Fragment Recruitment Research Articles

Population growth of a gorgonian coral: equilibrium and non-equilibrium sensitivity to changes in life history variables.

A size dependent model of population growth of the Caribbean gorgonian Plexaura A is developed based on observed rates of survival, growth and colony fragmentation at a site in the San Blas Islands, Panama. Sensitivity and elasticity analyses indicate that the fate of large colonies has the greatest effect on population growth. Variables which directly affect the generation of large colonies have the next greatest effect on population growth. These variables include the recruitment of large fragments, and the survivorship of colonies in the next smaller size class. Sexual reproduction has an extremely limited ability to affect population growth. Vegetative reproduction has a greater potential effect on growth rates. Environmental conditions regularly change the matrix of transition probabilities which predicts population growth. This keeps the population from approaching its stable size class distribution. Deviations from the stable size class distribution alter sensitivity and elasticity and in this case have the effect of increasing the importance of survivorship of the smallest colonies. Nonequilibrium conditions alter sensitivity analyses and it is important to assess whether populations are at equilibrium and to determine the effects of such deviations on the sensitivity analysis.

Variation in clone structure of fragmenting coral reef sponges

Populations of three branching Caribbean demosponge species are composed of clones produced by asexual fragmentation. Dispersal of the fragments before they become established as independent individuals scatters clone members widely and intermixes members of different clones, complicating study of the clone structure of these populations and contrasting with many other sessile clonal organisms. Clone structures of these populations were inferred using a combination of tissue-compatibility relationships and an analysis of variations in morphology and colour. Although tissue compatibility cannot be used for precise identification of sponge clones, in general, patterns of variation in morphological characters influencing fragmentation and patterns of fragment dispersal and recruitment suggest that, in these populations, tissue-compatibility relationships closely reflect clone structure. Conditions that must be met in order to use tissue compatibility for study of sponge clones are discussed, and previous results, from which conflicting conclusions have been drawn, reconciled in this context. Variations among clones in numbers of physiologically independent members and in size and shape of areal extent are discussed in the context of processes that may affect evolution of clonal characters in these populations and in other species that propagate by dispersing asexual fragments.