Natural dynamics of a Fucus distichus (Phaeophyceae, Fucales) population: reproduction and recruitment

Abstract

ABSTRACT. Various phenomena related to reproduction and recruitment in a population of Fucus distichus L. emend. Powell in Vancouver, British Columbia. Canada were evaluated. Using log linear analysis and tests for simple, multiple and partial associations, a g e and size were both found to b e significant, but size slightly more so than age, as descriptors of reproductive events. Reproductive plants were found throughout the sampling period, from September 1985 to November 1987, but peaked in fall and winter of each year. Potential egg production, based on number of eggs produced per conceptacle and number of conceptacles per unit area of receptacle, is size-dependent. However, estimated monthly egg production, calculated by observed number of eggs in clusters extruded from the receptacle, is independent of plant size. Two types of recruits were monitored Microrecruits (< 1 mo-old of microscopic size) are germlings developed from fertilized eggs. Their numbers were assessed using settling blocks. Macrorecruits are detectable by the unaided eye and are plants appearing in the permanent quadrats for the first time. They can first be detected when about 3 to 4 mo old. The recruitment pattern of microrecruits is significantly correlated with reproductive phenology and patterns of potential and estimated monthly egg production. The pattern of recruitment of macrorecruits is negatively correlated with reproductive phenology and that of the estimated monthly egg production. Peaks in microrecruitment are not always followed by peaks in macro-recruitment. This apparent discrepancy is probably due to a differential survivorship of microrecruits over time or to the possible existence of a 'germling bank'. Patterns of survival and emergence of macrorecruits may b e independent of those of microrecruits or may be unrelated to the prevailing reproductive phenology.

Effects of density on the vital rates of a modular seaweed

“…On the other hand, similar results have been observed in other studies of density dependence in macroalgae (Black 1974, Reed 1990, Creed et al 1996. Self-thinning in marine algae occurred mainly among small recruits (Black 1974, Dean et al 1989, Ang 1991. Certainly, mortality of A. nodosum germlings under an adult canopy increased at higher germling density (Viejo et al 1999).…”

“…Second, other density-dependent processes affected the performance of the alga, increasing the risk of breakage to smaller sizes. Large (longer) plants broke more frequently, probably because they are more vulnerable to wave action (Gaylord et al 1994) and they can be more exposed to desiccation stress during low water than plants growing beneath the canopy (see Ang 1991). The breakages of large plants may mask the dominance and suppression in plant growth.…”

Recovery of the brown alga Fucus gardneri following a range of removal intensities

“…The amelioration of physical stress by adults often improves Fucus germling survival Johnson, 1991, 1993;van Tamelen et al, 1997). Furthermore, reproductive adults are an important source of local recruits in species with short-distance dispersal such as Fucus (Ang, 1991a). However, Fucus germlings were no more or less abundant in open areas over the course of our experiment.…”

The development of size structure in a youngFucus serratuspopulation

“…It therefore seems likely that, in F. serratus populations on some shores, individuals are retarded in a "seed bank" year round. "Seed banks" have recently been found in other seaweed species (Ang, 1991;Hoffmann & Santelices, 1991;Ang & De Wreede, 1992;Kendrick & Walker, I994, but contrast Creed, 1995) and the seed bank contingent may buffer stochastic events which remove macroscopic plants from the population. The implication is that macroalgal population studies which ignore the microscopic phase do so at their peril.…”