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Experiments examining fish sensitivities to future oceanic CO2 levels have greatly expanded over past decades and identified many potentially affected traits. Curiously, data on reproductive trait responses to high CO2 are still scarce, despite their strong link to Darwinian fitness and thus to population vulnerability to ocean acidification. We conducted two rearing experiments on the first broadcast-spawning marine fish model (Atlantic silverside, Menidia menidia) to examine how long-term and novel whole life-cycle exposures to predicted future CO2 levels (∼2,000 µatm) affect laboratory spawning, temperature-specific reproductive investment, fecundity, and size distributions of maturing oocytes. At low temperatures (17°C), female body size and therefore potential fecundity (FPot, oocytes/female) slightly increased with CO2, while relative fecundity (FRel, oocytes/g female) remained unaffected. At high temperatures (24°C), high CO2 substantially reduced both FPot (−19%) and FRel (−28%) relative to control treatments. Irrespective of CO2, females at 24°C grew larger and heavier than those at 17°C, and although larger females produced larger oocytes at some developmental stages, they also had lower gonadosomatic indices and lower FRel. Our findings contrast with most previous studies and thus highlight the need to investigate reproductive impacts of increasing CO2 on multiple fish species with contrasting life history strategies.

Organisms with long generation times require phenotypic plasticity to survive in changing environments until genetic adaptation can be achieved. Marine calcifiers are particularly vulnerable to ocean acidification due to dissolution and a reduction in shell-building carbonate ions. Long-term experiments assess organisms' abilities to acclimatize or even adapt to environmental change. Here we present an unexpected compensatory response to extensive shell dissolution in a highly calcium-carbonate-dependent organism after long-term culture in predicted end-century acidification and warming conditions. Substantial shell dissolution with decreasing pH posed a threat to both a polar ( Liothyrella uva) and a temperate ( Calloria inconspicua) brachiopod after 7 months and 3 months exposure, respectively, with more extensive dissolution in the polar species. This impact was reflected in decreased outer primary layer thickness in the polar brachiopod. A compensatory response of increasing inner secondary layer thickness, and thereby producing a thicker shell, was exhibited by the polar species. Less extensive dissolution in the temperate brachiopod did not affect shell thickness. Increased temperature did not impact shell dissolution or thickness. Brachiopod ability to produce a thicker shell when extensive shell dissolution occurs suggests this marine calcifier has great plasticity in calcification providing insights into how similar species might cope under future environmental change.

Coastal ecosystems experience substantial natural fluctuations in pCO2 and dissolved oxygen (DO) conditions on diel, tidal, seasonal and interannual timescales. Rising carbon dioxide emissions and anthropogenic nutrient input are expected to increase these pCO2 and DO cycles in severity and duration of acidification and hypoxia. How coastal marine organisms respond to natural pCO2 × DO variability and future climate change remains largely unknown. Here, we assess the impact of static and cycling pCO2 × DO conditions of various magnitudes and frequencies on early life survival and growth of an important coastal forage fish, Menidia menidia. Static low DO conditions severely decreased embryo survival, larval survival, time to 50% hatch, size at hatch and post-larval growth rates. Static elevated pCO2 did not affect most response traits, however, a synergistic negative effect did occur on embryo survival under hypoxic conditions (3.0 mg L−1). Cycling pCO2 × DO, however, reduced these negative effects of static conditions on all response traits with the magnitude of fluctuations influencing the extent of this reduction. This indicates that fluctuations in pCO2 and DO may benefit coastal organisms by providing periodic physiological refuge from stressful conditions, which could promote species adaptability to climate change.

Surface seawaters are becoming more acidic due to the absorption of rising anthropogenic CO2. Marine calcifiers are considered to be the most vulnerable organisms to ocean acidification due to the reduction in the availability of carbonate ions for shell or skeletal production. Rhychonelliform brachiopods are potentially one of the most calcium carbonate-dependent groups of marine organisms because of their large skeletal content. Little is known, however, about the effects of lowered pH on these taxa. A CO2 perturbation experiment was performed on the New Zealand terebratulide brachiopod Calloria inconspicua to investigate the effects of pH conditions predicted for 2050 and 2100 on the growth rate and ability to repair shell. Three treatments were used: an ambient pH control (pH 8.16), a mid-century scenario (pH 7.79), and an end-century scenario (pH 7.62). The ability to repair shell was not affected by acidified conditions with >80% of all damaged individuals at the start of the experiment completing shell repair after 12 weeks. Growth rates in undamaged individuals >3 mm in length were also not affected by lowered pH conditions, whereas undamaged individuals

