Tube Feet Research Articles

Short-term exposure to okadaic acid induces behavioral and physiological responses in sea urchin (Strongylocentrotus intermedius)

Massive harmful algal blooms (HABs) have increased the risk of marine organisms encountering the dinoflagellate toxin, okadaic acid (OA). Strongylocentrotus intermedius, a globally significant benthic aquaculture species, has a large appetite for benthic algae. During red tide events, there is a high risk of red tide toxin accumulation. This study systematically evaluated the potential impact of short-term OA exposure on the behavior and physiological functions of juvenile S. intermedius. From typical (5 μg/L) to extreme OA concentrations (20 μg/L) during HAB outbreaks, OA exposure gradually inhibited a series of tube foot-related behaviors (sheltering, foraging, righting, and tube-foot tenacity). At OA concentrations during HAB outbreaks (5 μg/L), the tube foot function of S. intermedius was progressively inhibited. Further physiological indicator analyses revealed that the activity of antioxidants increased over a short period to prevent damage from reactive oxygen species induced by OA. However, OA ultimately suppressed the immune response of S. intermedius, leading to apoptosis. Although HAB-associated concentrations of OA (5 μg/L) did not induce a continuous increase in the integrated biological response index of S. intermedius, this study speculated that HABs pose a future risk to echinoderm species. Notably, principal component analysis results showed that OA exposure eventually induced significant changes in the production of O2-, malondialdehyde, and total glutathione, as well as in glutathione S-transferase activity and caspase-7, -8, and -9 levels. This study provides preliminary evidence of OA’s toxic effects on sea urchins and essential data for urgent risk assessments of algal toxin pollution in aquaculture during HABs.

Gearing in a hydrostatic skeleton: the tube feet of juvenile sea stars (Leptasterias sp.).

Hydrostatic skeletons, such as an elephant trunk or a squid tentacle, permit the transmission of mechanical work through a soft body. Despite the ubiquity of these structures among animals, we generally do not understand how differences in their morphology affect their ability to transmit muscular work. Therefore, the present study used mathematical modeling, morphometrics, and kinematics to understand the transmission of force and displacement in the tube feet of the juvenile six-rayed star (Leptasterias sp.). An inverse-dynamic analysis revealed that the forces generated by the feet during crawling primarily serve to overcome the submerged weight of the body. These forces were disproportionately generated by the feet at more proximal positions along each ray, which were used more frequently for crawling. Owing to a combination of mechanical advantage and muscle mass, these proximal feet exhibited a greater capacity for force generation than the distal feet. However, the higher displacement advantage of the more elongated distal feet offer a superior ability to extend the feet into the environment. Therefore, the morphology of tube feet demonstrates a gradient in gearing along each ray that compliments their role in behavior.

Isolation and characterization of NGFFYamide neuropeptide from Patiria pectinifera pyloric caeca extract

Neuropeptides are small molecules that mediate intercellular signaling and regulate physiological processes. Starfish possess various myoactive neuropeptides, including starfish myorelaxant peptide (SMP) and a calcitonin-type peptide with apical muscle relaxing properties. In this study, we report the purification of a neuropeptide from starfish (Patiria pectinifera) pyloric caeca extract using high-performance liquid chromatography (HPLC) and an in vitro bioassay to screen for fractions and peptides with relaxing effects on P. pectinifera apical muscle preparations. A series of HPLC steps using reversed-phase and cation-exchange columns yielded a purified peptide with muscle-relaxing effects. The purified peptide's structure was determined by LC-MS and Edman degradation, revealing a pentapeptide with an amidated C-terminus (NGFFYamide) and a molecular mass of 646.2930 Da. This is the first report of NGFFYamide purification from P. pectinifera through biochemical methods. The nucleotide sequence encoding the NGFFYamide precursor was determined, showing the presence of a conserved neurophysin domain in the C-terminal region. RT-qPCR results confirmed high expression in radial nerves cord, consistent with previous findings on NG peptides in echinoderms. In vitro pharmacological studies on muscle preparations from P. pectinifera and Asterias amurensis revealed differential relaxing activity of NGFFYamide on apical muscles, while its effects on tube foot preparations were similar in both species. NGFFYamide also induced potent contraction in P. pectinifera cardiac stomach. Comparison of three NG peptides (NGFFYamide, NGFFFamide, and NGIWYamide) on P. pectinifera cardiac stomach revealed varying potency, suggesting class-specific receptor interactions. Tachyphylaxis was observed in P. pectinifera apical muscle but not in A. amurensis, warranting further investigation. Based on these results, it is plausible that NGFFYamide could be involved in regulating locomotion and feeding behavior in P. pectinifera, consistent with findings in Asterias rubens.

