Phytoplankton nutrient limitation in the Ria Formosa:

implications for eutrophication assessment

Rita B. Domingues1,2, Cátia C. Guerra1, Ana B. Barbosa1, Helena M. Galvão1

1 Centro de Investigação Marinha e Ambiental, Universidade do Algarve2 Centro de Oceanografia, Faculdade de Ciências, Universidade de Lisboa

What is phytoplankton?

unicellular, photosynthetic prokaryotic and eukaryotic organisms whose powers of locomotion are such that they drift freely in the water column

diatoms, dinoflagellates, coccolithophores, cyanobacteria, …

Why is phytoplankton so important?

phytoplankton is the main primary producer in most aquatic ecosystems

phytoplankton is a fundamental player in many ecosystem processes

phytoplankton is a gauge of ecological condition and change

phytoplankton can be used to predict the functioning of aquatic ecosystems and ecosystem responses to natural and anthropogenic perturbations

Studying phytoplankton is not straightforward…

the ecological role played by different phytoplankton groups and species varies significantly

phytoplankton in coastal ecosystems is undergoing marked changes (biomass, composition, phenology) – linked to local anthropogenic influences and climate change

links between environmental and phytoplankton changes are difficult to establish

Importance of nutrients

Nutrient availability is a key driver of phytoplankton dynamics

Nutrient limitation is a central question for eutrophication control

How do nutrients affect phytoplankton growth, diversity and

production?

Assessment of the impact of nutrient enrichment

(eutrophication) and subsequent nutrient reduction strategies

Why the Ria Formosa coastal lagoon?

multiple anthropogenic influences very vulnerable to climate change

phytoplankton regulation is a critical aspect in a fast-changing ecosystem

lack of information on phytoplankton regulation in the Ria Formosa studies are mostly descriptive

Goals• to determine the limiting nutrients for phytoplankton growth and their seasonal variation in the Ria Formosa coastal lagoon

• to understand the effects of potential anthropogenic nutrient enrichment on phytoplankton structure in the Ria Formosa

Project PHYTORIA – Environmental Regulation of Phytoplankton in the Ria Formosa coastal lagoon (PTDC/MAR/114380/2009)

Approaches

nutrient addition experiments in 2 L microcosms containing natural phytoplankton assemblages from the Ria Formosa coastal lagoon

autumn, winter, spring, summer

addition of dissolved inorganic macronutrients, alone and in combinations, in a single, saturating pulse

control+NO3

- +NH4

+ +P +Si +NP +SiN +SiP +NPSi

in situ incubation (under in situ T and light) phytoplankton growth (epifluorescence and inverted microscopy) nutrient consumption

higher N uptake in N-enriched treatments in relation to the control indicate N limitation phytoplankton in the Ria Formosa is N-limited throughout the year

NO3- concentrations up to 12 µM were limiting to phytoplankton

growth

control

Nit Amm P Si NP SiN SiP NPSi-5

0

5

10

15

20

25

30

N u

ptak

e (µ

M d

-1)

control

Nit Amm P Si NP SiN SiP NPSi-5

0

5

10

15

20

25

N u

ptak

e (µ

M d

-1)

control

Nit Amm P Si NP SiN SiP NPSi-2.5

-0.5

1.5

3.5

5.5

7.5

9.5

11.5

13.5

N u

ptak

e (µ

M d

-1)

control

Nit Amm P Si NP SiN SiP NPSi-5

0

5

10

15

20

25

30

35

N u

ptak

e (µ

M d

-1)

Results – N consumption

Autumn

Winter

Spring

Summer

Application of nutrient limitation criteria based on Ks – problems…

Ks obtained for unialgal cultures under equilibrium conditions

Ks vary temporally, spatially, inter- and intraspecifically

Establishment of nutrient criteria

- should consider the seasonal variation of phytoplankton community (different spp. are limited in different ways by different nutrients)

- should consider that limiting concentrations don’t have to be necessarily low concentrations (e.g., in the Guadiana estuary N is limiting up to 20 µM: Domingues et al., 2011)

Results – Establishing nutrient criteria

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

0,5

control N P Si NP SiN SiP NPSi

Co

mm

un

ity

net

gro

wth

rat

e (d

-1)

**

**

**

**

B

spring Initial N = 22 µM

control

Nit Amm P Si NP SiN SiP NPSi-0.5

-0.3

-0.1

0.1

0.3

0.5

0.7

0.9

1.1

Com

mun

ity

net

grow

th r

ate

(d-1

)

Results – Phytoplankton net growth

Increased nutrient uptake

phytoplankton growth

control

Nit Amm P Si NP SiN SiP NPSi0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45N

et g

row

th r

ate

(d-1

)luxury consumption

Summer

Winter

Effects of ultraviolet radiation and CO2 increase on winter

phytoplankton assemblages in a temperate coastal lagoon (Ria

Formosa)

Rita B. Domingues, Ana B. Barbosa, Vanda Brotas

18h15

Bottle effects on microcosm experiments

Effects of nutrient enrichment on bacterioplankton in the RF

Phytoplankton mortality in the Ria Formosa

Acknowledgements

FCT project Phytoria – Environmental regulation of phytoplankton in the Ria Formosa coastal lagoon (PTDC/MAR/114380/2009)

Postdoctoral fellowship awarded to RBD (SFRH/BPD/68688/2010)

Thank You for Your Attention!