Sea Urchin Size Research Articles

Abundance, size and biomass of long-spined sea urchins (Centrostephanus rodgersii) and red sea urchins (Heliocidaris tuberculata) in New South Wales, Australia

Context Detailed demographic information for the commercially harvested long-spined sea urchins (Centrostephanus rodgersii) and red sea urchins (Heliocidaris tuberculata) on nearshore reefs of New South Wales is unavailable. Aims This is the first detailed study of abundances and sizes of these sea urchin species on shallow reefs of New South Wales where the fishery operates. Methods Divers counted sea urchins and measured their sizes in transects in the nearshore mosaic habitat and in extensive barrens habitat at 51 sites along ~800 km of coast. Key results Centrostephanus was found at most sites in both habitats, whereas Heliocidaris was found at lower densities and at fewer sites. Heliocidaris was rare in the far south and in barrens habitat. Centrostephanus was, on average, smaller in barrens habitat than in the nearshore mosaic habitat, and size structures shifted towards smaller individuals from north to south. Conclusions Centrostephanus occurred at higher densities than did Heliocidaris and had a broader distribution along the coast and across the nearshore reefs where the fishery operates. Implications This study provides a historical baseline for these commercially and ecologically important species. The small biomass of Heliocidaris (~3% that of Centrostephanus) and its restricted distribution suggest it is vulnerable to overfishing.

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.

Effects of artificial light at night on the mobility of the sea urchin Paracentrotus lividus

Light pollution poses a significant global threat to biodiversity, driven by the increasing coastal urbanization and the resulting growth of artificial light at night (ALAN). However, to date, the scientific community has focused mainly on studying its ecological effects within the terrestrial environment. It is only recently that attention has turned to coastal marine systems which are crucial due to their essential contribution at the ecosystem level. These environments, characterized by their high productivity, also play a crucial role in protecting coasts against erosion. The aim of this case study was to investigate the possible effects of ALAN on the sea urchin species Paracentrotus lividus in four areas of an Italian rocky coast, selected according to a gradient of light intensity (0, 0.4, 3 and 25 lux), from April 2022 to February 2023. Effects of ALAN were examined by measuring the density and size of sea urchins and also their reactivity to a stress condition through an innovative technique of overturning sea urchins to study their physiological response in the presence or absence of artificial light. In addition, the permanence of sea urchins in the four areas was evaluated through an efficient tagging test. Results show how these organisms, typically nocturnal, suffer negative effects of ALAN in terms of minor density and mobility, expressed as the speed of response to an adverse event, compared to a dark area.

Fitness benefits and costs of shelters to the sea urchin Glyptocidaris crenularis.

Understanding the ecological role of shelters is greatly hampered by the scarcity of long-term laboratory experiments on the trade-off between fitness benefits and costs. This lack probably leads to an underestimation of the negative and/or positive effects on behaviors and growth of marine invertebrates in benthic ecosystems. Although our previous study revealed a significant effect on fitness-related traits of Glyptocidaris crenularis after 31 months, the present study extended it and investigated fitness benefits and/or costs of long-term sheltering on sea urchins to over 7 years. The present long-term study suggests that the previously reported reduction in feeding rate probably resulted from a reduction in reflexive feeding motions (Aristotle’s lantern reflex) rather than changes in foraging behavior. Actively seeking sheltering behavior was negatively impacted in individuals with continuous access to shelters. However, covering and righting behaviors did not differ in sheltered sea urchins, indicating that these behaviors are maintained to escape from adverse environments regardless of shelter. Body size of sea urchins in the group with shelters was significantly lower than those without shelters after 7 years. Weights of gonads and gut were not significantly different after 7 years despite previous observations of differences after ~2.5 years. The present study provides valuable information on the trade-off between fitness benefits and costs to sea urchins residing in shelters. However, the present study is only a laboratory investigation for one urchin species (G. crenularis) which does not consider the complexity of natural environments. Field studies should be carried out with G. crenularis and other sea urchin species, before a more universal conclusion can be drawn.

