Purple Urchin Strongylocentrotus Purpuratus Research Articles

Kelp-associated variability in seawater chemistry during a marine heatwave event connects to transgenerational effects in the purple urchin Strongylocentrotus purpuratus

Giant kelp Macrocystis pyrifera provides the foundation for immense biodiversity on the coast of California, USA. Kelp forests can change seawater retention time, altering water chemistry, including pH and dissolved oxygen (DO), as well as the magnitude and predictability of variability in the same properties. Environmental heterogeneity across space and time could drive organismal performance and processes such as transgenerational plasticity (TGP), where parental experience modifies the offspring phenotype, potentially conferring tolerance to future environmental stress. We monitored environmental variability by deploying temperature, pH, and DO sensors inside and outside a temperate kelp forest in the Santa Barbara Channel (SBC) throughout the gametogenesis period of a key herbivore, the purple urchin Strongylocentrotus purpuratus. Over the 6 mo period, pH and temperature were slightly elevated inside the kelp forest, accompanied by more predictable, low-frequency variability relative to outside. Adult S. purpuratus were conditioned inside and outside the kelp spanning gametogenesis. The urchins were spawned and their larvae were raised under high (1053 µatm) and low pCO2 (435 µatm) at 15°C in the laboratory to assess their physiological response to the maternal and developmental environments. Larvae raised under high pCO2 were more susceptible to acute thermal stress; however, within each larval treatment, progeny from outside-conditioned mothers had a 0.4°C higher lethal temperature (LT50). Our results indicate that heterogeneity in abiotic factors associated with kelp can have transgenerational effects in the field, and interactions between factors, including temperature and pH, will impact purple urchins as local variability associated with marine heatwaves and upwelling evolves with climate change.

Sea urchin microbiomes vary with habitat and resource availability

AbstractSea urchins are key grazers in coastal seas, where they can survive a variety of conditions and diets, enhancing their ecological impact on kelp forests and other ecosystems. Using 16S rRNA gene sequencing, we characterized bacterial communities associated with guts of the two dominant sea urchin species in southern California, the red urchin Mesocentrotus franciscanus, and the purple urchin Strongylocentrotus purpuratus. Our results show that the two urchin species have distinct gut microbiomes that vary with habitat. The taxonomic composition of their microbiomes suggests that they may facilitate digestion of food and be a source of nutrition themselves. These results highlight the role of microbiomes within macroorganisms as an extended ecological trait, and suggest that microbes may be crucial to resource use and partitioning in co‐occurring species.

The painted sea urchin, Lytechinus pictus, as a genetically-enabled developmental model.

Although sea urchins are one of the oldest and most widely used marine model systems, few species have been routinely kept in culture through multiple generations. The workhorse of the field is the purple urchin Strongylocentrotus purpuratus. However, one disadvantage of S. purpuratus is its long generation time, making it impractical as a model for generating and maintaining transgenic lines. In an effort to develop a sea urchin that is suitable for transgenerational experiments and the generation of transgenic lines, we have focused on development of updated culturing methods and genomic resources for the painted sea urchin, Lytechinus pictus. Compared to S. purpuratus, L. pictus have relatively large eggs, develop into optically clear embryos, and the smaller adults can become gravid in under a year. Fifty years ago, Hinegardner developed culturing methods for raising L. pictus through metamorphosis. Here, we provide an updated protocol for establishing and maintaining L. pictus in the laboratory, and describe a new genome resource for this urchin. In our hands, L. pictus reach the 4-armed pluteus stage at 4 days; become competent to metamorphosis at 24 days; and are gravid by 6 months. Plutei and juveniles are fed on a diet of algae and diatoms, and adults are fed on kelp. We also make available a L. pictus transcriptome generated from developmental stages (eggs to 2-day-old plutei) to support the annotation of our genome sequencing project, and to enhance the utility of this species for molecular studies and transgenesis.

