Effects Of Ocean Acidification Research Articles

Metabolomics Approach to Reveal the Effects of Ocean Acidification on the Toxicity of Harmful Microalgae: A Review of the Literature

Climate change has been associated with intensified harmful algal blooms (HABs). Some harmful microalgae produce toxins that accumulate in food webs, adversely affecting the environment, public health and economy. Ocean acidification (OA) is a major consequence of high anthropogenic CO2 emissions. The carbon chemistry and pH of aquatic ecosystems have been significantly altered as a result. The impacts of climate change on the metabolisms of microalgae, especially toxin biosynthesis, remain largely unknown. This hinders the optimization of HAB mitigation for changed climate conditions. To bridge this knowledge gap, previous studies on the effects of ocean acidification on toxin biosynthesis in microalgae were reviewed. There was no solid conclusion for the toxicity change of saxitoxin-producing dinoflagellates from the genus Alexandrium after high CO2 treatment. Increased domoic acid content was observed in the diatom Pseudo-nitzschia. The brevetoxin content of Karenia brevis remained largely unchanged. The underlying regulatory mechanisms that account for the different toxicity levels observed have not been elucidated. Metabolic flux analysis is useful for investigating the carbon allocations of toxic microalgae under OA and revealing related metabolic pathways for toxin biosynthesis. Gaining knowledge of the responses of microalgae in high CO2 conditions will allow the better risk assessment of HABs in the future.

Effects of ocean acidification on dopamine-mediated behavioral responses of a coral reef damselfish

We investigated whether CO2-induced ocean acidification (OA) affects dopamine receptor-dependent behavior in bicolor damselfish (Stegastes partitus). Damselfish were kept in aquaria receiving flow through control (pH ~ 8.03; pCO2 ~ 384 μatm) or OA (pH ~ 7.64; CO2 ~ 1100 μatm) seawater at a rate of 1 L min−1. Despite this relatively fast flow rate, fish respiration further acidified the seawater in both control (pH ~7.88; pCO2 ~ 595 μatm) and OA (pH ~7.55; pCO2 ~ 1450 μatm) fish-holding aquaria. After five days of exposure, damselfish locomotion, boldness, anxiety, and aggression were assessed using a battery of behavioral tests using automated video analysis. Two days later, these tests were repeated following application of the dopamine D1 receptor agonist SKF 38393. OA-exposure induced ceiling anxiety levels that were significantly higher than in control damselfish, and SKF 38393 increased anxiety in control damselfish to a level not significantly different than that of OA-exposed damselfish. Additionally, SKF 38393 decreased locomotion and increased boldness in control damselfish but had no effect in OA-exposed damselfish, suggesting an alteration in activity of dopaminergic pathways that regulate behavior under OA conditions. These results indicate that changes in dopamine D1 receptor function affects fish behavior during exposure to OA. However, subsequent measurements of seawater sampled using syringes during the daytime (~3–4 pm local time) from crevasses in coral reef colonies, which are used as shelter by damselfish, revealed an average pH of 7.73 ± 0.03 and pCO2 of 925.8 ± 62.2 μatm; levels which are comparable to Representative Concentration Pathway (RCP) 8.5 predicted end-of-century mean OA levels in the open ocean. Further studies considering the immediate environmental conditions experienced by fish as well as individual variability and effect size are required to understand potential implications of the observed OA-induced behavioral effects on damselfish fitness in the wild.

Chromosome-level genome of the three-spot damselfish, Dascyllus trimaculatus.

