Effects of predation on Zostera marina L. seed abundance

153

142

Eleven years of eelgrass Zostera marina seed additions conducted in a coastal bay system where Z. marina had not been reported since 1933 have resulted in rapid Z. marina expansion beyond the initially seeded plots. From 1999 through 2010, 37.8 million viable seeds were added to 369 individual plots ranging in size from 0.01 to 2 ha totaling 125.2 ha in 4 coastal bays. Subsequent expansion from these initial plots to approximately 1700 ha of bay bottom populated with Z. marina through 2010 is attributable to seed export from the original plots and subsequent generations of seedlings originating from those exports. Estimates of annual patch vegetative expansion showed mean estimated diameter increasing at varying rates from 10 to 36 cm yr −1 , consistent with rhizome elongation rates reported for Z. marina. Water quality data collected over 7 yr by spatially intensive sampling, as well as fixed-location continuous monitoring, document conditions in all 4 bays that are adequate to support Z. marina growth. In particular, median chlorophyll levels for the entire sampling period were between 5 and 6 µg l −1 for each of the bays, and median turbidity levels, while exhibiting seasonal differences, were between 8 and 9 NTU. The recovery of Z. marina initiated in this coastal bay system may be unique in seagrass recovery studies because of how the recovery was initiated (seeds rather than adult plants), how rapidly it occurred (years rather than decades), and the explicit demonstration of how one meadow modulated water clarity and altered sediments as it developed and expanded. Our results offer a new perspective on the role seeds can play in recovery dynamics at large spatial scales.

Section: Seed Collection and Distributionmentioning

confidence: 99%

Seed addition facilitates eelgrass recovery in a coastal bay system

Orth¹,

Moore²,

Marion³

et al. 2012

153

142

Section: Attributes Of a Mixed-annual Life Historymentioning

confidence: 99%

“…Similar large losses of seeds, ranging from 25 to 78% of total seed production, have been reported for both annual and perennial Zostera marina beds (Santamaría-Gallegos et al 2000, Harwell & Orth 2002b, Morita et al 2007). These losses may be the result of dispersal (Harwell & Orth 2002a, Källström et al 2008), decay (Morita et al 2007), predation (Fishman & Orth 1996), or germination (Harper 1977.The persistence of vegetative shoots after the senescence of reproductive shoots is another feature of the mixed-annual life history strategy that distinguishes it from annual populations. Annual populations of Zostera marina produce only reproductive shoots which senesce at the end of the flowering period (Keddy & Patriquin, 1978, Gagnon et al 1980, De Cock 1981, Harlin et al 1982, Phillips et al 1983a, Robertson & Mann 1984, Santamaría-Gallegos et al 2000.…”

mentioning

confidence: 99%

Characterization and ecological implication of eelgrass life history strategies near the species’ southern limit in the western North Atlantic

Jarvis¹,

Moore²,

Kenworthy³

2012

Eelgrass Zostera marina L. populations located near the species southern limit in the western North Atlantic were assessed monthly from July 2007 through November 2008. We identified (1) dominant life history strategies and local environmental conditions in southern Z. marina populations, (2) quantified differences in reproductive phenology between populations and different local environmental conditions, and (3) compared reproductive strategies to established annual and perennial life history paradigms. Observed populations expressed both life history strategies with one Z. marina population completely losing aboveground biomass and reestablishing from seeds (annual model) while another population retained aboveground biomass throughout the year (perennial model). A third life history strategy, characterized here as a mixed-annual population, was also observed after some seedlings were found to reproduce both sexually and asexually during their first year of growth thereby not conforming to any currently established life history paradigm. Development of multiple life history strategies within this region may be in response to stressful summer water temperatures associated with the southern edge of the species' range. We suggest that neither annual nor perennial life history strategies always provide a superior mechanism for population persistence as perennial populations can be susceptible to multiple consecutive years of stress, and annual populations are unable to fully exploit available resources throughout much of the year. The mixed-annual strategy observed here represents another possible life history model which may provide the mechanism necessary for Z. marina populations to persist during times of environmental transition.KEY WORDS: Zostera marina · Life-history · Annual · Perennial · Seed bank · Biomass Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 444: [43][44][45][46][47][48][49][50][51][52][53][54][55][56] 2012 populations have also been documented to express behavior similar to the biennial life history model (Setchell, 1929). After germinating, seedling growth in biennial populations occurred via clonal expansion only and flowering stem development and fruiting were not observed until after a period of 1 to 2 yr of growth (Setchell 1929;Thayer et al. 1984). More recently an annual life history strategy has been described for Z. marina populations, where mature plants consist of reproductive (flowering) shoots only and all plants complete their life cycle (seeds germinate, flower, produce seeds) and die within 12 mo (Keddy & Patriquin, 1978, Gagnon et al. 1980, De Cock 1981, Harlin et al. 1982, Phillips et al. 1983a, Robertson & Mann 1984, Santamaría-Gallegos et al. 2000.Although they have been documented throughout the species' geographic distribution, annual forms of Zostera marina are primarily found in areas characterized by stressful environmental conditions such as ice scour (Robertson & Mann 1984), extreme temperatures (Phillips...