Feeding and growth are regulated by light and opsins-mediated phototransduction in sea cucumber Apostichopus japonicus

Light is a crucial environmental ecological factor that affects physiological processes including feeding and growth of marine invertebrates. Although nonvisual photosensitivity has long been known in echinoderms, the underlying molecular regulation mechanism remains unclear. Here, we firstly reported opsins-mediated phototransduction signaling and the cross-talk between light and feeding/growth in Apostichopus japonicus, an important economic species with high medicinal and nutritional values. Molecular characterization analysis of Ajopsins revealed that they were mainly distributed in the epidermis of potential photosensitive tissues (tentacles, papillae and tube feet). And all four Ajopsins including Rhodopsin 5-like (AjRH5), long-wavelength-sensitive opsin (AjLWS), peropsin (AjPOP), and peropsin-like (AjPOPL) exhibited different expression patterns in response to different light conditions. Moreover, four Ajopsins all conjugated with Gαi/o to reduce intracellular cAMP levels. Besides, three Ajopsins (AjRH5, AjPOP and AjPOPL) conjugated with Gαq to activate Gαq/Ca2+/PKC signaling. And all four opsins could activate downstream ERK1/2 phosphorylation. In addition, the photosensitivities of these four Ajopsins were different in response to different wavelength of light, AjPOP and AjPOPL were sensitive to short-medium-long wavelength light, AjRH5 and AjLWS were sensitive to medium-long wavelength light. Furthermore, indoor aquaculture experiment showed that 150 lx and 300 lx light intensity could significantly promote feeding and growth of A. japonicus, which might be mediated by AjOXP1 and AjMAP2K4. Under different light wavelength treatment, red light (655–665 nm) significantly promoted the feeding and growth of A. japonicus, which may be mediated by AjOXP1/2, AjMAP2K4 and AjMegf6. And siRNA experiment further confirmed the crosstalk between AjPOPL and AjOXP1, suggesting AjPOPL may regulate feeding by AjOXP1 in A. japonicus. Our findings showed a comprehensive description of Ajopsins signaling, providing new insights on the molecular mechanism of photoreception involved in regulating feeding and growth in A. japonicus and suggested the optimum light conditions for optimizing the lighting scheme of A. japonicus aquaculture.

Starfish tube feet inspired hydrogel electrode for durable underwater sEMG acquisition

Underwater surface electromyography (UW-sEMG) acquisition with long-term high quality is crucial to underwater activities, including rehabilitation, fatigue measurement, and sports monitoring. However, most UW-sEMG electrodes suffer significant performance decline, especially for hydrogel electrodes, due to the swelling-induced mechanical, electrical, and adhesive degradation. Maintaining high performance underwater over extended periods is challenging. The controlled underwater adhesion-detachment behavior of starfish is inspirative. Here, a starfish tube feet-inspired hydrogel (STFH) electrode is developed for UW-sEMG recording, including a micro-swelling hydrogel pillar, a biomimetic silicone sucker, and an Ag/AgCl disc electrode. By soaking freeze-dried hydrophilic hydrogel in tannic acid (TA) solution, the hydrogel exhibits skin-like modulus of 22.4 kPa, low skin impedance of 18.3 kΩ (10 Hz) and low equilibrium swelling ratio. Unlike traditional strategies for improving anti-swelling properties, this work leverages the interaction between the sucker and the swollen hydrogel to promote conformal contact. Consequently, the sEMG signal exhibits SNR of 26.7 dB and baseline noise of 12.8 μV even after 60 min of underwater working. The STFH electrode also shows anti-noise capability to resist skin vibration and wave oscillation. This STFH electrode enables durable UW-sEMG acquisition, which could further extend from the arm to the wrist to adapt wearing habits.

