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Marine fishery stakeholders are beginning to consider and implement adaptation strategies in the face of growing consumer demand and potential deleterious climate change impacts such as ocean warming, ocean acidification, and deoxygenation. This study investigates the potential for development of a novel climate change-tolerant sea urchin fishery i...
Contexts in source publication
Context 1
... the ROV Jason dive in December 2016, the community changed abruptly to a S. fragilis urchin-dominated community from an asteroid- dominated community between 505 and 510 m water depth. Table 3 shows the mean environmental conditions in which S. fragilis abundances were 25-75% of the maximum abundances counted during each dive. ...
Context 2
... is also possible that differences in food availability at different depths can con- tribute to the greater relative growth rates at shallower depths ( Figure 6), which has been found to explain growth rate variabil- ity in other urchin species (Ebert, 1968(Ebert, , 2007Ebert et al., 1999;Britton-Simmons et al., 2012). Ranges of pH and DO concentra- tions at the ROV sites in San Diego where abundant populations of S. fragilis persist at different seasons ( Figure 3; Table 3) further demonstrate the resilience of this species to extreme pH and oxy- gen conditions. However, there are lessons to consider from the existing urchin fisheries. ...
Citations
... In addition to their importance in terms of ecological services (Matranga et al., 2005;Pearse, 2006;Sweet et al., 2016), sea urchins are widely exploited for commercial purposes, supporting a growing market of considerable wealth: a global production of 73,000 metric tons with an estimated value of 208 million US$ (FAO, 2016;Sato et al., 2018). Although recent studies emphasise the growing importance of echinoid farming within integrated multitrophic aquaculture (IMTA) systems (Grosso et al., 2021;Shpigel et al., 2018), sea urchin fisheries account for more than 99.9% of total sold per year, with aquaculture providing the remainder (Stefánsson et al., 2017). ...
... Such works well describe the potential vulnerability of southern populations of red sea urchins to the conditions imposed by OW&A. According to Sato et al. (2018) Strongylocentrotus fragilis could be a valuable candidate to fill potential production gaps of M. franciscanus in southern California. This species is well adapted to low oxygen levels (11.7-16.9 ...
... mmol kg −1 ) and low pH (<7.44) as it lives mainly at great depths (500 m). Despite these characteristics, the clear technological limitations for fishing and the relatively low profitability of its gonads (e.g., 80% reduced gonad size by weight; Sato et al., 2018) limit the potential future marketability of this species. ...
Ongoing 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&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&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&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&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.
... Given the considerable ecological and economic importance of M. franciscanus, determining how this species will be affected by continuing environmental change in coastal oceans remains an overlooked and critical area of research [11]. Due to their habitat and life history, these urchins are threatened by climate change impacts [12] such as ocean warming, which may include sudden and extreme marine heat waves [13,14], and ocean acidification, which may amplify the low pH conditions that episodically occur in upwelling regions [15]. The upwelling season in the California Current System (CCS) typically extends from early spring until late summer or fall; it is characterized by fluctuations between periods of upwelling, when cold, low pH water is transported to the surface, and periods in which upwelling is relaxed (i.e., wind conditions are not conducive for driving upwelling) [16,17]. ...
... This is particularly pertinent for fishery species in which accurate predictions are necessary for adaptive, climate-ready fisheries management [42]. Although a clear understanding of how M. franciscanus responds to environmental stress is lacking, suggestions have already been made to replace or offset the M. franciscanus fishery with Strongylocentrotus fragilis, a sea urchin species expected to be more tolerant to climate change [12]. Here, both temperature and pCO 2 conditions were manipulated in a laboratory setting to investigate their influence on the gene expression patterns of M. franciscanus during its early development. ...
