Chapter 13
Light and Photosynthesis in Seagrass Meadows
Richard C. Zimmerman
Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University,
Norfolk, VA 23529
I. Introduction
The distribution of radiant energy in plant canopies
determines one of the fundamental interactions of
biophysical ecology—that of energy exchange between photosynthetic organisms and their environment. Accurate knowledge of light absorption by
plant canopies permits the calculation of important plant- and ecosystem-level properties, including rates of primary production, which will be the
focus of this chapter. Knowledge of the interaction
between light and plant canopies is also crucial for
remote sensing, quantification of vegetation abundance and distribution, as well as for the development of inversion, techniques to infer plant chemical composition, important for ecosystem-scale
estimates of plant growth and biogeochemical fluxes
(Jacquemoud et al., 1996; Lacapra et al., 1996; Broge
and Leblanc, 2000). Submerged aquatic vegetation,
including seagrass beds, provide a strong optical signature that can be tracked using satellite and airborne remote sensing (Armstrong, 1993; Mumby
et al., 1997; Chauvaud et al., 2001; Dierssen et al.,
2003), and this will be the subject of Dekker et al.,
Chapter 15.
Seagrasses represent an ecologically important
structuring element and major source of primary
production in shallow waters, worldwide. The primacy of light availability in determining seagrass
bed density, distribution and productivity is particularly acute (Hemminga and Duarte, 2000). Although
minimum light requirements for most marine macrophytes are on the order of 0.1 to 1% of in-water
surface irradiance [E d (0)], seagrasses have unusually high light requirements, ranging from 10% to
as much as 37% of E d (0) (Duarte, 1991b; Olesen
Author for correspondence, email: rzimmer197@aol.com
and Sand-Jensen, 1993; Kenworthy and Fonseca,
1996). These high light requirements, which can
be traced, at least partially, to inefficient carbonconcentrating mechanisms for photosynthesis (Durako, 1993; Beer and Rehnberg, 1997; Zimmerman
et al., 1997; Invers et al., 2001; Larkum et al., Chapter
14), make seagrasses particularly vulnerable to deteriorated water quality and light competition from
micro- and macroalgal blooms induced by eutrophication (Short and Wyllie-Echeverria, 1996; Ralph
et al., Chapter 24). Consequently, the development
of robust mechanistic relationships between the submarine light field and photosynthesis of submerged
plant canopies will facilitate our fundamental understanding of coastal biogeochemical processes and
assist in the management of these important coastal
resources.
Light-dependent productivity of seagrass beds
has been estimated from photosynthesis vs. irradiance (P vs. E) relationships measured at scales
ranging from individual leaves (e.g. Dennison and
Alberte, 1982, 1985; Zimmerman et al., 1994; Zimmerman et al., 2001) to individual multi-leaved
shoots (Fourqurean and Zieman, 1991) to in situ benthic chambers enclosing multiple shoots (Dunton,
1994; Herzka and Dunton, 1997; Mateo et al., Chapter 7). Each approach can provide reasonable local
estimates of whole plant photosynthesis, carbon balance and light requirements, which has made this
general approach extremely useful for exploring the
relationship between environmental forcing and primary productivity in tightly focused local studies.
Unfortunately, the functional relationships behind
these relatively simple “big leaf ” budgets are not
readily transported to seagrass beds growing in different light environments because they do not account for the interactions between the overlying water column and the distribution and orientation of the
303–321.
A. W. D. Larkum et al. (eds.), Seagrasses: Biology, Ecology and Conservation, pp.
c
2006 Springer. Printed in the Netherlands.
Light and Photosynthesis in Seagrass Meadows
Richard C. Zimmerman
Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University,
Norfolk, VA 23529
I. Introduction
The distribution of radiant energy in plant canopies
determines one of the fundamental interactions of
biophysical ecology—that of energy exchange between photosynthetic organisms and their environment. Accurate knowledge of light absorption by
plant canopies permits the calculation of important plant- and ecosystem-level properties, including rates of primary production, which will be the
focus of this chapter. Knowledge of the interaction
between light and plant canopies is also crucial for
remote sensing, quantification of vegetation abundance and distribution, as well as for the development of inversion, techniques to infer plant chemical composition, important for ecosystem-scale
estimates of plant growth and biogeochemical fluxes
(Jacquemoud et al., 1996; Lacapra et al., 1996; Broge
and Leblanc, 2000). Submerged aquatic vegetation,
including seagrass beds, provide a strong optical signature that can be tracked using satellite and airborne remote sensing (Armstrong, 1993; Mumby
et al., 1997; Chauvaud et al., 2001; Dierssen et al.,
2003), and this will be the subject of Dekker et al.,
Chapter 15.
Seagrasses represent an ecologically important
structuring element and major source of primary
production in shallow waters, worldwide. The primacy of light availability in determining seagrass
bed density, distribution and productivity is particularly acute (Hemminga and Duarte, 2000). Although
minimum light requirements for most marine macrophytes are on the order of 0.1 to 1% of in-water
surface irradiance [E d (0)], seagrasses have unusually high light requirements, ranging from 10% to
as much as 37% of E d (0) (Duarte, 1991b; Olesen
Author for correspondence, email: rzimmer197@aol.com
and Sand-Jensen, 1993; Kenworthy and Fonseca,
1996). These high light requirements, which can
be traced, at least partially, to inefficient carbonconcentrating mechanisms for photosynthesis (Durako, 1993; Beer and Rehnberg, 1997; Zimmerman
et al., 1997; Invers et al., 2001; Larkum et al., Chapter
14), make seagrasses particularly vulnerable to deteriorated water quality and light competition from
micro- and macroalgal blooms induced by eutrophication (Short and Wyllie-Echeverria, 1996; Ralph
et al., Chapter 24). Consequently, the development
of robust mechanistic relationships between the submarine light field and photosynthesis of submerged
plant canopies will facilitate our fundamental understanding of coastal biogeochemical processes and
assist in the management of these important coastal
resources.
Light-dependent productivity of seagrass beds
has been estimated from photosynthesis vs. irradiance (P vs. E) relationships measured at scales
ranging from individual leaves (e.g. Dennison and
Alberte, 1982, 1985; Zimmerman et al., 1994; Zimmerman et al., 2001) to individual multi-leaved
shoots (Fourqurean and Zieman, 1991) to in situ benthic chambers enclosing multiple shoots (Dunton,
1994; Herzka and Dunton, 1997; Mateo et al., Chapter 7). Each approach can provide reasonable local
estimates of whole plant photosynthesis, carbon balance and light requirements, which has made this
general approach extremely useful for exploring the
relationship between environmental forcing and primary productivity in tightly focused local studies.
Unfortunately, the functional relationships behind
these relatively simple “big leaf ” budgets are not
readily transported to seagrass beds growing in different light environments because they do not account for the interactions between the overlying water column and the distribution and orientation of the
303–321.
A. W. D. Larkum et al. (eds.), Seagrasses: Biology, Ecology and Conservation, pp.
c
2006 Springer. Printed in the Netherlands.