Sea Urchin Populations Research Articles

Are Microfibers a Threat to Marine Invertebrates? A Sea Urchin Toxicity Assessment.

The rise of "fast fashion" has driven up the production of low-cost, short-lived clothing, significantly increasing global textile fiber production and, consequently, exacerbating environmental pollution. This study investigated the ecotoxicological effects of different types of anthropogenic microfibers-cotton, polyester, and mixed fibers (50% cotton: 50% polyester)-on marine organisms, specifically sea urchin embryos. All tested fibers exhibited toxicity, with cotton fibers causing notable effects on embryonic development even at environmentally relevant concentrations. The research also simulated a scenario where microfibers were immersed in seawater for 30 days to assess changes in toxicity over time. The results showed that the toxicity of microfibers increased with both concentration and exposure duration, with polyester being the most toxic among the fibers tested. Although synthetic fibers have been the primary focus of previous research, this study highlights that natural fibers like cotton, which are often overlooked, can also be toxic due to the presence of harmful additives. These natural fibers, despite decomposing faster than synthetic ones, can persist in aquatic environments for extended periods. The findings underline the critical need for further research on both natural and synthetic microfibers to understand their environmental impact and potential threats to marine ecosystems and sea urchin populations.

Successful large-scale and long-term kelp forest restoration by culling sea urchins with quicklime and supported by crab predation

In 2013, a large scale (70 hectare) kelp forest restoration experiment was conducted in a sea urchin barren that had been stable for 45 years. We used 200 tons of quicklime to eradicate the sea urchin population. Kelp recovered within a year in the lime-treated sites. Quickliming did not significantly affect the abundance of non-target species. Mobile kelp fauna colonized the restored kelps, but at a slower rate than kelp and other macroalgae, probably due to slower dispersal abilities. The monitoring period (2012–2021) encompassed the expansion of invasive red king crabs, which emerged as a novel predator of sea urchins. This led to a gradual decline in sea urchin populations and facilitated kelp recovery also in the control sites. This delayed recovery does not invalid the conclusions of the short-term efficiency of the quicklime treatment, but it makes it difficult to conclude about the long-term effects. The study shows that quickliming can initiate kelp recovery within large urchin barrens. We postulate that the recovery of kelps outside the limed areas was due to crab predation, and that successful kelp restoration in areas with recruitment of sea urchins depends on a persistent top-down control of the urchins.

Fine-scale phylogeography of Tripneustes gratilla revealed a core-periphery pattern in the South China sea

The Core-Periphery Hypothesis (CPH) is a theoretical framework in phylogeography used to examine the spatial distribution of genetic diversity. The tropical Indian-Western Pacific (IWP), serving as a prominent marine biodiversity hotspot, constantly exports species and evolutionary novelties to peripheral habitats. Many species display genetic patterns consistent with CPH predictions from the IWP to periphery regions. However, the presence of CPH’s genetic signals in intermediate distribution zones remains underexplored. Here, we collected four sea urchin populations of Tripneustes gratilla in the South China Sea and analysed their population structure and evolutionary patterns using 13 morphological parameters, one mitochondrial 16S rRNA gene and nine polymorphic microsatellites. The results revealed substantial genetic homogeneity among the populations, implying a single origin from a glacial refugium. Nonetheless, morphological and microsatellite data distinctly differentiate the northernmost Fengjiawan population from the others, which could be attributed to increased environmental selection pressures such as temperature. Analysis of genetic diversity variation along latitudinal gradients and the relationship between geographic and genetic distances align with CPH expectations for both 16S and microsatellites, albeit to varying degrees of significance. This study enhances our understanding of tropical marine invertebrate evolution and supports the applicability of the CPH model at a fine-scale level.

Effects of Rock Type and Food Availability on Bioerosion by the Purple Sea Urchin, Strongylocentrotus purpuratus.

