128
R. J. Orth, M. C. Harwell and G. J. Inglis
et al., 2000; Orth et al., 2003). Predation and genetic
stock may be important aspects governing seed distribution and viability in some species. Studies are
needed to determine if seagrass dispersal strategies,
like those of terrestrial angiosperms, have evolved to
cope with higher rates of predation and disturbance
within existing beds (Harms et al., 2000; Howe and
Miriti, 2000).
F. Seed Stocks
We are only beginning to gain insight into the importance of genetic variation to the long-term success
of clonal populations. In some species of seagrass
(Z. marina), there appears to be a strong relationship
between genetic diversity and plant vigor (Williams,
2001), while others maintain vast sexual populations
that have almost no detectable genetic variation (Amphibolis antarctica; Waycott et al., 1996; Waycott
et al., Chapter 2). Understanding the role of seeds in
the long-term dynamics of seagrass populations has
taken on an extra sense of urgency with predictions
of present and future global change (Short and Neckles, 1999; Ferriere et al., 2000; Twilley et al., 2001;
Scavia et al., 2002; Johnson et al., 2003; Kenworthy et al., Chapter 25) and with the fragmentation of
habitats into isolated patches that theoretically could
result in lower overall seed sets (Reusch, 2003). The
emerging importance of seeds to the long-term dynamics of seagrass populations, and perhaps even
more importantly in creating new patches distant
from parent stock or in the recolonization of disturbed areas rather than maintaining existing, wellestablished beds (Olesen, 1999; Olesen et al., 2004),
means that scientists and managers must place
greater emphasis on conserving existing beds to provide a seed bank, and possibly in exploring ways to
use seeds to restore areas that may have lost seagrass
and are far away from potential seed sources.
Acknowledgments
We appreciate constructive comments provided by
S. Marion, J. Vermaat, and J. Ackerman and several
anonymous reviewers. Contribution number 2654
from the Virginia Institute of Marine Science. Fig. 3e
reprinted from Aquatic Botany, vol. 10, de Cock,
A. W. A. M., Development of the flowering shoot
of Zostera marina l. under controlled conditions in
comparison to the development in two different natural habitats in The Netherlands. 99–113 (1981) with
permission from Elsevier.
References
Ackerman JD (1995) Convergence of filiform pollen morphologies in seagrasses: Functional mechanisms. Evol Ecol 9: 139–
153
Ackerman JD (1997a) Submarine pollination in the marine angiosperm Zostera marina: Part I. The influence of floral morphology on fluid flow. Am J Bot 84: 1099–1109
Ackerman JD (1997b) Submarine pollination in the marine angiosperm Zostera marina: Part II. Pollen transport in flow
fields and capture by stigmas. Am J Bot 84: 1110–1119
Ackerman JD (2000) Abiotic pollen and pollination: Ecological,
functional, and evolutionary perspectives. Plant Systematics
Evol 222: 167–185
Ackerman JD (2002) Diffusivity in a marine macrophyte bed:
Implications for submarine pollination and dispersal. Am J
Bot 89: 1119–1127
Baldwin JR and Lovvorn JR (1994) Expansion of seagrass habitat
by the exotic Zostera japonica, and its use by dabbling ducks
and brant in Boundary Bay, British Columbia. Mar Ecol Prog
Ser 103: 119–127
Balestri E and Bertini S (2003) Growth and development of Posidonia oceanica seedlings treated with plant growth regulators:
possible implications for meadow restoration. Aquat Bot 76:
291–297
Balestri E, Piazzi L and Francesco C (1998) In vitro germination
and seedling development of Posidonia oceanica. Aquat Bot
60: 83–93
Balestri E and Cinelli F (2003) Sexual reproductive success in
Posidonia oceanica. Aquat Bot 75: 21–32
Baskin CC and Baskin JM (1998) Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination. Academic
Press, New York
Bearlin AR, Burgman MA and Regan HM (1999) A stochastic model for seagrass (Zostera muelleri) in Port Phillip Bay,
Victoria, Australia. Ecol Model 118: 131–148
Beck MW, Heck KL, Able KW, Childers DL, Eggleston DB,
Gilanders BM, Halpern B, Hays CG, Hoshino K, Minello TJ,
Orth RJ, Sheridan PF and Weinstein MP (2001) Towards better identification, conservation, and management of estuarine
and marine nurseries for fish and invertebrates. Bioscience 51:
633–641
Billingham MR, Reusch TBH, Alberto F and Serrao EA (2003) Is
asexual reproduction more important at geographical limits?
A genetic study of the seagrass Zostera marina in the Ria
Formosa, Portugal. Mar Ecol Prog Ser 265: 77–83
Birch WR (1981) Morphology of germinating seeds of the
seagrass Halophila spinulosa (R.Br.) Aschers. (Hydrocharitaceae). Aquat Bot 11: 79–90
Blanchette CA, Worcester SE, Reed D and Holbrook SJ (1999)
Algal morphology, flow, and spatially variable recruitment of
surfgrass Phyllospadix torreyi. Mar Ecol Prog Ser 184: 119–
128
Bragg LH and McMillan C (1986) SEM comparison of fruits of
a seagrass, Halodule (Cymodoceaceae), from Australia and
Texas. Am J Bot 73: 815–821
R. J. Orth, M. C. Harwell and G. J. Inglis
et al., 2000; Orth et al., 2003). Predation and genetic
stock may be important aspects governing seed distribution and viability in some species. Studies are
needed to determine if seagrass dispersal strategies,
like those of terrestrial angiosperms, have evolved to
cope with higher rates of predation and disturbance
within existing beds (Harms et al., 2000; Howe and
Miriti, 2000).
