Contrasting ecological implications of food limitation in sea urchins and herbivorous gastropods

Abstract

Populations of sea urchins often fluctuate greatly in density. The density of sea urchins is usually inversely correlated with the abundance of macrolagae. It is argued that fluctuations in density are a predictable consequence of the unique morphology and physiology of sea urchins. An extraordinary ability to accomodate food Limitation through variations in growth rate means that surv~vorship and food abundance are largely decoupled. These features of sea urchins differ from those of the herbivorous gastropods. The ecological implications of these differences are discussed. A different perspective is required for the interpretation of the population dynamics of sea urchins.