Impacts of ocean acidification on survival, growth, and swimming behaviours differ between larval urchins and brittlestars

Abstract Ocean acidification (OA) is widely recognized as an increasing threat to marine ecosystems. Many marine invertebrates have dual-phase life cycles in which planktonic larvae connect and sustain otherwise disconnected benthic adult populations. Many planktonic larvae are particularly sensitive to environmental stresses including OA. Here, we compared the developmental dynamics, survivorship, and swimming behaviours of plutei of two ecologically important echinoderm species that naturally experience variability in ambient pH: the purple urchin Strongylocentrotus purpuratus and the infaunal brittlestar Amphiura filiformis. Sensitivity to decreased pH differed between these two species and between maternal lineages. Larvae of both species experienced increased mortality and reduced growth rate under low pH conditions. However, larval brittlestars appeared more sensitive and experienced over 80% mortality after 7-d exposure to pH 7.7. Larval urchins from one maternal lineage underwent highly synchronized budding (release of blastula-like particles) at low pH. Observed budding temporarily increased numerical density and reduced individual size, leading to differences in growth and mortality rates between the two half-sibling groups and another population. Swimming speeds of larval brittlestars were reduced in decreased pH. In contrast, acidification had either no effect or positive effect on swimming speeds of larval urchins. The observed differences between species may be a reflection of pre-exposure in their natural habitats: larval brittlestars experience a relatively stable in situ pH environment, whereas larval urchins are occasionally exposed to low pH in upwelling regions. Urchins may therefore exhibit short-term compensatory responses such as budding and increased swimming speed. Natural selection could act upon the significant variations we observed between maternal lineages, resulting in more resilient populations confronting chronic exposure to OA.

California spiny lobster preference for urchins from kelp forests: implications for urchin barren persistence

Overfishing of urchin predators, in combination with natural disturbances, has been linked to an increase in the occurrence of urchin barrens. Marine reserves have been proposed as a means to re-establish the interactions between urchins and their predators in California kelp forests. Whether increased densities of lobsters and other predators in reserves are sufficient to convert barrens back to kelp forests depends on the degree to which predators avoid urchins from barren habitats. Urchins from these barrens may be less appealing to predators due to their diminished gonad production and thus decreased quality. In this study, we compared consumption rates of California spiny lobster Panulirus interruptus on purple urchins Strongylocentrotus purpuratus that were collected from kelp forests or from urchin barrens. All size classes of lobster prefer urchins from kelp forests relative to those from barrens and will actively select kelp-bed urchins when given a choice. Lobsters also showed higher consumption rates of kelp-bed urchins when either kelp-bed or barren urchins were presented alone. The large size class of lobsters consumed more and larger urchins than did smaller size classes of lobsters. These results suggest a potential mechanism for the persistence of urchin barrens despite high lobster densities and indicate that lobster foraging preferences may delay phase shifts from barrens back to kelp forests. The results also suggest that preferential foraging by lobsters on kelp-bed urchins may increase the resistance of kelp-beds to changes in state.

Species-specific effects of fluid shear on grazing by sea urchin larvae: comparison of experimental results with encounter-model predictions

Small-scale turbulence can alter the rate of plankton predator–prey encounters. Encounter models predict that prey ingestion by slow-swimming zooplankton is enhanced at low levels of turbulence. We investigated whether small-scale turbulence increases ingestion for the slow-swimming, suspension-feeding pluteus larvae of the white urchin Lytechinus pictus and the purple urchin Strongylocentrotus purpuratus. Model predictions of the critical level of turbulence, ecr, above which encounters due to turbulence are greater than those due to behavior (swimming or suspension feeding) alone, were experimentally tested using shortand long-term grazing treatments. Because urchin larvae are smaller than the smallest eddy scales of turbulence and thus experience turbulence as laminar shear, larvae were exposed to flow conditions using a simple laminar shear flow with dissipation rates, e, of 0, 0.1, 0.4, and 1 cm2 s–3. Short-term ingestion of beads by L. pictus larvae was unaffected by e < 1 cm2 s–3 but was 30% greater at this level, which was greater than ecr based on flow speeds produced in suspension feeding. Long-term flow treatments with algal prey had no significant effect on grazing or growth. Short-term ingestion of beads by S. purpuratus larvae was unaffected by e < ecr based on suspension feeding; the effect of long-term flow exposure on ingestion and growth could not be investigated because of high mortality, suggesting greater sensitivity to flow exposure compared to L. pictus. Experimental results are consistent with model predictions that ecr is high, and thus levels of turbulence in the ocean are not expected to significantly increase ingestion and reduce food limitation in suspension-feeding urchin larvae.