Purple sea urchins (Strongylocentrotus purpuratus) profoundly impact nearshore rocky coasts through their feeding habits. Their intense grazing sculpts substrates through bioerosion using their teeth and spines and controls the alternative stable state dynamic between kelp bed and urchin barrens. These states have contrasting food availability for sea urchins, with abundant food in kelp beds and scarce food in barren grounds. However, the relationship between food availability and bioerosion is unknown. We predicted that when kelp is available, it would ameliorate the action of teeth on the substrate. Our 11-weeks long, 2×2 factorial experiment, crossed community state (kelp present vs absent) and rock type (sandstone vs mudstone). We also quantified the contribution of spine abrasion to bioerosion on the two rock types. The bioerosion rates did not differ between treatments with and without kelp. Although there was no significant difference in net bioerosion between the rock types, there was a large difference between the proportion of bioerosion from teeth vs spine abrasion. Approximately a third of the sandstone bioerosion was from spines whereas less than 2% of mudstone bioerosion could be attributed to spines. As anticipated, growth of sea urchins fed kelp ad-libitum was higher than food-limited sea urchins. Surprisingly, sea urchins on mudstone (which has a higher organic component) grew faster than sea urchins on sandstone. Although bioerosion rates may not differ on a per-urchin basis between community states, the sea urchin population densities between kelp beds and urchin barrens likely causes a difference in net bioerosion between these communities. Our results point to the importance of lithology on the mechanics of sea urchin bioerosion. Differences in texture, grain size, and hardness of rock substrates undoubtedly contribute to bioerosion rates and dynamics.

Inorganic UV filter-based sunscreens labelled as eco-friendly threaten sea urchin populations

Although the negative effects of inorganic UV filters have been documented on several marine organisms, sunscreen products containing such filters are available in the market and proposed as eco-friendly substitutes for harmful, and already banned, organic UV filters (e.g. octinoxate and oxybenzone). In the present study, we investigated the effects of four sunscreen products, labelled by cosmetic companies as “eco-friendly”, on the early developmental stages of the sea urchin Paracentrotus lividus, a keystone species occurring in vulnerable coastal habitats. Among sunscreens tested, those containing ZnO and TiO2 or their mix caused severe impacts on sea urchin embryos. We show that inorganic UV filters were incorporated by larvae during their development and, despite the activation of defence strategies (e.g. phagocytosis by coelomocytes), generated anomalies such as skeletal malformations and tissue necrosis. Conversely, the sunscreen product containing only new-generation organic UV filters (e.g. methylene bis-benzotriazolyl tetramethyl, ethylhexyl triazone, butylphenol diethylamino hydroxybenzoyl hexyl benzoate) did not affect sea urchins, thus resulting actually eco-compatible. Our findings expand information on the impact of inorganic UV filters on marine life, corroborate the need to improve the eco-friendliness assessment of sunscreen products and warn of the risk of bioaccumulation and potential biomagnification of inorganic UV filters along the marine food chain.

Taxa-dependent temporal trends in the abundance and size of sea urchins in subtropical eastern Australia.

Subtropical reefs host a dynamic mix of tropical, subtropical, and temperate species that is changing due to shifts in the abundance and distribution of species in response to ocean warming. In these transitional communities, biogeographic affinity is expected to predict changes in species composition, with projected increases of tropical species and declines in cool-affinity temperate species. Understanding population dynamics of species along biogeographic transition zones is critical, especially for habitat engineers such as sea urchins that can facilitate ecosystem shifts through grazing. We investigated the population dynamics of sea urchins on coral-associated subtropical reefs at 7 sites in eastern Australia (28.196° S to 30.95° S) over 9 years (2010-2019), a period impacted by warming and heatwaves. Specifically, we investigated the density and population size structure of taxa with temperate (Centrostephanus rodgersii, Phyllacanthus parvispinus), subtropical (Tripneustes australiae) and tropical (Diadema spp.) affinities. Counter to expectation, biogeographic affinity did not explain shifts in species abundances in this region. Although we expected the abundance of tropical species to increase at their cold range boundaries, tropical Diadema species declined across all sites. The subtropical T. australiae also showed declines, while populations of the temperate C. rodgersii were remarkably stable throughout our study period. Our results show that temporal patterns of sea urchin populations in this region cannot be predicted by bio-geographic affinity alone and contribute critical information about the population dynamics of these important herbivores along this biogeographic transition zone.

