Red Sea Urchin Strongylocentrotus Franciscanus Research Articles

Thermoregulatory Behavior of Red Sea Urchin Strongylocentrotus Fran-ciscanus (Agassiz, 1863) and Purple Sea Urchin Strongylocentrotus Purpu-ratus (Stimpson, 1857) (Echinodermata: Echinoidea)

Thermoregulatory behavior of red sea urchin Strongylocentrotus franciscanus and purple sea urchin S. purpu- ratus was determined in a horizontal thermal gradient. The preferred temperature select by the red sea urchin was 17.5 ± 0.3 oC during the diurnal cycle and 16.8 ± 0.4 oC for the night. The purple sea urchin preferred temperature during day- time of 18.8 ± 0.2 oC and night was 17.4 ± 0.3 oC. For both species of sea urchin preferendum between day and night cy- cles were different (P < 0.05), the purple sea urchin preferred higher temperatures that red read urchin, suggesting that S. purpuratus use thermoregulatory behavior as a mechanism of environmental segregation to avoid competition for space and food with red sea urchin.

Impact of substrate and the presence of adults on recruitment of the red sea urchin Strongylocentrotus franciscanus in Baja California

Several authors have studied the protection that adult red sea urchins (Strongylocentrotus franciscanus) offer their juveniles and have found that post-settlement mortality due to the absence of adults can diminish recruitment to adult populations. It is also well documented that adult sea urchin densities are low in overexploited populations, reducing the protection adults can offer juveniles. When adults are absent, habitat structure plays a key role in the protection of juveniles against predation. In this study we analyze the spatial variation in S. franciscanus recruitment and assess the impact of substrate availability (percentage of crevices) and adult sea urchin density on recruitment along the west coast of Baja California. Recruit and adult red sea urchin densities were estimated at 10 sites by scuba diving. Habitat structure was assessed by the analysis of digital video images. Temporal variation in red sea urchin recruitment as well as its relation to substrate availability and adult density were analyzed at two sites during three consecutive years. There were significant differences in recruit density among sites and substrate structure was the main factor that explained these differences. Adult densities did not explain recruitment differences among sites; however, the temporal analysis results showed that both substrate structure and adult densities were important in explaining recruit densities at both sites. The absence of a clear spatial pattern suggests that other factors such as harvesting and larval retention may explain the differences observed in the density of recruits among sites.

Moving from Data Poor to Data Rich: A Case Study of Community‐Based Data Collection for the San Diego Red Sea Urchin Fishery

AbstractResponding to the need for management of California's nearshore fisheries mandated in state law by the Marine Life Management and Marine Life Protection acts, the San Diego Watermen's Association (SDWA), which includes divers that target local red sea urchins Strongylocentrotus franciscanus, initiated a community‐based data collection program in 2001. In collaboration with independent scientists and biologists from the California Department of Fish and Game, the SDWA developed an ongoing program to gather, organize, and analyze both fishery‐dependent and fishery‐independent data on the local red sea urchin fishery. The goal of the program is to collect data that will support periodical stock assessments needed for sustainable management of existing nearshore fisheries (including red sea urchins) as well as the kelp forest ecosystem on which these fisheries depend. Here, we discuss sampling designs, methods for determining data quality (bias and precision), and methods for detecting change, and we provide some examples of results from the ongoing community‐based data collection program. We also report on (1) the design and implementation of scientifically valid sampling protocols; (2) data quality assurance and control collaboratively conducted with scientists and resource agency biologists; (3) calibration studies to determine accuracy and precision and the magnitude of detectable changes in red sea urchin populations; and (4) visualization and dissemination of data and results and incremental changes in protocols that would facilitate the monitoring of associated biological communities. Finally, we discuss keys for success in this cooperative‐based data collection program and its implications for stock assessment and management of the red sea urchin fishery in California.

Longevity and lack of senescence in the red sea urchin Strongylocentrotus franciscanus

The red sea urchin Strongylocentrotus franciscanus is a long-lived species and may live in excess of 100 years based on tagging studies in the field and corroboration from radiocarbon analyses as reported in the literature. Size-specific survival estimates reported here show no change in annual survival probability across the 6 largest 0.5 cm size classes from 14.6 to 18.1 cm. In addition to no change in survival probability there is no reduction in reproductive capacity with size. Red sea urchins show no evidence of senescence and so do not fit well within the context of the disposable soma theory of the evolution of longevity.

