Mechanisms of recolonization of the clonal intertidal alga Mazzaella cornucopiae (Rhodophyta, Gigartinaceae) after disturbances

The recolonization of the clonal intertidal alga Mazzaella cornucopiae (Pos tels et Ruprecht) Hommersand is considered here, as part of a larger projec t on its population ecology. Recolonization in Barkley Sound, Pacific Canad a, started a few months after completely clearing experimental 100-cm(2) qu adrats in late spring and occurred both by vegetative growth of perennating holdfasts bordering disturbed quadrats and by recruitment from spores. In terms of percent cover, both mechanisms contributed similarly to recoloniza tion during the first 2 years, although vegetative recolonization was highl y variable among quadrats. Great spatial variability prevented the detectio n of a temporal pattern for recruit density on statistical grounds. However , cohort demography showed some degree of seasonality. Turnover rates of re cruits were high; they lived 2.6 months on average. Recruitment was highest between fall or winter and midspring (as might be expected, given that rep roductive structures appeared in fall and winter) and null in the first two summer seasons. The highest mortality was recorded in summer, when desicca tion and irradiance are highest on an annual basis. Frond density was very variable on a spatial scale and did not follow a clear temporal pattern. Th e average number of fronds per recruit apparently increased between winter and summer, paralleling frond dynamics in mature stands. By monitoring reco lonization in quadrats of the same size cleared previously by other researc hers, the time of full recovery of M. cornucapiae was estimated to be 2.7-3 .5 years.