Gulf of St. Lawrence aster COSEWIC assessment and status report: chapter 10

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Limiting factors and threats

Boudreau and Houle (1998) and Houle et al. (2002) have demonstrated that interspecific competition appears to play 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 main abiotic factor that has a significant effect on the growth and reproduction of Gulf of St. Lawrence Aster (Houle et al., 2002). Astonishingly, the availability of nutrients has no significant effect on growth and reproduction. The salinity of the substrate has a marked inhibiting effect on seed germination, even though the seeds retain their viability when rinsed with distilled water after 30 days of exposure to salt (Houle et al., 2002). However, salinity does not appear to have an effect on reproduction. Dry, hot years could have a major impact on the populations, since Gulf of St. Lawrence Aster is sensitive to water stresses.

A major storm (September 12, 2002, “Gustave”) flooded or buried several populations in New Brunswick and Prince Edward Island under masses of eelgrass or sand (David Mazerolle, 2003, Jean Gagnon, Denyse Lajeunesse, pers. comm.). The populations of Kouchibouguac, flooded in 1999, have still not re-appeared although plants have re-established at the Dune de Bouctouche (David Mazerolle, 2003.).

Anthropogenic disturbances, such as the construction of cottages and fill operations, completely destroy the species’ habitat. This is believed to have impacted at least two sites in the past, although protection exists at several of the current sites. In Prince Edward Island National Park, the type locality of Brackley Point disappeared following development work carried out by the park. Extensive dredging operations have been carried out at the Long Pond site and it is possible that Gulf of St. Lawrence Aster disappeared following this.

All Terrain Vehicles (ATV) tracks have occasionally been observed, particularly at the Clarke Bay site (Cap de l’Est, Magdalen Islands [MI]), in the Barachois salt marsh, at Fatima (Cap de l’Hôpital, MI) and in the habitats of Kouchibouguac National Park (Dietz and Chiasson, 2001). The impact of these disturbances would be expected to vary with extent and intensity, but may have temporarily favoured its establishment by creating gaps in the plant cover, notably in Clarke Bay, where Gulf of St. Lawrence Aster has been found colonizing ruts.

Finally, artificial changes in saltwater levels or circulation patterns (permanent opening or closing of a lagoon, etc.) could affect the health of Gulf of St. Lawrence Aster populations by altering the disturbance cycle needed to maintain its habitat. This situation has occurred, for example, at Bassin aux Huîtres, Îles de la Grande Entrée, MI, where circulation in the basin was modified after its entrance was moved.