42
red algae, as well as in calcified green Halimeda. In the rhodophyte Corallina officinalis, the processes of inorganic carbon and nutrient uptake and assimilation are
affected by elevated CO 2 due to changes in enzyme activity (Hofmann et al. 2012a).
Ocean acidification can also alter periplasmic electrode potential and affect proton
or ion channels by altering the structure of periplasmic proteins or the activity of
periplasmic extracellular carbonic anhydrase (Gattuso and Hansson 2011).
Acclimation to a rapid change in CO 2 concentration likely affects most photosynthetic processes and associated metabolic activities. At a community level, tank
experiments have shown that the cover of noncalcifying species increases with
increasing pCO 2 (Hofmann et al. 2012a, b). However, the effects of CO 2 -driven pH
changes in noncalcifying seaweeds remain poorly understood, even though these
algae play an important ecological role in modulating marine biodiversity. For
example, Gail (1919) reported that maximum germination in Fucus spp. occurs in
seawater at pH values between 8.0 and 8.2 and the growth of spores, as well as of
larger plants, was inhibited when pH dropped below 7.5. More recently, Zou (2005)
found that growth rates and nitrogen assimilation of the brown seaweed Hizikia
fusiforme were enhanced when grown at relatively high CO 2 levels. Similarly, Xu
et al. (2010) showed that CO 2 enrichment increased growth rate of the red macroalga Gracilaria lemaneiformis. In contrast, the growth rate of the red alga
Porphyra linearis decreased when exposed to high CO 2 levels (Israel et al. 1999).
Zou and Gao (2002) found that some intertidal macroalgae increased the photosynthetic fixation of carbon at high CO 2 levels. At a biochemical level, the cellular
composition of the red alga Porphyra leucosticta was significantly affected by
increased pCO 2 ; while soluble proteins decreased, carbohydrates increased threefold (Mercado et al. 1999). García-Sánchez et al. (1994) reported similar results
while studying the red alga Gracilaria tenuistipitata, and experiments conducted on
Ulva rigida showed that under CO 2 enrichment, this alga has enhanced growth and
net photosynthesis rates but decreased soluble protein and internal carbon contents,
thus maintaining a constant C:N ratio (Gordillo et al. 2001). Recently, Duarte et al.
(2016) registered a decrease in protein and organic matter contents in the tissues of
Durvillaea antarctica (Phaeophyceae) exposed to high pCO 2 levels. Altogether, the
published evidence suggests that algal responses to elevated CO 2 levels are species
dependent and the ways in which CO 2 enrichment affects the physiology of a species are poorly understood.
3.4 Seaweeds as a Study Model for Heavy Metal Toxicity
and Ocean Acidification
Multiple environmental factors are predicted to shift throughout the twenty-first century, and there is an urgent need to examine the interactive effect of these stressors to
estimate potential impacts on the marine environment. Heavy metal enrichment and
ocean acidification may have a particularly wide range of impacts on habitat-forming
seaweed species such as L. spicata (Phaeophyceae), M. pyrifera (Phaeophyceae), and
L. Contreras-Porcia et al.
red algae, as well as in calcified green Halimeda. In the rhodophyte Corallina officinalis, the processes of inorganic carbon and nutrient uptake and assimilation are
affected by elevated CO 2 due to changes in enzyme activity (Hofmann et al. 2012a).
Ocean acidification can also alter periplasmic electrode potential and affect proton
or ion channels by altering the structure of periplasmic proteins or the activity of
periplasmic extracellular carbonic anhydrase (Gattuso and Hansson 2011).
Acclimation to a rapid change in CO 2 concentration likely affects most photosynthetic processes and associated metabolic activities. At a community level, tank
experiments have shown that the cover of noncalcifying species increases with
increasing pCO 2 (Hofmann et al. 2012a, b). However, the effects of CO 2 -driven pH
changes in noncalcifying seaweeds remain poorly understood, even though these
algae play an important ecological role in modulating marine biodiversity. For
example, Gail (1919) reported that maximum germination in Fucus spp. occurs in
seawater at pH values between 8.0 and 8.2 and the growth of spores, as well as of
larger plants, was inhibited when pH dropped below 7.5. More recently, Zou (2005)
found that growth rates and nitrogen assimilation of the brown seaweed Hizikia
fusiforme were enhanced when grown at relatively high CO 2 levels. Similarly, Xu
et al. (2010) showed that CO 2 enrichment increased growth rate of the red macroalga Gracilaria lemaneiformis. In contrast, the growth rate of the red alga
Porphyra linearis decreased when exposed to high CO 2 levels (Israel et al. 1999).
Zou and Gao (2002) found that some intertidal macroalgae increased the photosynthetic fixation of carbon at high CO 2 levels. At a biochemical level, the cellular
composition of the red alga Porphyra leucosticta was significantly affected by
increased pCO 2 ; while soluble proteins decreased, carbohydrates increased threefold (Mercado et al. 1999). García-Sánchez et al. (1994) reported similar results
while studying the red alga Gracilaria tenuistipitata, and experiments conducted on
Ulva rigida showed that under CO 2 enrichment, this alga has enhanced growth and
net photosynthesis rates but decreased soluble protein and internal carbon contents,
thus maintaining a constant C:N ratio (Gordillo et al. 2001). Recently, Duarte et al.
(2016) registered a decrease in protein and organic matter contents in the tissues of
Durvillaea antarctica (Phaeophyceae) exposed to high pCO 2 levels. Altogether, the
published evidence suggests that algal responses to elevated CO 2 levels are species
dependent and the ways in which CO 2 enrichment affects the physiology of a species are poorly understood.
3.4 Seaweeds as a Study Model for Heavy Metal Toxicity
and Ocean Acidification
Multiple environmental factors are predicted to shift throughout the twenty-first century, and there is an urgent need to examine the interactive effect of these stressors to
estimate potential impacts on the marine environment. Heavy metal enrichment and
ocean acidification may have a particularly wide range of impacts on habitat-forming
seaweed species such as L. spicata (Phaeophyceae), M. pyrifera (Phaeophyceae), and
L. Contreras-Porcia et al.