Gulf of St. Lawrence aster COSEWIC assessment and status report: chapter 2
COSEWIC
Executive summary
Gulf of St. Lawrence Aster
Symphyotrichum laurentianum
Species information
Gulf of St. Lawrence Aster, Symphyotrichum laurentianum (synonym: Aster laurentianus), is a halophytic, herbaceous annual that occurs in coastal habitats in New Brunswick (NB), Prince Edward Island (PEI) and the Magdalen Islands (MI). It is a rare endemic of the Gulf of St. Lawrence. Twenty-nine populations are known and verified, including 15 in the MI, eight in PEI and six in NB. Apart from these, there are four historical occurrences, whose habitat has been destroyed or that have not been seen for more than 25 years (one in the MI, two in PEI and one in NB).
Distribution
Gulf of St. Lawrence Aster has been reported from five areas of the Magdalen archipelago, for a total of 16 occurrences, one of which is historical. One of the populations constitutes a new observation relative to the data of Gilbert et al. (1999) and three are new relative to the data in the last Committee on the Status of Endangered Wildlife in Canada (COSEWIC) report (Houle and Haber, 1990). Virtually all of the individuals are concentrated at three sites: the Havre aux Basques lagoon, the Bassin aux Huîtres and the Barachois salt marsh at Fatima.
The New Brunswick populations are known from four localities. One is located on Miscou Island, another near Tracadie (Val-Comeau), a third in Kouchibouguac National Park and one at Bouctouche Dune. There are a total of seven occurrences, one of which is historical. Recent survey efforts have located four new occurrences since 1999.
Of the ten occurrences in Prince Edward Island, two are historical. These are all the same as in Gilbert et al. (1999), but the East Marsh occurrence has been subdivided into two separate populations. Most of the occurrences are reported in Prince Edward Island National Park. The one at Tignish, Prince County, in the north of the island, has not been seen since 1986.
Habitat
Gulf of St. Lawrence Aster occurs on wet, predominantly sandy substrates exposed to equinoctial high waters and storm waves: sheltered beaches near sea level on open and slightly sloping ground and areas of scattered vegetation in high salt marshes.
Biology
Gulf of St. Lawrence Aster is in full flower by mid-September and fruits in late September. Fruit dispersal is in late October (Houle, 1988b). The development of Gulf of St. Lawrence Aster in the greenhouse is very rapid (two-three months). Gulf of St. Lawrence Aster and the other species of the genus Symphyotrichum are self-fertile. Although unidirectional interspecific hybrids can be produced experimentally, this species is reproductively isolated by two factors: geographic isolation and self-fertility.
Population sizes and trends
The total population in the Magdalen Islands is estimated at more than 12 million individuals, distributed over approximately 10 ha. The higher population estimate, compared to the data of Houle and Haber, appears to be explained both by a more exhaustive survey and perhaps by ecological conditions favourable to the species during the surveys, in particular the low water level in the lagoons in 1994. Certain populations have declined or disappeared, possibly owing either to vegetation canopy closure, coverage by eelgrass debris or burial under sand following storms or human activity. Since the habitat is denuded more or less cyclically by natural phenomena (waves, storms, etc.), the disappearance of these sub-populations may be only temporary.
The seven New Brunswick populations total approximately 2000 to 3000 individuals; however, there have been large fluctuations in the last two years due mainly to storm events. The population at the St. Louis wharf in Kouchibouguac National Park has probably disappeared since 1979. The population around the lighthouse on Miscou Island has not been seen since 1984 and has almost certainly disappeared. In contrast, four new populations have been discovered: one on Miscou Island (Malbaie south), two in Kouchibouguac National Park and one at Bouctouche Dune.
Of the ten populations in Prince Edward Island, two are historical (Brackley Point and Grand Tracadie). Of the six sites surveyed in 1999 in Prince Edward Island National Park, one has since been subdivided into two separate occurrences (East Marsh). Outside the park, only the occurrence at Tignish, Prince County, in the north of the island, was still extant in 1986. In the national park, the Dune Slack and East Marsh Blocalities have the largest populations, together comprising nearly 100 000 individuals.
Limiting factors and threats
Interspecific competition plays a significant role in the population dynamics of Gulf of St. Lawrence Aster. Vegetation canopy closure is not conducive either to its reproductive effort or to its survival rate. Light appears to be the most important abiotic factor in the growth and reproduction of Gulf of St. Lawrence Aster. Thus, natural disturbance from wave action, ice or storm events appears to play a role in maintaining or creating habitat. Anthropogenic disturbances such as cottage construction and fill operations completely destroy the species’ habitat.
Special significance of the species
Gulf of St. Lawrence Aster is an example of an endemic taxon restricted to the Gulf of St. Lawrence. Other rare species are sometimes associated with this species. There is no known economic use for Gulf of St. Lawrence Aster, nor any particular use by Aboriginal peoples.
Existing protection or other status designations
The occurrences located in Prince Edward Island and Kouchibouguac national parks are protected by the park managers and monitored annually. Gulf of St. Lawrence Aster has been designated by COSEWIC as Special Concern in Canada in 1989. The species is currently designated threatened in Quebec and endangered in New Brunswick. It is considered rare, but has not yet received any special designation in Prince Edward Island.
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