Sea Urchin Strongylocentrotus Franciscanus Research Articles

Do Sperm Really Compete and Do Eggs Ever Have a Choice? Adult Distribution and Gamete Mixing Influence Sexual Selection, Sexual Conflict, and the Evolution of Gamete Recognition Proteins in the Sea.

The evolution of gametic compatibility and the effectiveness of compatibility, within and across species, depend on whether sperm from different males directly compete for an egg and whether eggs ever have a choice. Direct sperm competition and egg choice depend on whether sperm from different males arrive at an egg in the brief interval between first sperm contact and fertilization. Although this process may be relevant for all sexually reproducing organisms, it is most easily examined in aquatic external fertilizers. When sperm are released into the sea, packets of seawater at the spatial scale relevant to single eggs might contain sperm from only one male, eliminating the potential for direct sperm competition and egg choice. Field experiments and a simple heuristic model examining the degree of sperm mixing for the sea urchin Strongylocentrotus franciscanus indicate that degree of competitive fertilization depends on density and distribution of competing males and that the nature of this competition influences whether males with high- or low-affinity gamete recognition protein genotypes have higher reproductive success. These results provide a potential explanation for the generation and maintenance of variation in gamete recognition proteins and why effectiveness of conspecific sperm precedence can be density dependent.

Exploring benefits of spatial cooperative harvesting in a sea urchin fishery: an agent‐based approach

AbstractSedentary or low‐mobility organisms show a high degree of dependency with their substrate, where its heterogeneity often determines small‐scale spatial patterns of distribution, life history traits, and fishery yields. For sea urchins, this spatial structure is usually shaped by food availability, habitat structure, individual movement, and fishery dynamics. All of these have a significant impact on their physiological and reproductive status and in particular on their gonadal content. These patterns are of particular interest considering that the sea urchin fishery is a roe fishery where marketability depends on gonad yield and quality, which in turn is related to spatial and temporal variations in associated kelp beds. Thus, better gonad quality and yields generate higher profits for both fishers (divers) and processors. However, competition among divers within a non‐cooperative system creates a “race for shellfish” precluding higher gonad yields per unit of effort. A spatially explicit agent‐based model for the San Diego, California red sea urchin (Strongylocentrotus franciscanus) fishery was developed in order to assess the benefits of cooperative harvesting by depicting spatial and temporal variations in fishery yields. A cooperative harvesting scenario where divers consistently target those areas with higher yields avoiding low‐quality sea urchins was compared against a non‐cooperative situation where divers harvest at random or based only on densities of sea urchins. Sea urchin population at the end of the simulation period was 20% higher for the most cooperative scenario compared to the non‐cooperative fishery. Further, for the most cooperative scenario where information sharing among divers is greatest and harvest is coordinated, sea urchin catches were at least 10% higher and gonad yield 35% higher than in the non‐cooperative scenario. In this model, information sharing and organized harvesting typical of well‐functioning cooperatives allowed fishers to optimize the use of the resource in terms of higher gonad yields per unit of effort while maintaining the productivity of the stock. This study also highlights the importance of community‐based management (i.e., collaborative efforts in assessment, management, and governance of fisheries between fishers, scientists, and managers) toward improving fisheries sustainability.

Indirect effects of sea otters on rockfish (Sebastes spp.) in giant kelp forests.

Sea otters are a classic example of a predator controlling ecosystem productivity through cascading effects on basal, habitat-forming kelp species. However, their indirect effects on other kelp-associated taxa like fishes are poorly understood. We examined the effects of sea otter (Enhydra lutris) reintroduction along the west coast of Vancouver Island, Canada on giant kelp (Macrocystis pyrifera) distributions and the trophic niches and growth of two common kelp forest fishes, black (Sebastes melanops) and copper (S. caurinus) rockfishes. We sampled 47 kelp forests, and found that red sea urchins (Strongylocentrotus franciscanus) were eliminated in the presence of otters, and that kelp forests were 3.7 times deeper and 18.8 times larger. Despite order-of-magnitude differences in kelp forest size, adult black and copper rockfishes contained less kelp-derived carbon in their tissues (as measured by stable isotopes of C and N) in regions with otters. Adults of both species had higher mean trophic positions in the presence of otters, indicating more frequent consumption of higher trophic level prey such as fishes. Smaller trophic niche space of rockfishes in the presence of otters indicated a higher degree of trophic specialization. Juvenile black rockfishes rapidly shifted to higher kelp-carbon contents, trophic positions, and body condition factors after settling in kelp forests. The relationships of growth to length, percentage of kelp carbon, and trophic position varied between the two regions, indicating that potential effects of kelp forest size on trophic ontogeny may also affect individual performance. Our results provide evidence that the indirect effects of otters on rockfishes arise largely through the creation of habitat for fishes and other prey rather than a direct trophic connection through invertebrates or other consumers of kelp productivity.

