A range of sizes of eight sea urchin species in the Family Echinometridae (Echinostrephus aciculatus, Heliocidaris erythrogramma, Colobocentrotus atratus, Heterocentrotus mamillatus, Heterocentrotus trigonarius, Echinometra mathaei, Echinometra lucunter, and Echinometra vanbrunti) were digitized and their shapes decomposed using elliptical Fourier analysis to quantify shape differences. Coefficients of sines and cosines of harmonics were used in a principal components analysis to show the separation of species. The principal component analysis shows the Echinometridae shape morphospace with the greatest separation of Echinostrephus and Colobocentrotus from other species. Major loadings were related to morphological measurements: height/diameter, lift of the oral surface above the substrate, and position of the ambitus to height. All species showed an increase in height/diameter with size, but only some species showed a correlation of oral lift or position of the ambitus with Fourier coefficients.

The starfish family Asterinidae shows a diversity of reproductive modes, and a number of species have sufficient life-history data that can be used for analysis, using life-cycle graphs. These include four species that reproduce by fission (Aquilonastra yairi, Nepanthia belcheri, Aquilonastra burtonii, and Ailsastra heteractis), a viviparous species (Parvulastra vivipara), two species with benthic egg masses (Asterina gibbosa and Asterina phylactica), one with planktonic larvae that do not feed (Cryptasterina pentagona), and one with larvae that feed in the plankton (Patiria miniata). Species are compared using adult and first-year survival and, for some species, the age at first reproduction, number of offspring (eggs or newly released juveniles), and individual growth parameters of the von Bertalanffy model. The sensitivity of population growth, fitness, to changes in these traits is shown by elasticity analysis, which aids in understanding possible consequences of environmental forces as well as possible directions of selection.

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.

Evidence is reviewed on growth rings in echinoid spines as indicators of age and the hypothesis is rejected that rings are periodic. Studies on Heterocentrotus mammillatus in Hawaii are consistent with the hypothesis that some if not all growth lines are formed in response to trauma.

Publisher Summary This chapter discusses the growth and survival of postsettlement sea urchins. Growth in echinoids means change in mass, diameter, and shape of the testes, which requires the expansion, calcification, and production of soft tissues. Skeletal growth is based on cellular processes that result in both shape changes during growth and rates of diameter change. Various forces that determine shape during growth have been explored in earlier studies, but shape seems best described as a response to forces generated by skeletal weight. Different skeletal elements of echinoids from a wide range of habitats are analyzed by using X-ray diffraction. Echinoid skeletons consist of ossicles that include spines, elements of Aristotle's lantern, and plates of the test that are attached to each other by small projections and collagen threads. Growth is by calcification around individual plates and the addition of new plates at the aboral ends of the ambulacral and interambulacral rows. Ossicles are calcite that contains various amounts of magnesium and are constructed as a fenestrated stereom that varies in porosity and construction. The resorption of calcite appears to be a general phenomenon in echinoids.

Estimating survival rate is a basic part of population studies. Generally it is assumed that populations being studied are both stable and stationary. This probably is seldom the case although as a long-term average populations may persist at a mean density. Estimating survival in short-term studies may fail to capture average rates. A long-term study of the purple sea urchin Strongylocentrotus purpuratus at Sunset Bay, OR, USA from 1964–2009 is used to demonstrate methods for estimating survival based on the coefficient of variation of size distributions, the fraction of new recruits in a population, means of size data coupled with estimates of growth, and a method that uses rates of flow through size categories. A short-term study of just a few years may by chance sample when an unusual recruitment event drives a population far from stationary structure and so distorts the estimate of mean survival. The best solution, as shown for S. purpuratus, is a long time series but in advance it cannot be determined how long this should be. If a study of three years shows no substantial change in population size structure it may be reasonable to accept estimates of survival.

Estimating survival rate is a basic part of population studies. Generally it is assumed that populations being studied are both stable and stationary. This probably is seldom the case although as a long-term average populations may persist at a mean density. Estimating survival in short-term studies may fail to capture average rates. A long-term study of the purple sea urchin Strongylocentrotus purpuratus at Sunset Bay, OR, USA from 1964-2009 is used to demonstrate methods for estimating survival based on the coefficient of variation of size distributions, the fraction of new recruits in a population, means of size data coupled with estimates of growth, and a method that uses rates of flow through size categories. A short-term study of just a few years may by chance sample when an unusual recruitment event drives a population far from stationary structure and so distorts the estimate of mean survival. The best solution, as shown for S. purpuratus, is a long time series but in advance it cannot be determined how long this should be. If a study of three years shows no substantial change in population size structure it may be reasonable to accept estimates of survival.

