Abstract
Introduction: There are problems and puzzles in understanding reproduction, growth and mortality in echinoderm life cycles. Objective: Explore problems and puzzles in life cycles that are important and challenging. Methods: The literature is used to elucidate problems associated with all life stages. Results: Sources of larvae that settle at a site are explored using oceanographic modelling and genetic methods. There are few studies that have estimated larval mortality in the plankton under field conditions and results differ from experimental results or patterns of settlement. In a small number of studies, mortality rate of newly settled larvae appears to change rapidly as individuals grow. There are problems measuring size, and measurement bias that interferes with many tagging methods used to estimate growth. There also are problems with the use of natural growth lines and commonly used software to estimate both growth and mortality from size-frequency data. An interesting puzzle is that echinoderms may show negative senescence with mortality rate decreasing with size. There is a problem in fertilization success based on density so there should not be rare species where sexes are separate with free spawning of gametes yet there seem to be rare echinoderms. Conclusions: All parts of echinoderm life cycles provide problems and puzzles that are important and challenging.
Highlights
There are problems and puzzles in understanding reproduction, growth and mortality in echinoderm life cycles
A second problem is found in old individuals that are growing so slowly that annual lines cannot be resolved. This problem usually is not addressed and the result is that age of large individuals is seriously underestimated and a growth model that is selected may be flawed and estimates of mortality underestimated
Common programs for doing this are FISAT II, ELEFAN in R, and TropFishR. These methods use the von Bertalanffy growth model and so have an asymptotic size, S∞, which has problems associated with estimation (Schwamborn, 2018)
Summary
Reference Lamare & Barker, 1999 Lamare & Barker, 1999 Lamare & Barker, 1999 Lamare & Barker, 1999 Rumrill, 1987, 1990 Rumrill, 1987, 1990 Rumrill, 1987, 1990 Johnson & Shanks, 2003 Ebert & Janies, 2020 Ebert & Janies, 2020. A second problem is found in old individuals that are growing so slowly that annual lines cannot be resolved This problem usually is not addressed and the result is that age of large individuals is seriously underestimated and a growth model that is selected may be flawed and estimates of mortality underestimated. Common programs for doing this are FISAT II, ELEFAN in R, and TropFishR These methods use the von Bertalanffy growth model and so have an asymptotic size, S∞, which has problems associated with estimation (Schwamborn, 2018). Three sea urchin species have sufficient data that show changes in size-specific reproduction, growth, and mortality (Ebert, 2019). S. purpuratus, shows indeterminate growth, increased reproductive output with size, and decreased mortality with size (Fig. 8) It is unknown how common this pattern might be for other echinoderms. Problems with fertilization close the life-cycle (Fig. 1) started at the beginning of this manuscript
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