The effects of temperature and pCO2 on the size, thermal tolerance and metabolic rate of the red sea urchin (Mesocentrotus franciscanus) during early development

The red sea urchin Mesocentrotus franciscanus supports a highly valuable wild fishery along the West Coast of North America, but despite its importance in the ecology of kelp forests and as a harvested species, little is known about how M. franciscanus responds to abiotic stressors associated with ocean warming and acidification during its early development. Here, embryos of M. franciscanus were raised under combinations of two temperatures (13 °C and 17 °C) and two pCO2 levels (475 μatm and 1050 μatm) that represent current and future coastal environments. Elevated pCO2 levels led to a decrease in body size of gastrula stage embryos while temperature had no effect. At the prism stage, both temperature and pCO2 affected body size. The warmer temperature increased the body size of prism stage embryos, offsetting the stunting effect of elevated pCO2 on growth. Thermal tolerance, which was estimated by exposing prism stage embryos to a range of temperatures and estimating the survivorship, was found to be slightly higher in those raised under warmer temperatures. The developmental temperature and pCO2 conditions under which embryos were raised did not have an effect on the metabolic rate as measured by oxygen consumption rate at the prism stage. This study provides important insights into a species of high ecological and economic value. Overall, early development under elevated pCO2 conditions may adversely impact M. franciscanus while moderate warming may improve growth and thermal tolerance. Understanding how fishery species respond to abiotic stressors will facilitate our predictive capacity of how climate change will impact future populations, which links to issues such as sustainability and food security.

Long-term study of behaviors of two cohabiting sea urchin species, Mesocentrotus nudus and Strongylocentrotus intermedius, under conditions of high food quantity and predation risk in situ.

BackgroundIn the predator–sea urchin–macrophyte trophic cascade, the ecological effect of sea urchins as grazers depends both on their density and the changes in foraging activity, which are influenced by various disturbing factors. However, the complete duration of the alarm reactions of echinoids has not been studied until now. Here, we tested a hypothesis that two cohabiting sea urchins, Mesocentrotus nudus and Strongylocentrotus intermedius, which differ morphologically, might display different behavioral responses to high hydrodynamic activity and predation.MethodsWe used continuous time-lapse video recording to clarify behavioral patterns of M. nudus and S. intermedius in presence of a large quantity of food (the kelp Saccharina japonica) but under different weather conditions and different types of predation threat: (1) calm weather conditions, (2) stormy weather conditions, (3) predation risk associated with the presence of several sea star species and (4) predation risk associated with an alarm stimulus (crushed conspecifics or heterospecifics). Three separate video recording experiments (134 days in total) were conducted under field conditions. Video recording analysis was performed to determine the number of specimens of each sea urchin species in the cameras’ field of view, size of sea urchins’ groups, movement patterns and the duration of the alarm responses of both sea urchin species.ResultsWe showed that in the presence of kelp, M. nudus and S. intermedius exhibited both similar and different behavioral responses to hydrodynamics and predation threat. Under calm weather, movement patterns of both echinoids were similar but M. nudus exhibited the higher locomotion speed and distance traveled. Furthermore, S. intermedius but not M. nudus tended to group near the food substrate. The stormy weather caused a sharp decrease in movement activity followed by escape response in both echinoids. Six starfish species failed to predate on healthy sea urchins of either species and only a few attacks on ailing S. intermedius specimens were successful. The alarm response of S. intermedius lasted approximately 90 h and 20 h for starfish attacks on ailing conspecifics and for simulated attacks (crushed conspecifics or heterospecifics), respectively and involved several phases: (1) flight response, (2) grouping close to the food, (3) leaving the food and (4) return to the food. Phase three was the more pronounced in a case of starfish attack. M. nudus only responded to crushed conspecifics and exhibited no grouping behavior but displayed fast escape (during 4 h) and prolonged (up to 19 days) avoidance of the food source. This outcome is the longest alarm response reported for sea urchins.DiscussionThe most interesting finding is that two cohabiting sea urchin species, M. nudus and S. intermedius, display different alarm responses to predation threat. Both alarm responses are interpreted as defensive adaptations against visual predators.

