Near-future Ocean Acidification Research Articles

Simultaneous ocean acidification and warming do not alter the lipid-associated biochemistry but induce enzyme activities in an asterinid starfish

Ocean acidification and warming affect marine ecosystems from the molecular scale in organismal physiology to broad alterations of ecosystem functions. However, knowledge of their combined effects on tropical-subtropical intertidal species remains limited. Pushing the environmental range of marine species away from the optimum initiates stress impacting biochemical metabolic characteristics, with consequences on lipid-associated and enzyme biochemistry. This study investigates lipid-associated fatty acids (FAs) and enzyme activities involved in biomineralization of the tropical-subtropical starfish Aquilonastra yairi in response to projected near-future global change. The starfish were acclimatized to two temperature levels (27 °C, 32 °C) crossed with three pCO2 concentrations (455 μatm, 1052 μatm, 2066 μatm). Total lipid (ΣLC) and FAs composition were unaffected by combined elevated temperature and pCO2, but at elevated temperature, there was an increase in ΣLC, SFAs (saturated FAs) and PUFAs (polyunsaturated FAs), and a decrease in MUFAs (monounsaturated FAs). However, temperature was the sole factor to significantly alter SFAs composition. Positive parabolic responses of Ca-ATPase and Mg-ATPase enzyme activities were detected at 27 °C with elevated pCO2, while stable enzyme activities were observed at 32 °C with elevated pCO2. Our results indicate that the lipid-associated biochemistry of A. yairi is resilient and capable of coping with near-future ocean acidification and warming. However, the calcification-related enzymes Ca-ATPase and Mg-ATPase activity appear to be more sensitive to pCO2/pH changes, leading to vulnerability concerning the skeletal structure.

Calcareous sponges can synthesize their skeleton under short-term ocean acidification

Calcifying organisms are considered as threatened by ocean acidification, because of their calcium carbonate skeleton. This study investigated if a calcareous sponge could synthesize its skeleton (i.e. spicules) under ocean-acidification conditions. Sponge cell aggregates that have the potential to develop into a functional sponge, called primmorphs, were submitted to a 5-day experiment, with two treatments: control (pH 8.1) and acidified conditions (pH 7.6). Primmorphs of the calcareous sponge Paraleucilla magna were able to synthesize a skeleton, even under low pH, and to develop into functional sponges. The spicules had the same shape in both conditions, although the spicules synthesized in low pH were slightly thinner than those in the control. These results suggest that P. magna may be able to survive near-future ocean-acidification conditions.

Evaluating the Evolving Ocean Acidification Risk to Dungeness Crab: Time-Series Observations and Modeling on the Olympic Coast, Washington, USA

The state of Washington’s Olympic coast is home to four US coastal treaty tribes who have relied on the region’s rich marine resources since time immemorial. The region is characterized by large dynamic ranges of physical and biogeochemical oceanographic parameters, particularly during the upwelling season (April–September). Here, we present novel estimates of ocean acidification metrics—pH and calcium carbonate saturation states (Ω)—representing pre-industrial, present-day (using 2010 as the index year), and near-future (2030) conditions. We compare these new estimates of past, present, and near-future ocean acidification status and seasonality to published end-of-century (2100) ocean acidification projections under a high CO2 emissions scenario, and also to sensitivity information for Dungeness crab, a regionally important subsistence and commercial fishery species projected to show strong declines in fisheries yields and revenues later this century.

