BIOGEOCHEMICAL EFFECTS OF GREEN MACROALGAE BLOOMS FROM INITIATION

BIOGEOCHEMICAL EFFECTS OF GREEN MACROALGAE BLOOMS FROM INITIATION TO COLLAPSE ON AUTOTROPHIC SEDIMENTS 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. alfonso. corzo@uca. es

Bloom biomass increases with nutrient load 156 km 2 170. 000 tons 1. 200 vessels 20. 000 people Ulva prolifera Qingdao, 3 Julio 2008 (El Pais)

Typical plant zonation pattern in Cádiz Bay saltmarshes Pinus pinea Altura de marea (m) Juniperus phoenicea 3. 5 Limoniastrum monopetalum Máximo nivel mareas vivas Sarcocornia sp. Nivel marea alta media Spartina maritima Ulva sp. Zoostera noltii Nivel marea baja media Mínimo nivel mareas vivas 0 Caulerpa prolifera Cymodocea nodosa Limite inferior zona fótica Distancia

Stages of macroalgae annual cycle Exponential Stationary Biomass Initiation Senescence & Mineralization Nov Dec Jan Feb Mar Apr

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

1. Bloom initiation Ulva spores from previos cycle germinates when environmental conditions are suitables 3 2 1 O 2 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 Water column nutrients P/R > 1 Sediment nutrients

2. Bloom exponential growth Macroalgae P/R > 1

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

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

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

2. Bloom exponential growth Heterotrophic activity in the sediment consumed previously stored C and N in absence of a fresh source Table 2. Means sediment contents ± SE of organic carbon (Corg), total nitrogen (N) and Corg: N in the Control and +Macroalgae microcosms during the duration of the experiment (20 days, n = 12). Mean (%) ± SE Corg N Corg: N Control 2. 17 ± 0. 04 0. 22 ± 0. 004 12. 24 ± 0. 20 +Macroalgae 1. 96 ± 0. 04 0. 19 ± 0. 005 13. 72 ± 0. 26

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

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

3. Bloom plateau and senescence - Macroalgae are an important source of MOPD for the sediment and therefore inorganic nutrients - Macroalgae are a important source of DOC, DON and inorganic nutrients for the water column as well

4. Bloom collapse and mineralization NH 4 NO 3 + MPB POMD NH 4+ O 2 NH 4+ N 2 Nitrification NO 3 DNR N 2

4. Bloom collapse and mineralization Degradation of macroalgal detritus in a microcosm

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

4. Bloom collapse and mineralization t=0 t=2 Oxygen profiles at the sediment-water interface 3000 4000 t=1 t=3 t=6 t=14 t=20 3000 2000 1000 0 100 200 300 Profundidad (µm) 0 t =-1000 6 0 t = 20 -2000 -3000 Luz Light -4000 0 200 400 -1000 -2000 -3000 Dark Covered areas Áreas cubiertas Covered areas Áreas descubiertas Uncovered areas Oscuridad -4000 -5000 O 2 (µM) 600

Some calculations for the Cádiz Bay: - 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

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.

The people involved Departamento de Biología, Universidad de Cádiz, 11510 Puerto Real, Spain A. Corzo E. García Robledo J. L. Jiménez Arias D. Villahermosa Instituto de Ciencias Marinas de Andalucía (CSIC). 11510 Puerto Real, Cádiz, Spain S. Papaspyrou Funding - Ministerio de Ciencia e Innovación, Spain ( CTM 2006 -04015/MAR , CTM 200910736) - Junta de Andalucía (P 06 -RNM-01787 PAI/EXCEL ) - European Union (ECOLAGUNES, SOE 1/P 2/F 153)

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