Spatial Abundance and Colour Morphotype Densities of the Rock-Boring Sea Urchin (Echinometra lucunter) at Two Different Habitats

The rock-boring sea urchin Echinometra lucunter is a common echinoderm found throughout the intertidal zone along the northeastern coast of, Toco, Trinidad. Sea urchin abundance, size distribution, and colour morphotypes at two sites: Pequelle Bay (SB) and Grande L’Anse (GA) were quantified using 1 m2 quadrats, accessible during extreme low tides, and in two environments, notably low and high wave action. Percent coverage of cnidarian and macroalgae were estimated in each quadrat. Sea urchin densities were 9.9–17.8 urchins/m2 in high wave action, and 25.2–60.7 urchins/m2 in low wave action environments. Size (measured as maximum sea urchin diameter) are highest between 21 and 50 mm for both black and red colour morphotypes. Black colour morphs were significantly larger than red morphs (ANOVA, F2, 175 = 5.55, p < 0.05). Sea urchins at low energy environments were significantly larger than those found in high energy environments for all years (p < 0.05). Mean hard coral, soft coral, and macroalgae cover did not show any relationship with habitat type or urchin densities. Although sea urchin abundance and distribution were variable, larger urchins were more likely to be found in low wave action environments, and smaller urchins were mostly found in the open, and exposed to high wave action.

Consumptive and non-consumptive effects of predators vary with the ontogeny of their prey.

Predators exert a strong influence on ecological communities by reducing the abundance of prey (consumptive effects) and shaping their foraging behavior (non-consumptive effects). Although the prevalence of trophic cascades triggered by non-consumptive effects is increasingly recognized in a wide range of ecosystems, how its relative strength changes as prey individuals grow in size along various life stages remains poorly resolved. We investigated how the effects of predators vary with the ontogeny of a key herbivorous sea urchin, which is responsible for transforming diverse macroalgal forests to a barren state dominated by bare rock and encrusting coralline algae. We conducted a series of field and laboratory experiments to determine how susceptibility to predation, prey behavioral responses, and grazing impact on algal cover vary with sea urchin size. The consumptive effects of predators were greater on smaller sea urchin size classes, which were more susceptible to predation. Unexpectedly however, predator non-consumptive effects acted only on larger sea urchins, significantly reducing their grazing activity in the presence of predator cues. Crucially, only these larger sea urchins were capable of overgrazing macroalgae in the field, with non-consumptive effects reducing sea urchin foraging activity and macroalgal grazing impact by 60%. The decoupling between risk and fear as prey grow indicates that the strength of consumptive and non-consumptive trophic cascades may act differently at different ontogenetic stages of prey. While the consumptive effects of predators directly influence population numbers, the consequences of non-consumptive effects may far outlive consumptive effects as prey grow, finding refuge in size, but not from fear.

Tool Use by Four Species of Indo-Pacific Sea Urchins

We compared the covering behavior of four sea urchin species, Tripneustes gratilla, Pseudoboletia maculata, Toxopneustes pileolus, and Salmacis sphaeroides found in the waters of Malapascua Island, Cebu Province and Bolinao, Panagsinan Province, Philippines. Specifically, we measured the amount and type of covering material on each sea urchin, and in several cases, the recovery of debris material after stripping the animal of its cover. We found that Tripneustes gratilla and Salmacis sphaeroides have a higher affinity for plant material, especially seagrass, compared to Pseudoboletia maculata and Toxopneustes pileolus, which prefer to cover themselves with coral rubble and other calcified material. Only in Toxopneustes pileolus did we find a significant corresponding depth-dependent decrease in total cover area, confirming previous work that covering behavior serves as a protection mechanism against UV radiation. We found no dependence of particle size on either species or size of sea urchin, but we observed that larger sea urchins generally carried more and heavier debris. We observed a transport mechanism of debris onto the echinoid body surface utilizing a combination of tube feet and spines. We compare our results to previous studies, comment on the phylogeny of sea urchin covering behavior, and discuss the interpretation of this behavior as animal tool use.

