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in Thalassia hemprichii net primary production and growth are not affected by nitrate
enrichment. However, Zostera marina seems resistant to CO 2 enrichment, whereas
ocean acidification will increase productivity of seagrass meadows in specific coastal
areas (Palacios and Zimmerman 2007). Jiang et al. (2010) studied the effects of CO 2
enrichment on photosynthesis, growth, and biochemical composition of T. hemprichii.
Their results indicate that T. hemprichii may respond positively to CO 2 -induced ocean
acidification due to its enhanced relative electron transport rate (RETR), minimum
saturating irradiance (E(k)), and enhanced carbon/nitrogen ratio.
However, seagrass habitats can provide true shelter to associated communities of
invertebrate taxa in highly acidified environments (Garrard et al. 2014). Arnold
et al. (2012) found decreased phenolic substances in near undersea CO 2 vents,
which suggest that ocean acidification may alter coastal carbon fluxes by affecting
rates of seagrass decomposition, grazing, and disease diffusion.
6.3.2 Light Stress
The depth of the euphotic zone, where photosynthesis occurs, depends largely on
the concentration of suspended materials in the water column. Thus, with more
dissolved materials, such as in coastal waters, the depth of the euphotic zone will
be shallow, perhaps only a few meters deep. Seagrasses are distributed in depth
gradient; thus, they are adapted to survive in various light intensities. Seagrasses
cope with shifted light spectrum, compared to their terrestrial counterparts,
where ultraviolet, red, and far-red light gradually do not penetrate. Olsen et al.
(2016) observed that genes associated with UV sensing and response and red/
far-red receptors have been eliminated through adaptive gene loss. Genes of UV
light resistance were evolutionary lost in Zostera muelleri (Lee et al. 2016).
Dattolo et al. (2014) revealed that light-associated gene expression profile is connected with depth distribution. Furthermore, the photosynthetic light-harvesting
complex B (LHCB) genes are more abundant in Z. marina probably by enhancing photosynthetic performance at lower irradiances (Olsen et al. 2016).
Phytochrome PHYC is absent in seagrasses probably due to their marine lifestyle,
because the role of this receptor is a red light detection (Franklin et al.2003).
Greco et al. (2013) observed photoreceptors for blue and red in P. oceanica suggesting that the importance of these genes lie within the water column.
Brassinosteroids provide resistance to low light stress in plants (Saini et al. 2015),
and these hormones were also detected in seagrasses (Olsen et al. 2016). On the
other hand, photosystems I and II have been expanded (gene gain) for increased
performance in attenuated light. Light attenuation due to both natural and anthropogenically driven processes leads to reduced photosynthesis. The submarine
light deterioration is one among the most serious threats experienced by the seagrass meadows across the globe (Waycott et al. 2009). Within this context a
plethora of bioindicators has been developed to monitor such environmental
pressures (reviewed in McMahon et al. 2013).
E.E. Malandrakis et al.
in Thalassia hemprichii net primary production and growth are not affected by nitrate
enrichment. However, Zostera marina seems resistant to CO 2 enrichment, whereas
ocean acidification will increase productivity of seagrass meadows in specific coastal
areas (Palacios and Zimmerman 2007). Jiang et al. (2010) studied the effects of CO 2
enrichment on photosynthesis, growth, and biochemical composition of T. hemprichii.
Their results indicate that T. hemprichii may respond positively to CO 2 -induced ocean
acidification due to its enhanced relative electron transport rate (RETR), minimum
saturating irradiance (E(k)), and enhanced carbon/nitrogen ratio.
However, seagrass habitats can provide true shelter to associated communities of
invertebrate taxa in highly acidified environments (Garrard et al. 2014). Arnold
et al. (2012) found decreased phenolic substances in near undersea CO 2 vents,
which suggest that ocean acidification may alter coastal carbon fluxes by affecting
rates of seagrass decomposition, grazing, and disease diffusion.
6.3.2 Light Stress
The depth of the euphotic zone, where photosynthesis occurs, depends largely on
the concentration of suspended materials in the water column. Thus, with more
dissolved materials, such as in coastal waters, the depth of the euphotic zone will
be shallow, perhaps only a few meters deep. Seagrasses are distributed in depth
gradient; thus, they are adapted to survive in various light intensities. Seagrasses
cope with shifted light spectrum, compared to their terrestrial counterparts,
where ultraviolet, red, and far-red light gradually do not penetrate. Olsen et al.
(2016) observed that genes associated with UV sensing and response and red/
far-red receptors have been eliminated through adaptive gene loss. Genes of UV
light resistance were evolutionary lost in Zostera muelleri (Lee et al. 2016).
Dattolo et al. (2014) revealed that light-associated gene expression profile is connected with depth distribution. Furthermore, the photosynthetic light-harvesting
complex B (LHCB) genes are more abundant in Z. marina probably by enhancing photosynthetic performance at lower irradiances (Olsen et al. 2016).
Phytochrome PHYC is absent in seagrasses probably due to their marine lifestyle,
because the role of this receptor is a red light detection (Franklin et al.2003).
Greco et al. (2013) observed photoreceptors for blue and red in P. oceanica suggesting that the importance of these genes lie within the water column.
Brassinosteroids provide resistance to low light stress in plants (Saini et al. 2015),
and these hormones were also detected in seagrasses (Olsen et al. 2016). On the
other hand, photosystems I and II have been expanded (gene gain) for increased
performance in attenuated light. Light attenuation due to both natural and anthropogenically driven processes leads to reduced photosynthesis. The submarine
light deterioration is one among the most serious threats experienced by the seagrass meadows across the globe (Waycott et al. 2009). Within this context a
plethora of bioindicators has been developed to monitor such environmental
pressures (reviewed in McMahon et al. 2013).
E.E. Malandrakis et al.