Postoral Arms Research Articles

The dopamine effect on sea urchin larvae depends on their age.

Activation of the dopamine type-D2 receptor in late gastrula of sea urchins is known to decrease the growth rate of post-oral arms of larvae, and, as a result, the phenotype of these larvae mimics that of larvae developing in the abundance of food. Our data indicate that the effect of dopamine on sea urchin larvae is stage-dependent. In our experiment, the early four-armed plutei (96 hours post fertilization, hpf) of Strongylocentrotus intermedius had substantially shorter post-oral arms if they developed from the larvae treated with dopamine at the early pluteus stage (48 hpf), when they had already formed the first dopaminergic neurons, as compared to the plutei from the larvae treated with dopamine at the mid to late gastrula stage (24 hpf), when they did not have any neurons yet. The pre-treatment of larvae in 6-hydroxydopamine, a neurotoxic analog of dopamine that specifically disrupts activity of dopaminergic neurons, prevented the development of the short post-oral arms phenotype in larvae. These results confirm the assumption that dopaminergic neurons play an important role in the development of the short post-oral arms phenotype in sea urchin larvae. Another finding of our study is that the dopamine treatment also affects the growth of the body rods and the overall larval body growth. Based on these observations, we suggest researchers to carefully select the developmental stage, pharmacological agents, and incubation time for experimental manipulation of sea urchin larvae phenotypes through dopaminergic nervous system.

High dietary protein, n − 3/ n − 6 ratio and β ‐carotene enhances Paracentrotus lividus (Lamarck, 1816) larval development

The nutritional characteristics of microalgae affect the growth, survival and fatty acid composition of sea urchin larvae. This study aimed to evaluate the influence of nutritive characteristics of single microalgal diets in Paracentrotus lividus (Lamarck, 1816) larval development, growth, and condition. Larvae of P. lividus were fed with three monospecific microalgal diets, Rhodomonas sp. (Rho), Dunaliella tertiolecta (Duna) and the diatom Chaetoceros calcitrans (Chae), and their development and growth were analysed until competence. Additionally, the fatty acid (FA) profile of larvae was analysed at competence and compared with the FA profile of the correspondent diet. The three groups of larvae attained competence simultaneously with differences in growth performance. The larvae fed with Chae attained the largest stomach and the shortest post-oral arm. The larvae were able to accumulate long-chain polyunsaturated fatty acids (PUFA), such as docosahexaenoic (DHA, C22:6n − 3), eicosapentaenoic (EPA, C20:5n − 3) and arachidonic (ARA, C20:4n − 6) acids, either by assimilation and retention of dietary FA or by the synthesis from α-linolenic acid (ALA, C18:3n − 3) and linoleic acid (LA, C18:2n − 6). Furthermore, the low DHA/EPA ratio and high EPA/ARA and n − 3/n − 6 ratios of Rho and Chae and the high levels of the β-carotene present in Chae improved larval growth and development. In conclusion, the results indicated that of the three microalgal diets tested, C. calcitrans provided important nutritional characteristics, especially in terms of FA composition and carotenoids, improving P. lividus larval growth and condition.

Dietary effects on the reproductive performance of the sea urchin Tripneustes gratilla ll: Implications for offspring performance

Aquaculture practices can result in declines in the genetic diversity observed in progenitor natural populations, resulting in subsequent poor production output, particularly for broadcast spawning animals that frequently display differential parental contributions. This study aimed to assess the effect of different Tripneustes gratilla broodstock feeding regimes [formulated feed, kelp (Ecklonia maxima), green seaweed (Ulva lacinulata) and mixture of the three diets for four months] on larval growth, parental contributions and juvenile performance after a factorial breeding design was implemented. Larvae produced from broodstock fed kelp and the mixed diet survived for the full duration of larval rearing and displayed similar growth rates throughout (p > 0.05). Though larvae from Ulva-fed broodstock did not survive for the full duration of larval rearing, this could have been a consequence of larval rearing practices, as these larvae displayed a rapid increase in post-oral arm lengths prior to the mortality event. Furthermore, these larvae survived for the longest amount of time when left unfed, suggesting that the maternal reserves from animals fed Ulva as a broodstock conditioning diet could be beneficial to development in early larval stages. In contrast, larvae from animals fed a formulated feed did not survive the full duration of larval rearing and had developmental abnormalities. Three months post-metamorphosis, 10 species-specific microsatellite markers were PCR amplified across 16 broodstock and 364 offspring from kelp and mixed diet fed animals. Genetic diversity analyses showed that there were no statistically significant (p > 0.05) differences between the broodstock animals and their offspring, showing that factorial breeding designs are advantageous to preserve genetic diversity present in cultured cohorts. Parentage analyses revealed that a total of 26 out of 32 possible F1 parent pairs contributed to the F2 generation, with a low heritability estimate of approximately zero (0.050 ± 0.058) for offspring body diameter, likely as offspring phenotypic performance is not influenced by additive genetic effects during these early growth stages.

