Chapter 25 Seagrass Conservation Biology
609
could affect the overall biodiversity of the community.
Reproductively viable populations of another
seagrass, Halophila stipulacea, migrated into the
Mediterranean from the Red Sea, following the
opening of Suez Canal, and has moved as far east
as Italy (Lipkin, 1975; Boudouresque and Verlaque,
2002). Introduction and dispersal were thought to
occur by vessels; however, this has not been verified. The recent report of H. stipulacea in the tropical west Atlantic (Ruiz and Ballantine, 2004) suggests the potential for long-distance introduction of
some species. Although there could be numerous
mechanisms of seagrass introductions, our knowledge of the transport vectors for any seagrass dispersal is minimal (Philbrick and Les, 1996; Waycott
and Barnes, 2001).
Neither of these seagrass invasions suggests that
non-native species can displace indigenous seagrasses; however, recent molecular studies with Thalassia testudinum indicate that even the slowest
growing climax species can disperse long distances
(Waycott and Barnes, 2001). They found representatives of the same individuals in populations on
the Caribbean Coast of Panama and at the very
northern limits of the species’ geographic range in
Bermuda. They hypothesized that since the last retreat of sea-level associated with the most recent
glacial event 10,000 years ago, T. testudinum must
have re-occupied a large portion of its original range
in the Caribbean basin. The surviving source populations must have been located in deeper water refuges
and were dispersed by currents, either vegetatively
or by sexual propagules (Kaldy and Dunton, 1999;
Whitfield et al., 2004). Assuming it was present prior
to the last retreat of sea-level, T. testudinum was able
to disperse back into its normal thermal range with
the increased sea level. These observations, and reports of the recent spread globally Halophila decipiens, suggest that seagrasses have the capability
to disperse long distances and interact with nonindigenous species (Waycott et al., 2002). The successful introduction and clonal spread of a dominant
species like T. testudinum could result in the invasion of a superior clone that slowly displaces local
populations. A critical need in seagrass conservation
science is to link studies of genetic diversity with life
history traits and experimentation on seagrass dispersal and competition so that we can better predict
the outcome of an invasion (Waycott, 2000; see also
Waycott et al., Chapter 2).
C. Scientific Disciplines
and Research Priorities
1. Species and Population Level Science
Although conservation efforts in general are beginning to focus more on integrated landscape scale
studies of systems and entire biomes, rather than on
single species, there is a need to understand the biology and ecology of individual seagrass species and
their populations. There are two important reasons
for this. First, single species stands or stands dominated by a few species are common (Fig. 2: Duarte,
2000). Consequently, the interaction between ramets or genets within the same species, or plants from
as few as two or three other species, is a common
feature of the seagrass system. Second, community
and biome level instruments of protection (e.g. light
thresholds and nutrient criteria) are largely based on
the understanding of individual species responses to
environmental and anthropogenic stressors (Ralph
et al., Chapter 24). Preventing the decline or extinction of seagrasses will be improved with a better
understanding of individual species living requirements balanced by knowledge of community interactions and competition between species.
At the species and population levels, life history
dynamics, dispersal, and genetics are among some of
the most important scientific topics pertaining to the
conservation of seagrasses (Philbrick and Les, 1996;
Kenworthy, 2000; Waycott, 2000; Reusch, 2001).
The common denominator for all these subjects is
the question of population stability. Surprisingly, the
least understood aspect of seagrass life history is
the role of sexual reproduction including seed production, dispersal, and the survival and autecology
of seedlings (Churchill, 1991; Terrados, 1993; Orth
et al., 1994; Philbrick and Les, 1996; Inglis, 2000a;
Orth et al., 2000; Kenworthy, 2000; Orth et al., 2003;
Wyllie-Echeverria et al., 2003; Whitfield et al., 2004;
Ackerman, Chapter 4; Orth et al., Chapter 5). A combination of clonal spread, seed rain, seed banks, and
methods of sexual and vegetative dispersal enables
these plants to survive, disperse and re-establish their
populations (Duarte and Sand-Jensen, 1990; Duarte
et al., 1994; Marb` a and Duarte, 1998; Kenworthy and
Schwarzschild, 1998; Harwell and Orth, 2002). Still,
we do not know what constitutes an effective population size for maintaining individual species or what
constitutes a seagrass metapopulation? For most seagrass species these subjects are poorly understood, a
609
could affect the overall biodiversity of the community.