Spine reorientation influences drift particle capture efficiency in sea urchins

Many marine organisms use behavior to navigate hydrodynamic landscapes. The subtidal sea urchin Strongylocentrotus franciscanus reorients its spines as water velocity increases to reduce drag and remain attached to the substratum. Streamlining may be advantageous in this regard, but it is unclear how this change in drag profile will affect particle capture, a feeding strategy employed by these organisms. Streamlining in urchins results in a “spines down” posture while particle capture benefits from spines remaining erect, a difference that could potentially lead to decreased feeding rates in high water velocities. To investigate this we ran flow tank experiments with three species of urchin (Strongylocentrotus droebachiensis, Strongylocentrotus franciscanus, and Strongylocentrotus purpuratus) which differ in size and spine length. All urchins studied displayed some degree of streamlining, although the threshold water velocity at which the behavior occurred varied among species. Particle capture was highly dependent on urchin size, with S. franciscanus, the largest of the three species studied, capturing the highest total mass across water velocities. However, taking into account urchin size and the changes in particle flux at each water velocity, S. purpuratus was significantly more efficient at capturing particles with “spines up” — an advantage which disappeared once spines were lowered. These results show that size and spine orientation affect how particles interact with urchins in flow and imply that spine morphology plays a role in whether or not an individual adopts a streamlined posture.

Age-related NADH oxidase (arNOX) activity is significantly reduced in coelomic fluid of long-lived sea urchins

Abstract Age-related NADH oxidase (arNOX) is a cell surface protein shed into the circulation and other body fluids, which generates superoxide. The activity increases with age in human tissues and body fluids (serum, saliva, and perspiration) and is a potential source of age-related oxidative damage. We measured arNOX activity in the coelomic fluid of sea urchin species with different life spans. Coelomic fluid of long-lived sea urchin species Strongylocentrotus purpuratus and Strongylocentrotus franciscanus exhibited low levels of arNOX compared to the short-lived urchin species Lytechinus variegatus. arNOX activity was positively correlated with animal size in L. variegatus, whereas with S. purpuratus and S. franciscanus, arNOX activity and animal size were inversely correlated. The inverse correlation of arNOX activity with life span and decreased levels of arNOX with age in the long-lived species is consistent with a contribution of reduced arNOX activity to slower aging.

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.

CONTEMPORARY EVOLUTION OF SEA URCHIN GAMETE-RECOGNITION PROTEINS: EXPERIMENTAL EVIDENCE OF DENSITY-DEPENDENT GAMETE PERFORMANCE PREDICTS SHIFTS IN ALLELE FREQUENCIES OVER TIME

Species whose reproductive strategies evolved at one density regime might be poorly adapted to other regimes. Field and laboratory experiments on the sea urchin Strongylocentrotus franciscanus examined the influences of the two most common sperm-bindin alleles, which differ at two amino acid sites, on fertilization success. In the field experiment, the arginine/glycine (RG) genotype performed best at low densities and the glycine/arginine (GR) genotype at high densities. In the laboratory experiment, the RG genotype had a higher affinity with available eggs, whereas the GR genotype was less likely to induce polyspermy. These sea urchins can reach 200 years of age. The RG allele dominates in larger/old sea urchins, whereas smaller/younger sea urchins have near-equal RG and GR allele frequencies. A latitudinal cline in RG and GR genotypes is consistent with longer survival of sea urchins in the north and with predominance of RG genotypes in older individuals. The largest/oldest sea urchins were likely conceived at low densities, before sea-urchin predators, such as sea otters, were overharvested and sea-urchin densities exploded off the west coast of North America. Contemporary evolution of gamete-recognition proteins might allow species to adapt to shifts in abundances and reduces the risk of reproductive failure in altered populations.