Negative senescence, a decrease in size-specific mortality of large individuals, is shown by sea urchins. Sea urchins have indeterminate growth and size-specific gamete production increases throughout life. These characteristics are present in short-lived species, Lytechinus pictus and L. variegatus as well as ones that are long-lived: Mesocentrotus franciscanus, Strongylocentrotus purpuratus, Echinometra mathaei, and Stomopneustes variolaris. Both short and long-lived species have cellular mechanisms that counter senescence. Many groups of organisms have species that are short-lived as well species with individuals that may attain ages of many hundreds of years. Generally it is assumed that short-lived species show senescence but results for sea urchins indicate that lack senescence may be present even when mortality is high.

Two juvenile specimens of a new species of Oreaster were collected at Parque Nacional Arrecife Alacranes and Triángulos Oeste in the southern Gulf of Mexico. DNA of mitochondrial loci identifies them as members of the same clade as cloning larvae of Oreaster found abundantly in waters of the Florida Current-Gulf Stream system, and distinct from Oreaster clavatus and Oreaster reticulatus, the two known Oreasteridae species in the North Atlantic. Larvae from the new species of Oreaster persist as clones but also metamorphose and settle to the benthos with typical asteroid morphology.

Larval cloning occurs in echinoderm species and has been viewed as possibly adaptive. A species of Oreaster currently being described has linked a rare benthic stage with common planktonic larvae that clone, and this calls attention to questions in life stage linkages. Life cycle analysis shows that there are unresolved problems in our understanding of the dynamics of species with cloning larvae, in particular their survival and duration in the plankton. Possible solutions are (1) benthic adults that are rare are also very long-lived or (2) survival in the plankton is much higher than has been reported.

Size, growth, and density have been studied for North American Pacific coast sea urchins Strongylocentrotus purpuratus, S. droebachiensis, S. polyacanthus, Mesocentrotus (Strongylocentrotus) franciscanus, Lytechinus pictus, Centrostephanus coronatus, and Arbacia stellata by various workers at diverse sites and for varying lengths of time from 1956 to present. Numerous peer-reviewed publications have used some of these data but some data have appeared only in graduate theses or the gray literature. There also are data that have never appeared outside original data sheets. Motivation for studies has included fisheries management and environmental monitoring of sewer and power plant outfalls as well as changes associated with disease epidemics. Studies also have focused on kelp restoration, community effects of sea otters, basic sea urchin biology, and monitoring. The data sets presented here are a historical record of size, density, and growth for a common group of marine invertebrates in intertidal and nearshore environments that can be used to test hypotheses concerning future changes associated with fisheries practices, shifts of predator distributions, climate and ecosystem changes, and ocean acidification along the Pacific Coast of North America and islands of the north Pacific. No copyright restrictions apply. Please credit this paper when using the data.

Rising atmospheric CO2 concentrations will significantly reduce ocean pH during the 21st century (ocean acidification, OA). This may hamper calcification in marine organisms such as corals and echinoderms, as shown in many laboratory-based experiments. Sea urchins are considered highly vulnerable to OA. We studied an Echinometra species on natural volcanic CO2 vents in Papua New Guinea, where they are CO2-acclimatized and also subjected to secondary ecological changes from elevated CO2. Near the vent site, the urchins experienced large daily variations in pH (>1 unit) and pCO(2) (>2000ppm) and average pH values (pH(T) 7.73) much below those expected under the most pessimistic future emission scenarios. Growth was measured over a 17-month period using tetracycline tagging of the calcareous feeding lanterns. Average-sized urchins grew more than twice as fast at the vent compared with those at an adjacent control site and assumed larger sizes at the vent compared to the control site and two other sites at another reef near-by. A small reduction in gonad weight was detected at the vents, but no differences in mortality, respiration, or degree of test calcification were detected between urchins from vent and control populations. Thus, urchins did not only persist but actually thrived' under extreme CO2 conditions. We suggest an ecological basis for this response: Increased algal productivity under increased pCO(2) provided more food at the vent, resulting in higher growth rates. The wider implication of our observation is that laboratory studies on non-acclimatized specimens, which typically do not consider ecological changes, can lead to erroneous conclusions on responses to global change.