Damselfishes (Family: Pomacentridae) are a group of ecologically important, primarily coral reef fishes that include over 400 species. Damselfishes have been used as model organisms to study recruitment (anemonefishes), the effects of ocean acidification (spiny damselfish), population structure, and speciation (Dascyllus). The genus Dascyllus includes a group of small-bodied species, and a complex of relatively larger bodied species, the Dascyllus trimaculatus species complex that is comprised of several species including D. trimaculatus itself. The three-spot damselfish, D. trimaculatus, is a widespread and common coral reef fish species found across the tropical Indo-Pacific. Here, we present the first-genome assembly of this species. This assembly contains 910 Mb, 90% of the bases are in 24 chromosome-scale scaffolds, and the Benchmarking Universal Single-Copy Orthologs score of the assembly is 97.9%. Our findings confirm previous reports of a karyotype of 2n = 47 in D. trimaculatus in which one parent contributes 24 chromosomes and the other 23. We find evidence that this karyotype is the result of a heterozygous Robertsonian fusion. We also find that the D. trimaculatus chromosomes are each homologous with single chromosomes of the closely related clownfish species, Amphiprion percula. This assembly will be a valuable resource in the population genomics and conservation of Damselfishes, and continued studies of the karyotypic diversity in this clade.

Effects of ocean acidification and warming on the specific dynamic action of California Grunion (Leuresthes tenuis) larvae

Ocean acidification (OA) and Ocean Warming (OW) are ongoing environmental changes that present a suite of physiological challenges to marine organisms. Larval stages may be especially sensitive to the effects of climate change because the larval phase is a time of critical growth and development. Of particular importance to growth is Specific Dynamic Action (SDA) – the energy used in digestion, absorption, and assimilation of food. Relatively little is known about the energetics of SDA for larval fishes and even less is known about how SDA may be affected by climate change. In this study we used feeding experiments and respirometry assays to characterize the functional form of SDA for California Grunion (Leuresthes tenuis). In a second set of experiments, we tested the independent and combined effects of ocean acidification and warming on SDA. Our first experiment revealed that an elevated metabolic rate was detectable within an hour of feeding, peaked at 3–6 h post feeding, and lasted about 24 h in total. Experiments testing the effects of acidification and warming revealed that temperature generally increased the maximum rate of postprandial respiration and the total amount of energy expended via SDA. In an experiment where feeding level was the same for fish held at different temperatures, elevated pCO2 increased the maximum rate of postprandial respiration and shortened the SDA response. However, in an experiment that allowed fish to consume more food at high temperatures, effects of pCO2 on SDA were minimal. The effects of OA on SDA may depend on a combination of temperature and food availability, and the disruption of SDA with OA may be part of a chain of events where digestion and assimilation efficiency are impaired with potential consequences for growth, survival, and population replenishment.

Field development of Posidonia oceanica seedlings changes under predicted acidification conditions

Ocean acidification has been consistently evidenced to have profound and lasting impacts on marine species. Observations have shown seagrasses to be highly susceptible to future increased pCO2 conditions, but the responses of early life stages as seedlings are poorly understood. This study aimed at evaluating how projected Mediterranean Sea acidification affects the survival, morphological and biochemical development of Posidonia oceanica seedlings through a long-term field experiment along a natural low pH gradient. Future ocean conditions seem to constrain the morphological development of seedlings. However, high pCO2 exposures caused an initial increase in the degree of saturation of fatty acids in leaves and then improved the fatty acid adjustment increasing unsaturation levels in leaves (but not in seeds), suggesting a nutritional compound translocation. Results also suggested a P. oceanica structural components remodelling which may counteract the effects of ocean acidification but would not enhance seagrass seedling productivity.

Sediment-seawater exchange altered adverse effects of ocean acidification towards marine microalgae