Background
The red sea urchin Mesocentrotus franciscanus is an ecologically important kelp forest herbivore and an economically valuable wild fishery species. To examine how M. franciscanus responds to its environment on a molecular level, differences in gene expression patterns were observed in embryos raised under combinations of two temperatures (13 °C or 17 °C) and two p CO 2 levels (475 μatm or 1050 μatm). These combinations mimic various present-day conditions measured during and between upwelling events in the highly dynamic California Current System with the exception of the 17 °C and 1050 μatm combination, which does not currently occur. However, as ocean warming and acidification continues, warmer temperatures and higher p CO 2 conditions are expected to increase in frequency and to occur simultaneously. The transcriptomic responses of the embryos were assessed at two developmental stages (gastrula and prism) in light of previously described plasticity in body size and thermotolerance under these temperature and p CO 2 treatments.
Results
Although transcriptomic patterns primarily varied by developmental stage, there were pronounced differences in gene expression as a result of the treatment conditions. Temperature and p CO 2 treatments led to the differential expression of genes related to the cellular stress response, transmembrane transport, metabolic processes, and the regulation of gene expression. At each developmental stage, temperature contributed significantly to the observed variance in gene expression, which was also correlated to the phenotypic attributes of the embryos. On the other hand, the transcriptomic response to p CO 2 was relatively muted, particularly at the prism stage.
Conclusions
M. franciscanus exhibited transcriptomic plasticity under different temperatures, indicating their capacity for a molecular-level response that may facilitate red sea urchins facing ocean warming as climate change continues. In contrast, the lack of a robust transcriptomic response, in combination with observations of decreased body size, under elevated p CO 2 levels suggest that this species may be negatively affected by ocean acidification. High present-day p CO 2 conditions that occur due to coastal upwelling may already be influencing populations of M. franciscanus .
... This is particularly pertinent for shery species in which accurate predictions are necessary for adaptive, climate-ready sheries management [42]. Although a clear understanding of how M. franciscanus responds to environmental stress is lacking, suggestions have already been made to replace or offset the M. franciscanus shery with Strongylocentrotus fragilis, a sea urchin species expected to be more tolerant to climate change [12]. Here, both temperature and pCO 2 conditions were manipulated in a laboratory setting to investigate their in uence on the gene expression patterns of M. ...
Background: The red sea urchin Mesocentrotus franciscanus is an ecologically important kelp forest herbivore and an economically valuable wild fishery species. To examine how M. franciscanus responds to its environment on a molecular level, differences in gene expression patterns were observed in embryos raised under combinations of two temperatures (13 °C or 17 °C) and two pCO2 levels (475 matm or 1050 matm). These combinations mimic various present-day conditions measured during and between upwelling events in the highly dynamic California Current System with the exception of the 17 °C and 1050 matm combination, which does not currently occur. However, as ocean warming and acidification continues, warmer temperatures and higher pCO2 conditions are expected to increase in frequency and to occur simultaneously. The transcriptomic responses of the embryos were assessed at two developmental stages (gastrula and prism) in light of previously described plasticity in body size and thermotolerance under these temperature and pCO2 treatments.
Results: Although transcriptomic patterns primarily varied by developmental stage, there were pronounced differences in gene expression as a result of the treatment conditions. Temperature and pCO2 treatments led to the differential expression of genes related to the cellular stress response, transmembrane transport, metabolic processes, and the regulation of gene expression. At each developmental stage, temperature contributed significantly to the observed variance in gene expression, which was also correlated to the phenotypic attributes of the embryos. On the other hand, the transcriptomic response to pCO2 was relatively muted, particularly at the prism stage.
Conclusions: M. franciscanus exhibited transcriptomic plasticity under different temperatures, indicating their capacity for a molecular-level response that may facilitate red sea urchins facing ocean warming as climate change continues. In contrast, the lack of a robust transcriptomic response, in combination with observations of decreased body size, under elevated pCO2 levels suggest that this species may be negatively affected by ocean acidification. High present-day pCO2 conditions that occur due to coastal upwelling may already be influencing populations of M. franciscanus.
