspondence: Dr. Juan M. Ruiz, Oceanographic Center of Murcia, Spanish Institute of Oceanography, Seagrass Ecology Group, Murcia, Murcia, Spain, juanm.ruiz@ieo.es Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Maria Dolores B Torrente Juan M. Ruiz Rocío G Muñoz Aranzazu R Segura Jaime B Esteller Judit J Casero Lázaro M Guirao Pedro G Moreno Ignacio F Navarro Eugenio F Nuez Jesús M Mercado Google Maria Dolores B Torrente Juan M. Ruiz Rocío G Muñoz Aranzazu R Segura Jaime B Esteller Judit J Casero Lázaro M Guirao Pedro G Moreno Ignacio F Navarro Eugenio F Nuez Jesús M Mercado Google Scholar Maria Dolores B Torrente Juan M. Ruiz Rocío G Muñoz Aranzazu R Segura Jaime B Esteller Judit J Casero Lázaro M Guirao Pedro G Moreno Ignacio F Navarro Eugenio F Nuez Jesús M Mercado PubMed Maria Dolores B Torrente Juan M. Ruiz Rocío G Muñoz Aranzazu R Segura Jaime B Esteller Judit J Casero Lázaro M Guirao Pedro G Moreno Ignacio F Navarro Eugenio F Nuez Jesús M Mercado Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.