Echinoid larvae can express food-conditioned morphological plasticity at ecologically relevant culture densities

The feeding larvae of many echinoids develop long postoral arms relative to body length when food is sparse but relatively short postoral arms when food is abundant, a response thought to adaptively adjust feeding capability. However, in an important recent study, larvae of Dendraster excentricus exhibited this food-conditioned plasticity only when reared at a high density typical of laboratory cultures; when reared at a lower density more representative of larval densities in nature, they did not exhibit this plastic response. This finding suggests that laboratory results cannot be easily extended to make inferences about phenotypic plasticity in nature. We replicated this study and extended it to an even lower larval culture density and to a second species, Lytechinus pictus. Larvae of D. excentricus developed longer arms adjusted for body length when fed the lower of 2 food rations at all culture densities, though differences were only marginally significant at the lower culture density in one experiment. Larvae of L. pictus tended to develop longer arms adjusted for body length at lower food rations, though differences only approached statistical significance at the highest culture density in one experiment. For both species, contrasts between food rations almost always showed an inverse relationship between postoral arm length and stomach length, consistent with prior work demonstrating trade-offs in investment in these 2 features characteristic of phenotypic plasticity. These results suggest that the feeding larvae of echinoids may exhibit food-conditioned plasticity of postoral arm length even at low natural densities.

Effects of Bisphenol-A on the morphology and survival of larvae of the sand dollar Dendraster excentricus (Echinodermata, Echinoidea)

ABSTRACT Bisphenol-A (BPA) is an ingredient used in phenol resins, epoxy resins, polyesters and polycarbonate plastics. BPA gets released into the aquatic environment through toxic waste disposal, groundwater, sewage runoff and plastic leaching. When BPA enters aquatic environments, it can affect the development and physiology of marine organisms. This study aimed to understand the effects of relatively low concentrations of BPA on the larvae of the sand dollar Dendraster excentricus. Embryos and larvae were exposed to four treatment solutions (no additives, vehicle control, 50 µg/L BPA, and 500 µg/L BPA) for 7 days. The two BPA treatment concentrations were higher than have usually been detected in coastal marine waters, but lower than those used in most other studies of BPA effects on echinoderm development. After exposure, larval midline body length, postoral arm length, frequency of normal development and survyivorship were measured. Midline body length, frequency of normal development and survivorship all decreased in the presence of BPA, in a dose-dependent manner. Relatively low concentrations of BPA can thus have strong effects on the development of sand dollar larvae.

Combined effect of microplastics and global warming factors on early growth and development of the sea urchin (Paracentrotus lividus)

The aim of this work was to estimate the potential risk of the combined effect of global change factors (acidification, temperature increase) and microplastic (MP) pollution on the growth and development of the sea urchin P. lividus. Embryo-larval bioassays were conducted to determine growth and morphology after 48 h of incubation with MP (1000 and 3000 particles/mL); with filtered sea water at pH = 7.6; and with their combinations. A second experiment was conducted to study the effect of pH and MP in combination with a temperature increase of 4 °C compared to control (20 °C). We found that the inhibition of growth in embryos reared at pH = 7.6 was around 75%. Larvae incubated at 3000 MP particles/mL showed a 20% decrease in growth compared to controls. The exposure to MP also induced an increase in the postoral arm separation or rounded vertices. The combined exposure to a pH 7.6 and MP caused a significant decrease of larval growth compared to control, to MP and to pH 7.6 treatments. Morphological alterations were observed in these treatments, including the development of only two arms. Increasing the temperature resulted in an increased growth in control, in pH 7.6 and pH 7.6 + MP3000 treatments, but the relative stomach volume decreased. However, when growth parameters were expressed per Degree-Days the lower growth provoked by the thermal stress was evidenced in all treatments. In this work we demonstrated that MP could aggravate the effect of a decreased pH and that an increase in water temperature generated an additional stress on P. lividus larvae, manifested in a lower growth and an altered development. Therefore, the combined stress caused by ocean warming, ocean acidification, and microplastic pollution, could threaten sea urchin populations leading to a potential impact on coastal ecosystems.

