Gulf of St. Lawrence aster COSEWIC assessment and status report: chapter 7
Habitat
Habitat requirements
In the maritime climate where Gulf of St. Lawrence Aster is found, the average temperature ranges from 18 to 20ºC in July and from -5 to -10ºC in January (Thannheiser, 1984). A high level of humidity, with frequent fog and regular winds also characterize the climatic zone occupied by Gulf of St. Lawrence Aster. The microclimate is distinguished by its full sunlight, more or less saline habitats flooded only at extreme high waters and during storms, corresponding to a submergence of about 10 cm in the Magdalen Islands (Gilbert et al., 1999). This habitat is relatively protected from the winds by dunes.
Gulf of St. Lawrence Aster occurs on wet, predominantly sandy substrates exposed to equinoctial high waters and storm waves, sheltered beaches and areas of scattered vegetation in high salt marshes (Gagnon et al., 1995a and b). It grows near sea level on open and slightly sloping ground (Gilbert et al. 1999) and requires full light for its growth (Reynolds et al., 2001; Houle et al., 2002). Its germination and growth can be affected by saltwater, but the seeds are quite resistant to salt and can germinate again in freshwater after being immersed in saltwater (Houle et al., 2002, Houle et al., 2001).
The dynamic nature of coastal features creates much year-to-year variation in the abundance and distribution of Gulf of St. Lawrence Aster at a given site. Deposition and erosion may have an impact on germination and survival. For example, the deposition of eelgrass debris or sand on its habitat in the aftermath of storms in New Brunswick and Prince Edward Island in 2001 and 2002 contributed to the recent population declines (Éric Tremblay, Kate MacQuarrie and Jean Gagnon, pers. comm.).
The salinity of the substrate is also a limiting factor in the distribution of Gulf of St. Lawrence Aster (Reynolds and Houle, 2002). The influence of freshwater at growing sites is evident from the list of companion plants of Gulf of St. Lawrence Aster (Godbout, 2000).
Hydrology and moisture conditions are also important. For example, water availability during bud differentiation appears to be critical, with drought conditions causing reproductive failure, making populations potentially susceptible to local extinction (Houle and Belleau, 2000). Substrate particle size appears to be of little importance since this Aster occurs on fine sand, coarse sand, gravel and clay (Houle 1988b). The average pH of its substrate ranges from 5.5 (Grandtner, 1967) to 6.9 (CDPNQ, 2002).
In short, a combination of the following factors contributes to its presence: a maritime climate, a slow current favouring fine sediment deposition, the deposition of silt or sand by extreme high waters and storm floods, a particular flood frequency during the growing season, a non-saline substrate in the germination and growth period, the proximity of the water table, some protection from wind, a certain percentage of exposed substrate, little interspecific competition, full sunlight, exposure to certain natural (waves, storms) or artificial changes (Jacques Whitford Env. Ltd., 1994; Gilbert et al., 1999; Houle and Belleau, 2000; Houle et al. 2001; Reynolds et al., 2001; Houle et al., 2002; Reynolds and Houle, 2002).
Trends
Associated species of Gulf of St. Lawrence Aster are taxa of salt marshes, coastal dunes or littoral fringes. They are nitrophytes and obligate to salt-tolerant halophytes (Dansereau, 1959; Grandtner, 1966, 1967; Chapman, 1976; Lamoureux and Grandtner, 1976; Géhu and Grandtner, 1982; Thannheiser, 1984).
Most coastal species, including Gulf of St. Lawrence Aster, can be considered colonizers of new or changeable habitats. Also, natural or artificial disturbances in secondary associations can enable Gulf of St. Lawrence Aster to become established. It generally appears not as a dominant species or, if dominant, only on clearly defined and relatively small patches in the community types. For example, in Spartina alterniflora, Carex paleacea or Scirpus pungens associations.
Gulf of St. Lawrence Aster is an annual and the habitats it occupies fluctuate significantly. Its populations therefore have the particular characteristic of being quite variable in number following natural (e.g., storms) or artificial disturbances.
Protection/ownership
All the known populations occur in coastal habitats, including beaches, lagoons, dunes and dune slacks. In Quebec, all the sites where Gulf of St. Lawrence Aster is found are under provincial jurisdiction, since beaches fall under the Department of Environment and Wildlife, whereas dunes and dune slacks fall under the Department of Energy and Resources (Chap. 20 of the Loi des terres des Îles-de-la-Madeleine, 1958-59: An Act to facilitate the redemption of constituted rents in the Magdalen Islands. Chapter 20, Statuts de Québec. 1958-59, Assented to, the 18th of December, 1958.).
In Prince Edward Island, most of the sites are located in Prince Edward Island National Park. The wet sand marsh at the Tignish site is on littoral land under provincial jurisdiction.
In New Brunswick, Gulf of St. Lawrence Aster is protected under the provincial Endangered Species Act and one site falls within a national park. Of the remaining sites, two (Tracadie and Miscou) are on lands with multiple owners, including the Crown. The sites at the Bouctouche Dune are on private land, though in an area that is managed for conservation.
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