1. alfonso.corzo@uca.es Corzo, A. 1, García-Robledo, E. 1, Papaspyrou, S. 1,2, Jiménez- Arias, J.L. 1, Villahermosa, D. 1 1 Dpto. Biología. Facultad de Ciencias del Mar y Ambientales, Pol. Río San Pedro s/n. 11510- Puerto Real, Cádiz, Spain. 2 Unidad Asociada de Oceanografía Interdisciplinar, UCA-Instituto de Ciencias Marinas de Andalucia— CSIC, Pol. Rio San Pedro s/n, 11510 Puerto Real (Cadiz), Spain. BIOGEOCHEMICAL EFFECTS OF GREEN MACROALGAE BLOOMS FROM INITIATION TO COLLAPSE ON AUTOTROPHIC SEDIMENTS

2. Ulva prolifera Bloom biomass increases with nutrient load Qingdao, 3 Julio 2008 (El Pais) 156 km 2 170.000 tons 1.200 vessels 20.000 people

3. Limite inferior zona fótica Máximo nivel mareas vivas Mínimo nivel mareas vivas Pinus pinea Juniperus phoenicea Spartina maritima Sarcocornia sp. Caulerpa prolifera Zoostera noltii Cymodocea nodosa Distancia Altura de marea (m) 0 Nivel marea baja media Nivel marea alta media Limoniastrum monopetalum 3.5 Ulva sp. Typical plant zonation pattern in Cádiz Bay saltmarshes

4. Biomass NovDecJanFebMarApr Exponential Stationary Senescence & Mineralization Initiation Stages of macroalgae annual cycle

5. 1. Bloom initiation Vertical structure of unvegetated sediment and microscale N cycle

6. Ulva spores from previos cycle germinates when environmental conditions are suitables O2O2 O2O2 1 2 3 NH 4 + NO 3 - NH 4 + NO 3 - NH 4 + NO 3 - The vertical growth of Ulva sp seedlings generate a tridimensional structure in the benthic-pelagic interface favouring nutrient uptake from the water column 1. Bloom initiation

7. P/R > 1 Water column nutrients Sediment nutrients

8. 2. Bloom exponential growth Macroalgae P/R > 1

9. -microelectrodes 25-30 µm Ø -vertical resolution 100 µm 2. Bloom exponential growth Microcosm experiment with healthy macroalgae

10. - Oxygen microprofiles showed an inhibition of microphytobenthic photosynthetic activity below the macroalgae canopy - Net metabolism of microbenthic community changed from net autotrophic to heterotrophic Depth (  m) 2. Bloom exponential growth

11. Pore water nutrients 2. Bloom exponential growth Cascading effects of the inhibition of microphytobenthic photosynthetic activity and growth

12. Mean (%) ± SE C org NC org :N Control 2.17 ± 0.040.22 ± 0.00412.24 ± 0.20 +Macroalgae1.96 ± 0.040.19 ± 0.00513.72 ± 0.26 Table 2. Means sediment contents ± SE of organic carbon (C org ), total nitrogen (N) and C org :N in the Control and +Macroalgae microcosms during the duration of the experiment (20 days, n = 12). 2. Bloom exponential growth Heterotrophic activity in the sediment consumed previously stored C and N in absence of a fresh source

13. 3. Bloom plateau and senescence (P/R ≤ 1)

14. Macroalgae P/R < 1 3. Bloom plateau and senescence

15. - Macroalgae are an important source of MOP D for the sediment and therefore inorganic nutrients - Macroalgae are a important source of DOC, DON and inorganic nutrients for the water column as well

16. NO 3 - O2O2 N2N2 MPB NH 4 + POM D Nitrification DNR N2N2 NH 4 + 4. Bloom collapse and mineralization

17. Degradation of macroalgal detritus in a microcosm

18. t = 0t = 2 t = 6t = 20 4. Bloom collapse and mineralization

19. t = 0t = 2 t = 6t = 20 Luz Oscuridad Áreas cubiertas Áreas descubiertas Oxygen profiles at the sediment-water interface 4. Bloom collapse and mineralization

20. - Area affected by macroalgae blooms in Cadiz Bay: 76.73 Ha - Bloom density measured in Cadiz Bay: 50 - 400 g DW m -2 - 38 ­ 304 tons (dry weight) of Macroalgae - 12 ­ 101 tons of C - 2 ­ 14 tons of N Some calculations for the Cádiz Bay:

21. Conclusions -The biogeochemical impact of macroalgae blooms on the sediment is largely dependent on the physiological stage of the bloom. -The inhibition of MPB photosynthetic activity by shading triggers a number of cascading effects on sediment microbial ecology and biogeochemistry that we are just beginning to understand. -On annual basis, the macroalgae blooms increase the C and N contents of sediment favouring sequestration of C and N. -The storage of C and N would favour the initiation and partially support the macroalgal bloom in the next growing season. - The contribution of the seasonal macroalgae bloom to the total fluxes of C and N in shallow coastal systems is very important and should be better quantify.

22. A. Corzo E. García-Robledo J. L. Jiménez-Arias D. Villahermosa S. Papaspyrou Instituto de Ciencias Marinas de Andalucía (CSIC). 11510 Puerto Real, Cádiz, Spain Departamento de Biología, Universidad de Cádiz, 11510 Puerto Real, Spain The people involved - Ministerio de Ciencia e Innovación, Spain ( CTM2006-04015/MAR, CTM2009- 10736) - Junta de Andalucía (P06-RNM-01787 PAI/EXCEL ) - European Union (ECOLAGUNES, SOE1/P2/F153) Funding

23. Gracias por vuestra atención !