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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)
0
5
10
15
20
25
initial control highCO2 UVR UVR highCO2
Ab
un
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!