The influence of density on survival and larval development in the sea urchin Arbacia dufresnii (Echinodermata: Echinoidea)

Introduction: Density is one of the critical factors in echinoderm larvae for aquaculture purposes. Echinoplutei larvae are very sensitive to overcrowding. High culture density can lead to problems with bacteria or protozoa, decreasing survival and generating abnormal morphotypes. Objective: To evaluate the effect of culture density on survival and larval growth in the sea urchin Arbacia dufresnii. Methods: Two days after fertilization of A. dufresnii we we kept treatments at 1, 3, 5 and 10 larvae.ml-1, with three replicates each. We recorded survival and abnormal morphotypes periodically, as well as growth:somatic rod length, total length, and length of the post oral arms,. we applied generalized linear models. Results: Survival is dependent on density, time and replicates, and their interactions. Larval growth depended on density and time, also with interaction between the variables. The treatment of 5 larvae.ml-1 had the highest survival and larval condition. Conclusions: Larval culture of A. dufresnii had the best results at 5 larvae.ml-1.

Effects of single and mixed-diatom diets on growth, condition, and survival of larvae of the sea urchin Paracentrotus lividus (Lamarck, 1816)

The development of rearing protocols promoting the larval development, pre and post-metamorphosis are key for echinoculture. Mixed diets combining diatom with other microalgae have been used with success and Rhodomonas sp. (Rho)-based diets showed promising results in larval survival. This study was aimed to evaluate the rearing success of Paracentrotus lividus larvae fed with mixed diets combining Rho with two diatoms, Phaedactylum tricornutum (Phae) and Chaetoceros calcitrans (Chae) in two experiments. In experiment I, the effect of the mixed diet of Rho and Phae (Mix I) was compared with monospecific diets of both species, while in experiment II, Rho was combined with Chae (Mix II) and compared with both monospecific diets. In experiment I, larvae fed with Rho I and Mix I diets grew faster than larvae fed with Phae I diet, attained the competence earlier with survival rates of 15-16%. In experiment II, the larvae fed with Rho were larger and the larvae fed with Mix II attained the highest survival rate (32.22%). The analysis of the larval biometric models showed that the larger larvae, with bigger stomachs, and shorter post-oral arm attained the age-at-competence earlier with higher survival rates. In conclusion, the larvae fed with a combination of Rho with the selected diatoms showed identical growth performance and condition to larvae fed with Rho monospecific diet but obtained higher survival rate. These results indicate that mixed-diatoms diets may be more suitable for P. lividus larval rearing.

Spawning and larval rearing of red sea urchin Salmacis bicolor (L. Agassiz and Desor, 1846;Echinodermata: Echinoidea)

Gonads of sea urchin attract consumers due to its high nutritional value than any other seafood delicacies. Aquaculturists are also very keen on developing larval culture methods for large-scale cultivation. The present investigation systematically examined the larval rearing, development, survival and growth rate of Salmacis bicolor fed with various microalgal diets under laboratory condition. Fertilization rate was estimated as 95%. The blastula and gastrula stages attained at 8.25 h and 23.10 h post-fertilization. The 4 - armed pluteus larvae were formed with two well - developed post-oral arms at 44.20 h following post-fertilization. The 8 - armed pluteus attained at 9 days post fertilization. The competent larva with complete rudiment growth was developed on 25th days post - fertilization. Monodiet algal feed - Chaetoceros calcitrans and Dunaliella salina resulted medium (50.6 ± 2.7%) and low survival rate (36.8 ± 1.7%) of S. bicolor larvae. However, combination algal feed – Isochrysis galbana and Chaetoceros calcitrans has promoted high survival rate (68.3 ± 2.5%) which was significantly different between the mono and combination diet. From the observations of the study, combination diet could be adopted as an effective feed measure to promote the production of nutritionally valuable roes of S. bicolor.

