Recruitment in most marine invertebrates depends on the larval supply and the success of metamorphosis as well as on the growth and survival of the early juveniles. These two aspects of the early-life history of the burrowing echinoid Echinocardium cordatum have been investigated in the laboratory. Seven natural substrata were tested with competent larvae to assess their metamorphosis inducing capacity. Sediment (the natural substratum inhabited by the echinoids) - har-bouring or not conspecific adults - was the most effective inductor, with nearly 100% metamorphosis. Cleaned sediment was much less inducing, indicating that associated microbes and/or organic matter might be the cues responsible for the starting of metamorphosis. Coralline algae were the second most inductive substratum (50-64% metamorphosis), while biofilm, detritic particles and green macroalgae (Enteromorpha sp.) were significantly less effective. A 47d survey of the survival and growth of early juvenile E. cordatum in sediment with various grain sizes (very coarse, coarse, medium, fine and silty) was undertaken. Survival was the highest in the medium grain sand, although the obtained differences among the five sediment types were not statistically significant. During the first month, growth was significantly faster in the finer sediments (fine and silt), but at the end of the experiment all sediment types were equivalent in terms of sizes reached by the juveniles. The results indicate that neither the competent larvae nor the juveniles appear to be very specific in terms of sediment type, suggesting that other factors (e.g., mortality or migration) would determine the distribution and abundance of adult populations. |
