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

Abstract

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...

Experimental impacts of climate warming and ocean carbonation on eelgrass Zostera marina

“…This experiment demonstrated that CO 2 stimulation of primary production can enhance the summertime survival, growth, and proliferation of perennial eelgrass from the Chesapeake region that is regularly impacted by summer heat stress (Moore & Jarvis 2008, Jarvis et al 2012. These results reinforce the emer ging paradigm that eelgrass may benefit significantly from a high-CO 2 world.…”

Life history events of eelgrass Zostera marina L. populations across gradients of latitude and temperature

“…This submerged plant creates shelter for ecologically and economically important faunal species, enhances biodiversity, contributes to sediment stability, carbon and nutrient storage, and improves water clarity (Gutiérrez et al 2011, Duarte et al 2013. Eelgrass is the most widely dis-tributed seagrass species across a range of latitudes, from warm temperate waters up to northern Arctic regions (den Hartog 1970, Jarvis et al 2012, Olesen et al 2015. Distinct life history strategies and a wide tolerance to a range of salinity and temperature conditions allow this seagrass species to exploit areas from brackish estuaries to open oceans over a large geographical range (den Hartog 1970, Walker et al 2001, Lee et al 2007a, Nejrup & Pedersen 2008.…”

Eelgrass Zostera marina in subarctic Greenland: dense meadows with slow biomass turnover in cold waters

“…High water temperatures decrease growth and increase mortality, and these negative effects may be exacerbated by the interaction with other stressors such as reduced light availability, low salinity, or low oxygen levels (Olesen & Sand-Jensen 1993, Nejrup & Pedersen 2008, Raun & Borum 2013. Hence, diebacks have been recorded at summer temperatures above 25°C (Orth & Moore 1986, Sfriso & Ghetti 1998, Moore & Jarvis 2008, and at the southern distribution limit eelgrass populations may adopt an annual or a mixed-annual life strategy to escape the warm summertime conditions (Phillips & Backman 1983, Meling-López & Ibarra-Obando 1999, Jarvis et al 2012. Water temperature also affects the timing of life-history events with progressively later flowering and seed maturation at increasing latitudes , Silberhorn et al 1983.…”