... This is particularly pertinent for shery species in which accurate predictions are necessary for adaptive, climate-ready sheries management [42]. Although a clear understanding of how M. franciscanus responds to environmental stress is lacking, suggestions have already been made to replace or offset the M. franciscanus shery with a species expected to be more tolerant to climate change [12]. Here, both temperature and pCO 2 conditions were manipulated in a laboratory setting to investigate their in uence on the gene expression patterns of M. franciscanus during its early development. ...
Background: The red sea urchin Mesocentrotus franciscanus is an ecologically important kelp forest herbivore and an economically valuable wild fishery species. To examine of how M. franciscanus responds to its environment on a molecular level, differences in gene expression patterns were observed in embryos raised under combinations of two temperatures (13 °C or 17 °C) and two pCO2 levels (475 matm or 1050 matm). These combinations mimic various present-day conditions measured during and between upwelling events in the highly dynamic California Current System with the exception of the 17 °C and 1050 matm combination, which does not currently occur. However, as ocean warming and acidification continues, warmer temperatures and higher pCO2 conditions are expected to increase in frequency and to occur simultaneously. The transcriptomic responses of the embryos were assessed at two developmental stages (gastrula and prism) in light of previously described plasticity in body size and thermotolerance under these temperature and pCO2 treatments.
Results: Although transcriptomic patterns primarily varied by developmental stage, there were pronounced differences in gene expression as a result of the treatment conditions. Temperature and pCO2 treatments led to the differential expression of genes related to the cellular stress response, transmembrane transport, metabolic processes, and the regulation of gene expression. At each developmental stage, temperature contributed significantly to the observed variance in gene expression, which was also correlated to the phenotypic attributes of the embryos. On the other hand, the transcriptomic response to pCO2 was relatively muted, particularly at the prism stage.
Conclusions: M. franciscanus exhibited transcriptomic plasticity under different temperatures, indicating their capacity for a molecular-level response that may facilitate red sea urchins facing ocean warming as climate change continues. In contrast, the lack of a robust transcriptomic response, in combination with observations of decreased body size, under elevated pCO2 levels suggest that this species may be negatively affected by ocean acidification. High present-day pCO2 conditions that occur due to coastal upwelling may already be influencing populations of M. franciscanus.
... While knowledge of the ecological dynamics associated with these urchin species is fairly extensive, the densities at which other urchin species in other geographic locations have notable macroalgae-controlling impact is poorly studied. The lack of understanding could prove detrimental to coral reef ecosystems if urchin populations are targeted for exploitation (Furesi et al. 2016;Parvez, Rahman & Yusoff 2016;Sato et al. 2017). ...
Coral reefs are degrading under global stressors that are increasing in frequency and severity as the Anthropocene accelerates. My thesis contributes to our scientific understanding of the dynamics that govern degraded coral reef states. More specifically, I contribute to our understanding of feedback processes on degraded coral reefs in conceptual and experimental ways by confronting both ecological and social-ecological feedbacks in ways that may have merit in triggering coral recovery.
My four presented studies (Chapters 1-4) pursue the following research questions:
1. Which habitat drivers best predict juvenile coral densities following bleaching?
2. Can macroalgae-reinforcing feedbacks be weakened through shading?
3. Can sea urchins effectively weaken macroalgal feedbacks given their current natural densities?
4. Can red and green loops uncover missing social-ecological feedbacks?
Juvenile corals are a critical life history stage representing survival and growth of new recruits into the population. Chapter 1 compares juvenile coral densities from before the 2016 bleaching event with those after and identifies abiotic and biotic habitat drivers collected in the inner Seychelles that predict juvenile coral densities. Following the 2016 bleaching event, juvenile coral densities were significantly reduced by about 70 %, with a particularly severe decline in juvenile Acropora corals. Macroalgae present a major obstacle to survival of juvenile corals shortly following mass bleaching, but their influence varies as a function of herbivore biomass, reef structure, and reef type. In contrast, increasing structural complexity on granitic reefs is a strong positive predictor of juvenile coral density. Macroalgae can maintain and increase their dominance with effective self-reinforcing feedback
mechanisms and can significantly compromise ecosystem function.
