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 andis a potential economic resource. In both 1993 and 1994, the abundanceof M. cornucopiae from Prasiola Point, southern Barkley Sound, washigh in spring and summer and low in fall and winter. In 1995, however,the abundance in summer was unexpectedly low, and this trend deepenedin 1996. Correlations between the temporal changes of abundance and ofsome abiotic variables were done as a first approach to explaining thesechanges of abundance. The abiotic variables used were air temperature,sea surface temperature, wave height, all three measured on an oceanicbuoy close to Prasiola Point, and seawater salinity, determined for coastalwaters from northern Barkley Sound. These were the closest sites toPrasiola Point for which reliable abiotic data existed. None of thecorrelations were significant. Field observations done at Prasiola Pointsuggest that air temperatures reached higher values there than at theoceanic buoy. Together with irradiance, in situ air temperature may havehad an important role in the interannual differences of abundance througha higher physical stress on thalli, resulting in the high proportion ofbleached tissues observed in summer 1996. Future studies on thepopulation dynamics of M. cornucopiae should benefit fromquantifying these variables in situ.