F. Seed Stocks
We are only beginning to gain insight into the importance of genetic variation to the long-term success
of clonal populations. In some species of seagrass
(Z. marina), there appears to be a strong relationship
between genetic diversity and plant vigor (Williams,
2001), while others maintain vast sexual populations
that have almost no detectable genetic variation (Amphibolis antarctica; Waycott et al., 1996; Waycott
et al., Chapter 2). Understanding the role of seeds in
the long-term dynamics of seagrass populations has
taken on an extra sense of urgency with predictions
of present and future global change (Short and Neckles, 1999; Ferriere et al., 2000; Twilley et al., 2001;
Scavia et al., 2002; Johnson et al., 2003; Kenworthy et al., Chapter 25) and with the fragmentation of
habitats into isolated patches that theoretically could
result in lower overall seed sets (Reusch, 2003). The
emerging importance of seeds to the long-term dynamics of seagrass populations, and perhaps even
more importantly in creating new patches distant
from parent stock or in the recolonization of disturbed areas rather than maintaining existing, wellestablished beds (Olesen, 1999; Olesen et al., 2004),
means that scientists and managers must place
greater emphasis on conserving existing beds to provide a seed bank, and possibly in exploring ways to
use seeds to restore areas that may have lost seagrass
and are far away from potential seed sources.
Acknowledgments
We appreciate constructive comments provided by
S. Marion, J. Vermaat, and J. Ackerman and several
anonymous reviewers. Contribution number 2654
from the Virginia Institute of Marine Science. Fig. 3e
reprinted from Aquatic Botany, vol. 10, de Cock,
A. W. A. M., Development of the flowering shoot
of Zostera marina l. under controlled conditions in
comparison to the development in two different natural habitats in The Netherlands. 99–113 (1981) with
permission from Elsevier.
References
Ackerman JD (1995) Convergence of filiform pollen morphologies in seagrasses: Functional mechanisms. Evol Ecol 9: 139–
153
Ackerman JD (1997a) Submarine pollination in the marine angiosperm Zostera marina: Part I. The influence of floral morphology on fluid flow. Am J Bot 84: 1099–1109
Ackerman JD (1997b) Submarine pollination in the marine angiosperm Zostera marina: Part II. Pollen transport in flow
fields and capture by stigmas. Am J Bot 84: 1110–1119
Ackerman JD (2000) Abiotic pollen and pollination: Ecological,
functional, and evolutionary perspectives. Plant Systematics
Evol 222: 167–185
Ackerman JD (2002) Diffusivity in a marine macrophyte bed:
Implications for submarine pollination and dispersal. Am J
Bot 89: 1119–1127
Baldwin JR and Lovvorn JR (1994) Expansion of seagrass habitat
by the exotic Zostera japonica, and its use by dabbling ducks
and brant in Boundary Bay, British Columbia. Mar Ecol Prog
Ser 103: 119–127
Balestri E and Bertini S (2003) Growth and development of Posidonia oceanica seedlings treated with plant growth regulators:
possible implications for meadow restoration. Aquat Bot 76:
291–297
Balestri E, Piazzi L and Francesco C (1998) In vitro germination
and seedling development of Posidonia oceanica. Aquat Bot
60: 83–93
Balestri E and Cinelli F (2003) Sexual reproductive success in
Posidonia oceanica. Aquat Bot 75: 21–32
Baskin CC and Baskin JM (1998) Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination. Academic
Press, New York
Bearlin AR, Burgman MA and Regan HM (1999) A stochastic model for seagrass (Zostera muelleri) in Port Phillip Bay,
Victoria, Australia. Ecol Model 118: 131–148
Beck MW, Heck KL, Able KW, Childers DL, Eggleston DB,
Gilanders BM, Halpern B, Hays CG, Hoshino K, Minello TJ,
Orth RJ, Sheridan PF and Weinstein MP (2001) Towards better identification, conservation, and management of estuarine
and marine nurseries for fish and invertebrates. Bioscience 51:
633–641
Billingham MR, Reusch TBH, Alberto F and Serrao EA (2003) Is
asexual reproduction more important at geographical limits?
A genetic study of the seagrass Zostera marina in the Ria
Formosa, Portugal. Mar Ecol Prog Ser 265: 77–83
Birch WR (1981) Morphology of germinating seeds of the
seagrass Halophila spinulosa (R.Br.) Aschers. (Hydrocharitaceae). Aquat Bot 11: 79–90
Blanchette CA, Worcester SE, Reed D and Holbrook SJ (1999)
Algal morphology, flow, and spatially variable recruitment of
surfgrass Phyllospadix torreyi. Mar Ecol Prog Ser 184: 119–
128
Bragg LH and McMillan C (1986) SEM comparison of fruits of
a seagrass, Halodule (Cymodoceaceae), from Australia and
Texas. Am J Bot 73: 815–821