Recombinant SpTransformer proteins are functionally diverse for binding and phagocytosis by three subtypes of sea urchin phagocytes.

The California purple sea urchin, Strongylocentrotus purpuratus, relies solely on an innate immune system to combat the many pathogens in the marine environment. One aspect of their molecular defenses is the SpTransformer (SpTrf) gene family that is upregulated in response to immune challenge. The gene sequences are highly variable both within and among animals and likely encode thousands of SpTrf isoforms within the sea urchin population. The native SpTrf proteins bind foreign targets and augment phagocytosis of a marine Vibrio. A recombinant (r)SpTrf-E1-Ec protein produced by E. coli also binds Vibrio but does not augment phagocytosis. To address the question of whether other rSpTrf isoforms function as opsonins and augment phagocytosis, six rSpTrf proteins were expressed in insect cells. The rSpTrf proteins are larger than expected, are glycosylated, and one dimerized irreversibly. Each rSpTrf protein cross-linked to inert magnetic beads (rSpTrf::beads) results in different levels of surface binding and phagocytosis by phagocytes. Initial analysis shows that significantly more rSpTrf::beads associate with cells compared to control BSA::beads. Binding specificity was verified by pre-incubating the rSpTrf::beads with antibodies, which reduces the association with phagocytes. The different rSpTrf::beads show significant differences for cell surface binding and phagocytosis by phagocytes. Furthermore, there are differences among the three distinct types of phagocytes that show specific vs. constitutive binding and phagocytosis. These findings illustrate the complexity and effectiveness of the sea urchin innate immune system driven by the natSpTrf proteins and the phagocyte cell populations that act to neutralize a wide range of foreign pathogens.

Predation risk of the sea urchin Paracentrotus lividus juveniles in an overfished area reveal system stability mechanisms and restocking challenges.

Where sea urchin harvest has been so intense that populations have drastically regressed, concerns have arisen about the effectiveness of harvesting management. According to the theory of phase transition in shallow rocky reefs between vegetated and barren habitats, sea urchin recruitment, a key population structuring process, seems hampered by some stabilizing feedback despite an end to local human harvest of sea urchins. To shed a light on predation effects on sea urchin recruits, a 27-day field experiment was conducted using mega-predator exclusion cages (40x40x40 cm, 1 cm in mesh size) in barren and turf substrates. To facilitate this, 672 recruits (1.1 ± 0.02 cm in size) reared under control conditions were positioned in groups of 42 in each experimental unit (n = 4). Exclusion of mega-predators had a significant effect regardless the substrate, since a higher number of recruits was found under cages both in turf and barren. However, the results showed that in uncaged treatments the size of recruits that survived was larger in turf than in barren, as in the former substrate predation had reduced the abundance of the smallest recruits, highlighting that mega-predator presence affects differently the size of the recruits that had survived depending on the substrate. Overall, these results provide valuable information to address restocking actions of sea urchin populations in overharvested areas, where algal turfs are widespread, and assist studies on habitat stability mechanisms.

Leachates of weathering plastics from an urban sandy beach: Toxicity to sea urchin fertilization and early development

Plastic leachates have chemical and biological implications for marine environments. This study experimentally evaluated acute effects of weathering plastic leachates (0, 25, 50, 75 and 100 %) on fertilization and early development of the sea urchin Lytechinus variegatus. Fertilization, embryonic and larval development were drastically inhibited (~75 %) when gametes were exposed to intermediate and high leachate concentrations or delayed when exposed to the lowest concentration. Fertilization and first cleavage stages were highly affected by exposure to intermediate and high leachate concentrations. None of the cells incubated at concentrations from 50 % reached blastula stage, suggesting that embryonic development was the most sensitive stage. Abnormalities in embryos and larvae were observed in all leachate treatments. Chemical analysis detected high concentration of bisphenol A, which may induce these observed effects. Our results highlight the potential threats of plastic pollution to sea urchin populations, which may severely affect the structure and functioning of coastal ecosystems.