A wide variety of organisms show morphologically plastic responses to environmental stressors but in general these changes are not reversible. Though less common, reversible morphological structures are shown by a range of species in response to changes in predators, competitors or food. Theoretical analysis indicates that reversible plasticity increases fitness if organisms are long-lived relative to the frequency of changes in the stressor and morphological changes are rapid. Many sea urchin species show differences in the sizes of jaws (demi-pyramids) of the feeding apparatus, Aristotle's lantern, relative to overall body size, and these differences have been correlated with available food. The question addressed here is whether reversible changes of relative jaw size occur in the field as available food changes with season. Monthly samples of the North American Pacific coast sea urchin Strongylocentrotus purpuratus were collected from Gregory Point on the Oregon (USA) coast and showed an annual cycle of relative jaw size together with a linear trend from 2007 to 2009. Strongylocentrotus purpuratus is a long-lived species and under field conditions individuals experience multiple episodes of changes in food resources both seasonally and from year to year. Their rapid and reversible jaw plasticity fits well with theoretical expectations.

We evaluated the effects of potential predators from intertidal habitats on Strongylocentrotus purpuratus survival using laboratory experiments and assessed abundances of main predatory species along the Pacific coast of North America. The interactive effects of urchins’ and predators’ sizes in mediating predation were quantified. Habitat complexity (substrate pits, adult spine canopy) was manipulated to examine its effects on predation of most susceptible individuals (<14 mm). Pachygrapsus crassipes was identified as a major predator of urchins up to ≈30 mm. A positive effect of predator size on consumption of progressively larger urchins was detected, probably due to a mechanical limitation on crabs’ ability to consume large prey. Larger claws of males with respect to females of comparable sizes facilitated the handling of larger prey. Substrate refuges significantly reduced mortality on juvenile urchins. These results show that crab predation may be important in organizing intertidal communities, despite multiple ecological mechanisms promoting sea urchin survival.

We conducted a tagging study of Lytechinus variegatus for 1 year (2005-2006) in Bermuda. At two sites, Flatts Inlet (n = 248) and Emily's Bay (n = 116), we collected all individuals, recorded test diameters, injected them with calcein, and released them. We also held a laboratory sample (n = 119) of tagged urchins in a tank stocked periodically with seagrass. In 2006, samples were collected, skeletal elements cleaned, and demipyramids (jaws) from Aristotle's lanterns measured and examined for the tag. We recovered 505 sea urchins with 11 tagged and 21 with 4 tagged from Flatts Inlet and Emily's Bay respectively. In the lab only one individual was not tagged. The jaw-test allometry indicated food-limitation in the laboratory sample. Early growth is rapid and individuals between 25-35 mm can grow as large as 60 mm in one year. Subsequent growth is slower and individuals > 70 mm may be 5-7 years old.

Various models have been used to describe sea urchin growth including the von Bertalanffy, Richards, logistic, Tanaka, Gaussian, Gompertz, logistic dose response, and one derived from the Gamma function. Data from three sea urchins, Mesocentrotus (Strongylocentrotus) franciscanus, Echinometra mathaei, and Stomopeustes variolaris, tagged with tetracycline were used to order models based on levels of support determined by the wi measure of the Akaike's Information Criterion. Growth parameters were combined with the mean of measured size-frequency data to estimate survival and showed that estimates were insensitive to the growth model selected.

Total body size, mass or linear measurements, and gonad mass or volumes have been recorded for the North American Pacific coast sea urchins Strongylocentrotus purpuratus, Mesocentrotus (Strongylocentrotus) franciscanus, and Lytechinus pictus by various workers at diverse sites and for varying lengths of time from 1954 to 2009. Some dissections included other body components such as the gut, body wall, and Aristotle's lantern, and some dissections included both wet and dry mass. There are numerous peer‐reviewed publications that have used some of these data, but some data have appeared only in graduate theses or in the gray literature. There also are data that have never appeared outside the original data sheets. Historically, data were used to describe reproductive cycles and then to compare responses to stressors such as food limitation or pollution. Differences in temperature among sites also have been explored. More recently, dissection data have linked gonad development to ocean conditions, so called bottom‐up forcing. The data set presented here is a historical record of gonad development for a common group of marine invertebrates in intertidal and nearshore environments, which can be used to test hypotheses concerning future changes associated with climate change and ocean acidification along the Pacific Coast of North America.

Comparing life histories has used measures of growth or a combination of growth and survival. A useful relationship is between the growth-rate constant, K, of the Brody-Bertalanffy growth model, and the instantaneous mortality rate, M. Asymptotic size, S-infinity, and K have been combined as KS infinity in different forms but this is not useful because small K and large S-infinity can have the same product as large K and small S-infinity. Life history comparisons are more difficult with other growth models. Biomass and production provide a currency that is independent of any particular growth model but require measurements in units of mass or energy so models with linear dimensions need conversion. Analysis is illustrated using the red sea urchin Strongylocentrotus franciscanus. In addition to P/B, production of spawn mass relative to total production is a measure of relative allocation and adds an extra dimension to life-history comparisons of sea urchins.