A new species of holothuroid from the Labrador Sea (eastern Canada): Pseudothyonelabradorensis sp. nov. (Echinodermata, Holothuroidea, Dendrochirotida, Sclerodactylidae).

A new species of holothuroid, Pseudothyonelabradorensis sp. nov. (order Dendrochirotida and family Sclerodactylidae), was discovered off the coast of Labrador (eastern Canada) at a depth of 740-969 m. Two specimens were described based on morphological and genetic parameters. Distinctive characters included pinkish body colour, presence of tube feet on a 'tail', supporting rod-shaped ossicles in the tube feet, and rod-shaped ossicles in the tentacles. To investigate its phylogenetic relationships, partial sequences of COI were obtained for the new species as well as for the type species P.raphanus and another North Atlantic species P.serrifera. According to the phylogenetic analysis, P.labradorensis sp. nov. appeared in a well-supported clade with P.raphanus and P.serrifera. Molecular data also suggest polyphyly of the genus, showing the Northeast Pacific species Pseudothyonebelli recovered outside of the clade containing the type species. Pseudothyonelabradorensis sp. nov. is the first species of the genus from the Northwest Atlantic. A key to the North Atlantic Pseudothyone is provided.

Limb coordination: Coming together to bounce along

Experimental, modeling, and robotic research shows that switching of sea stars from crawling to bouncing gaits does not require centralized neural control. Bouncing can instead arise cooperatively, with synchronization of sea star tube feet occurring by locally acting mechanisms alone.

Soft skeletons transmit force with variable gearing.

A hydrostatic skeleton allows a soft body to transmit muscular force via internal pressure. A human's tongue, an octopus' arm and a nematode's body illustrate the pervasive presence of hydrostatic skeletons among animals, which has inspired the design of soft engineered actuators. However, there is a need for a theoretical basis for understanding how hydrostatic skeletons apply mechanical work. We therefore modeled the shape change and mechanics of natural and engineered hydrostatic skeletons to determine their mechanical advantage (MA) and displacement advantage (DA). These models apply to a variety of biological structures, but we explicitly consider the tube feet of a sea star and the body segments of an earthworm, and contrast them with a hydraulic press and a McKibben actuator. A helical winding of stiff, elastic fibers around these soft actuators plays a critical role in their mechanics by maintaining a cylindrical shape, distributing forces throughout the structure and storing elastic energy. In contrast to a single-joint lever system, soft hydrostats exhibit variable gearing with changes in MA generated by deformation in the skeleton. We found that this gearing is affected by the transmission efficiency of mechanical work (MA×DA) or, equivalently, the ratio of output to input work. The transmission efficiency changes with the capacity to store elastic energy within helically wrapped fibers or associated musculature. This modeling offers a conceptual basis for understanding the relationship between the morphology of hydrostatic skeletons and their mechanical performance.

Underwater Gesture Recognition Meta-Gloves for Marine Immersive Communication.

Rapid advancements in immersive communications and artificial intelligence have created a pressing demand for high-performance tactile sensing gloves capable of delivering high sensitivity and a wide sensing range. Unfortunately, existing tactile sensing gloves fall short in terms of user comfort and are ill-suited for underwater applications. To address these limitations, we propose a flexible hand gesture recognition glove (GRG) that contains high-performance micropillar tactile sensors (MPTSs) inspired by the flexible tube foot of a starfish. The as-prepared flexible sensors offer a wide working range (5 Pa to 450 kPa), superfast response time (23 ms), reliable repeatability (∼10000 cycles), and a low limit of detection. Furthermore, these MPTSs are waterproof, which makes them well-suited for underwater applications. By integrating the high-performance MPTSs with a machine learning algorithm, the proposed GRG system achieves intelligent recognition of 16 hand gestures under water, which significantly extends real-time and effective communication capabilities for divers. The GRG system holds tremendous potential for a wide range of applications in the field of underwater communications.