Effect of dopamine on early larvae of sea urchins, Mesocentrotus nudus and Strongylocentrotus intermedius.

Larvae of many echinoids are known to be phenotypically plastic and capable of changing the growth rate of their post-oral arms depending on the microalgae concentration in their habitat. As literature data show, developing larvae use chemosensation to detect algae in the environment and "adjust" the rate of growth of their post-oral arms through dopamine signaling. According to our results, dopamine has a significant effect on the post-oral arm growth in early larvae of two sea urchin species, Mesocentrotus nudus and Strongylocentrotus intermedius. The dopamine effect depends on concentration: the higher the dopamine concentration in the water, the shorter the post-oral arms. We suggest that the pattern of response to variation in dopamine concentration, manifested by early larvae of both species, is similar to that observed at different concentrations of microalgae.

Transgenerational effects of UV-B radiation on egg size, fertilization, hatching and larval size of sea urchins Strongylocentrotus intermedius.

Transgenerational effects are important for phenotypic plasticity and adaptation of marine invertebrates in the changing ocean. Ultraviolet-B (UV-B) radiation is an increasing threat to marine invertebrates. For the first time, we reported positive and negative transgenerational effects of UV-B radiation on egg size, fertilization, hatchability and larval size of a marine invertebrate. Strongylocentrotus intermedius exposed to UV-B radiation showed positive transgenerational effects and adaptation on egg size, hatching rate and post-oral arm length of larvae. Negative transgenerational effects were found in body length, stomach length and stomach width of larvae whose parents were exposed to UV-B radiation. Sires probably play important roles in transgenerational effects of UV-B. The present study provides valuable information into transgenerational effects of UV-B radiation on fitness related traits of sea urchins (at least Strongylocentrotus intermedius).

More than morphology: Differences in food ration drive physiological plasticity in echinoid larvae

Previous studies examining echinoid larval development have observed food-dependent allometric growth in morphological features related to particle capture ability. The aim of the current study was to determine if in conjunction with this morphological plasticity, there was also evidence for physiological plasticity (i.e., food-dependent differences in mass-specific rates and/or energetic efficiencies). Larvae of the Pacific sand dollar, Dendraster excentricus, were fed relatively low and high amounts of algae (1,000 and 10,000algalcellsml−1, respectively). Morphological plasticity was observed, with low-fed larvae possessing longer ciliated bands and postoral arms relative to midline body length and stomach length. Rates of ingestion, metabolism, and growth (protein and lipid biomass) were measured throughout larval development to investigate differences in larval energy partitioning and growth efficiencies. Mass-specific rates of ingestion and respiration were ~2-fold higher in high-fed larvae, indicative of significant differences in physiological state. While total energy ingested reflected the 10-fold difference in feeding concentration, partitioning of energy between growth and metabolism was significantly different. Low-fed larvae possessed higher ingestion-related efficiencies (assimilation, gross growth, and protein growth efficiencies) that decreased with age. High-fed larvae exhibited consistently greater values of net growth efficiency throughout development. This increase was driven by increasing metabolic efficiency of protein deposition. A correlative analysis between rates of ingestion and metabolism demonstrated that both low- and high-fed larvae had a similar cost of feeding of 0.29 (±0.01; SE) μJ (algal cell ingested)−1. These results demonstrate that larval responses to food levels are not just morphologically plastic, but also physiologically plastic. It is important to further understand these mechanisms of physiological plasticity and their potential link to morphology. Such information will result in a more comprehensive understanding of larval growth and factors that influence recruitment success.