Chapter 2 assesses shading as a management tool in an experimental confrontation of macroalgal feedbacks, aiming to maximise the benefit of habitat mosaic reefscapes in the inner Seychelles. Shading reduces the algae’s ability to photosynthesise by 29 % to the point where macroalgal cover can be reduced by 51 % and turf algal growth can be reduced by 82 % within six weeks of shading. After removal of shading structures, herbivore grazing rates decreased at shading plots, and algal beds recovered quickly, almost completely regrowing within three months.
Tropical sea urchins are often considered as macroalgal grazers, but this assumption relies heavily on geographically limited observations of select species. Chapter 3 addresses these gaps for a common urchin species in the Seychelles, Echinothrix calamaris, using a combination of survey and experimental approaches in the inner Seychelles. Habitat driver models revealed patch-reef types as the best positive predictor and macroalgae as the best negative predictor of urchin densities. Experimentally penning urchin densities (maximum 4.44 urchins m-²) resulted in a reduction of macroalgal cover by only 13 %. Therefore E. calamaris at current densities in Seychelles (mean: 0.02 urchins m-2, maximum: 0.16 urchins m-2) are unlikely to perform significant macroalgae controlling functions.
People use their local ecosystems and can retrieve signals about how their actions affect ecosystem health. Capturing, interpreting, and responding to signals that indicate changes in ecosystems is key for their sustainable management and breaks in this signal-response, called missing feedbacks, will allow ecosystem health to degrade unnoticed. Chapter 4 applies an existing concept from sustainability science, the red-loop green-loop (RL-GL) model, to uncover missing feedbacks between reefs and people of Jamaica from the year 600 until now. This allowed the factors responsible for missing feedbacks to be identified – a main factor in Jamaica was seafood exports. An intervention to move Jamaica back to more sustainable dynamics between people and reefs could be to gradually move away from seafood exports and build ownership and management capacity in local seafoods.
Overall, my thesis emphasises the importance of habitat for coral recruitment following severe coral bleaching as well as for urchin density and function in Seychelles. Furthermore, I cover management approaches to confront reinforcing feedbacks of expanding macroalgal fields, especially for a mosaic reefscape setting. I test the first method to reduce macroalgal cover via the alteration of the light regime. My thesis also includes the first study to apply the RL-GL concept to a coral reef social-ecological system and I advocate for its practicality in uncovering missing feedbacks and in gaining an understanding of past, present, and future sustainability that can be of use in other systems.
... In contrast, passive management systems that respond reactively to declines in population quality and size will be improperly suited to cope with the negative impacts of climate change (Wilson et al. 2018). Growing concerns of climate change effects on the red urchin fishery have already led to suggestions of replacing or supplementing M. franciscanus with more resilient and climate change-tolerant urchin species, such as the pink sea urchin, Strongylocentrotus fragilis (Sato et al. 2018). Alternatively, the establishment of marine protected areas (MPAs) have been shown to lead to increased biomass of M. franciscanus (Teck et al. 2017). ...
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.
... Landings have been so low that the commercial divers in the north have filed for federal disaster relief to make up for lost income. The potential for more climate change resilient species are being examined, with the marketability of S. fragilis, being explored (Sato et al., 2017). ...