Three new species and one new record of Deimatidae (Echinodermata, Holothuroidea, Synallactida) discovered in the South China Sea and the Mariana fore-arc area using integrative taxonomic methods.

Deep-sea holothurian specimens were collected during five scientific expeditions (2018-2023) using the submersible vehicle 'Shenhaiyongshi'. Our examination of specimens of Deimatidae from the South China Sea and the Mariana fore-arc area revealed three new species, which were described as Oneirophantaidsseicasp. nov., Oneirophantabrunneannulatasp. nov., and Oneirophantalucernasp. nov. These species were distinguished from each other and from congeners by the arrangement, and number of ventrolateral tube feet and ossicle types. We also reported Oneirophantamutabilismutabilis Théel, 1879 for the first time from the Mariana fore-arc area, and we recorded Deimavalidumvalidum for the second time from the South China Sea. The taxonomy of these new species and new records is discussed, and a phylogenetic analysis based on a concatenated dataset of 16S and COI genes was conducted. Additionally, the inter- and intraspecific genetic divergences we calculated among deimatid species. The results support the assignment of these new species to the genus Oneirophanta and their separation from congeners. A description of the main morphological characters of Oneirophanta species is also provided. The data were collected from geographically diverse areas and suggest that species of Deimatidae were abundant in the Pacific Ocean and occupied a wide range of depths.

Repeated Hyposalinity Pulses Immediately and Persistently Impair the Sea Urchin Adhesive System.

Climate change will increase the frequency and intensity of extreme climatic events (e.g., storms) that result in repeated pulses of hyposalinity in nearshore ecosystems. Sea urchins inhabit these ecosystems and are stenohaline (restricted to salinity levels ∼32‰), thus are particularly susceptible to hyposalinity events. As key benthic omnivores, sea urchins use hydrostatic adhesive tube feet for numerous functions, including attachment to and locomotion on the substratum as they graze for food. Hyposalinity severely impacts sea urchin locomotor and adhesive performance but several ecologically relevant and climate change-related questions remain. First, do sea urchin locomotion and adhesion acclimate to repeated pulses of hyposalinity? Second, how do tube feet respond to tensile forces during single and repeated hyposalinity events? Third, do the negative effects of hyposalinity exposure persist following a return to normal salinity levels? To answer these questions, we repeatedly exposed green sea urchins (Strongylocentrotus droebachiensis) to pulses of three different salinities (control: 32‰, moderate hyposalinity: 22‰, severe hyposalinity: 16‰) over the course of two months and measured locomotor performance, adhesive performance, and tube foot tensile behavior. We also measured these parameters 20 h after sea urchins returned to normal salinity levels. We found no evidence that tube feet performance and properties acclimate to repeated pulses of hyposalinity, at least over the timescale examined in this study. In contrast, hyposalinity has severe consequences on locomotion, adhesion, and tube foot tensile behavior, and these impacts are not limited to the hyposalinity exposure. Our results suggest both moderate and severe hyposalinity events have the potential to increase sea urchin dislodgment and reduce movement, which may impact sea urchin distribution and their role in marine communities.