Influence of some environmental factors on growth of gray sea urchin (Strongylocentrotus intermedius) at the northwestern coast of the Japan Sea

Habitat conditions, as qualitative and quantitative composition of aquatic vegetation and oceanographic factors, are compared for six populations of sea urchinStrongylocentrotus intermediuswith different growth rate and mean size of individuals. The highest growth rate is observed in the areas between Cape Sosunov and Plitniak Bay, between Oprichnik Bay and Cape Grozny, and between Cape Lisuchenko and Kreiser Rock Island; all these areas are distinguished by high density and species diversity of macrophytes. On the contrary, the growth rate is the lowest at Cape Yuzhny where the vegetation is less abundant. All populations of slow-growing sea urchins inhabit the areas exposed to wave action that usually forms flat rocky platforms: at Cape Yuzhny, at Cape Nadezhda, and between the Yezhovaya Bay and Cape Khitrovo. However, density of sea urchin populations in these areas is higher (on average from 9.8 to 20.8 ind./m2) than in the areas with relatively high growth rate (from 0.16 to 7.20 ind./m2). Any signifcant correlation between the water temperature and mean size of sea urchins, by ages, is not detected.

Early time course of variation in coelomic fluid ionic concentrations in sea urchins abruptly exposed to hypo- and hyper-osmotic salinity challenges: Role of size and cross-section area of test holes.

Echinoderms are restricted to the marine environment and are osmoconformer invertebrates. However, some species live in unstable environments. Especially those species, and those of larger body size, tend to show variable, albeit transient, ionic gradients between their coelomic fluid and external seawater. In order to further examine how sea urchin size relates to apparent ionic permeability of their body wall/epithelia, specimens of Echinometra lucunter, Lytechinus variegatus, Paracentrotus gaimardi, and Arbacia lixula-A. lixula of two distinct populations, Rio de Janeiro and Santa Catarina-were abruptly transferred from 35 psu to either 25 or 45 psu. Sodium, chloride, magnesium, and potassium concentrations were assayed in their coelomic fluids after 0, 1, 2, and 3hr of exposure. Relative area of putative permeable (i.e., cross section areas of soft tissues, or test holes) surfaces (PPS) was estimated in empty tests as the sum of the peristomial area (oral hole in the empty test) and the total cross-section area of ambulacral holes, divided by the total volume (TV) of the test. L. variegatus and E. lucunter, the largest species, had PPS/TV values similar to that of the much smaller P. gaimardi. A. lixula was the "most putatively-permeable and conformer" among them all, especially urchins from the Santa Catarina population. Internal ionic levels equilibrated faster with external water in 45 than in 25, and differences among ions were observed. Body size is relevant, among many other factors, to aid conformers such as sea urchins to dwell in intertidal unstable habitats.

In situ measurements of righting behavior in the common sea urchin Lytechinus variegatus: the importance of body size, substrate type, and covering material

