738
increase in S. alterniflora density observed in 2014 and 2015 was primarily due to
the appearance of S. alterniflora seedlings (Figs. 21.22 and 21.23). These grew over
their first summer and started to produce clones in their second summer (similar to
as described in Redfield 1972). Our observed pattern for S. alterniflora dynamics
was opposite to what is typically described in the literature, summarized by Smith
and Warren (2012, p. 193): “Colonization of new areas by S. alterniflora initially
depends upon seeds, but thereafter vegetative growth becomes important in the
expansion of these populations (Metcalf et al. 1986)”. As also noted by Smith and
Warren (2012) and others, the importance of these two types of reproduction (vegetatively by rhizomes and sexually by seeds) depends on circumstances. Vegetative
spread is generally more important in already established or natural salt marshes.
Spread by seeds is successful in “disturbed” or unvegetated areas (Metcalfe et al.
1986), although germination of these seeds requires fairly narrow abiotic conditions
(Biber and Caldwell 2008; Mooring et al. 1971; Redfield 1972). The extensive
appearance of S. alterniflora in our restoration cells in 2014 may be due to soil conditions ameliorating sufficiently to enable seeds to geminate. Seeds of S. alterniflora
can survive floating for up to 25 days in seawater (Elsey-Quirk et al. 2009), which
would allow their dispersal into our restoration cells from other salt marshes surrounding the Cumberland Basin and other regions of the upper Bay of Fundy. We
think, however, that the large cohorts of seedlings are offspring of the plants that had
colonized in 2012 and 2013 and grown in our sites. Tall vibrant plants full of seeds
were observed in the autumn of 2013 (which is before the seedlings appeared en
masse). Genetic analyses of the S. alterniflora plants are planned for the future
(specimens are already collected and preserved) to determine parentage. In any
case, with the establishment of seedlings, a very rapid increase in plant cover
throughout the restoration cells was observed.
Most other biological communities that we monitored are lagging behind the
plant community, and this has been observed in other salt marsh restoration projects
(Roman and Burdick 2012). The invertebrates on the emergent surface of the restoration cells are just starting (after 5 years) to approach the assemblage in the reference marshes (consisting of herbivorous insects and arachnids). On the relevant
nMDS graph (Fig. 21.20b), the data points for the restoration cells after the breaching initially showed a very tight and distinct cluster of extremely low densities as
well as the occasional presence of intertidal mudsnails. In 2013, 2014 and particularly 2015, the data points approached those of the reference marshes. The trajectory is somewhat reminiscent of the plant dynamics (though not as smooth).
The salt pools have not yet fully stabilized since sedimentation is still quite high
(Fig. 21.13, Table 21.2) and plants have just recently extensively covered the restoration cells. Small salt pools (5–53 m
2
in area) are beginning to form in the restoration cells (Dykstra 2015). The minnow and aquatic invertebrate community in the
large salt pools is still different (Fig. 21.24a), with fewer or no sticklebacks
(Gasterosteus aculeatus and Pungitius pungitus), mummichog (Fundulus heteroclitus), and water boatmen (Corixa spp.) in the restoration cells compared to the reference marshes. This community in the restoration cells is more variable and
sometimes reflective of oceanic animals appearing there (such as ctenophores).
L.K. Boone et al.
increase in S. alterniflora density observed in 2014 and 2015 was primarily due to
the appearance of S. alterniflora seedlings (Figs. 21.22 and 21.23). These grew over
their first summer and started to produce clones in their second summer (similar to
as described in Redfield 1972). Our observed pattern for S. alterniflora dynamics
was opposite to what is typically described in the literature, summarized by Smith
and Warren (2012, p. 193): “Colonization of new areas by S. alterniflora initially
depends upon seeds, but thereafter vegetative growth becomes important in the
expansion of these populations (Metcalf et al. 1986)”. As also noted by Smith and
Warren (2012) and others, the importance of these two types of reproduction (vegetatively by rhizomes and sexually by seeds) depends on circumstances. Vegetative
spread is generally more important in already established or natural salt marshes.
Spread by seeds is successful in “disturbed” or unvegetated areas (Metcalfe et al.
1986), although germination of these seeds requires fairly narrow abiotic conditions
(Biber and Caldwell 2008; Mooring et al. 1971; Redfield 1972). The extensive
appearance of S. alterniflora in our restoration cells in 2014 may be due to soil conditions ameliorating sufficiently to enable seeds to geminate. Seeds of S. alterniflora
can survive floating for up to 25 days in seawater (Elsey-Quirk et al. 2009), which
would allow their dispersal into our restoration cells from other salt marshes surrounding the Cumberland Basin and other regions of the upper Bay of Fundy. We
think, however, that the large cohorts of seedlings are offspring of the plants that had
colonized in 2012 and 2013 and grown in our sites. Tall vibrant plants full of seeds
were observed in the autumn of 2013 (which is before the seedlings appeared en
masse). Genetic analyses of the S. alterniflora plants are planned for the future
(specimens are already collected and preserved) to determine parentage. In any
case, with the establishment of seedlings, a very rapid increase in plant cover
throughout the restoration cells was observed.
Most other biological communities that we monitored are lagging behind the
plant community, and this has been observed in other salt marsh restoration projects
(Roman and Burdick 2012). The invertebrates on the emergent surface of the restoration cells are just starting (after 5 years) to approach the assemblage in the reference marshes (consisting of herbivorous insects and arachnids). On the relevant
nMDS graph (Fig. 21.20b), the data points for the restoration cells after the breaching initially showed a very tight and distinct cluster of extremely low densities as
well as the occasional presence of intertidal mudsnails. In 2013, 2014 and particularly 2015, the data points approached those of the reference marshes. The trajectory is somewhat reminiscent of the plant dynamics (though not as smooth).
The salt pools have not yet fully stabilized since sedimentation is still quite high
(Fig. 21.13, Table 21.2) and plants have just recently extensively covered the restoration cells. Small salt pools (5–53 m
2
in area) are beginning to form in the restoration cells (Dykstra 2015). The minnow and aquatic invertebrate community in the
large salt pools is still different (Fig. 21.24a), with fewer or no sticklebacks
(Gasterosteus aculeatus and Pungitius pungitus), mummichog (Fundulus heteroclitus), and water boatmen (Corixa spp.) in the restoration cells compared to the reference marshes. This community in the restoration cells is more variable and
sometimes reflective of oceanic animals appearing there (such as ctenophores).
L.K. Boone et al.