Evaluation of Sampling Designs for Red Sea Urchins Strongylocentrotus franciscanus in British Columbia

AbstractEstimates of the total stock biomass of marine invertebrates that aggregate, such as red sea urchins Strongylocentrotus franciscanus, are often highly uncertain, partly because it is difficult to estimate their density. To improve estimates, we used 200 simulated red sea urchin populations with spatial and numerical properties based on field data to evaluate various simulated survey designs for a given number of transects in terms of the precision, bias, and efficiency (relative variance) of their estimates. We considered a random transect sampling method that is currently used in British Columbia for red sea urchins, which samples every other quadrat within each transect, as well as a complete version of that transect method, which samples every quadrat. We also evaluated more complex random transect sampling designs, including restricted adaptive cluster sampling and a design stratified by type of substrate within each transect. The complete transect method produced essentially unbiased estimates of red sea urchin density (as did the currently used sampling design) and had lower variance than the current method, but the complete method used twice as many quadrat samples per transect to do so (incurring higher costs of sampling by divers). In contrast, the design stratified by substrate required 33% fewer sampled quadrats per transect than the current sampling method to achieve the same variance as that method, but it had a median bias of 10%. Finally, the restricted adaptive cluster sampling design gave estimates that had lower variance than the current method and used 18% fewer sampled quadrats, but the median urchin density estimate was biased downward by 8%. Choosing among sampling designs thus involves making trade‐offs among bias, precision, and sampling cost as well as considering practical constraints on scuba divers who attempt to implement complex designs in field situations.

Evaluating Age Determination and Spatial Patterns of Growth in Red Sea Urchins in Southeast Alaska

AbstractThe goals of this study were to characterize growth of the commercially harvested red sea urchin Strongylocentrotus franciscanus in southeastern Alaska and test the validity of an aging technique. We aged urchins by counting growth rings on a part (rotula) of the Aristotle's lantern complex from urchins collected at three sites. A subset of collected urchins had three or more years of size measurements from passive integrated transponder (PIT) tag data, allowing us to fit and compare PIT tag and ring‐derived growth curves and test the assumption that rings were formed annually. Growth from PIT‐tagged individuals approximated the growth derived from ring counts for two of three sites. The third site deviated slightly from predicted growth, providing support for our aging technique. However, we failed to detect any extremely old urchins, suggesting that this technique is not appropriate for assessing the longevity or growth trajectory of very large urchins. An additional five sites without PIT‐tagged urchins were sampled to examine spatial variation in growth. Estimates of time to fishery entry varied substantially among sites, but four nonlinear growth functions produced similar estimates at individual sites. Time to fishery entry was positively correlated with an index of food availability, which suggests that the technique revealed true variation in growth rates.

Producción de juveniles de erizo rojo Strongylocentrotus franciscanus (Echinodermata: Echinoidea) en Baja California, México

Juvenile production of the red sea urchin Strongylocentrotus franciscanus (Echinodermata: Echinoidea) in Baja California, Mexico. The red sea urchin Strongylocentrotus franciscanus (Agassiz 1863) is harvested commercially in Baja California, Mexico, since 1970; however, in the last ten years the capture per unit effort (CPUE) has decreased from 310 kg/fishing unit/day to 120 kg/fishing unit/day. For this reason, actions were taken to develop a culture technology allowing massive production of juveniles for re-stocking natural populations or for growing them commercially. We summarize some of the basic studies and main achievements in this effort. In Baja California, considerably faster larval development (~21 days) has been attained than in the US northwest coast (62 days). Spawning of red sea urchins was routinely induced with KCl while egg fertilization was performed using a 100 000-sperm/ml solution. Six microalgae species were tested and Rhodomonas sp. produced the best larval development. The mean survival rate at the end of the larval period was 25%, but results varied widely with bactch. From the feed ratios tested, best results were obtained using 7 000 cel/ml during the first week of larval development, followed by 10 000 cel/ml during the second and 15 000 cel/ml during the third week. KCl proved the most consistent metamorphic inducer, regularly yielding metamorphosis percentages higher than 90%. Metamorphosis was considered complete when the functional jaw that juveniles use for first benthic feeding appeared (as soon as 20 days after induction). With this method several thousands of red sea urchin juveniles were produced. They reached up to 1.5 mm in size during the first 50 days of culture after metamorphosis, showing the great potential for mass production of this species in the laboratory. Rev. Biol. Trop. 53(Suppl. 3): 345-355. Epub 2006 Jan 30.

