Effects of ultraviolet radiation and CO2 increase on winter

phytoplankton assemblages in a temperate coastal lagoon

(Ria Formosa, southern Portugal)

Rita B. Domingues1,2, Cátia C. Guerra1, Ana B. Barbosa1, Vanda Brotas2, Helena M. Galvão1

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

Global Climate Change

significant threat to the environment one of the most pressing social concerns of the XXI century affects all biological communities, up to the ecosystem level

Phytoplankton - vital component of aquatic ecosystems- sensitive ecological indicator of environmental changes

Fundamental to detect and forecast ecosystem responses to global climate change

Ultraviolet radiation deleterious effects on nutrient uptake and growth, inhibition of photosynthesis,damage of nucleic acids, oxidative damage…

Carbon dioxide ocean acidification… but may enhance phytoplankton production

UVR + CO2

interactions between them may produce different results than those observed foreach individual variable effects of UVR and CO2 depend on and interact with other environmental drivers(temperature, PAR, nutrients, grazing…)

Ria Formosa coastal lagoon

one of the most important coastal ecosystems in Portugal

breeding and feeding ground for many bird and fishspecies

supports wide range of human activities (fishing,shellfish farming, tourism)

subjected to strong anthropogenic pressures

occurrence of harmful algal blooms

affect food web and human activities

may exacerbate effects of climate change

UVR and T have been increasing in the winter

Aim

Evaluate the effects of UVR and CO2 increase on winter phytoplanktonassemblages in the Ria Formosa coastal lagoon(effects on growth, photosynthesis and community structure)

Methods

January 2012, typical winter conditions (Tw = 13ºC; 10 hours daily solar insolation)

sampling at inner location (to minimize influence of adjacent coastal waters)

sub-superficial water samples collected into 4.5 L UVR-transparent LDPE cubitainers anddifferent spectral and CO2 treatments were prepared

48-hour in situ incubation (based on rapid metabolism of phytoplankton in the RF; doublingtimes - diatoms = 8.1 h, eukaryotic picophytoplankton = 6.5 h, Synechococcus = 16.5 h: Barbosa 2006)

phytoplankton (community and specific) net growth rates (epifluorescence and invertedmicroscopy)

phytoplankton production (14C incorporation – PE curves: Eilers & Peeters 1988)

+CO2

UV-absorbing film (Llumar SHE ER PS7)eliminates >99% UVRtransmits 87% PAR

control

high CO2 UVR + high CO2

UVR

Experimental set-up

PAR + UVRPAR only

Additions of CO32- (as Na2CO3), HCO3

- (as NaHCO3) and HCl 0.01 N to increase pCO2 and DIC to levels expected in 2100

(according to Gattuso et al. 2010)

Results & Discussion - Methodological concerns in phytoplankton/climate change studies

pre-filtration to remove large grazers bottle volume incubation time (Domingues et al. 2011 ECSS; Nogueira et al. in prep.)

cell acclimation after several generations pre-acclimation of cells (Domingues et al. 2014 JPR)

Pre-acclimation of cellsmaintaining cells under the conditions to be tested for a specific period of time before theactual experiment begins can affect already compromised cells and, thus, add artifacts (because cells will be enclosedin a limited volume of water for a longer period)

Acclimation and adaptation of cells after several generations is a possibility in short-term experiments abrupt changes can lead to transient responses and acclimation may then occur within a fewdays (e.g., Satoh et al. 2001)

• most perturbation experiments evaluate only the short-term effects of climate change onphytoplankton – the “worst-case scenario”• microalgae, mainly those with short generation times, are able to respond to climate changethrough adaptive evolution (Lohbeck et al. 2012)

Changes in phytoplankton community growth and structure

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

control highCO2 UVR UVR highCO2

Co

mm

un

ity

net

gro

wth

rat

e (d

-1) no significant changes on community

net growth rates (based on chlorophylla concentration) in relation to the control

But…

significant changes on the relativeabundance of phytoplankton groups

changes in community structure

Dominance of nano-cryptophytes and solitary centric diatoms (Thalassiosira)

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5

10

15

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initial control highCO2 UVR UVR highCO2

Ab

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dan

ce (

x10

5ce

lls L

-1)

diatoms

cryptophytes

cyanobacteria

Effects on specific phytoplankton groups

mortality under UVR exposurelow levels of photoprotection due to their small size

mortality under high CO2 levelscompetition?

mortality under high CO2 and UVRCO2 did not counteract negative effects of UVR

Cyanobacteria

Cryptophytes

Diatoms

no effects of UVR and CO2 on growth rates

diatoms (Thalassiosira) responded positively to high CO2, UVR and UVR + CO2

diatoms are usually more resistant to UVR

enhancement of summer Pseudo-nitzschia blooms?

Effects on phytoplankton production

diatoms clearly benefited from increased CO2 and UVR exposureincreased protection provided by silicon frustuleseffective xantophyll cycledetrimental effect on grazers – grazing pressure - net growth

no significant differences in P-E curves and photosynthetic characteristics under high CO2 and UVR exposure

Conclusions – Effects of UVR and CO2 increase on phytoplankton

taxa-specific responses with changes in phytoplankton community structure

increased cyanobacteria (Synechococcus) mortality

no significant effects on cryptophytes

higher net growth rates of diatoms

no significant changes in production

damaging effect on grazers rather than stimulatory effect on diatoms?

Current/Future prospects

effects of CO2 , UVR and T on phytoplankton mortality (dilution experiments)

effects of CO2 and UVR on nutrient enrichment and uptake (nutrient addition experiments)

36: 672-684 (2014)

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!