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.

Developing a Bayesian framework for stock assessment and decision analysis of the red sea urchin fishery in Baja California, Mexico

The red sea urchin (Strongylocentrotus franciscanus) fishery is of importance to the economy of Baja California (Mexico). The commercial fishery started in the early 1970s as a result of expanding export markets, but has experienced substantial decline in landings and abundance since 1986. Fishery-independent surveys have not been conducted for all fishing areas, thus CPUE and catch data were used to conduct a stock assessment and decision analysis for the red sea urchin stock. The red sea urchin population dynamics was described with the Schaefer biomass dynamic model. Bayesian approaches were used for the estimation of the model parameters and for projecting the population dynamics of the species under different management scenarios, including constant harvest rate and constant catch strategies. This study suggests that the current stock is only 17% of the virgin stock biomass and that, for a constant catch policy, a 10% increase in the current catch rate could potentially cause the collapse of the fishery in 20 years. Simulation results suggested that a constant harvest rate between 15% and 25% would cause the population to recover and maximize the catch in 2024. Higher harvest rate levels would increase the probability of the biomass being less than 40% of the population carrying capacity.

Experimental displacement trials of the red sea urchin Strongylocentrotus franciscanus (Aggassiz, 1863) (Echinodermata: Echinoidea) at different current velocities

Displacement of marine animals is affected by diverse environmental factors, including hydrodynamics performance. We evaluated the effect of current velocity on the displacement of the sea urchin Strongylocentrotus franciscanus in an experimental flume, in both light and dark conditions. We observed that movement of S. franciscanus was directly proportional to the current speed. Our results differ from previous studies in the amount and the direction of displacement of other strongylocentrotids, because sea urchins displacements were similar in the current direction and countercurrent irrespective of current velocity and our results showed displacements of circa 7 m per day, smaller to that reported for experiments in the same urchin species in British Columbia. The differences may be due to the absence of predators or food, or the trials in day and night conditions. Day and night differences in the displacement of S. franciscanus were not observed.

Susceptibility of non-indigenous ascidian species in British Columbia (Canada) to invertebrate predation

Non-indigenous ascidians are known to significantly alter the structure and composition of benthic communities and adversely affect shellfish aquaculture by fouling both the cultured species and the infrastructure. The ability of these species to persist in new locations and their current and potential distributions are dependent upon physiological tolerances to environmental factors and biotic resistance to competition and predation. Despite significant data on global invasion patterns, potential biotic resistance to non-indigenous ascidians is poorly understood. We identified potential predators of four non-indigenous ascidians (Styela clava, Botryllus schlosseri, Botrylloides violaceus, and Didemnumvexillum) in British Columbia (BC), Canada in order to: (1) assess the potential for biotic interference to limit the establishment and/or spread of these ascidian species in BC, and (2) identify candidate species to be used as ascidian biofouling control agents in shellfish aquaculture. Using a series of single- and multiple-choice laboratory experiments, potential benthic predators (including various species of molluscs, echinoderms, and arthropods) were offered non-indigenous ascidians as prey. The sea urchins Strongylocentrotus droebachiensis and Strongylocentrotus franciscanus, the sea stars Dermasterias imbricata and Evasterias troschelii, the nudibranch Hermissenda crassicornis, and the crabs Cancer productus and Carcinus maenas were found to consume one or more species of non-indigenous ascidians in single-choice experiments. However, when provided a choice, all predators chose their respective preferred food over ascidians. Thus, predation alone is unlikely to prevent large-scale establishment and spread of non-indigenous ascidians in BC, but it may have the potential to significantly reduce localized populations of ascidians. Green sea urchins, S. droebachiensis, were found to be efficient grazers of all four ascidian species, consuming 12.7 ± 5.14 cm2 (mean ± SD) of adult B. violaceus over a 3-day period, 15 ± 3.7 juvenile colonies of B. violaceus over a 2-day period, and 63 ± 28.8 juvenile colonies of B. schlosseri over a 2-day period. Using sea urchins as biological control organisms may significantly reduce ascidian fouling in shellfish aquaculture.

