Climate Change Effects on Marine Phytoplankton - Marine Ecology in a Changing World - page 74

be aggravated at elevated atmospheric CO 2 concentrations (Schippers et al.
2004). On the other hand, combined ocean CO 2 enrichment with nutrient
depletion in the upper layers due to thermal stratifi cation may cause C-to-
nutrient ratios imbalance with signifi cant implications on phytoplankton
stoichiometry, food quality and on the structure of the pelagic food webs
(van de Waal et al. 2010), as we will discuss later. Accordingly, recent
experiments demonstrated that the composition and structure of fatty acids
in the diatom Thalassiosira pseudonana change signifi cantly when cultivated
under high CO 2 levels, and such changes are likely to permeate the food
web as they constrain somatic growth and eggs production of the copepod
Acartia tonsa (Rossoll et al. 2012).
Overall, contrasting responses-stimulation (Schippers et al. 2004) and
reduction (Steinacher et al. 2009), have been acknowledged concerning
the effects of ocean acidifi cation on global marine primary production,
particularly by shell-forming and calcifying organisms (Riebesell et al.
2000, Kroeker et al. 2010). Indeed, two recent meta-analysis of empirical and
fi eld assessments yielded rather contrasting conclusions on the responses
of marine biota to increased CO 2 (Hendriks et al. 2010, Kroeker et al. 2010).
Meanwhile, other studies reported that marine phytoplankton in general
appear resistant to ocean acidifi cation, showing no increase or decrease
in responses in growth rates under ecological relevant ranges of pH and
CO 2 (Berge et al. 2010). Hence, the extent to which rising atmospheric CO 2
will enhance or reduce global primary production in the oceans remains
equivocal. Further fi eld research and accurate empirical representation of
future projections of the carbonate systems are needed to assess both direct
and indirect effects of ocean acidifi cation on marine phytoplankton.
Water warming
Direct effects on phytoplankton : Temperature is a key parameter that
directly affects physiological rates of marine biota at multiple scales, e.g.,
enzymatic reactions, respiration, body size, generation time, ecological
interactions, community metabolism, etc. (Peters 1983). Phytoplankton
experience an increase in enzymatic activity and growth rates over a
moderate range of temperature rise with an average Q 10 = 1.88 (Eppley 1972),
which suggest that an increase in SST from 18°C today to 21.5°C in 2100
(McNeil and Matear 2006), may lead to an increase of ~25% in growth rate
assuming that there are no other factors (Finkel et al. 2010). Nevertheless,
considering the polyphyletic complexity of the phytoplankton community,
the temperature impact on metabolic rates is intricate by individual species'
vulnerability to warming (Huertas et al. 2011). Further consequences of
rising temperatures are related with the germination of resting spores in
sediments (Shikata et al. 2008). The increase in both water temperature and