A novel short-type peptidoglycan recognition protein with unique polysaccharide recognition specificity in sea cucumber, Apostichopus japonicus

Pattern recognition receptors (PRRs) are the first line of immune defense in invertebrates against pathogen infection; they recognize pathogens and transmit signals to downstream immune pathways. Among these, peptidoglycan recognition proteins (PGRPs) are an important family in invertebrates that generally comprise of complicated isoforms. A comprehensive understanding of PGRPs in evolutionarily and economically important marine invertebrates, such as the sea cucumber, Apostichopus japonicus, is crucial. Previous studies have identified two PGRPs in sea cucumber, AjPGRP-S and AjPGRP-S1, and another novel short-type PGRP, AjPGRP-S3, was additionally identified here. The full-length cDNA sequence of AjPGRP-S3 was obtained here by PCR-RACE, followed by which showed its gene expression analyses by in situ hybridization that showed it to be relatively highly expressed in coelomocytes and tube feet. Based on an analysis of the recombinant protein, rAjPGRP-S3, a board-spectrum pathogen recognition ability was noted that covered diverse Gram-negative and -positive bacteria, and fungi. Moreover, according to the results of yeast two-hybridization, it was suggested that rAJPGRP-S3 interacted with multiple immune-related factors, including proteins involved in the complement system, extracellular matrix, vesicle trafficking, and antioxidant system. These findings prove the important functions of AjPGRP-S3 in the transduction of pathogen signals to downstream immune effectors and help explore the functional differences in the AjPGRP isoforms.

Podia histology and ultrastructure of tropical sea cucumber Phyllophorus sp. (Phyllophoridae) and Colochirus quadrangularis (Cucumaridae) from Madura Strait, Indonesia

Abstract. Winarni D, Eridianti SA, Suhargo L, Khaleyla F, Wirawati I. 2023. Podia histology and ultrastructure of tropical sea cucumber Phyllophorus sp. (Phyllophoridae) and Colochirus quadrangularis (Cucumaridae) from Madura Strait, Indonesia. Biodiversitas 24: 5685-5692. Phyllophorus sp. and Colochirus quadrangularis are sea cucumber species found in Madura Strait, East Java, Indonesia. Both species possess distinctive podia structures, which are protrusions on their body walls resembling spines. These structures serve as tube feet for movement (ventral podia) and sensory organs (dorsal papillae). This research aimed to compare the podia structures of Phyllophorus sp. and Colochirus quadrangularis. Five samples of each species were collected from the Madura Strait. Histological slides were prepared for the papillae (dorsal) and podia (ventral) on the anterior, median, and posterior body sections. Simultaneously, an examination of the ultrastructure was conducted using a scanning electron microscope (SEM). Analysis revealed differences between the podia of the two species. Phyllophorus sp. papillae had semi-flat tips, were non-suckered (SFNS), and exhibited squamous to short columnar epithelia, while their tube feet had flat tips, were non-suckered, and had columnar epithelia. Papillae were denser than tube feet. Conversely, C. quadrangularis papillae were pointed and non-suckered (PNS), and tube feet were flat and non-suckered (FNS). Notably, ossicle-dense areas in C. quadrangularis papillae had a pyramidal shape. In summary, the histology and ultrastructure of podia in these species displayed significant differences, highlighting their unique characteristics. They also imply to the adaptation biology of sea cucumber in Indonesian waters.

Effects of alarm cues on behavior and physiology of the sea cucumber Apostichopus japonicus