Ocean acidification and seasonal temperature extremes combine to impair the thermal physiology of a sub-Antarctic fish

To predict the potential impacts of climate change on marine organisms, it is critical to understand how multiple stressors constrain the physiology and distribution of species. We evaluated the effects of seasonal changes in seawater temperature and near-future ocean acidification (OA) on organismal and sub-organismal traits associated with the thermal performance of Eleginops maclovinus, a sub-Antarctic notothenioid species with economic importance to sport and artisanal fisheries in southern South America. Juveniles were exposed to mean winter and summer sea surface temperatures (4 and 10 °C) at present-day and near-future pCO2 levels (~500 and 1800 μatm). After a month, the Critical Thermal maximum and minimum (CTmax, CTmin) of fish were measured using the Critical Thermal Methodology and the aerobic scope of fish was measured based on the difference between their maximal and standard rates determined from intermittent flow respirometry. Lipid peroxidation and the antioxidant capacity were also quantified to estimate the oxidative damage potentially caused to gill and liver tissue. Although CTmax and CTmin were higher in individuals acclimated to summer versus winter temperatures, the increase in CTmax was minimal in juveniles exposed to the near-future compared to present-day pCO2 levels (there was a significant interaction between temperature and pCO2 on CTmax). The reduction in the thermal tolerance range under summer temperatures and near-future OA conditions was associated with a reduction in the aerobic scope observed at the elevated pCO2 level. Moreover, an oxidative stress condition was detected in the gill and liver tissues. Thus, chronic exposure to OA and the current summer temperatures pose limits to the thermal performance of juvenile E. maclovinus at the organismal and sub-organismal levels, making this species vulnerable to projected climate-driven warming.

Elevated CO2 does not alter behavioural lateralization in free‐swimming juvenile European sea bass (Dicentrarchus labrax) tested in groups

The authors investigated left-right turning preferences of n=260 juvenile European sea bass (Dicentrarchus labrax) reared in ambient conditions and ocean acidification (OA) conditions or in ambient conditions but tested in OA water. Groups of 10 individuals were observed alone in a circular tank, and individuals' left and right turning during free-swimming was quantified using trajectory data from the video. The authors showed that near-future OA levels do not affect the number of turns made, or behavioural lateralization (turning preference), in juvenile D. labrax tested in groups.

Is Ocean Acidification Really a Threat to Marine Calcifiers? A Systematic Review and Meta-Analysis of 980+ Studies Spanning Two Decades.

Ocean acidification is considered detrimental to marine calcifiers, but mounting contradictory evidence suggests a need to revisit this concept. This systematic review and meta-analysis aim to critically re-evaluate the prevailing paradigm of negative effects of ocean acidification on calcifiers. Based on 5153 observations from 985 studies, many calcifiers (e.g., echinoderms, crustaceans, and cephalopods) are found to be tolerant to near-future ocean acidification (pH ≈ 7.8 by the year 2100), but coccolithophores, calcifying algae, and corals appear to be sensitive. Calcifiers are generally more sensitive at the larval stage than adult stage. Over 70% of the observations in growth and calcification are non-negative, implying the acclimation capacity of many calcifiers to ocean acidification. This capacity can be mediated by phenotypic plasticity (e.g., physiological, mineralogical, structural, and molecular adjustments), transgenerational plasticity, increased food availability, or species interactions. The results suggest that the impacts of ocean acidification on calcifiers are less deleterious than initially thought as their adaptability has been underestimated. Therefore, in the forthcoming era of ocean acidification research, it is advocated that studying how marine organisms persist is as important as studying how they perish, and that future hypotheses and experimental designs are not constrained within the paradigm of negative effects.

Global assessment of coralline algae mineralogy points to high vulnerability of Southwestern Atlantic reefs and rhodolith beds to ocean acidification

