Variation in Suspension Feeding Rates among Larvae of Some Temperate, Eastern Pacific Echinoderms

Abstract

Larvae of many echinoderms and other benthic marine invertebrates depend on ciliary suspension feeding for growth and development, but some larvae may be superior feeding devices (with consequences for variation in growth, size, and fitness). I measured differences in feeding performance among larvae of 9 echinoderm species from 4 taxonomic classes (Asteroidea, Ophiuroidea, Holothuroidea, Echinoidea). Maximum clearance rates (relative to size of the feeding structure) of some larvae were much higher than the rates of others, indicating substantial variation in feeding capabilities among larvae of similar size. In order to interpret these differences in feeding capability, I also give some preliminary data on larval form, development, and organic content. Although incomplete in several respects, these data do not indicate a simple relation between larval feeding and growth. This surprising result indicates that functional morphology is not always the most appropriate perspective from which to examine variation in growth and development of planktonic larvae. Additional key words: larval morphology, cilia The feeding planktonic larvae of benthic marine invertebrates are life-history devices for turning eggs into juveniles (Strathmann 1985). Adult females can increase their fecundity by spawning large numbers of relatively small eggs. Small eggs develop into larvae that feed on small suspended particles or other zooplankton, grow, and metamorphose at a large size relative to the contents of an egg. Efficient and rapid growth from a small egg to a large juvenile is an important component of fitness in marine invertebrates with feeding larvae (Havenhand 1995), but some larvae may be more equal to this task than are others. Connections between feeding capability, larval morphology, and components of fitness might be strong but have not been considered in much detail. Differences in larval form may be correlated with differences in feeding capabilities (e.g., McEdward & Strathmann 1987). Despite a large number of studies of larval feeding (reviewed by R. Strathmann 1987; Hart & Strathmann 1995), there is little information that can be used to compare feeding rates or other measures of the feeding capabilities of different larvae (e.g., Pearse et al. 1991). a Present address: Section of Evolution and Ecology, Division of Biological Sciences, University of California, Davis, CA 95616-8755, USA. Here I show that feeding capability varies substantially among larvae of some co-occurring, shallow-water echinoderms from the eastern temperate Pacific. I measured maximum clearance rates for larvae of different sizes and developmental stages for each species, and compared the relationship between larval size and maximum clearance rate among species. I found some large differences in this relationship, which indicate that some larvae are better suspension feeders than are others. These differences were weakly associated with variation in larval body form among echinoderm class-