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

Ulva prolifera

Bloom biomass increases with nutrient load

Qingdao, 3 Julio 2008 (El Pais)

156 km2 170.000 tons1.200 vessels20.000 people

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

Altu

ra d

e m

area

(m)

0

Nivel marea baja media

Nivel marea alta media

Limoniastrum monopetalum3.5

Ulva sp.

Typical plant zonation pattern in Cádiz Bay saltmarshes

Nov Dec Jan Feb Mar Apr

Exponential

Stationary

Senescence&

MineralizationInitiation

Stages of macroalgae annual cycle

1. Bloom initiation

Vertical structure of unvegetated sediment and microscale N cycle

Ulva spores from previos cycle germinates when environmental conditions are suitables

O2

O2

1

2

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

1. Bloom initiation

P/R > 1

Water column nutrients

Sediment nutrients

2. Bloom exponential growth

Macroalgae

P/R > 1

-microelectrodes 25-30 µm Ø-vertical resolution 100 µm

2. Bloom exponential growth

Microcosm experiment with healthy macroalgae

- Oxygen microprofiles showed an inhibition of microphytobenthic photosynthetic activity below the macroalgae canopy

- Net metabolism of microbenthic community changed from net autotrophic to heterotrophic

Dep

th (m

)

Dep

th (m

)

2. Bloom exponential growth

Pore water nutrients

2. Bloom exponential growth

Cascading effects of the inhibition of microphytobenthic photosynthetic activity and growth

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

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).

2. Bloom exponential growth

Heterotrophic activity in the sediment consumed previously stored C and N in absence of a fresh source

3. Bloom plateau and senescence

(P/R ≤ 1)

Macroalgae

P/R < 1

3. Bloom plateau and senescence

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

NO3-

O2N2

NO3-

MPB

NH4+

POMD

Nitrification

DNR

N2

NH4+

NH4+

4. Bloom collapse and mineralization

4. Bloom collapse and mineralization

Degradation of macroalgal detritus in a microcosm

t = 0 t = 2

t = 6 t = 20

4. Bloom collapse and mineralization

t = 0 t = 2

t = 6 t = 20

Luz

Oscuridad

Áreas cubiertas

Áreas descubiertas

Oxygen profiles at the sediment-water interface

4. Bloom collapse and mineralization

  - 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:

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.

A. CorzoE. García-RobledoJ. L. Jiménez-AriasD. 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

Gracias por vuestra atención !