Coralline algae constitute one of the main groups of highly vulnerable calcified benthic organisms to ocean acidification. Although damaging effects of seawater acidification on the coralline algae skeleton have been widely demonstrated, the susceptibility to dissolution varies according to the Mg2+ in the calcite lattice. Even though the Southwest Atlantic Ocean exhibits the world’s largest rhodolith beds, which occupies 20,902 km2, there is no information regarding the coralline algae species mineralogy in this area. Here, we provide mineralogical data of twenty-four coralline algae species, examine the similarity in taxonomic groups, spatial occurrence and the vulnerability of these algae to seawater acidification. Mineralogy revealed that coralline algae skeletons were mainly composed of high-Mg calcite (> 70%) with minor presence of aragonite (< 30%) and dolomite (< 3%). There were no similarities between the skeletal mineralogy of taxonomic groups and sampling regions. Remarkably, the mean Mg-substitution of encrusting coralline algae from the Brazilian Shelf was 46.3% higher than global average. Because of the higher mean Mg-substitution in calcite compared with worldwide coralline algae, these algae from Southwest Atlantic Ocean would be highly susceptible to dissolution caused by the expected near-future ocean acidification and will compromise CaCO3 net production across the Brazilian Shelf.

Impact of near-future ocean warming and acidification on the larval development of coral-eating starfish Acanthaster cf. solaris after parental exposure

Outbreaks of crown-of-thorns starfish Acanthaster spp. (COTS) are among the most severe local threats to Indo-Pacific coral reefs. Despite intensive research, the factors triggering outbreaks remain unclear, though could involve enhanced COTS larval fitness due to ocean warming and acidification. Nevertheless, the effect of these combined stressors has never been tested on larval development and survivorship after parental exposure. We investigated the effects of ocean warming (+2 °C above ambient) and/or acidification (pH 7.75) on early COTS life-history stages of offspring after exposing the parental generation for 20 weeks to the same treatments. We hypothesized that prior adult exposure would modulate the effects measured in previous studies that omitted this phase, providing a more realistic scenario. Our results showed detrimental effects of elevated temperature towards lower gastrulation success and smaller advanced bipinnaria. Both elevated temperature and lower pH produced developmental delay from early to advanced bipinnaria, eventually translating into retarded achievement of mid-late brachiolaria. On average, larvae were significantly bigger in low pH treatments, independent of stages. We suggest a link between developmental delay and larger larvae due to acidification, where larvae could be blocked at a developmental stage but continue growing. Finally, we found that larval mortality was not impacted by treatments, potentially due to prior adult exposure. If adult COTS were able to acclimatize their reproductive physiology in 15 weeks to produce larvae withstanding warming and/or acidification, slow climatic changes might not affect survival at this life stage. However, the developmental delays displayed might elongate their fragile pelagic phase, potentially decreasing their chances to reach recruitment. We specified the natural spawning peak in New Caledonia, and show caution in directly linking high fertilisation rates with high larval success. Our study reinforces the need to include parental exposure when investigating climate change effects on echinoderm larvae, as punctual stress over single-life stages may produce misleading results.

Individual and Interactive Effects of Ocean Warming and Acidification on Adult Favites colemani

Tropical coral reefs are threatened by local-scale stressors that are exacerbated by global ocean warming and acidification from the post-industrial increase of atmospheric CO2 levels. Despite their observed decline in the past four decades, little is known on how Philippine coral reefs will respond to ocean warming and acidification. This study explored individual and synergistic effects of present-day (pH 8.0, 28°C) and near-future (pH 7.7, 32°C) scenarios of ocean temperature and pH on the adult Favites colemani, a common massive reef-building coral in Bolinao-Anda, Philippines. Changes in seawater temperature drive the physiological responses of F. colemani, whereas changes in pH create an additive effect on survival, growth, and photosynthetic efficiency. Under near-future scenarios, F. colemani showed sustained photosynthetic competency despite the decline in growth rate and zooxanthellae density. F. colemani exhibited specificity with the Cladocopium clade C3u. This coral experienced lower growth rates but survived projected near-future ocean warming and acidification scenarios. Its pH-thermal stress threshold is possibly a consequence of acclimation and adaptation to local environmental conditions and past bleaching events. This research highlights the importance of examining the susceptibility and resilience of Philippine corals to climate-driven stressors for future conservation and restoration efforts in the changing ocean.

