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angiosperms, root/rhizome anoxia interrupts the translocation of sucrose from
leaves and induces alcoholic fermentation in these belowground tissues (Pregnall
et al. 1984; Smith et al. 1984; Zimmerman and Alberte 1996). When deprived of
oxygen, most facultative anaerobes (including most angiosperms) exhibit a Pasteur
effect that increases the rate of glycolysis to maintain ATP production necessary for
metabolic function. The resulting ability to tolerate anoxia is linked to the supply of
glucose, and anoxic death results when tissues become depleted of sugar reserves
and cannot maintain ATP and NADPH production (Bailey-Serres and Voesenek
2008). Seagrass roots, however, exhibit a low-oxygen quiescence strategy (LOQS),
in which the onset of anoxia reduces the rate of metabolic glucose consumption and
ATP production. The reduced nighttime carbon demand of anaerobic tissues extends
the period of anoxia tolerated by eelgrass roots and further reduces carbon demand
by belowground tissues (Smith et al. 1988; Zimmerman et al. 1996). The LOQS
appears to be highly conserved among vascular plants to maintain cellular homeostasis under low-O 2 stress and enables the synthesis of proteins involved in
metabolite transport, protection from reactive oxygen species (ROS), and chaperone
activity (Voesenek and Bailey-Serres 2015).
Finally, all species of seagrasses (except Enhalus spp.) are adapted for completely submerged pollination. The filiform pollen grains of Zostera marina tumble
as they encounter turbulent velocity gradients induced by the anatomy of flowers
and inflorescences, increasing the probability of attachment to the stigmatic surfaces (Ackerman 2006). In Thalassia testudinum, invertebrates may also facilitate
pollen transfer from male flowers to female stigma (van Tussenbroek et al. 2016).
8.2.2 Sensitivity to Environmental Change Results from High
Light Requirements
Although seagrasses possess a remarkable assemblage of successful adaptations to
a submerged aquatic life history, their light requirements for survival are 10- to
20-fold higher than many marine autotrophs, which renders them vulnerable to a
variety of habitat disturbances, often of anthropogenic origin (Duarte 1991; Short
and Wyllie-Echeverria 1996). More than 40 large-scale seagrass declines involving
at least 24 different species were reported worldwide during the twentieth century,
and the losses have continued to the point where seagrasses may be nearing a crisis
with respect to global sustainability (Orth et al. 2006; Short et al. 2011).
Eutrophication, which promotes the growth of light-absorbing phytoplankton and
opportunistic macroalgae, is a critical factor in many of these disturbance events,
including the extensive and persistent losses throughout the Chesapeake Bay, USA
(Orth and Moore 1983). However, even when algal competitors are brought under
control, seagrass recovery can be hampered by the destabilization and resuspension
of marine sediments that further reduces light availability to the benthos (Lawson
et al. 2007; Carr et al. 2010; McPherson et al. 2011).
8 Systems Biology and the Seagrass Paradox…
angiosperms, root/rhizome anoxia interrupts the translocation of sucrose from
leaves and induces alcoholic fermentation in these belowground tissues (Pregnall
et al. 1984; Smith et al. 1984; Zimmerman and Alberte 1996). When deprived of
oxygen, most facultative anaerobes (including most angiosperms) exhibit a Pasteur
effect that increases the rate of glycolysis to maintain ATP production necessary for
metabolic function. The resulting ability to tolerate anoxia is linked to the supply of
glucose, and anoxic death results when tissues become depleted of sugar reserves
and cannot maintain ATP and NADPH production (Bailey-Serres and Voesenek
2008). Seagrass roots, however, exhibit a low-oxygen quiescence strategy (LOQS),
in which the onset of anoxia reduces the rate of metabolic glucose consumption and
ATP production. The reduced nighttime carbon demand of anaerobic tissues extends
the period of anoxia tolerated by eelgrass roots and further reduces carbon demand
by belowground tissues (Smith et al. 1988; Zimmerman et al. 1996). The LOQS
appears to be highly conserved among vascular plants to maintain cellular homeostasis under low-O 2 stress and enables the synthesis of proteins involved in
metabolite transport, protection from reactive oxygen species (ROS), and chaperone
activity (Voesenek and Bailey-Serres 2015).
Finally, all species of seagrasses (except Enhalus spp.) are adapted for completely submerged pollination. The filiform pollen grains of Zostera marina tumble
as they encounter turbulent velocity gradients induced by the anatomy of flowers
and inflorescences, increasing the probability of attachment to the stigmatic surfaces (Ackerman 2006). In Thalassia testudinum, invertebrates may also facilitate
pollen transfer from male flowers to female stigma (van Tussenbroek et al. 2016).
8.2.2 Sensitivity to Environmental Change Results from High
Light Requirements
Although seagrasses possess a remarkable assemblage of successful adaptations to
a submerged aquatic life history, their light requirements for survival are 10- to
20-fold higher than many marine autotrophs, which renders them vulnerable to a
variety of habitat disturbances, often of anthropogenic origin (Duarte 1991; Short
and Wyllie-Echeverria 1996). More than 40 large-scale seagrass declines involving
at least 24 different species were reported worldwide during the twentieth century,
and the losses have continued to the point where seagrasses may be nearing a crisis
with respect to global sustainability (Orth et al. 2006; Short et al. 2011).
Eutrophication, which promotes the growth of light-absorbing phytoplankton and
opportunistic macroalgae, is a critical factor in many of these disturbance events,
including the extensive and persistent losses throughout the Chesapeake Bay, USA
(Orth and Moore 1983). However, even when algal competitors are brought under
control, seagrass recovery can be hampered by the destabilization and resuspension
of marine sediments that further reduces light availability to the benthos (Lawson
et al. 2007; Carr et al. 2010; McPherson et al. 2011).
8 Systems Biology and the Seagrass Paradox…