Alarm cues have an inevitable impact on organisms in aquaculture. The present study investigated the effects of alarm cues on the sea cucumber Apostichopus japonicus from behavioral and physiological perspectives. We found that the adhesion time significantly increased in sea cucumbers exposed to alarm cues (P = 0.008), indicating that sea cucumbers do not easily fall off the attachment substance into a harsh environment in seed production. Novelly, this present study clarified that fleeing response of sea cucumbers exposed to alarm cues was driven by tail movement rather than head movement. There was no significant difference in tentacle activity frequency (P = 0.705), indicating that alarm cues would not affect feeding behavior of sea cucumbers. In addition, there was also no significant difference in righting behavior of A. japonicus (P = 0.724), indicating that sea cucumbers probably respond to alarm cues through tube feet rather than tentacles or muscles. We reveal that alarm cues do not affect all but some the behaviors of sea cucumbers. Further, the present study found no significant difference in cortisol concentration (P = 0.583). In contrast, 5-hydroxytryptamine (5-HT) concentration significantly increased in sea cucumbers exposed to alarm cues (P = 0.004). These results suggest that the effect of alarm cues is probably mediated by 5-HT in sea cucumbers. Further, the present study found that the movement speed had a significant decrease in sea cucumbers fed with 3% dietary tryptophan when being exposed to alarm cues (P < 0.001). Thus, we suggest aqua-farmers feed 3% tryptophan to optimize behaviors of A. japonicus in seed production. In addition, the present study found that the artificial reef significantly shortened the righting response time of sea cucumbers (P = 0.002), indicating that artificial reefs are beneficial to righting behavior of sea cucumbers exposed to alarm cues. This present study provides new insights into behavioral and physiological reactions to alarm cues and into seed production of sea cucumbers.

A Bionic Starfish Adsorption Crawling Soft Robot

A variety of soft wall-climbing robots have been developed that can move in certain patterns. Most of these soft robots can only move on conventional surfaces and lack adaptability to complex surfaces. Improving the adaptability of soft robots on complex surfaces is still a challenging problem. To this end, we study the layered structure of the starfish tube foot and the valve flap structure in the water vascular system, and use an ultrasonic stress detector to study the stiffness distribution of the arm structure. Inspired by the motion of the starfish, we present a bionic soft wall-climbing robot, which is driven by two groups of pneumatic feet and achieves body bending through active adaptation layers. We design the structure of the foot to flex to provide driving force, and there are suction cups at the end of the foot to provide suction. The soft foot has a simple structure design, adapts to a variety of surfaces, and does not damage the surface of the substrate. Variable stiffness layers achieve stiffness changes by the principle of line blocking. The Central Pattern Generator theory is introduced to coordinately control the multiple feet of the robot. After experiments, we verify the adaptability of the soft robot to curved surfaces. The research may provide a reference for the design and development of crawling soft robots on complex surfaces.

Highly rearranged gene orders and rapid evolutionary rates in the mitochondrial genomes of Apodida (Echinodermata: Holothuroidea)

Mitochondrial genome (mitogenome) is a frequently-used tool for phylogenetic and evolutionary studies among metazoans, however, it was still poorly represented in some invertebrate groups, including holothurians. Apodida is one of the most ancient orders of Holothuroidea, with unique characteristics in lacking tube feet and the respiratory tree. Here, we sequenced six mitogenomes from the holothurian order Apodida (Synaptidae and Chiridotidae) and compared them with other available holothurian mitogenomes. The apodan mitogenomes present positive GC skews and negative AT skews, a pattern diametrically opposite to that found in the mitogenomes of other holothurians. The amino acid genetic distances of the 13 protein-coding genes (PCGs) were the highest between Apodida and other holothurians. The mitochondrial gene orders within Apodida were extensively rearranged at the species level, and also were unique from the arrangement patterns of other holothurians. Phylogenetic relationships based on two different criteria: (i) nucleotides sequences with all codon positions (PCG123) and (ii) Neutral Transitions Excluded model (NTE) confirmed the monophyly and basal position of the order Apodida with a long branch. The NTE phylogeny generated a low variation of branch length, but it did not ameliorate the long branch length of Apodida. The divergence time estimation suggested that the Apodida originated in the Middle Carboniferous, implying that they survived the extinction event that occurred in the boundary of the Permian and Triassic. The NTE dataset revealed younger age than that generated by PCG123 dataset. Apodida is accompanied by a faster evolutionary rate than other holothurians (0.0069 vs 0.0043 subs/s/my). The absence of tube feet and the respiratory tree may play an important role in the dramatic evolutionary changes of apodan mitogenomes.