Projected near-future ocean acidification decreases mercury toxicity in marine copepods

Here, we examined the combinational effect of ocean acidification (OA) and mercury (Hg) in the planktonic copepod Pseudodiaptomus annandalei in cross-factored response to different pCO2 (400, 800 μatm) and Hg (control, 1.0 and 2.5 μg/L) exposures for three generations (F0–F2), followed by single-generation recovery (F3) under clean condition. Several phenotypic traits and Hg accumulation were analyzed for F0–F3. Furthermore, shotgun-based quantitative proteomics was performed for F0 and F2. Our results showed that OA insignificantly influenced the traits. During F0–F2, combined exposure reduced Hg accumulation as compared with the counterpart Hg treatment, supporting the mitigating effect of OA on Hg toxicity in copepods. Proteomics analysis indicated that the copepods probably increased energy production/storage and stress response to ensure physiological resilience against OA. However, Hg induced many toxic events (e.g., energy depletion and degenerated organomorphogenesis/embryogenesis for F0; cell cycle arrest and detrimental stress-defense for F2), which were translated to the population-level adverse outcome, i.e., compromised growth/reproduction. Particularly, compensatory proteome response was identified (e.g., increased immune defense for F0; energetic compensation and enhanced embryogenesis for F2), accounting for a negative interaction between OA and Hg. Together, this study provides the molecular mechanisms behind the effects of OA and Hg pollution in marine copepods.

The combined effects of ocean acidification and warming on a habitat-forming shell-crushing predatory crab

In mid rocky intertidal habitats the mussel Perumytilus purpurarus monopolizes the substratum to the detriment of many other species. However, the consumption of mussels by the shell-crushing crab Acanthocyclus hassleri creates within the mussel beds space and habitat for several other species. This crab uses its disproportionately large claw to crush its shelled prey and plays an important role in maintaining species biodiversity. This study evaluated the consequences of projected near-future ocean acidification (OA) and warming (OW) on traits of A. hassleri linked with their predatory performance. Individual A. hassleri were maintained for 10–16 weeks under contrasting pCO2 (~500 and 1400 μatm) and temperature (~15 and 20 °C) levels. We compared traits at the organismal (oxygen consumption rate, survival, calcification rate, feeding rates, crusher claw pinching strength, self-righting speed, sarcomere length of the crusher claw muscles) and cellular (nutritional status ATP provisioning capacity through citrate synthase activity, expression of HSP70) level. Survival, calcification rate and sarcomere length were not affected by OA and OW. However, OW increased significantly feeding and oxygen consumption. Pinching strength was reduced by OA; meanwhile self-righting was increased by OA and OW. At 20 °C, carbohydrate content was reduced significantly by OA. Regardless of temperature, a significant reduction in energy reserves in terms of protein content by OA was found. The ATP provisioning capacity was significantly affected by the interaction between temperature and pCO2 and was highest at 15 °C and present day pCO2 levels. The HSP70 levels of crabs exposed to OW were higher than in the control crabs. We conclude that OA and OW might affect the amount and size of prey consumed by this crab. Therefore, by reducing the crab feeding performance these stressors might pose limits on their role in generating microhabitat for other rocky intertidal species inhabiting within mussel beds.

Temperature affects the reproductive outputs of coral-eating starfish Acanthaster spp. after adult exposure to near-future ocean warming and acidification

Outbreaks of the coral-eating crown-of-thorns starfish Acanthaster spp. (COTS) have become to be amongst the most severe threats to coral reefs worldwide. Although most research has focused on COTS early development, it remains unclear how COTS populations will keep pace with changing ocean conditions. Since reproduction is a key process contributing to outbreaks, we investigated the reproductive success of adult COTS acclimated for 3–4 months to different treatment combinations of ambient conditions, ocean warming (+2 °C) and acidification (−0.35 pH). Our results suggest that the optimal breeding season in New Caledonia is concentrated around the end of the calendar year, when water temperature reaches >26 °C. We found negative effects of temperature on egg metrics, fertilisation success, and GSI, conflicting with previously documented effects of temperature on echinoderm reproductive outputs. Fertilisation success dropped drastically (more than threefold) with elevated temperature during the late breeding season. In contrast, we detected no effects of near-future acidification conditions on fertilisation success nor GSI. This is the first time that COTS reproduction is compared among individuals acclimated to different conditions of warming and acidification. Our results highlight the importance of accounting for adult exposure to better understand how COTS reproduction may be impacted in the face of global change.