Edible Sea urchin (Paracentrotus lividus) larval dispersal and connectivity modelling in the northwestern Mediterranean Sea

The edible sea urchin (Paracentrotus lividus) is of significant economic importance due to high demand for its consumption in various Mediterranean countries. This echinoderm plays a crucial ecological role by regulating the dynamics of seaweed and seagrass through its grazing behaviour. The abundance of sea urchin is variable in time and space, but it is currently potentially declining in the Mediterranean Sea, and likely to be negatively affected by global change. Therefore, gaining a more comprehensive understanding of sea urchin larval dispersal patterns over an extended period could contribute to our understanding of how their dynamics relate to population connectivity. To investigate the trajectories of larval dispersal of this sea urchin in the Northwestern Mediterranean Sea, we combined a Lagrangian model (Ichthyop) with a hydrodynamic model (MARS3D). This study covered the years 2010–2018 and aimed to quantify the connectivity between the preferred habitats of the sea urchin (seagrasses and rocky substrates). The present study explores seasonal variations in dispersal routes and habitat connectivity relationships for two spawning scenarios identified in the literature (spring and autumn). The results enable us to identify dispersal routes, and their regularity over time. They highlight a consistent connection between Sardinia, Corsica, and the coastlines of the Ligurian and Tyrrhenian Seas, indicating a lack of genetic structuring within the edible sea urchin population in this area, particularly in Corsica. The connectivity matrices confirm the observed dispersal trajectories and highlight certain areas of significant and enduring local retention over time. The results also reveal minimal seasonal variability. Conversely, interannual variability appears pronounced, particularly in relation with trends in the warming of surface waters in the Mediterranean, which seem to impact the dispersal routes taken by P. lividus larvae. Lastly, a connectivity map was created to explore spatial resource management perspectives, aiming to identify frequent connections over an extended time period and assign varying levels of intensity to them. This approach can provide guidance with regard to resource management issues for different coastal areas that can be connected by larvae.

Reproductive Cycle of the Sea Urchin Paracentrotus lividus (Lamarck, 1816) on the Central West Coast of Portugal: New Perspective on the Gametogenic Cycle

A population of sea urchins, Paracentrotus lividus, from the central west coast of Portugal was studied to characterise their reproductive biology and possible relationships with environmental factors. An annual gametogenic cycle was found, with a broad spawning season, from May to November, according to a relatively synchronous gamete maturation process. Depending on the environmental factors (temperature, photoperiod), two separate periods could be distinguished, with more individuals maturing and spawning at the same time. When this happened, the first event evolved when temperature rose to a critical point, and the second occurred afterwards, when temperature decreased significantly. Notwithstanding, it was found that individuals matured later than previously described for other populations (e.g., north of Portugal), mostly in late spring, with a higher gonadosomatic index in May. A new classification scale was proposed for identifying the stages of P. lividus gametogenic cycle, based on new findings. It contributed to its simplification and easier comprehension. This study provides useful information for a differentiated sustainable management of P. lividus, according to local conditions. Establishing a closed harvesting season might be considered, based on the differences observed between Portuguese populations and other European ones.

A Preliminary Assessment of Microalgal Diets for Echinopluteus Larvae Culture of the Sea Urchin Sphaerechinus granularis (Lamarck, 1816) (Echinoidea: Toxopneustidae)