Predicted impact of ocean acidification on a marine invertebrate: elevated CO2 alters response to thermal stress in sea urchin larvae

Ocean acidification (OA) and the biological consequences of altered seawater chemistry have emerged as a significant environmental threat to healthy marine ecosystems. Because a more acidic ocean interferes with fixation of calcium carbonate to form shells or calcified skeletons, future ocean chemistry may significantly alter the physiology of calcifying marine organisms. These alterations may manifest themselves directly in the calcification process, or have synergistic effects with other environmental factors such as elevated temperatures. New tools permit us to explore subtle changes in gene expression patterns in response to environmental conditions. We raised sea urchins (Strongylocentrotus franciscanus) under conditions simulating future atmospheric CO2 levels of 540 and 970 ppm. When larvae raised under elevated CO2 conditions were subjected to 1-h acute temperature stress, their ability to mount a physiological response (as measured by expression of the molecular chaperone hsp70) was reduced relative to those raised under ambient CO2 conditions. These results represent the first use of gene expression assays to study the effects of OA on sea urchin development. They highlight the importance of looking at multiple environmental factors simultaneously as this approach may reveal previously unsuspected biological impacts of atmospheric changes.

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.

Egg size and the evolution of phenotypic plasticity in larvae of the echinoid genus Strongylocentrotus

Planktotrophic larvae grow by utilizing energy obtained from food gathered in the plankton. Morphological plasticity of feeding structures has been demonstrated in multiple phyla, in which food-limited larvae increase feeding structure size to increase feeding rates. However, before larvae can feed exogenously they depend largely on material contained within the egg to build larval structures and to fuel larval metabolism. Thus, the capacity for plasticity of feeding structures early in development may depend on egg size. Using the congeneric sea urchins Strongylocentrotus franciscanus and S. purpuratus, which differ in egg volume by 5-fold, I tested whether the degree of expression of feeding structure (larval arm length) plasticity is correlated with differences in the size of the egg. I experimentally manipulated egg size of S. franciscanus (the larger-egged species) by separating blastomeres at the 2-cell stage to produce half-sized larvae. I reared half-size and normal-size larvae under high and low food treatments for 20 days. I measured arm and body lengths at multiple ages during development and calculated the degree of plasticity expressed by larvae from all treatments. Control and unmanipulated S. franciscanus larvae (from ∼ 1.0 nl eggs) had significantly longer arms relative to body size and a significantly greater degree of plasticity than half-sized S. franciscanus larvae (from < 0.18 nl eggs), which in turn expressed a significantly greater degree of plasticity than S. purpuratus larvae (from ∼ 0.3 nl eggs). These results indicate that egg size affects larval arm length plasticity in the genus Strongylocentrotus; larger eggs produce more-plastic larvae both in an experimental and a comparative context. However, changes in egg size alone are not sufficient to account for evolved differences in the pattern of plasticity expressed by each species over time and may not be sufficient for the evolutionary transition from feeding to non-feeding.

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.

Critical thermal maximum and osmotic pressure of the red sea urchin Strongylocentrotus franciscanus acclimated at different temperatures

1. The sea urchin Strongylocentrotus franciscanus acclimated at 15°C, 18°C and 21°C exposed to a rising thermal stress showed a series of well-defined responses. 2. All responses were significantly different and stage E4, characterized when the sea urchins ceased moving, relaxed the large spines but the smaller spines continued to make small movements. This was considered to be the critical thermal maximum (CTMax). 3. The resistance of S. franciscanus is independent of the acclimation interval used in this work. 4. The effect of the CTMax on the osmotic pressure of the sea urchin body fluid acclimated at 18°C was significantly different ( P<0.05) when compare to the 15°C and 21°C conditions.

Density-Dependent Sexual Selection in External Fertilizers: Variances in Male and Female Fertilization Success along the Continuum from Sperm Limitation to Sexual Conflict in the Sea Urchin Strongylocentrotus franciscanus

Density-Dependent Sexual Selection in External Fertilizers: Variances in Male and Female Fertilization Success along the Continuum from Sperm Limitation to Sexual Conflict in the Sea Urchin Strongylocentrotus franciscanus