Epiphytes provide micro-scale refuge from ocean acidification

Coralline algae, a major calcifying component of coastal shallow water communities, have been shown to be one of the more vulnerable taxonomic groups to ocean acidification (OA). Under OA, the interaction between corallines and epiphytes was previously described as both positive and negative. We hypothesized that the photosynthetic activity and the complex structure of non-calcifying epiphytic algae that grow on corallines ameliorate the chemical microenvironmental conditions around them, providing protection from OA. Using mesocosm and microsensor experiments, we showed that the widespread coralline Ellisolandia elongata is less susceptible to the detrimental effects of OA when covered with non-calcifying epiphytic algae, and its diffusive boundary layer is thicker than when not covered by epiphytes. By modifying the microenvironmental carbonate chemistry, epiphytes, facilitated by OA, create micro-scale shield (and refuge) with more basic conditions that may allow the persistence of corallines associated with them during acidified conditions. Such ecological refugia could also assist corallines under near-future anthropogenic OA conditions.

Near-future ocean warming and acidification alter foraging behaviour, locomotion, and metabolic rate in a keystone marine mollusc

Environmentally-induced changes in fitness are mediated by direct effects on physiology and behaviour, which are tightly linked. We investigated how predicted ocean warming (OW) and acidification (OA) affect key ecological behaviours (locomotion speed and foraging success) and metabolic rate of a keystone marine mollusc, the sea hare Stylocheilus striatus, a specialist grazer of the toxic cyanobacterium Lyngbya majuscula. We acclimated sea hares to OW and/or OA across three developmental stages (metamorphic, juvenile, and adult) or as adults only, and compare these to sea hares maintained under current-day conditions. Generally, locomotion speed and time to locate food were reduced ~1.5- to 2-fold when the stressors (OW or OA) were experienced in isolation, but reduced ~3-fold when combined. Decision-making was also severely altered, with correct foraging choice nearly 40% lower under combined stressors. Metabolic rate appeared to acclimate to the stressors in isolation, but was significantly elevated under combined stressors. Overall, sea hares that developed under OW and/or OA exhibited a less severe impact, indicating beneficial phenotypic plasticity. Reduced foraging success coupled with increased metabolic demands may impact fitness in this species and highlight potentially large ecological consequences under unabated OW and OA, namely in regulating toxic cyanobacteria blooms on coral reefs.

Linking energy budget to physiological adaptation: How a calcifying gastropod adjusts or succumbs to ocean acidification and warming.

Accelerating CO2 emissions have driven physico-chemical changes in the world's oceans, such as ocean acidification and warming. How marine organisms adjust or succumb to such environmental changes may be determined by their ability to balance energy intake against expenditure (i.e. energy budget) as energy supports physiological functions, including those with adaptive value. Here, we examined whether energy budget is a driver of physiological adaptability of marine calcifiers to the near-future ocean acidification and warming; i.e. how physiological energetics (respiration rate, feeding rate, energy assimilation and energy budget) relates to adjustments in shell growth and shell properties of a calcifying gastropod (Austrocochlea concamerata). We found that ocean warming boosted the energy budget of gastropods due to increased feeding rate, resulting in faster shell growth and greater shell strength (i.e. more mechanically resilient). When combined with ocean acidification, however, the gastropods had a substantial decrease in energy budget due to reduced feeding rate and energy assimilation, leading to the reduction in shell growth and shell strength. By linking energy budget to the adjustability of shell building, we revealed that energy availability can be critical to determine the physiological adaptability of marine calcifiers to the changing oceanic climate.