Sea urchins play an important role in coastal marine ecosystems and are an economically valuable resource for their gonads (roe or uni). Increased demand by Asian and European countries caused overfishing of wild stocks resulting in a sharp decline of sea urchin populations. The increased efforts in developing cost-effective protocols are focused on larval development up to pre- and post-metamorphosis stages, as they are one of the main difficulties of echinoculture. This is a preliminary study to evaluate the influence of microalgal varying diet rationing on larval development, growth, and survivorship at pre-metamorphosis of Sphaerechinus granularis echinopluteus (30 days post-fertilization). Three microalgae diets based on Dunaliella tertiolecta and Rhodomonas marina and the combination of both species were tested. Each diet used three ration treatments: low ration (500–3000 cells⋅ml−1); medium ration (1000–6000 cells⋅ml−1); and high ration (4000–24,000 cells⋅ml−1), which were cell-density adjusted to larval development. Assays used three triplicated treatments in 8 L cylindrical–conical glass incubators. Results showed that the survival of S. granularis echinopluteus was positively influenced by diets of lower cellular densities and a combined microalgae diet. Adoption of this type of diet regime is expected to improve larval production and provide the groundwork for future research on S. granularis in aquaculture.

Sea urchin utilisation in Eastern Indonesia

Sea urchins have long been an important component of gleaning invertebrate fisheries and are valued for their highly nutritious gonads. Sea urchin fisheries are often unreported and unregulated, despite increasing indications of overexploitation. Data on the post-harvest utilization of sea urchins are limited, particularly in the Indo-Pacific region. This study at 12 sites across four regions in Indonesia (Sulawesi, Moluccas, Nusa Tenggara, Papua) aimed to provide an overview of sea urchin utilization in eastern Indonesia. Data were collected from July to September 2020 using a questionnaire with a snowballing sampling method. There were 187 respondents (62.6% male and 37.4% female) ranged in age from 3-76 years old, and most had been collecting sea urchins for more than five years. Respondents mostly collected the sea urchins from coral reef or seagrass habitats. Four genera (Tripneustes, Diadema, Echinometra and Echinothrix) were identified. Mean catch ranged from 32 (Makassar) to 169 (Maluku Tengah) individual sea urchin per collection. Most respondents knew local names for sea urchins, especially those they collected. Almost 70% respondents used their catch mainly for home consumption, and only 4.8% respondents mainly selling their catch. Most urchins sold were whole or crudely de-spined, typically fetching IDR 500-1000 each. Additional post-harvest processing before sale included removing the gonads from the test and/or cooking, with a unit price of IDR 5,000-25,000/product. Commonly consumed raw, urchins were sometimes cooked (mostly barbecued). These data indicate a need for efforts towards socio-ecologically appropriate sea urchin conservation and fisheries management to address the widespread indications of increasing exploitation levels and declining sea urchin populations.

Increased sensitivity of sea urchin larvae to metal toxicity as a consequence of the past two decades of Climate Change and Ocean Acidification in the Mediterranean Sea

The Mediterranean Sea represents a natural laboratory to infer the possible impacts of climate change and ocean acidification. In this article, we report the deteriorating ability of sea urchin larvae (Paracentrotus lividus) to cope with toxicity of a reference contaminant (Cu EC50) over the past 20 years and assessed the influence of 5 environmental factors from satellite measurements. This timeframe was divided in before and after January 2016 (46.57 μg/L vs 28.56 μg/L respectively, p < 0.001). In the second subset of data, correlation of the biological variable with CO2 and pH strengthened compared to the first part (rCO2-EC50: −0.21 vs −0.83 and rpH-EC50: 0.25 vs 0.87 respectively), with a causal link starting from one year and ending 4 months prior to EC50 measurements. Considering the continuous increase in CO2 concentrations recorded recently, this study could reveal a rapid deterioration of the health condition of this population of sea urchins in a coastal ecosystem.

Study of the sea urchins (echinoidea) influence on the coral reef communities in the Nusa Dua Bali conservation area

Coral reef ecosystems are crucial for marine ecosystems as they support various other marine organisms. Sea urchins, such as Diadema setosum and Echinometra mathaei influence the coral reef communities by consuming algae that disrupt coral growth. This study aims to determine reef star coral media quantity, identify the dominant coral species at three points (BTN, Coral Garden, and Cluster 5) in Nusa Dua Beach, and assess the influence of sea urchins on coral reefs. The sampling method used was Purposive sampling, and visual observations which were conducted from June 27 to June 30, 2022. Results showed the varying sea urchin populations, with Acropora sp. and Pocillopora sp. dominating at BTN, Acropora sp. and Pectinia sp. at Coral Garden, and Acropora sp. at Cluster 5. The findings suggest that sea urchins play a key role in maintaining coral reefs by consuming macroalgae and supporting coral survival.

