1. Effects of ultraviolet radiation
and CO2 increase on winter
phytoplankton assemblages in
a temperate coastal lagoon
(Ria Formosa, Portugal)
Rita B. Domingues1,2, Ana B. Barbosa1, Vanda Brotas2
1Centro 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
Industrial development atmospheric CO2 air temperature
destruction ozone layer UV radiation
Alterations in climate influence organisms
directly – acting on their physiology and phenology
indirectly – modifying their environmental stressors
Affects the whole community, up to the ecosystem level…
Phytoplankton - basilar components of aquatic ecosystems
- sensitive ecological indicators of environmental changes
Key determinant to detect and forecast ecosystem responses to global climate
change

3. Effects of UV radiation on phytoplankton
 depends on intensity and spectral composition and interaction with other
environmental variables
 deleterious effects on nutrient uptake, growth, species composition
 inhibition of photosynthesis
 damage on nucleic acids
 overproduction of reactive oxygen species (ROS), leading to oxidative damage
Effects of CO2 increase on phytoplankton
 CO2 increase ocean acidification – dissolution of calcareous structures
 may enhance phytoplankton production

4. Effects of UVR and CO2 increase on phytoplankton
 UVR and CO2 act together – interactions between them may produce different
results than those observed for each individual variable
 e.g., elevated CO2 may increase sensitivity to UVR; UVR and CO2 may inhibit
photosynthesis
 effects of UVR and CO2 depend on and interact with other environmental
stressors (temperature, PAR, nutrients, …)
Studying the effects of climate change
 most common approach - unialgal cultures, lab-controlled conditions
 in situ response of natural phytoplankton communities and effect of climate change along
seasonal biomass cycle are still largely unknown
 most studies focused on polar and sub-polar areas (destruction ozone layer)
 coastal ecosystems in temperate regions
- provide wide range of ecosystem services and resources
- affected by anthropogenic pressures that can exacerbate effects of climate change

5. 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
assemblage in the Ria Formosa coastal lagoon
(effects on growth, photosynthesis and community structure)

6. Methods
 January 2012, typical winter conditions (Tw = 13ºC)
 sampling at inner location (to avoid influence of adjacent
coastal waters)
 sub-superficial water samples collected into 4.5 L UVR-
transparent LDPE cubitainers
control UVR
high CO2 UVR + high CO2
 48-hour in situ incubation
 phytoplankton (community and specific)
net growth rates (epifluorescence and
inverted microscopy)
 phytoplankton production UV-absorbing film +CO2
(14C incorporation – PE curves)

7. Results - Changes in phytoplankton community growth and structure
0.8
 no significant changes on community
Community net growth rate (d-1)
0.7
net growth rates (based on chlorophyll
0.6
0.5
a concentration) in relation to the control
0.4
0.3
0.2 But…
0.1
0
control highCO2 UVR UVR highCO2
25 diatoms  significant changes on the relative
abundance of phytoplankton groups
Abundance (x105cells L-1)
cryptophytes
20
cyanobacteria
15 changes in community structure
10
5
Dominance of nano-cryptophytes and
0 solitary centric diatoms (Thalassiosira)
initial control highCO2 UVR UVR highCO2

8. Results - Effects on specific phytoplankton groups
 mortality under UVR exposure
Cyanobacteria 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
Cryptophytes
 no effects of UVR and CO2 on growth rates
Diatoms  diatoms (Thalassiosira) responded significantly to
high CO2, UVR and UVR + CO2
 diatoms are usually more resistant to UVR
 enhancement of summer Pseudo-nitzschia blooms?

9. Results - 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
 changes in phytoplankton community structure
 cyanobacteria 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?
Future prospects
 effects of CO2 and UVR on phytoplankton mortality (dilution experiments)
 effects of CO2 and UVR on nutrient enrichment and uptake (nutrient addition
experiments)
 combined effects of CO2, UVR and temperature increase on phytoplankton
dynamics

11. Thank You for Your Attention!
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)