The larvae of Diadema setosum (Leske, 1778) (Camarodonta: Diadematidae) from South China Sea

Diadema setosum (Leske, 1778) develops from small isolecithal eggs with a diameter of 84 ± 3 μm. Embryonic development took about 6.5–7 h and finished when a blastula left the fertilization envelope and became a larva. At this stage, the first pigment cells had appeared. At 23 h a prism developed; at 44 h a pluteus with one pair of arms had appeared; at 45 h of development plutei had two pairs of arms. The pigment cells colour the pluteus of D. setosum dark red. When 20-day-old larvae were mechanically stimulated, they flared their arms which may be defensive behaviour. During further development, the post oral arms of plutei grew to 1900 μm or more. Metamorphosis took place at about 40–45 days. At this time, five primary ambulacral podia were visible within the larval body. The duration of metamorphosis from the moment of larval settlement until the juvenile sea urchins began to move along the bottom was 40–60 min. The diameter of the test of the newly metamorphosed juvenile sea urchins was about 500 μm.

Contrasting arm elevation angles of multi- and two-armed sea urchin echinoplutei supports Grünbaum and Strathmann’s hydromechanical model

The morphology of marine invertebrate larvae influences population maintenance and connectivity through functional consequences for swimming, feeding, dispersal and settlement. Sea urchin echinoplutei approximate one of two forms: multi-armed larvae with arms at high elevation angles or two-armed larvae with arms at low elevation angles. According to the hydromechanical model of Grunbaum and Strathmann in J Mar Res 61:659–691 (2003), these morphologies convey either high swimming speed and weight-carrying capacity (few arms at low angles) or high stability in shear (many arms at high angles). This dichotomy, as exemplified by the multi- and two-armed larvae of Heliocidaris tuberculata and Centrostephanus rodgersii, respectively, was investigated to assess model predictions with regard to the angle of elevation of the arms. It was hypothesised that this angle differs in the two forms, multi-armed with high angles (>60°) and two-armed with low angles (<40°) and that the angle would lower as the larvae increased in weight due to growth of the arm skeleton. Arm angles differed as hypothesised and decreased with growth, 7.7° and 10.6° in the advanced larvae of H. tuberculata and C. rodgersii, respectively. The angle of elevation of the outermost arms was also determined from images of 37 additional species of echinoplutei to examine trends in arm angle and change as larvae develop. Multi-armed larvae exhibited a 3°–16° decrease in postoral arm angle from the 2–4 to 6–8 arm stage. In general, multi-armed larvae had higher arm angles than two-armed larvae and, arm angles decreased with growth in both larval forms.

Development of the sea urchins Temnopleurus toreumaticus Leske, 1778 and Temnopleurus reevesii Gray, 1855 (Camarodonta: Temnopleuridae)

Sea urchin larvae near metamorphosis form an adult rudiment that is a complex of the juvenile structures. However, the details of the mechanisms that form the adult rudiment are unknown. The temnopleurid sea urchins Temnopleurus toreumaticus and Temnopleurus reevesii occur in Japan, but the development of their juvenile morphology has not been described. In this study, we observed their development by light and scanning electron microscopy to follow the adult rudiment formation and to consider the mechanisms of evolution of juvenile morphology in sea urchins. The prism embryos of both species formed two primary pore canals that elongated from the left and right coelomic sacs; the left canal connected the presumptive water vascular system to the hydropore. These organs were formed bilaterally and symmetrically in T. toreumaticus and with left-right asymmetry in T. reevesii. The right canal of both species had degenerated by the four-armed larval stage. At the prism stage, about six cells from the left oral ectoderm located between the left post-oral arm and the oral lobe formed a cell mass. The cell mass grew in diameter stepwise in T. toreumaticus by cell migration and by the formation of an epithelial pouch during the four- to six-armed larval stages and more rapidly in T. reevesii by the formation of a thin epithelium during the six-armed larval stage. In both species, the adult rudiment was formed by attachment of the cell mass to the hydrocoel. The larvae of T. toreumaticus metamorphosed from a tiny hole on the left ectoderm between the post-oral and postero-dorsal arms. These findings suggest that the developmental process involving the formation of two primary pore canals and a cell mass may have been acquired and conserved as common traits in the early development of indirect-developing temnopleurid species during evolutionary divergence from the Cidaroida.

