This document summarizes a study on the effects of increased ultraviolet radiation and carbon dioxide on winter phytoplankton assemblages in the Ria Formosa coastal lagoon in Portugal. The study found that specific phytoplankton groups responded differently, with cyanobacteria experiencing higher mortality, while diatoms showed higher net growth rates under increased CO2 and UV exposure. There were also changes in the phytoplankton community structure, but no significant effects on overall production. The results indicate that climate change could impact phytoplankton communities through taxon-specific responses.

1. 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 Algarve
2 Centro de Oceanografia, Faculdade de Ciências, Universidade de Lisboa

2. 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 for
each individual variable
 effects of UVR and CO2 depend on and interact with other environmental drivers
(temperature, PAR, nutrients, grazing…)

3. Ria Formosa coastal lagoon
 one of the most important coastal ecosystems in Portugal
 breeding and feeding ground for many bird and fish
species
 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 phytoplankton
assemblages in the Ria Formosa coastal lagoon
(effects on growth, photosynthesis and community structure)

4. 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 and
different spectral and CO2 treatments were prepared
 48-hour in situ incubation (based on rapid metabolism of phytoplankton in the RF; doubling
times - diatoms = 8.1 h, eukaryotic picophytoplankton = 6.5 h, Synechococcus = 16.5 h: Barbosa 2006)
 phytoplankton (community and specific) net growth rates (epifluorescence and inverted
microscopy)
 phytoplankton production (14C incorporation – PE curves: Eilers & Peeters 1988)

5. +CO2
UV-absorbing film (Llumar SHE ER PS7)
eliminates >99% UVR
transmits 87% PAR
control
high CO2 UVR + high CO2
UVR
Experimental set-up
PAR + UVRPAR only
Additions of CO3
2- (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)

6. 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 cells
 maintaining cells under the conditions to be tested for a specific period of time before the
actual experiment begins
 can affect already compromised cells and, thus, add artifacts (because cells will be enclosed
in 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 few
days (e.g., Satoh et al. 2001)
• most perturbation experiments evaluate only the short-term effects of climate change on
phytoplankton – the “worst-case scenario”
• microalgae, mainly those with short generation times, are able to respond to climate change
through adaptive evolution (Lohbeck et al. 2012)

7. 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
Communitynetgrowthrate(d-1)
 no significant changes on community
net growth rates (based on chlorophyll
a concentration) in relation to the control
But…
 significant changes on the relative
abundance of phytoplankton groups
changes in community structure
Dominance of nano-cryptophytes and
solitary centric diatoms (Thalassiosira)
0
5
10
15
20
25
initial control highCO2 UVR UVR
highCO2
Abundance(x105cellsL-1)
diatoms
cryptophytes
cyanobacteria

8. Effects on specific phytoplankton groups
 mortality under UVR exposure
low levels of photoprotection due to their small size
 mortality under high CO2 levels
competition?
 mortality under high CO2 and UVR
CO2 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?

9. Effects on phytoplankton production
 diatoms clearly benefited from increased CO2 and UVR exposure
increased protection provided by silicon frustules
effective xantophyll cycle
detrimental effect on grazers – grazing pressure - net growth
 no significant differences in P-E curves and photosynthetic characteristics under
high CO2 and UVR exposure

10. 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)

11. 36: 672-684 (2014)

12. 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!