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 26:33-40 (2017) - DOI: https://doi.org/10.3354/ab00669 In situ measurements of righting behavior in the common sea urchin Lytechinus variegatus: the importance of body size, substrate type, and covering material R. C. Challener1,*, J. B. McClintock2 1Bellarmine University, Department of Biology, Louisville, KY 40205, USA 2University of Alabama at Birmingham, Department of Biology, Birmingham, AL 35294, USA *Corresponding author: rchallener@bellarmine.edu ABSTRACT: Righting behavior has been used extensively in laboratory studies of sea urchins as an indicator of stress under various environmental conditions. In situ measurements of the natural righting response of sea urchins would serve to place such laboratory measurements in an ecological context as well as potentially validate laboratory control conditions. We investigated the righting response of the sea urchin Lytechinus variegatus in seagrass and sand bottom habitats of Saint Joseph’s Bay, Florida. Field-measured righting times (other than the exception mentioned below) in L. variegatus were similar to those measured in laboratory studies. Moreover, as seen in multiple sea urchin species in laboratory studies, smaller individuals exhibited significantly shorter righting times than larger individuals. Importantly, sea urchins lacking covering material (shell material, seagrass blades) that were placed on open sand patches took significantly longer to right than those with covering material placed on sand patches. Our field observations indicate the importance of sea urchin size, substrate type, and the presence or absence of covering materials when making righting measurements in the laboratory or the field. Our findings also suggest that higher water velocities facilitate righting, as at higher flows on sand patches, the presence/absence of covering material no longer significantly impacted righting time. These findings are ecologically important as they indicate that, under certain natural conditions (sand substrate, low availability of covering materials and low water velocities), L. variegatus that are displaced onto their aboral side are more vulnerable to predation. KEY WORDS: Righting response · Covering behavior · Soft bottom · Echinodermata · Echinoidea Full text in pdf format PreviousNextCite this article as: Challener RC, McClintock JB (2017) In situ measurements of righting behavior in the common sea urchin Lytechinus variegatus: the importance of body size, substrate type, and covering material. Aquat Biol 26:33-40. https://doi.org/10.3354/ab00669 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 26. Online publication date: February 21, 2017 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2017 Inter-Research.

Living on the edge: Diadema mexicanum in the upper Gulf of California

Sea urchins play a crucial role in the health and dynamics of reef ecosystems. Diadema mexicanum is a dominant grazer and erosive agent of the substratum in reef environments in the eastern tropical Pacific. Its reported distribution extends from the middle of the Gulf of California (26° N) to northern Peru (6°23′ S), including oceanic islands. Here, we report the occurrence of Diadema mexicanum in Isla San Jorge (31°0′38.53″ N, 113°14′34.84″ W), the northernmost island in the Gulf of California, which extends its range an additional 600 km northward. Sea urchins, ranging in test size from 4.5 to 12.4 cm, were present at 2–6 m in October 2015. This test size was one of the largest reported for this species in the eastern tropical Pacific. Spine length in sea urchins in the upper gulf ranged from 3.3 to 15.6 cm. Variation in body size of sea urchin may reflect variation in more structurally complex reefs from isolated islands that provide shelter from predation. The reef structure of Isla San Jorge is formed by high coral cover of the scleractinian coral Porites panamensis, with an average colony height of 26.27 cm (standard error, SE ±1.58, n = 60), similar to coral reef communities of the southern Gulf of California. Although D. mexicanum is considered a great force of erosion to the substratum in reef environments in the eastern tropical Pacific, no evidence of erosion was observed at Isla San Jorge, indicating a balanced dynamic between herbivores, macroalgae, and corals.

Bioerosive impact of Diadema mexicanum on southern Mexican Pacific coral reefs

Reef ecosystem growth and maintenance is closely related to sea urchin feeding activities. Hence, quantifying the bioerosive capacity of the sea urchin Diadema mexicanum is necessary to evaluate its impact on coral communities and reefs that develop off the Pacific coast of southern Mexico. Sea urchin density, size, bioerosion rate, and type of carbonate removed were estimated, and the carbonate budget of 15 coral communities and reefs found off Guerrero and Oaxaca was calculated. Sea urchin density (H = 13.4, P = 0.001) and size (H = 139.5, P = 0.000) varied over space and were significantly (density, r2 = 0.79, P = 0.00; size, r2 = 0.28, P = 0.03) related to substrate characteristics. In general, size (test diameter) and density were directly related to rock coverage but inversely related to live coral cover. Carbonate removal was directly related to sea urchin size (&lt;3.4 cm = 0.052 g/ind/d, 3.4–6.1 cm = 0.202 g/ind/d, &gt;6.1 cm = 0.325 g/ind/d). Of the total carbonate removed, 22% corresponded to aragonite and 78% to magnesium calcite, indicating that sea urchin impact on coral reef skeletons is small. When reef carbonate budget was calculated, only 3.1% of the total carbonate deposited by reef corals was removed. The above data indicate that sea urchin feeding activity alone does not compromise reef ecosystem growth and maintenance in southwestern Mexico. Nonetheless, in the near future, the current policy of use and development in and around reef systems may boost the bioerosive impact of D. mexicanum in the area.