Genetic heterogeneity among adult and recruit red sea urchins, Strongylocentrotus franciscanus

Allozyme electrophoresis was used to characterize genetic variation within and among natural populations of the red sea urchin Strongylocentrotus franciscanus. In 1995 to 1996, adult urchins were sampled from twelve geographically separated populations, seven from northern California and five from southern California (including Santa Rosa Island). Significant population heterogeneity in allelic frequencies was observed at five of six polymorphic loci. No geographic pattern of differentiation was evident; neighboring populations were often more genetically differentiated than distant populations. Northern and southern populations were not consistently distinguishable at any of the six loci. In order to assess within-population genetic variation and patterns of recruitment, large samples were collected from several northern California populations in 1996 and 1997, and were divided into three size classes, roughly representing large adults (>60 mm), medium-sized individuals (31 to 60 mm, “subadults”) and individuals <2 yr of age (≤30 mm test diam, referred to as “recruits”). Comparisons of allelic counts revealed significant spatial and temporal differentiation among size-stratified population samples. Recruit samples differed significantly from adult samples collected at the same locale, and showed extensive between-year variation. Genetic differentiation among recruit samples was much higher in 1997 than in 1996. Between-year differences within populations were always greater for recruits than for adults. Potential explanations for the differentiation of recruit samples include pre- and post-settlement natural selection and high interfamily variance in reproductive success or “sweepstakes” recruitment. Unless recruit differentiation can be attributed to an improbable combination of strong and spatially diverse selection, such differentiation across northern California populations indicates that the larval pool is not well mixed geographically (even on spatial scales <20 km), despite long planktonic larval duration.

Population dynamics and management implications of larval dispersal

Strong advective fields in coastal shelf ecosystems, particularly in eastern boundary currents, lead to significant longshore dispersal of the larval phase of meroplanktonic benthic invertebrates. Field observations of larvae and settlement in the California Current by recent workers are an example of the increasing research on the biological/physical mechanisms underlying larval transport. In particular, these studies identify physical/biological interactions that control the spatial distribution of larvae settling successfully. The current study demonstrates how the results of such studies contribute to (1) better understanding of population dynamics, and (2) better population management, using the cyclic covariability in the Dungeness crab Cancer magister population as an example of the former and management of the red sea urchin Strongylocentrotus franciscanus population as an example of the latter. Earlier modelling studies have shown that dispersal influences the stability and synchrony of variability in metapopulations such as the Dungeness crab, and that the spatial scale of covariability is roughly the scale of dispersal. The mechanism identified by recent research implies that the spatial scale of dispersal should be the distance between promontories in the California Current, roughly 100–200 km. Analysis of covariability between time-series of recruitment at different locations along the coast confirm that this is the spatial scale of longshore variability in the Dungeness crab. The spatial pattern in red sea urchin settlement caused by the identified mechanism provides: (1) the basis for spatially explicit management, and (2) an explanation for the observed spatial variability in the degree of overfishing. Research on larval dispersal is also providing the information necessary to design spatially explicit management strategies involving either permanent or temporary fishery closures. Both population dynamics and management require further research to describe the origins of larvae and the early larval phase, in addition to the transport just before settlement.

Bimodality in Size Distributions: The Red Sea Urchin Strongylocentrotus Franciscanus as an Example

We use a model based on the size—structured von Foerster equation to describe how size—dependent growth and mortality rates, pulsed recruitment, and variability in growth affect the shape of a size distribution. The deterministic, equilibrium size distribution with constant recruitment increases with size when the difference between mortality rate and the rate at which growth rate decreases with size is positive (growth dominated), and decreases when it is negative (mortality dominated). Pulsed recruitment causes modes whose relative amplitudes are indicated by the corresponding constant recruitment case. For typical animal growth patterns, the distance between pulses decreases with age. Pulses merge and can be selectively obscured by variability in growth so that their relative amplitudes no longer correspond to the constant recruitment case. We use this information to evaluate why bimodality occurs in size distributions of the red sea urchin, Strongylocentrotus franciscanus, in some habitats, but not others. The mode at larger sizes, which occurs in all habitats, arises because the distribution is mortality dominated and the final sizes of individuals vary. The upper half of a second mode at smaller sizes is caused by higher mortality rates at sizes greater than the peak of that mode. The lower half may be due either to a refuge from predation under the spine canopy of adults or to sampling selectivity.

Recruitment characteristics of the commercially harvested red sea urchin Strongylocentrotus franciscanus in Southern British Columbia, Canada

The test size frequencies of red sea urchin, Strongylocentrotus franciscanus (Agassiz), populations from British Columbia revealed low recruitment overall (≈9.5%) compared with populations from lower latitudes. Juvenile urchins tended to shelter under adult conspecifics. On a fine scale, i.e. over 0.5–8.0 km, high variability in recruitment was evident. Possible effects of commercial harvesting are discussed. Site-specific harvest controls based on local habitat and urchin population (size-frequency) data are desirable as a fishery management tool, but would be too costly to gather over such an extensive coastal area.