Telomere dynamics in the Pacific crown-of-thorns seastar (Acanthaster cf. solaris): effect of age, diet, and tissue type

Population irruptions of crown-of-thorns seastar (CoTS, Acanthaster spp.) represent a perennial threat to Indo-Pacific coral reefs. Age determination of CoTS is challenging, thereby hindering understanding and management of this nuisance species. Telomeres, which are protective DNA structure found at the ends of eukaryotic chromosomes that shorten at each cell division, have been used to estimate age in wild animals. To investigate the use of telomeres in CoTS, we optimized a quantitative PCR protocol to measure relative telomere length (rTL) in CoTS for the first time. Comparing rTL among four age groups (4, 7, 16, > 24 months post-settlement), we found that adult CoTS generally exhibit shorter rTL than juveniles, which is the first evidence of age-related telomere attrition in CoTS. However, there was large within-age class variation, and no significant relationships were found between adult CoTS rTL and potential age-indicating external features. Furthermore, we found accelerated telomere attrition under sub-optimal diet, where individuals that were fed crustose coralline algae for 16 months exhibited shorter rTL than their counterparts fed on coral. A positive correlation was found between rTL of tube feet and pyloric caeca, suggesting synchronization of telomere dynamics across somatic tissues in CoTS. Overall, our results suggest that rTL could be used to classify CoTS into broad age groups, though individual variation constrains the ability to resolve specific cohorts. The present study contributes to the understanding of telomere dynamics in marine invertebrates, while laying the groundwork for future research into rTL as biomarker for age and potentially stress for CoTS.

Blue-Green Algae as Stimulating and Attractive Feeding Substrates for a Mediterranean Commercial Sea Urchin Species, Paracentrotus lividus.

Sea urchins rely on chemical senses to localize suitable food resources, therefore representing model species for chemosensory studies. In the present study, we investigated the chemical sensitivity of the Mediterranean sea urchin Paracentrotus lividus to the blue-green alga Aphanizomenon flos-aquae, namely "Klamath", and to a few amino acids chosen from the biochemical composition of the same algae. To this end, we used the "urchinogram" method, which estimates the movement rate of the sea urchins in response to chemicals. Our results showed that Klamath represents a strong chemical stimulus for P. lividus as it elicits an overall movement of spines, pedicellariae, and tube feet coupled, in some cases, to a coordinated locomotion of the animals. Sea urchins also displayed a sensitivity, even if to a lesser extent, to leucine, threonine, arginine, and proline, thus implying that the amino acids contained in Klamath may account, at least in part, for the stimulating effects exerted by the whole algae. Additionally, our results show that Klamath, as well as spirulina, another blue-green alga with high nutritional value, is very attractive for this sea urchin species. These findings gain further importance considering the potential profit of echinoderms for commercial consumers and their growing role in aquaculture. Klamath and spirulina combine high nutritional profiles with attractive and stimulating abilities and may be considered potential valuable feed supplements in sea urchin aquaculture.

Hyposalinity reduces coordination and adhesion of sea urchin tube feet.

Climate change will increase the frequency and intensity of low-salinity (hyposalinity) events in coastal marine habitats. Sea urchins are dominant herbivores in these habitats and are generally intolerant of salinity fluctuations. Their adhesive tube feet are essential for survival, effecting secure attachment and locomotion in high wave energy habitats, yet little is known about how hyposalinity impacts their function. We exposed green sea urchins (Strongylocentrotus droebachiensis) to salinities ranging from ambient (32‰) to severe (14‰) and assessed tube feet coordination (righting response, locomotion) and adhesion [disc tenacity (force per unit area)]. Righting response, locomotion and disc tenacity decreased in response to hyposalinity. Severe reductions in coordinated tube foot activities occurred at higher salinities than those that affected adhesion. The results of this study suggest moderate hyposalinities (24-28‰) have little effect on S. droebachiensis dislodgement risk and survival post-dislodgment, while severe hyposalinity (below 24‰) likely reduces movement and prevents recovery from dislodgment.

Seismic response of slender storage tanks on tube feet or skirt support

Seismic response of slender storage tanks on tube feet or skirt support