Effects of Reduced Carbonate Saturation State on Early Development in the Common Edible Sea Urchin Lytechinus variegatus: Implications for Land-Based Aquaculture

Land-based aquaculture facilities often utilize additional bicarbonate sources such as commercial sea salts that are designed to boost alkalinity in order to buffer seawater against reductions in pH. Despite these preventative measures, many facilities are likely to face occasional reductions in pH and corresponding reductions in carbonate saturation states due to the accumulation of metabolic waste products. We investigated the impact of reduced carbonate saturation states (ΩCa, ΩAr) on embryonic developmental rates, larval developmental rates, and echinoplutei skeletal morphometrics in the common edible sea urchin Lytechinus variegatus under high alkalinity conditions. Commercial artificial seawater was bubbled with a mixture of air and CO2 gas to reduce the carbonate saturation state. Rates of embryonic and larval development were significantly delayed in both the low and extreme low carbonate saturation state groups relative to the control at a given time. Although symmetry of overall skeletal body lengths was not affected, allometric relationships were significantly different between treatment groups. Larvae reared under ambient conditions had significantly greater postoral arm and overall body lengths relative to body lengths than larvae grown under extreme low carbonate saturation state conditions, indicating that extreme changes in the carbonate system affected not only developmental rates but also larval skeletal shape. Reduced rates of embryonic development and delayed and altered larval skeletal growth are likely to negatively impact larval culturing of L. variegatus in land-based, intensive culture situations where calcite and aragonite saturation states are lowered by the accumulation of metabolic waste products.

Effects of different microalgal feeds and their influence on larval development in the white-spined sea urchin Tripneustes gratilla

Nutrition is a major factor governing early development of sea urchins. The morphological development and survival of Tripneustes gratilla larvae, from field-collected urchins, was investigated from two separate feeding trials under different feeding regimes. Microalgae Isochrysis sp., Pavlova lutheri and Chaetoceros muelleri were tested as feed in May 2010 and Tetraselmis suecica, Skeletonema pseudocostatum and C. muelleri were tested in September 2010. Morphometric measurements of post-oral arm (PO), total width, total length, stomach length and mid-body line (MBL) were recorded every second day. In May, larvae fed Pavlova died after 23 days and did not reach competence. Larvae grew significantly better on Chaetoceros and Isochrysis, reaching competence on day 16 and 18 respectively, and had survival rates of 5.12% and 13.8% respectively. In the September trial, larvae fed Tetraselmis died by day 9, whereas larvae fed Skeletonema and Chaetoceros reached competence by day 22. Survival rates for Skeletonema and Chaetoceros were 2.14% and 2.3% respectively. There was a significant difference in the body profile (PO:MBL) between feed treatments at day 8 in both trials. The study suggests that C. muelleri, S. pseudocostatum and Isochrysis sp. are all suitable feeds for rearing T. gratilla larvae.

Influence of microalgal species and dietary rations on larval development and survival of the purple sea urchin, Strongylocentrotus purpuratus (Stimpson, 1857)

This study evaluated the effect of diet and ration on the growth and survival of larvae of the purple sea urchin, Strongylocentrotus purpuratus. Larval total length, mid-line body length, body width, post-oral arm length, time to reach metamorphic competency, and survival rate were assessed during the experimental period (28 days). In the first experiment, seven algal diets [ i.e. Dunaliella tertiolecta, Chaetoceros muelleri, Isochrysis sp. (Tahitian strain) and all possible binary and tertiary combinations] were assessed, along with a control treatment of no food. Larvae reared on the bi-algal diet of D. tertiolecta/ Isochrysis sp. and the uni-algal diet of D. tertiolecta provided significantly better growth than all other treatments. Larvae were successfully raised to metamorphic competency with both the binary combination of D. tertiolecta/ Isochrysis sp. and the single species D. tertiolecta within 28 days of culture, whereas larvae in all other dietary treatments failed to reach competence within 28 days. In the second experiment, a bi-algal diet ( D. tertiolecta and Isochrysis sp. at equal biovolumes) was evaluated using five rations: (1) low ration: 1.25 × 10 3 cells ml − 1 ; (2) normal ration: 2.5 × 10 3 cells ml − 1 ; (3) standardized ration: 2.5 × 10 3 to 10.0 × 10 3 cells ml − 1 , with increasing ration according to developmental stage; (4) medium ration: 5.0 × 10 3 cells ml − 1 ; and (5) high ration: 10.0 × 10 3 cells ml − 1 . Typical echinoid larval development in all body dimensions was only achieved for larvae offered the standardized ration. Larvae reared on this ration attained metamorphic competency within 28 days, whereas larvae fed the fixed rations (lower or higher concentrations) failed to attain competency by the end of the experiment. In general, in comparison to larvae fed the standardized ration, larvae on the low ration showed longer post-oral arm length and narrower body width whereas larvae on the high ration showed shorter post-oral arm length and body width in relation to their total length. Overall survival (from prism stage to metamorphic competency) for the best treatments in both experiments was 44.4 ± 2.9 and 53.3 ± 1.9% (mean ± SE) for the binary diet of D. tertiolecta/ Isochrysis sp. and standardized ration treatments, respectively. Based on these results, larvae fed a binary combination of D. tertiolecta and Isochrysis sp. or D. tertiolecta alone with a ration increasing with developmental stage is recommended for hatchery production of S. purpuratus.