In the northeast Pacific, the sea urchins Mesocentrotus franciscanus and Strongylocentrotus purpuratus are ecologically important species that play a dominant role in intertidal and subtidal rocky ecosystems. M. franciscanus are the basis for important commercial fisheries and serve as an indigenous traditional food resource as well as model species in developmental research. Both species are important ecosystem structuring species (ecosystem engineers) that control the flow of resources within marine communities. Recent work continues to reveal factors that shape their population dynamics, role in the ecosystem, and how climate change may alter both of these. Over the past decade, the coast-wide collapse of the predatory sea star Pycnopodia helianthoides and a massive, long-lasting marine heat wave corresponded with historically stable, kelp forests transitioning to species-poor barrens dominated by M. franciscanus and S. purpuratus. In contrast, some sea urchin populations have experienced declines due to disease in southern California, toxins in northern California, expanding populations of the sea otter Enhydra lutris in Alaska and British Columbia or the recovery of sea urchin predators in California's marine protected areas. Such radical changes in population dynamics have direct and indirect consequences for the productivity and diversity of kelp forests. In northern California, the recent destruction of the kelp forest by sea urchins has had cascading impacts resulting in the collapse of both the commercial M. franciscanus and recreational red abalone, Haliotis rufescens, fisheries. Currently, there are efforts to ameliorate the proliferation of barrens or poor quality of sea urchin roe include kelp restoration through culling, sea urchin ranching, and plans for rebuilding populations of sea urchin predators. A looming question for both sea urchins and kelp forests is how climate change will affect reproduction and recruitment via larval production, development, ocean transport, budding, survival and settlement, and how these processes vary across space and time. Research continues to reveal both physiological sensitivity and resilience to effects of climate change of sea urchins, such as warming, food deficiencies, hypoxia, salinity, low pH, and ocean circulation. How both climatic effects and the ecological factors that impact the dynamics of sea urchin populations, and the ecosystems they control, remains a critical area of research for these ecologically, culturally, and commercially important species.
... As a valuable wild fishery, red sea urchins are found in temperate rocky reefs in nearshore coastal regions. As benthic marine invertebrates in coastal marine ecosystems, they are threatened by ocean change ( Sato et al., 2018), including future ocean acidification in regions dominated by episodic upwelling (Chan et al., 2017) and from marine heat waves ( Gentemann et al., 2017). For example, between 2013 and 2016, anomalous warming events associated with "the Blob" led to dramatically increased sea surface temperatures in the northeast Pacific Ocean ( Bond et al., 2015;Gentemann et al., 2017;Hu et al., 2017). ...
The red sea urchin, Mesocentrotus franciscanus, is an ecologically important kelp forest species that also serves as a valuable fisheries resource. In this study, we have assembled and annotated a developmental transcriptome for M. franciscanus that represents eggs and six stages of early development (8- to 16-cell, morula, hatched blastula, early gastrula, prism and early pluteus). Characterization of the transcriptome revealed distinct patterns of gene expression that corresponded to major developmental and morphological processes. In addition, the period during which maternally-controlled transcription was terminated and the zygotic genome was activated, the maternal-to-zygotic transition (MZT), was found to begin during early cleavage and persist through the hatched blastula stage, an observation that is similar to the timing of the MZT in other sea urchin species. The presented developmental transcriptome will serve as a useful resource for investigating, in both an ecological and fisheries context, how the early developmental stages of this species respond to environmental stressors.
... However, this in practicality might face new challenges, such as selecting species that also thrive under aquaculture conditions and avoiding selecting non-native species (Arismendi et al., 2009), and might require strategic management plants. In order to optimise protein supply and secure socio-economic benefits of mollusc aquaculture, research needs to focus on identifying and selecting native aquaculture species that are resilient to future climate conditions, and able to retain their beneficial nutritional properties (Cooley et al., 2012;Sato et al., 2018), without introducing new challenges. ...
Ocean acidification and warming may threaten future seafood production, safety and quality by negatively impacting the fitness of marine species. Identifying changes in nutritional quality, as well as species most at risk, is crucial if societies are to secure food production. Here, changes in the biochemical composition and nutritional properties of the commercially valuable oysters, Magallana gigas and Ostrea edulis, were evaluated following a 12-week exposure to six ocean acidification and warming scenarios that were designed to reflect the temperature (+3 °C above ambient) and atmospheric pCO2 conditions (increase of 350–600 ppm) predicted for the mid-to end-of-century. Results suggest that O. edulis, and especially M. gigas, are likely to become less nutritious (i.e. containing lower levels of protein, lipid, and carbohydrate), and have reduced caloric content under ocean acidification and warming. Important changes to essential mineral composition under ocean acidification and warming were evident in both species; enhanced accumulation of copper in M. gigas may be of concern regarding consumption safety. In light of these findings, the aquaculture industry may wish to consider a shift in focus toward species that are most robust to climate change and less prone to deterioration in quality, in order to secure future food provision and socio-economic benefits of aquaculture.