Sea urchins in the intertidal zone on Karanrang Island, Pangkep Regency; Density, abundance, community structure, and distribution patterns

Sea urchins were ecologically and economically important biota, but scientific information on sea urchins is still very minimal and there is no ongoing monitoring. The purpose of this study was to determine the density, abundance, community structure, and distribution patterns of sea urchins in the intertidal zone of Karanrang Island, Pangkep Regency. The research in June-July 2022 was carried out at high and low tide using three transects measuring 1 x 1 m consisting of four plots measuring 50 x 50 cm. Determination of stations based on information from local residents to get observation stations based on tidal conditions. The results showed that three species of sea urchins from two families were found, namely Diadema setosum, Echinothrix calamaris, and Tripneustes gratilla. The species of D. setosum was found to be very abundant (97.3-97.6%) and tended to be more abundant during high tide than during low tide. The index of diversity and uniformity of porcupine species is low (H' = 0.130-0.142 and E = 0.118-0.129). The species dominance index was in the range of 0.946-0.953 indicating high dominance of D. setosum. Spatially, D. setosum had a uniform distribution pattern, whereas E. calamaris and T. gratilla were distributed in clusters. Further spatial and temporal research is needed to comprehensively determinant the conditions of the sea urchin population on Karanrang Island, Pangkep Regency.

How ocean warming and acidification affect the life cycle of six worldwide commercialised sea urchin species: A review

AbstractOngoing global changes are expected to affect the worldwide production of many fisheries and aquaculture systems. Because invertebrates represent a relevant industry, it is crucial to anticipate challenges that are resulting from the current environmental alterations. In this review, we rely on the estimated physiological limits of six commercialised species of sea urchins (Loxechinus albus, Mesocentrotus franciscanus, Paracentrotus lividus, Strongylocentrotus droebachiensis, Strongylocentrotus intermedius and Strongylocentrotus purpuratus) to define the vulnerability (or resilience) of their populations facing ocean warming and acidification (OW&amp;A). Considering that coastal systems do not change uniformly and that the populations’ response to stressors varies depending on their origin, we investigate the effects of OW&amp;A by including studies that estimate future environmental mutations within their distribution areas. Cross‐referencing 79 studies, we find that several sea urchin populations are potentially vulnerable to the predicted OW&amp;A as environmental conditions in certain regions are expected to shift beyond their estimated physiological limit of tolerance. Specifically, while upper thermal thresholds seem to be respected for L. albus along the SW American coast, M. franciscanus and S. purpuratus southern populations appear to be vulnerable in NW America. Moreover, as a result of the strong warming expected in the Arctic and sub‐Arctic regions, the local productivity of S. droebachiensis is also potentially largely affected. Finally, populations of S. intermedius and P. lividus found in northern Japan and eastern Mediterranean respectively, are supposed to decline due to large environmental changes brought about by OW&amp;A. This review highlights the status and the potential of local adaptation of a number of sea urchin populations in response to changing environmental conditions, revealing possible future challenges for various local fishing industries.