Effect of ultraviolet radiation on growth and percent settlement of larval Lytechinus variegatus (Echinodermata: Echinoidea)

Lytechinus variegatus larvae were used to examine the effects of ecologically relevant short-term exposures of ultraviolet radiation (UVR) on larval morphology and settlement. A laboratory experiment tested the blastula, gastrula, and early pluteus stages of larval development for susceptibility to damage from exposure to UVR produced by an artificial light source. Larval post-oral arm length and percent settlement were measured to assess UVR effects. Larvae exposed at the blastula and gastrula stages had a reduction in larval post-oral arm length compared with non-exposure controls, while larvae exposed at the early pluteus stage were similar to controls. Larvae exposed in the gastrula stage had a significant reduction in percent settlement compared with controls. Negative consequences from ecologically relevant levels of UVR were differentially dependent on the larval stage at time of exposure suggesting time point in larval development at exposure will be important in interpreting effects on higher levels of biological organization.

The ocean acidification seascape and its relationship to the performance of calcifying marine invertebrates: Laboratory experiments on the development of urchin larvae framed by environmentally-relevant pCO 2/pH

Variation in ocean pH is a dynamic process occurring naturally in the upwelling zone of the California Current Large Marine Ecosystem. The nearshore carbonate chemistry is under-characterized and the physiology of local organisms may be under constant challenge from cyclical changes in pH and carbonate ion concentration of unexpectedly high magnitude. We looked to environmental pH conditions of coastal upwelling and used those values to examine effects of low pH on 4-arm larvae of purple sea urchin Strongylocentrotus purpuratus. We deployed a pH sensor at a nearshore shallow benthic site for 3 weeks during summer 2010 to assess the changes in pH in the Santa Barbara Channel, a region considered to have relatively less intense upwelling along the US Pacific Coast. Large fluctuations in pH of up to 0.67 pH units were observed over short time scales of several days. Daily pH fluctuations on a tidal pattern followed temperature fluctuations over short time scales, but not over scales greater than a day. The lowest pH values recorded (~ 7.70) are lower than some of those pH values predicted to occur in surface oceans at the end of the century. In the context of this dynamic pH exposure, larvae were raised at elevated pCO 2 levels of 1000 ppm and 1450 ppm CO 2 (pH 7.7 and 7.5 respectively) and measured for total larval length (from the spicule tip of the postoral arm to the spicule tip of the aboral point) along the spicules, to assess effects of low pH upwelling water on morphology. Larvae in all treatments maintained normal development and developmental schedule to day 6, and did not exhibit significant differences in larval asymmetry between treatments. At day 3 and day 6, larvae in the 1450 ppm CO 2 treatment were significantly smaller (p < 0.001) than the control larvae by only 7–13%. The observation of smaller larvae raised under high pCO 2 has an as yet undetermined physiological mechanism, but has implications for locomotion and feeding. These effects of small magnitude in these urchin larvae are indicative of a potential resilience to near-future levels of ocean acidification. Using environmental monitoring of pH to inform experimental parameters provides a means to improve our understanding of acclimatization of organisms in a dynamic ecosystem.