“…Eelgrass seed production has been found to be highly variable, ranging from 200 to about 80 000 seeds m -2 (Hootsmans et al 1987, Keddy 1987, Harrison 1993, Fishman & Orth 1996. A large proportion of seagrass seeds may be lost to predation, disease, and transport to unsuitable sites (Wigand & Churchill 1988, Fishman & Orth 1996, Inglis 2000, Nakaoka 2002, causing discrepancies between seed production and seedling abundance.The eelgrass Zostera marina is the most abundant seagrass species on the coasts of the Korean peninsula (Shin & Choi 1998, Lee & Lee 2003. New eelgrass shoots are created as lateral shoots by the branching of rhizomes during spring, and the expansion of eelgrass meadows coincides with the creation of new shoots in spring on the coast of Korea (Lee et al 2005).…”

mentioning

confidence: 99%

Recolonization of Zostera marina following destruction caused by a red tide algal bloom: the role of new shoot recruitment from seed banks

Lee¹,

Park²,

Kim³

et al. 2007

Harmful microalgal blooms such as red-tide or brown-tide events lead to abrupt light reductions and consequently cause immediate damage to seagrass beds. Because red tide algal blooms usually occur unexpectedly, seagrass responses to the microalgal blooms have rarely been documented. A red tide caused by a dense bloom of Heterosigma akashiwo, a noxious red-tide-causing alga of temperate and subtropical waters, occurred at a study site on the south coast of Korea in late May 2002. Because the red-tide event occurred on an eelgrass bed where seagrass monitoring was being conducted, pre-event conditions were well documented. Nearly all eelgrass shoots disappeared rapidly because of the reduction in light caused by the algal bloom. Additionally, a thick layer of mucilaginous material secreted from algal cysts suffocated eelgrass plants for weeks, directly causing eelgrass death. Eelgrass seedlings were found in the die-off area from December 2002; <1 yr after its destruction, the site was completely re-established by seedling recruitment via germination from the seed bank. Seedling mortality was very low. Seedlings grew exponentially during the spring, and their fast growth also contributed to rapid eelgrass recolonization. During the second year of recolonization, asexual reproduction through lateral shoot production by rhizome elongation and branching played the main role in the persistence and growth of the eelgrass bed. Seed density in the seed bank varied seasonally, increasing to a maximum after seed release and decreasing to nearly zero after seed germination. Many more seedlings were found and nearly all seedlings established successfully in the first year after the bloom, when no adult eelgrass shoots were observed, suggesting significant effects of shoot density on rates of seed germination and seedling establishment. This was a unique opportunity to examine eelgrass responses to dense microalgal blooms, which provided valuable information on the die-off process caused by red tide and the natural recolonization of seagrass after its destruction.KEY WORDS: Recolonization · Red tide algal bloom · Eelgrass · Zostera marina · Die-off · Seed bank · Seedling Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 342: [105][106][107][108][109][110][111][112][113][114][115] 2007 been reported (Onuf 1996). Red tide algal blooms usually occur unexpectedly; accordingly, seagrass conditions both before and after the occurrence of blooms have seldom been documented. On the coasts of Korea, red tide algal blooms occur frequently during the summer period; the frequency of bloom events has been increasing from 5 to 40 times yr -1 during the 1980s to 30 to 120 times yr -1 during the 1990s (Kim et al. 2000). At a study site on the south coast of Korea, where monitoring of seagrass beds was in progress, a red-tide event caused by a very dense bloom of Heterosigma akashiwo occurred in late May 2002 and lasted for about 2 wk. The seagrass bed and abiotic factors, such as un...