Long-term exposure to near-future ocean acidification does not affect the expression of neurogenesis- and synaptic transmission-related genes in the olfactory bulb of European sea bass (Dicentrarchus labrax).

The decrease in ocean pH that results from the increased concentration of dissolved carbon dioxide (CO2) is likely to influence many physiological functions in organisms. It has been shown in different fish species that ocean acidification (OA) mainly affects sensory systems, including olfaction. Impairment of olfactory function may be due to a dysfunction of the GABAergic system and to an alteration of neuronal plasticity in the whole brain and particularly in olfactory bulbs. Recent studies revealed that OA-driven effects on sensory systems are partly mediated by the regulation of the expression of genes involved in neurotransmission and neuronal development. However, these studies were performed in fish exposed to acidified waters for short periods, of only a few days. In the present paper, we investigated whether such effects could be observed in adult (4-years old) European sea bass (Dicentrarchus labrax) exposed to two hypercapnic and acidified conditions (PCO2 ≈ 980µatm; pH total = 7.7 and PCO2 ≈ 1520µatm; pH total = 7.5) from the larval stage. In a first approach, we analyzed by qPCR the expression of five genes involved in neurogenesis (DCX) or expressed in GABAergic (Gabra3), glutamatergic (Gria1) or dopaminergic (TH and DDC) neurons in the olfactory bulbs. The tested experimental conditions did not change the expression of any of the five genes. This result would indicate that a potential disruption of the olfactory function of sea bass exposed for a long term to near-future OA, either occurs at a level other than the transcriptional one or involves other actors of the sensory function.

The Effects of Aragonite Saturation State on Hatchery-Reared Larvae of the Greenshell Mussel Perna canaliculus

The major cultured mussel species Perna canaliculus is now supported by hatchery production, providing the opportunity to explore and optimize environmental parameters to enhance production. Other cultured bivalve larvae have demonstrated performance that is directly correlated to the aragonite saturation state (Ωar) of their tank water, with low or undersaturated water being detrimental and artificially elevated Ωar enhancing productivity. Trials were, therefore, designed to specifically explore Ωar sensitivity in preveliger (0–2 days old, prodissoconch I = “PD1″) and veliger (2–21 days old, prodissoconch II = “PD2″) stages of P. canaliculus separately. For the PD1 experiment, commercial incubation tanks (control Ωar 1.9) were modified to target Ωar 0.5 or 0.8 by elevating pCO2, or 2.9, 4.5, and ∼7 by the addition of sodium carbonate. In the control environment, 72.8% ± 2.9% of fertilized eggs formed viable “D” veligers within two days; an increased yield of 82.6% ± 3.8% in Ωar 4.5 was found to be nonsignificant. In comparison, only 12.7% of the Ωar ∼7 and <1% of the Ωar 0.5 and 0.8 eggs attained the veliger stage, with the remaining underdeveloped or malformed. By 2 days postfertilization, reactive oxygen species were significantly elevated in the undersaturated treatments, whereas DNA damage, lipid hydroperoxides, and protein carbonyls were significantly higher in the Ωar 0.5 and ∼7 treatments. Antioxidant enzyme levels were significantly lower in these extreme treatments, whereas Ωar 4.5 larvae showed elevated superoxide dismutase, glutathione reductase, and peroxidase levels. Carry-over effects persisted when veligers were transferred to control conditions, with no net recruitment from undersaturated Ωar, 29.4% of eggs surviving to pediveliger under control conditions, compared with 33.2% following Ωar 4.5 exposure or 1.9% from Ωar ∼7. In the PD2 veliger trial, linear shell growth halved in undersaturated water, but was unaffected by elevation of Ωar. Mortality rate was consistent across all treatments, suggesting relative resilience to different Ωar. It is recommended that hatcheries trial Ωar 4–4.5 enrichment in preveliger incubation water to improve yield and minimize oxidative stress. Preveliger stages present a potential survival bottleneck, and focused research exploring sensitivity to near-future ocean acidification is, therefore, needed.

