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Marine Ecology Progress Series

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MEPS 133:191-201 (1996)  -  doi:10.3354/meps133191

Are neighbours harmful or helpful in Fucus vesiculosus populations?

Creed JC, Norton TA, Kain (Jones) JM

In order to investigate the effect of density on Fucus vesiculosus L. at all stages of its development, 2 experiments were carried out. A culture study in the laboratory found that increased density resulted in depressed growth and a negatively skewed population structure during the first month in the lives of freshly settled germlings. Intraspecific competition acts even at this early stage, and the limiting factor was probably nutrients. 'Two-sided' ('resource depletion') competition and an early scramble phase of growth may explain negative skewness in plant sizes. On the shore experimental thinning by reduction of the canopy resulted in increased macrorecruitment (apparent density) from a bank of microscopic plants which must have been present for some time. With increased thinning more macrorecruits joined the remaining plants, making population size structures highly positively skewed. Thinning had no effect on reproduction in terms of the portion of biomass as reproductive tissue. Manipulative weeding allows an assessment of the potential spore bank in seasonally reproductive seaweeds and revealed that there are always replacement plants in reserve to compensate for canopy losses. In F. vesiculosus the performance of individuals early on is crucial to their subsequent survival to reproductive stage, as neighbours are generally competitively harmful. However, a failure to 'win' early on may not necessarily result in the ending of a small plant's life -- the 'seed' bank still offers the individual a slim chance of survival and protects the population from harmful stochastic events.

Culture . Density . Fucus vesiculosus . Intraspecific competition . Thinning

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