Density, size, and biomass of Diadema mexicanum (Echinoidea) in Eastern Tropical Pacific coral reefs

Diadema is among the most abundant, widely dispersed, and ecologically important genera of sea urchin in tropical shallow waters. D. mexicanum is distributed from the Gulf of California to northern Peru, including the oceanic islands of Revillagigedo, Clipperton, Coco, Malpelo, and Galapagos, and it is one of the most important sea urchin species in Eastern Tropical Pacific (ETP) coral reefs. In the 1980s, El Nino caused high coral mortality, resulting in an increase in macroalgal cover. This resulted in higher sea urchin bioerosion activity, which weakened the reef frameworks. Considering the high vulnerability of the ETP coral reefs, the aim of this study was to determine regional differences in the density, size (test diameter), and biomass of D. mex- icanum at 12 localities in 4 countries between 2009 and 2010, and to determine possible causes of these differences. The average density, size, and biomass of D. mexicanum were 0.47 ± 0.15 ind. m �2 , 4.38 ± 1.50 cm, and 0.26 ± 0.33 g m �2 . The test size frequency that predominated was 2 to 3 cm. Predation by macrophagous fishes seems to be one of the most important factors that explains the presence of low densities and small size of sea urchins throughout the region. The increase in D. mexicanum predators is probably a result of overfishing of top predators.

Accounting for size-specific predation improves our ability to predict the strength of a trophic cascade.

Predation can influence the magnitude of herbivory that grazers exert on primary producers by altering both grazer abundance and their per capita consumption rates via changes in behavior, density-dependent effects, and size. Therefore, models based solely on changes in abundance may miss key components of grazing pressure. We estimated shifts in grazing pressure associated with changes in the abundance and per capita consumption rates of sea urchins triggered by size-selective predation by sea otters (Enhydra lutris). Field surveys suggest that sea otters dramatically decreased the abundance and median size of sea urchins. Furthermore, laboratory experiments revealed that kelp consumption by sea urchins varied nonlinearly as a function of urchin size such that consumption rates increased to the 0.56 and 0.68 power of biomass for red and green urchins, respectively. This reveals that shifts in urchin size structure due to size-selective predation by sea otters alter sea urchin per capita grazing rates. Comparison of two quantitative models estimating total consumptive capacity revealed that a model incorporating shifts in urchin abundance while neglecting urchin size structure overestimated grazing pressure compared to a model that incorporated size. Consequently, incorporating shifts in urchin size better predicted field estimates of kelp abundance compared to equivalent models based on urchin abundance alone. We provide strong evidence that incorporating size-specific parameters increases our ability to describe and predict trophic interactions.

A FEAST FOR CROWS: BIRD PREDATION ON IRREGULAR ECHINOIDS FROM BRITTANY, FRANCE

Selective feeding behavior of birds on burrowing irregular spatangoid sea urchins, normally out of reach for such predators, is described. Behavioral observations were made on Carrion Crows (Corvus corone) feeding on spatangoid sea urchins (Echinocardium cordatum) during low tide on two different beaches in Brittany, France. The on-site searching behavior of individuals and flocks of crows on the surf line was observed together with characteristic feeding traces on the sediment. Wound morphologies on collected tests were documented with respect to possible preservation potential and recognition in the fossil record. Documented traces on feeding sites allow for clear identification of predator species and can be linked to observed bird behavior. The two sites differ in sea urchin size and the resulting predation traces on the echinoid tests. Predation on smaller specimens fragments the test, whereas predation on larger specimens leaves a characteristic wound morphology that is mainly restricted to the aboral side of the test. The wound morphology resulting from test puncturing involves both extensive inter- and intraplate fragmentation but does not completely destroy the tests. These predation traces are compared to other observed records of bird predation on echinoids. The potential for recognition and preservation in the rock record is then discussed.

