Future Potential Impact of Rapid Climate Change in the Region

Analysis of Atmosphere-Ocean General Circulation Models (AOGCMs) predicts that the average SST in the North Atlantic will increase by 2°C by 2060, and that the impact is expected to be greater during the winter period (Chmura et al., 2005). Although this increase is expected to significantly influence the distribution and abundance of marine organisms in the Northwest Atlantic, the rockweed abundance in the Maritime Provinces could in part benefit from an increase in SST, especially the stocks along the Bay of Fundy where the average SSTs would increase to around 14°C in summer. The southwestern and eastern shores of NS could reach average summer temperatures of 16-17°C, and probably up to 20°C in shallow embayments. The predicted maxima are around or below the 25°C that limits rockweed growth, and well below the lethal range of 27-28°C (Keser et al., 2005). Currently, the vegetative growth of Ascophyllum is almost nil from December to early March and increases by mid-March (R. Ugarte, 1999-2001, personal observation) in the Maritimes. Warmer water will promote an earlier growth season during spring and possibly slow but continuous growth during the winter period.

However, an increase in temperature will also promote the growth of other seaweeds with greater eurythermal capacity such as F. vesiculosus and similar opportunistic species. If an increased water temperature is the factor behind the current increase of F. vesiculosus in NS, then we should expect this trend to continue, with a potential Fucus/Ascophyllum mixture of up to 50% in some locations by 2060. Although we lack historical information for the Fucus/Ascophyllum proportions in NB, data collected during 2007 and 2008 by ASL showed that F. vesiculosus in area 6 (Fig. 3) is around 6-7% of the total fucoid biomass, and that rapid changes from Ascophyllum to Fucus have been observed in some sectors of this area (Ugarte et al., 2008).

Thus, it is probable that southern NB will also experience a significant increase in F. vesiculosus during the next half century. Although it is only an anecdotal observation, a shift in the fucoid composition from Ascophyllum to F. vesiculosus has also been observed in Ireland and it has been associated with a shift in prevailing wind patterns.

Invasive species are another potential problem associated with climate change and the Canadian Maritimes certainly will be affected to some degree. Grateloupia turuturu, a red seaweed native to Japan and Korea, has invaded the coasts of New England (Mathieson et al., 2008). The temperature tolerance of this species is 4-28°C (Simon et al., 1999, 2001) and a low SST has probably precluded its further northern invasion into Canadian waters. However, an increase in SST of 2° may well create a suitable habitat for such opportunistic species to develop along the coastline of the Maritime Provinces.

Another invasive species, Codium fragile, has already become established in the shallow subtidal and intertidal pools in areas 3 and 4 since the mid-1990s (Chapman et al., 2002), but so far it has been unable to colonize the waters of the Bay of Fundy due to the low summer SSTs. However, an increase in the SSTs may allow this species to survive in shallow warmer embayments of the Fundy region (Fig. 8 Photo. Raul Ugarte).

Figure 8. Codium fragile is commonly found in the subtidal zone and tide pools. We have also observed it as an epiphyte on A. nodosum in southwestern NS.

Another large change predicted by the AOGCMs models for the region by 2060 is a significant reduction of the ice season in the Gulf of Saint Lawrence during the winter (Chmura et al., 2005), a trend that we are clearly observing today (Ugarte et al., 2008). This trend will be even more dramatic in the shallow bays of NS, which will probably remain ice free during winter. Although this situation seems favorable for Ascophyllum, the ice also serves as a thermal insulation against sudden drops in air temperature (Scrosati and Eckersley, 2007) and as a protective barrier from winter storms. According to Environment Canada, Nova Scotia (along with Newfoundland and Labrador) has the highest storm frequency during the winter and early spring of any region in Canada owing to its proximity to the Gulf Stream. These storms can generate wave heights greater than 14 m, and storm surges in excess of 1 m. The frequency and intensity of storms have increased in the last decade in the Maritimes and this trend is expected to continue. Under this scenario, it is possible that a large percentage of rockweed biomass along the southern and eastern shores (areas 3 to 5) of NS may be lost to storm damage during the winter each year, with those in the most exposed area being unable to recoup the lost biomass during the summer months.

Information continues to be collected on the rockweed biomass and their associated flora in the Canadian Maritimes as part of the ASL harvesting responsibilities and the Company's environmental stewardship role. Such data are essential for understanding in detail the scale of changes occurring in this region, and are required when long-term retrospective analyses are carried out in the future.

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