Biologists have long sought to identify and explain patterns in the diverse array of marine life histories. The most famous speculation about such patterns is Gunnar Thorson's suggestion that species producing planktonic larvae are rarer at higher latitudes (Thorson's rule). Although some elements of Thorson's rule have proven incorrect, other elements remain untested. With a wealth of new life-history data, statistical approaches, and remote-sensing technology, new insights into marine reproduction can be generated. We gathered life-history data for more than 1,000 marine invertebrates and examined patterns in the prevalence of different life histories. Systematic patterns in marine life histories exist at a range of scales, some of which support Thorson, whereas others suggest previously unrecognized relationships between the marine environment and the life histories of marine invertebrates. Overall, marine life histories covary strongly with temperature and local ocean productivity, and different regions should be managed accordingly.

This study links offspring size and energetic content to offspring performance (measured as growth and survivorship) in the intertidal gastropod Nucella ostrina and examines the effect of hatching size on performance at different times of year and in contrasting environments. The relationships between individual hatchling size and organic content were compared both within and among clutches of N. ostrina. Hatchling size was positively, significantly, and predictively correlated with hatchling organic content both within and among clutches, demonstrating that hatching size could be reliably used as an indicator of maternal investment. The slope of the relationship between hatchling size and organic content varied between clutches, suggesting intrapopulation variation in embryonic growth geometry. In field outplants, hatching size always had a positive and significant effect on growth, and small hatchlings took approximately one month to reach the initial size of their larger siblings. More large hatchlings than small hatchlings were recovered in every experimental outplant. The effect of hatching size on recovery was not significant in short (9 d) outplants, but recovery of large hatchlings was significantly greater than recovery of small hatchlings in two out of three long‐term (36 or 54 d) outplants. Overall recovery was lower in the summer, the long‐term outplant in which size did not significantly affect recovery. In experiments testing the relationship between hatching size and survivorship in two environments that differed in degree of sun exposure, size significantly and positively affected recovery in the more shaded habitat (with higher overall recovery) but not in the sun‐exposed environment. Thus, larger hatching size in N. ostrina results in (1) increased hatchling growth, (2) considerably shortened time to maturity, and (3) higher survivorship. However, the advantage of large hatching size was decreased under more severe environmental conditions, those which resulted in higher overall hatchling mortality. Contrary to predictions, poor environmental conditions may not be more likely to select for large offspring size in intertidal habitats: during periods of high heat stress, mortality may be largely random with respect to size.

Abstract. Over the past 30 years, numerous attempts to understand the relationship between offspring size and fitness have been made, and it has become clear that this critical relationship is strongly affected by environmental heterogeneity. For marine invertebrates, there has been a long-standing interest in the evolution of offspring size, but there have been very few empirical and theoretical examinations of post-metamorphic offspring size effects, and almost none have considered the effect of environmental heterogeneity on the offspring size/fitness relationship. We investigated the post-metamorphic effects of offspring size in the field for the colonial marine invertebrate Botrylloides violaceus. We also examined how the relationship between offspring size and performance was affected by three different types of intraspecific competition. We found strong and persistent effects of offspring size on survival and growth, but these effects depended on the level and type of intraspecific competition. Generally, competition strengthened the advantages of increasing maternal investment. Interestingly, we found that offspring size determined the outcome of competitive interaction: juveniles that had more maternal investment were more likely to encroach on another juvenile's territory. This suggests that mothers have the previously unrecognized potential to influence the outcome of competitive interactions in benthic marine invertebrates. We created a simple optimality model, which utilized the data generated from our field experiments, and found that increasing intraspecific competition resulted in an increase in predicted optimal size. Our results suggest that the relationship between offspring size and fitness is highly variable in the marine environment and strongly dependent on the density of conspecifics.

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Nonfeeding larvae of the echinoid Heliocidaris erythrogramma were raised in culture and examined for expression of a larval skeleton and for the arrangement of the ciliated band. Opaque larvae were fixed, cleared, and examined under polarized light for evidence of calcification. By 35 hr after fertilization (at 22 degrees C), a pair of triradiate spicules was present at the posterior end of the larvae. Each member of this pair formed a fenestrated spicule as it grew laterally. This pair and another pair which formed subsequently, were arranged across a plane of bilateral symmetry orthagonal to the juvenile oral aboral axis. These paired larval spicules can be identified as reduced expressions of postoral and posterodorsal rods found in plutei, and their expression indicates that the juvenile rudiment of H. erythrogramma forms on the left side and that larval body axes are conserved in this modified larva. By 44 hr the ciliated band formed as an incomplete transverse loop of three segments at the posterior end and on the dorsal surface of the ovoid larva. Cilia in these segments grew to lengths of 45-50 microns, longer than other swimming and feeding cilia reported for echinoderm larvae. Band segments are interpreted as expressions of epaulettes (specialized swimming bands) rather than the feeding ciliated band of the pluteus. The ciliated band segments and the larval spicules are both bilaterally symmetrical with respect to the same plane and indicate conserved larval bilateral symmetry despite the major asymmetry of the fates of cells on either side of this plane in their contribution to juvenile development.