Effect of Implanted PIT-Tags on Growth, Survival, and Tag Retention in the Sea UrchinTripneustes ventricosus

The major goal of this study was to provide valuable information about the effectiveness of tagging the whitish sea urchin Tripneustes ventricosus in semi-captivity conditions using one type of internal mark. A field experimental study was conducted to assess the effect of Passive Integrated Transponders (PIT) tagging on the survival and growth rate of T. ventricosus as a function of body size, and evaluate PIT tag loss. PIT tags were injected into the coelomic cavity of sea urchins ranging from 29 to 125 mm of test diameter (TD). Sixty sea urchins (30 tagged and 30 non-tagged) of similar sizes were monitored over 10 weeks. For all sea urchin size categories, at the end of the study, tag retention rate was 100%, and survival rate was 75.0 ± 24.0 %. Small-sized urchins exhibited the highest Gross Growth Rate during the experiment (tagged: 3.16 ± 0.34 mm TD; control: 1.78 ± 0.36 mm TD), whereas large-sized individuals displayed the lowest rates (tagged: 0.53 ± 0.0 mm TD; control: 0.70 ± 0.18 mm TD). No significant differences in survival and growth rates were found between tagged and non-tagged animals within size classes. Results suggested that urchins can be tagged using PIT tags, with negligible effects on survival and growth, and this leads to a zero tag rejection rate. Therefore, we recommend use this accurate technique to improve estimation of demographic parameters in T. ventricosus populations for long term tagging studies.

Latitudinal, seasonal, and small-scale spatial differences of the giant kelp, Macrocystis pyrifera, and an herbivore at their southern range limit in the northern hemisphere

Abstract Although several studies have described kelp-urchin interactions, little is known about these interactions toward the distributional range limits of these species in areas that may experience different physical conditions than at the center of the distributional range. We explored seasonal and latitudinal changes in the population structure of the giant kelp and the purple sea urchin at their southern limits in the northern hemisphere. Densities of both organisms were positively correlated, showing a significant effect of season and latitude, and were highest in the temperate kelp populations and in the spring. The near subtropical kelp populations, however, contained significantly larger urchins. Along the boundary between the kelp beds and the urchin barrens studied, no significant spatial difference was found in sea urchin size or density. However, a general pattern of increasing probability of urchin presence with distance outside of the bed was found in spring at all sites. Spring bottom temperatures were generally colder and more variable in the temperate kelp populations, potentially explaining the larger seasonal variability found there. Data suggest seasonal differences may be modulated by the environmental variability in the temperate kelp populations and support local coupling of these two organisms at their southern range limit, in spite of the particularly unique physical conditions which occur in these populations at times.

Effects of ocean acidification and diet on thickness and carbonate elemental composition of the test of juvenile sea urchins

Continuous anthropogenic CO2 emissions to the atmosphere and uptake by the oceans will cause a reduction of seawater pH and saturation state (Ω) of CaCO3 minerals from which marine calcifiers build their shells and skeletons. Sea urchins use the most soluble form of calcium carbonate, high-magnesium calcite, to build their skeleton, spines and grazing apparatus. In order to highlight the effects of increased pCO2 on the test thickness and carbonate elemental composition of juvenile sea urchins and potential differences in their responses linked to the diet, we performed a laboratory experiment on juvenile Paracentrotus lividus, grazing on calcifying (Corallina elongata) and non-calcifying (Cystoseira amentacea, Dictyota dichotoma) macroalgae, under different pH (corresponding to pCO2 values of 390, 550, 750 and 1000 μatm). Results highlighted the importance of the diet in determining sea urchin size irrespectively of the pCO2 level, and the relevance of macroalgal diet in modulating urchin Mg/Ca ratio. The present study provides relevant clues both in terms of the mechanism of mineral incorporation and in terms of bottom-up processes (algal diet) affecting top-down ones (fish predation) in rocky subtidal communities.