Spread of Alsidium corallinum C. Ag. in a Tyrrhenian eutrophic lagoon dominated by opportunistic macroalgae |
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| Institution: | 1. Lagoon Ecology and Aquaculture Laboratory (LEALab), OPL s.r.l., Via G. Leopardi 9, 58015 Orbetello, Italy;2. Higher Institute for Environmental Protection and Research (ISPRA), Via di Casalotti 300, 00166 Rome, Italy;3. Department of Environmental Science, University of Siena, Via Mattioli 4, 53100 Siena, Italy;1. Department of Electronics and Communication Engineering, Delhi Technological University, Shahbad Daulatpur, New Delhi, 110042, India;2. Department of Electrical and Electronics Engineering, Dogus University, Umraniye, Istanbul, 34775, Turkey;1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. School of Environment, Guangzhou Key Laboratory of Environmental Exposure and Health, and Guangdong Key Laboratory of Environmental Pollution and Health, Jinan University, Guangzhou 510632, China;3. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA;4. University of Chinese Academy of Sciences, Beijing 100049, China;1. College of Chemical Science and Engineering, Teachers College, Qingdao University, Qingdao 266071, China;2. Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China |
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| Abstract: | In 2007, the Rhodophyceae Alsidium corallinum C. Ag., a marine taxon, bloomed in the eutrophic lagoon of Orbetello (Tuscany, Italy) for the first time, becoming the dominant species in spring and summer. In November, its biomass collapsed. The hypothesis examined in this study is that the bloom expressed a relatively low eutrophic level of the ecosystem after intense disposal of accumulated sedimentary organic matter (OM) by dystrophic processes in the two years preceding the bloom. To verify the hypothesis, we compared water physical–chemical variables, sediment redox (Eh) and OM, and standing crops of macroalgae and seagrass from the database of routine monitoring between 2005 and 2008. We also used dissolved nutrient data obtained in 2007 and 2008, as well as data on chlorophyll and total suspended matter in the water column during the microalgal bloom of 2007, and C, N and P content in thalli of the Chlorophycea Chaetomorpha linum and the Rhodophyceae Gracilariopsis longissima and A. corallinum obtained in 2007.In 2007, unusually low values of dissolved inorganic nitrogen (DIN) were recorded. Combined with stable values of soluble reactive phosphorus (SRPs), low DIN led to a reduction of about one order of magnitude in the DIN:SRP atomic ratio with respect to the past and to 2008. G. longissima accumulated C, N and P more than the other species and A. corallinum proved to be less demanding. Sediment OM was lower in the autumn of years characterized by dystrophy, confirming that summer dystrophic events coincided with maximum energy dissipation in this ecosystem. However, as soon as OM and DIN values increased (2008), the vegetation shifted towards blooms of G. longissima and C. linum, while A. corallinum almost disappeared. The results sustain the hypothesis that the bloom of A. corallinum was due to a decline in DIN that limited G. longissima, and to intense turbidity of the water caused by microphytes that developed after the dystrophic event of summer 2006. The latter probably limited the development of C. linum, which could only develop at the edges of the lagoon. |
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