The inability of organisms to cope in changing environments poses a major threat to their survival. Rising carbon dioxide concentrations, recently exceeding 400 μatm, are rapidly warming and acidifying our oceans. Current understanding of organism responses to this environmental phenomenon is based mainly on relatively short‐ to medium‐term laboratory and field experiments, which cannot evaluate the potential for long‐term acclimation and adaptation, the processes identified as most important to confer resistance. Here, we present data from a novel approach that assesses responses over a centennial timescale showing remarkable resilience to change in a species predicted to be vulnerable. Utilising museum collections allows the assessment of how organisms have coped with past environmental change. It also provides a historical reference for future climate change responses. We evaluated a unique specimen collection of a single species of brachiopod (Calloria inconspicua) collected every decade from 1900 to 2014 from one sampling site. The majority of brachiopod shell characteristics remained unchanged over the past century. One response, however, appears to reinforce their shell by constructing narrower punctae (shell perforations) and laying down more shell. This study indicates one of the most calcium‐carbonate‐dependent species globally to be highly resilient to environmental change over the last 120 years and provides a new insight for how similar species might react and possibly adapt to future change., Current knowledge of how organisms will respond to ocean warming and acidification is based on relatively short‐ to medium‐term laboratory and field experiments, which cannot evaluate the potential for adaptation. We present a novel approach of utilising museum collections of a brachiopod species collected every decade at one site from 1900 to 2014 to assess how organisms have coped with past environmental change. This study indicates the resilience of one of the most vulnerable species globally to environmental change over the past 120 years and provides an insight for how similar species might react to future change.

This study investigated the effects of long-term incubation to near-future combined warming (+2 °C) and ocean acidification (−0.3 and −0.5 pH units) stressors, relative to current conditions (−0.3 °C and pH 8.0), on the energetics of food processing in the Antarctic sea urchin, Sterechinus neumayeri. After an extended incubation of 40 months, energy absorbed, energy lost through respiration and lost as waste were monitored through two feeding cycles. Growth parameters (mass of somatic and gonad tissues and the CHN content of gonad) were also measured. There were no significant effects of combined ocean acidification (OA) and temperature stressors on the growth of somatic or reproductive tissue. Despite more food being consumed in the low temperature control, once food processing and maintenance costs were subtracted, there were no significant effects of treatment on the scope for growth. The biggest significant differences were between amounts of food consumed during the two feeding cycles. More food was consumed by the low temperature (0 °C) control animals, indicating a potential effect of the changed conditions on digestive efficiency. Also, in November, more food was consumed, with a higher absorption efficiency, which resulted in a higher scope for growth in November than September and may reflect increased energetic needs associated with a switch to summer physiology. The effect of endogenous seasonal cycles and environmental variability on organism capacity is discussed.

Despite the remarkable expansion of laboratory studies, robust estimates of single species CO 2 sensitivities remain largely elusive. We conducted a meta-analysis of 20 CO 2 exposure experiments conducted over 6 years on offspring of wild Atlantic silversides ( Menidia menidia ) to robustly constrain CO 2 effects on early life survival and growth. We conclude that early stages of this species are generally tolerant to CO 2 levels of approximately 2000 µatm, likely because they already experience these conditions on diel to seasonal timescales. Still, high CO 2 conditions measurably reduced fitness in this species by significantly decreasing average embryo survival (−9%) and embryo+larval survival (−13%). Survival traits had much larger coefficients of variation (greater than 30%) than larval length or growth (3–11%). CO 2 sensitivities varied seasonally and were highest at the beginning and end of the species' spawning season (April–July), likely due to the combined effects of transgenerational plasticity and maternal provisioning. Our analyses suggest that serial experimentation is a powerful, yet underused tool for robustly estimating small but true CO 2 effects in fish early life stages.

Marine calcifiers are amongst the most vulnerable organisms to ocean acidification due to reduction in the availability of carbonate ions for skeletal/shell deposition. However, there are limited long-term studies on the possible impacts of increased pCO2 on these taxa. A 7 month CO2 perturbation experiment was performed on one of the most calcium carbonate dependent species, the Antarctic brachiopod Liothyrella uva, which inhabits the Southern Ocean where carbonate ion saturation levels are amongst the lowest on Earth. The effects of the predicted environmental conditions in 2050 and 2100 on the growth rate and ability to repair shell in L. uva were tested with four treatments; a low temperature control (0 °C, pH 7.98), a pH control (2 °C, pH 8.05), mid-century scenario (2 °C, pH 7.75) and end-century scenario (2 °C, pH 7.54). Environmental change impacts on shell repair are rarely studied, but here repair was not affected by either acidified conditions or temperature. Growth rate was also not impacted by low pH. Elevated temperature did, however, increase growth rates. The ability of L. uva to continue, and even increase shell production in warmer and acidified seawater suggests that this species can acclimate to these combined stressors and generate suitable conditions for shell growth at the site of calcification.