Sea urchins of Peninsular Malaysia: Spatial distribution and species-habitat association

Sea urchins are keystone herbivores in coral reefs that can prevent coral-algae phase shifts and promote coral resilience in the Caribbean. However, knowledge of sea urchin populations in the Indo-Pacific region is less extensive and their role in marine ecosystems remains uncertain. To fill this knowledge gap, this study examined the spatial distribution and species-habitat association of sea urchins in Peninsular Malaysia as a first step in exploring their potential for promoting reef resilience. Firstly, geographical information on the population characteristics of sea urchins in Peninsular Malaysia (Sunda Shelf and Malacca Strait Marine Ecoregions) was gathered. Using literature, questionnaire, and field surveys, ten species of sea urchins from six families were identified in the species record for Peninsular Malaysia. Prionocidaris bispinosa represents the first record for Malaysia, documented in the intertidal seagrass meadow at Tanjung Kupang, Johor. Combining density data from literature and field surveys, sea urchin density for Peninsular Malaysia was estimated to be 46.94 ± 66 individuals/100 m2. Secondly, the species-habitat association of Diadema setosum and Echinothrix calamaris were determined in belt-transect surveys (n=57), with transects laid parallel to shore at Pulau Rawa, Johor. Multivariate regression analysis identified D. setosum to be more associated with live coral cover and coral growth form, while E. calamaris distribution was driven by habitat rugosity, water depth and live coral cover. These findings suggest contrasting species-habitat associations for the two co-existing species. Given the limited information about sea urchins in Malaysia, this study appears to be the first in-depth study of its kind in the country, deepening our knowledge of sea urchin distribution and the importance of habitat in shaping that distribution. This baseline data serves as valuable information in the planning and management of natural habitats for biodiversity and conservation in Malaysia’s marine ecosystem.

Sunflower sea star predation on urchins can facilitate kelp forest recovery.

The recent collapse of predatory sunflower sea stars (Pycnopodia helianthoides) owing to sea star wasting disease (SSWD) is hypothesized to have contributed to proliferation of sea urchin barrens and losses of kelp forests on the North American west coast. We used experiments and a model to test whether restored Pycnopodia populations may help recover kelp forests through their consumption of nutritionally poor purple sea urchins (Strongylocentrotus purpuratus) typical of barrens. Pycnopodia consumed 0.68 S. purpuratus d-1, and our model and sensitivity analysis shows that the magnitude of recent Pycnopodia declines is consistent with urchin proliferation after modest sea urchin recruitment, and even small Pycnopodia recoveries could generally lead to lower densities of sea urchins that are consistent with kelp-urchin coexistence. Pycnopodia seem unable to chemically distinguish starved from fed urchins and indeed have higher predation rates on starved urchins owing to shorter handling times. These results highlight the importance of Pycnopodia in regulating purple sea urchin populations and maintaining healthy kelp forests through top-down control. The recovery of this important predator to densities commonly found prior to SSWD, whether through natural means or human-assisted reintroductions, may therefore be a key step in kelp forest restoration at ecologically significant scales.

Evaluation of Sub-Antarctic and Antarctic sea urchins’ thermal reaction norm through righting behavior and comparison with in situ measurements

Sea urchin's survival may depend on their capacity to recover proper orientation rapidly and effectively after inversion, enabling escape from predator and preventing desiccation. This righting behavior has been used as a repeatable and reliable indicator to assess echinoderms performance across environmental conditions, including thermal sensitivity and thermal stress. The current study aims at evaluating and comparing the thermal reaction norm for righting behavior (time for righting (TFR) and capacity to self-right) of three common sea urchins from high latitude, the Patagonian sea urchins Loxechinus albus and Pseudechinus magellanicus, and the Antarctic sea urchin Sterechinus neumayeri. In addition, to infer the ecological implications of our experiments, we compared laboratory-based and in situ TFR of these three species. We observed that populations of the Patagonian sea urchins L. albus and P. magellanicus presented similar trend of righting behavior, overly accelerating with increasing temperature (from 0 to 22°C). Little variations and high inter-individual variability were observed below 6°C in the Antarctic sea urchin TFR, and righting success strongly decreased between 7 and 11°C. For the three species, TFR was lower in in situ experiments compared to the laboratory. Overall, our results suggest that the populations of Patagonian sea urchin exhibit a wide thermal tolerance and, based on S. neumayeri's TFR, aligning with the narrow thermal tolerance of Antarctic benthos. Finally, the differences between laboratory and in situ experiments highlights the importance of considering the complexity of marine environments for future predictions.