Interannual variation of the abundance of Mazzaella cornucopiae (Rhodophyta, Gigartinales) from Pacific Canada in relation to changes in abiotic variables

The seaweed Mazzaella cornucopiae (Postels & Ruprecht) Hommersand is common in rocky intertidal areas from Pacific Canada and is a potential economic resource. In both 1993 and 1994, the abundance of M. cornucopiae from Prasi ola Point, southern Barkley Sound, was high in spring and summer and low in fall and winter. In 1995, however, the abundance in summer was unexpectedl y low, and this trend deepened in 1996. Correlations between the temporal c hanges of abundance and of some abiotic variables were done as a first appr oach to explaining these changes of abundance. The abiotic variables used w ere air temperature, sea surface temperature, wave height, all three measur ed on an oceanic buoy close to Prasiola Point, and seawater salinity, deter mined for coastal waters from northern Barkley Sound. These were the closes t sites to Prasiola Point for which reliable abiotic data existed. None of the correlations were significant. Field observations done at Prasiola Poin t suggest that air temperatures reached higher values there than at the oce anic buoy. Together with irradiance, in situ air temperature may have had a n important role in the interannual differences of abundance through a high er physical stress on thalli, resulting in the high proportion of bleached tissues observed in summer 1996. Future studies on the population dynamics of M. cornucopiae should benefit from quantifying these variables in situ.