Are neighbours harmful or helpful in Fucus vesiculosus populations?

Abstract

In order to investigate the effect of density on Fucus vesjculosus 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 loined the remaining plants, making population size structures highly posit~vely skewed. Thinning had no effect on reproduction In terms of the portion of biomass as reproductive tissue. Manipulative weedlng allows an assessment of the potent~al spore bank in seasonally reproductive seaweeds and revealed that there are always replacement plants in reserve to compensate for canopy losses. In E 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

Effects of density on the vital rates of a modular seaweed

“…Considerable progress has recently been made with such experiments (Reed 1990, Ang & De Wreede 1992, Kendrik 1994, Creed et al 1996, Creed et al 1998, Lazo & Chapman 1998. However, observational studies are also valuable especially as a first attempt to investigate processes correlated with density.…”

“…Results from both manipulative and observational studies suggest that the algal responses to density are in many cases similar to those observed in terrestrial plants. Self-thinning or density-dependent mortality is common in macroalgal stands (Schiel & Choat 1980, Dean et al 1989, Kendrick 1994, Creed et al 1996 as it is in terrestrial systems (Harper 1977, Westoby & Howell 1986, Schmitt et al 1987. Algal individuals often have lower growth rates in crowded stands, and the effects are more dramatic in small plants (Reed 1990, Ang & De Wreede 1992, Creed et al 1998.…”

“…However, the strength of manipulative experiments in natural populations is that, when significant effects are found, the generality and predictive power are much higher than for other types of experiments. For perennial species, experiments on intraspecific competition in natural populations have been scarce and mostly restricted to manipulations where the density of established plants has been decreased (e.g., Fowler 1986, Fowler 1995, Creed et al 1996, but see Shaw 1987. For obvious reasons it would be very difficult to increase the density of plants in many species, e.g., trees.…”

A Competitive Hierarchy Model Integrating Roles of Physiological Competence and Competitive Ability Does Not Provide a Mechanistic Explanation for the Zonation of Three Intertidal Fucus Species in Europe

“…obs. and see Schonbeck and Norton 1979b: but see Creed et al 1996 for similar data on F, .serrntus).…”

Divergent responses in growth and nutritional quality of coastal macroalgae to the combination of increased pCO2 and nutrients

“…In the coastal ecosystems, perennial Fucus spp. can grow in high densities in the intertidal and shallow subtidal zones, up to 4,000 plants/m 2 (Creed et al, 1996). In Narragansett Bay, Fucus spp.…”