Organ health and development in larval kingfish are unaffected by ocean acidification and warming.

Anthropogenic CO2 emissions are causing global ocean warming and ocean acidification. The early life stages of some marine fish are vulnerable to elevated ocean temperatures and CO2 concentrations, with lowered survival and growth rates most frequently documented. Underlying these effects, damage to different organs has been found as a response to elevated CO2 in larvae of several species of marine fish, yet the combined effects of acidification and warming on organ health are unknown. Yellowtail kingfish, Seriola lalandi, a circumglobal subtropical pelagic fish of high commercial and recreational value, were reared from fertilization under control (21 °C) and elevated (25 °C) temperature conditions fully crossed with control (500 µatm) and elevated (1,000 µatm) pCO2 conditions. Larvae were sampled at 11 days and 21 days post hatch for histological analysis of the eye, gills, gut, liver, pancreas, kidney and liver. Previous work found elevated temperature, but not elevated CO2, significantly reduced larval kingfish survival while increasing growth and developmental rate. The current histological analysis aimed to determine whether there were additional sublethal effects on organ condition and development and whether underlying organ damage could be responsible for the documented effects of temperature on survivorship. While damage to different organs was found in a number of larvae, these effects were not related to temperature and/or CO2 treatment. We conclude that kingfish larvae are generally vulnerable during organogenesis of the digestive system in their early development, but that this will not be exacerbated by near-future ocean warming and acidification.

The effects of long-term exposure to low pH on the skeletal microstructure of the sea urchin Heliocidaris erythrogramma

Anthropogenic CO2 – driven ocean acidification (OA) is causing a decrease in seawater pH and the saturation state of calcium carbonate minerals, compromising the ability of calcifying species to produce and maintain their skeletons. Sea urchins are ecologically important calcifying species and we investigated the impacts of long-term (9 month) exposure to near-future OA (Ambient – pHNBS 8.01; OA – pHNBS 7.6) on the skeleton microstructure of Heliocidaris erythrogramma using scanning electron microscopy (SEM), micro-computed tomography (μCT) and nanoindentation. SEM revealed that the youngest plates (apical plates) which had likely grown in experimental conditions had larger pores in the OA group (pore surface area ~ 72% larger) compared with those of urchins maintained in ambient pH. High-resolution, μCT 3-D reconstructions of the apical plates revealed that the experimental OA treatment urchins had a ~14% greater porosity and ~17% less biomineral, suggesting an inability to finely regulate skeletogenesis. The mid-test ambital plates established prior to this study did not show any OA associated change in porosity. Nanoindentation of the apical plates indicated that OA reduced skeletal hardness and elasticity. Stereom pore size is a key trait of the sea urchin endoskeleton and increased porosity in H. erythrogramma is likely to impact its biological functions as well as its biomechanical capacity to defend against predation and physical disturbances.

Recoverable impacts of ocean acidification on the tubeworm, Hydroides elegans: implication for biofouling in future coastal oceans

Ocean uptake of anthropogenic CO2 causes ocean acidification (OA), which not only decreases the calcification rate, but also impairs the formation of calcareous shells or tubes in marine invertebrates such as the dominant biofouling tubeworm species, Hydroides elegans. This study examined the ability of tubeworms to resume normal tube calcification when returned to ambient pH 8.1 from a projected near-future OA level of pH 7.8. Tubeworms produced structurally impaired and mechanically weaker calcareous tubes at pH 7.8 compared to at pH 8.1, but were able to recover when the pH was restored to ambient levels. This suggests that tubeworms can physiologically recover from the impacts of OA on tube calcification, composition, density, hardness and stiffness when returned to optimal conditions. These results help understanding of the progression of biofouling communities dominated by tubeworms in future oceans with low pH induced by OA.