... The upper and lower boundaries of severe OMZs on upwelling margins exhibit strong vertical zonation of benthic invertebrate communities, with rapid shifts from dense benthic megafauna and calcareous invertebrates outside the OMZ to communities dominated by annelids and calcareous foraminifera within the OMZ (Levin, 2003;Gooday et al., 2010). Only recently has there been investigation of the interplay of temperature, oxygen and pH effects on extant benthos in these areas (Sperling et al., 2016;Sato et al., 2018). ...
... Echinoid sea urchins are important benthic grazers (Pearse, 2006), algal detritivores Sato et al., 2018) and deposit feeders (Lohrer et al., 2005). The pink urchin, Strongylocentrotus fragilis, is a dominant megafaunal species on the outer shelf (120-200 m) and upper slope (200-500 m) in southern California (Thompson et al., 1993;Sato et al., 2017;Walther et al., 2017). ...
... S. fragilis also occurs, although infrequently, in the OMZ core (500-900 m) and below the OMZ core, in the Lower OMZ (LOMZ; 900-1,200 m) where DO and pH are higher than in the OMZ core (Sumich and McCauley, 1973;Barry et al., 2014;Taylor et al., 2014; Figure 1). Sato et al. (2018) previously described natural history traits of S. fragilis in the SCB including spatial variability in density, distribution, feeding behavior, and relative growth rates, as well as seasonal patterns in reproductive potential. S. fragilis thus serves as a model species to evaluate how multiple parameters that are likely to be modified under climate change (e.g., temperature, DO, and pH) may potentially influence sublethal fitness traits on both macro-and microscale levels (Byrne et al., 2014;Taylor et al., 2014;Carrington et al., 2015;Swezey et al., 2017b). ...
Marine calcifiers are considered to be among the most vulnerable taxa to climate-forced environmental changes occurring on continental margins with effects hypothesized to occur on microstructural, biomechanical, and geochemical properties of carbonate structures. Natural gradients in temperature, salinity, oxygen, and pH on an upwelling margin combined with the broad depth distribution (100–1,100 m) of the pink fragile sea urchin, Strongylocentrotus (formerly Allocentrotus) fragilis, along the southern California shelf and slope provide an ideal system to evaluate potential effects of multiple climate variables on carbonate structures in situ. We measured, for the first time, trait variability across four distinct depth zones using natural gradients as analogues for species-specific implications of oxygen minimum zone (OMZ) expansion, deoxygenation and ocean acidification. Although S. fragilis may likely be tolerant of future oxygen and pH decreases predicted during the twenty-first century, we determine from adults collected across multiple depth zones that urchin size and potential reproductive fitness (gonad index) are drastically reduced in the OMZ core (450–900 m) compared to adjacent zones. Increases in porosity and mean pore size coupled with decreases in mechanical nanohardness and stiffness of the calcitic endoskeleton in individuals collected from lower pHTotal (7.57–7.59) and lower dissolved oxygen (13–42 μmol kg⁻¹) environments suggest that S. fragilis may be potentially vulnerable to crushing predators if these conditions become more widespread in the future. In addition, elemental composition indicates that S. fragilis has a skeleton composed of the low Mg-calcite mineral phase of calcium carbonate (mean Mg/Ca = 0.02 mol mol⁻¹), with Mg/Ca values measured in the lower end of values reported for sea urchins known to date. Together these findings suggest that ongoing declines in oxygen and pH will likely affect the ecology and fitness of a dominant echinoid on the California margin.
