Morphological relationships among fronds of giant kelp Macrocystis pyrifera off La Jolla, California

Abstract

Giant kelp Macrocystispyrifera is the dominant macrophyte along much of the California coast. Each plant is composed of several fronds, each of which can have more than 100 blades. We have developed equations which describe relationships between size and distance which account for variations in frond size and blade node number The most successful descriptions involve the separation of within-frond patterns from between-frond patterns. One useful within-frond description is the relationsh~p between the area of blade relative to the largest blade on its frond (e.g. a fractional area of 0.1) as a function of its relative position on the frond (e.g. the blade's node posit~on is 0.1 of the total number of nodes from the apex). A useful between-frond description is the relationship between the area of the largest blade on a frond and the frond size. The 2 types of descriptions used together form a compact description of frond morphology that accounts for most of the variability in blade size and position for a range of frond sizes. Similar relationships hold for the distributions of frond lengths within a kelp plant. The morphological relationships are expressed used power series that were fit to the data. The existence of power series relationships describing kelp morphology can be used for modelling studies of such factors as the light field around a plant.