Reproductively viable populations of another
seagrass, Halophila stipulacea, migrated into the
Mediterranean from the Red Sea, following the
opening of Suez Canal, and has moved as far east
as Italy (Lipkin, 1975; Boudouresque and Verlaque,
2002). Introduction and dispersal were thought to
occur by vessels; however, this has not been verified. The recent report of H. stipulacea in the tropical west Atlantic (Ruiz and Ballantine, 2004) suggests the potential for long-distance introduction of
some species. Although there could be numerous
mechanisms of seagrass introductions, our knowledge of the transport vectors for any seagrass dispersal is minimal (Philbrick and Les, 1996; Waycott
and Barnes, 2001).
Neither of these seagrass invasions suggests that
non-native species can displace indigenous seagrasses; however, recent molecular studies with Thalassia testudinum indicate that even the slowest
growing climax species can disperse long distances
(Waycott and Barnes, 2001). They found representatives of the same individuals in populations on
the Caribbean Coast of Panama and at the very
northern limits of the species’ geographic range in
Bermuda. They hypothesized that since the last retreat of sea-level associated with the most recent
glacial event 10,000 years ago, T. testudinum must
have re-occupied a large portion of its original range
in the Caribbean basin. The surviving source populations must have been located in deeper water refuges
and were dispersed by currents, either vegetatively
or by sexual propagules (Kaldy and Dunton, 1999;
Whitfield et al., 2004). Assuming it was present prior
to the last retreat of sea-level, T. testudinum was able
to disperse back into its normal thermal range with
the increased sea level. These observations, and reports of the recent spread globally Halophila decipiens, suggest that seagrasses have the capability
to disperse long distances and interact with nonindigenous species (Waycott et al., 2002). The successful introduction and clonal spread of a dominant
species like T. testudinum could result in the invasion of a superior clone that slowly displaces local
populations. A critical need in seagrass conservation
science is to link studies of genetic diversity with life
history traits and experimentation on seagrass dispersal and competition so that we can better predict
the outcome of an invasion (Waycott, 2000; see also
Waycott et al., Chapter 2).
C. Scientific Disciplines
and Research Priorities
1. Species and Population Level Science
Although conservation efforts in general are beginning to focus more on integrated landscape scale
studies of systems and entire biomes, rather than on
single species, there is a need to understand the biology and ecology of individual seagrass species and
their populations. There are two important reasons
for this. First, single species stands or stands dominated by a few species are common (Fig. 2: Duarte,
2000). Consequently, the interaction between ramets or genets within the same species, or plants from
as few as two or three other species, is a common
feature of the seagrass system. Second, community
and biome level instruments of protection (e.g. light
thresholds and nutrient criteria) are largely based on
the understanding of individual species responses to
environmental and anthropogenic stressors (Ralph
et al., Chapter 24). Preventing the decline or extinction of seagrasses will be improved with a better
understanding of individual species living requirements balanced by knowledge of community interactions and competition between species.
At the species and population levels, life history
dynamics, dispersal, and genetics are among some of
the most important scientific topics pertaining to the
conservation of seagrasses (Philbrick and Les, 1996;
Kenworthy, 2000; Waycott, 2000; Reusch, 2001).
The common denominator for all these subjects is
the question of population stability. Surprisingly, the
least understood aspect of seagrass life history is
the role of sexual reproduction including seed production, dispersal, and the survival and autecology
of seedlings (Churchill, 1991; Terrados, 1993; Orth
et al., 1994; Philbrick and Les, 1996; Inglis, 2000a;
Orth et al., 2000; Kenworthy, 2000; Orth et al., 2003;
Wyllie-Echeverria et al., 2003; Whitfield et al., 2004;
Ackerman, Chapter 4; Orth et al., Chapter 5). A combination of clonal spread, seed rain, seed banks, and
methods of sexual and vegetative dispersal enables
these plants to survive, disperse and re-establish their
populations (Duarte and Sand-Jensen, 1990; Duarte
et al., 1994; Marb` a and Duarte, 1998; Kenworthy and
Schwarzschild, 1998; Harwell and Orth, 2002). Still,
we do not know what constitutes an effective population size for maintaining individual species or what
constitutes a seagrass metapopulation? For most seagrass species these subjects are poorly understood, a