Ocean acidification (OA) exhibits high threat to marine microalgae. However, the role of marine sediment in the OA-induced adverse effect towards microalgae is largely unknown. In this work, the effects of OA (pH 7.50) on the growth of individual and co-cultured microalgae (Emiliania huxleyi, Isochrysis galbana, Chlorella vulgaris, Phaeodactylum tricornutum, and Platymonas helgolandica tsingtaoensis) were systematically investigated in the sediment-seawater systems. OA inhibited E. huxleyi growth by 25.21 %, promoted P. helgolandica (tsingtaoensis) growth by 15.49 %, while did not cause any effect on the other three microalgal species in the absence of sediment. In the presence of the sediment, OA-induced growth inhibition of E. huxleyi was significantly mitigated, because the released chemicals (N, P and Fe) from seawater-sediment interface increased the photosynthesis and reduced oxidative stress. For P. tricornutum, C. vulgaris and P. helgolandica (tsingtaoensis), the growth was significantly increased in the presence of sediment in comparison with those under OA alone or normal seawater (pH 8.10). For I. galbana, the growth was inhibited when the sediment was introduced. Additionally, in the co-culturing system, C. vulgaris and P. tricornutum were the dominant species, while OA increased the proportions of dominant species and decreased the community stability as indicated by Shannon and Pielou's indexes. After the introduction of sediment, the community stability was recovered, but remained lower than that under normal condition. This work demonstrated the role of sediment in the biological responses to OA, and could be helpful for better understanding the impact of OA on marine ecosystems.

Tidal cycle and time of day control pH levels in coastal habitats of the western Indian Ocean: the case of Mnazi and Chwaka Bays in Tanzania

Ocean acidification, a progressive decrease in the pH and change in the carbonate chemistry of seawater caused by the uptake of carbon dioxide (CO2) from the atmosphere, is a growing crisis that threatens marine species. pH data relevant to a species’ natural habitat in the coastal waters of the western Indian Ocean (WIO) is still sparse, limiting the capacity to undertake manipulative studies to better understand the impacts of ocean acidification on marine species. This study investigated tidal and day-night pH variations in mangrove, seagrass, and coral reef habitats of the WIO by using Tanzania as a case study. The mean pH of the studied coastal habitats was highest in seagrass (8.49 ± 0.29), followed by coral reef (8.33 ± 0.06), and lowest in mangrove (8.20 ± 0.17). Seagrass habitats had the highest pH (9.06) during the day at low spring tides, mangrove habitats had the highest pH (8.45) during the day at high spring tides, and coral reef habitats had the highest pH (8.47) during the day at low tides. Seagrass habitats had the widest pH range (1.03), followed by mangrove habitats (0.54), while coral reef habitats had the narrowest range (0.23). The water with the highest pH during the day was transported to nearby mangrove habitats during incoming tides and to coral reef habitats during outgoing tides, resulting in the highest mean pH in mangrove and coral reef habitats during spring high and low tides, respectively. pH within the seagrass habitats correlated strongly and positively with changes in temperature (r=0.80), dissolved oxygen (r=0.84), and salinity (r=0.72), while pH in mangrove habitats correlated moderately and positively with dissolved oxygen (r=0.59). This study provides in-situ evidence on the pH fluctuations in the WIO’s coastal habitats over time and space, with water from seagrass habitats capable of raising the pH of water in nearby mangrove and coral reef habitats during the day, thereby potentially helping in the mitigation of the effects of ocean acidification on these habitats.

Balance dysfunction in large yellow croaker in response to ocean acidification

Large yellow croaker (Larimichthys crocea) is a coastal-dwelling soniferous, commercially important fish species that is sensitive to sound. An understanding of how ocean acidification might affect its auditory system is therefore important for its long-term viability and management as a fisheries resource. We tested the effects of ocean acidification with four CO2 treatments (440 ppm (control), 1000 ppm, 1800 ppm, and 3000 ppm) on the inner ear system of this species. After exposure to acidified water for 50 d, the impacts on the perimeter and mass of the sagitta, asteriscus, and lapillus otoliths were determined. In the acidified water treatments, the shape of sagittal otoliths became more irregular, and the surface became rougher. Similar sound frequency ranges triggered startle responses of fish in all treatments. In the highest CO2 treatment (3000 ppm CO2), significant asymmetry of the left and right lapillus perimeter and weight was apparent. Moreover, in the higher CO2 treatments (1800 ppm and 3000 ppm CO2), the fish were unable to maintain a balanced dorsal-up posture and tilted to one side. This result suggested that the balance functions of the inner ear might be affected by ocean acidification, which may threaten large yellow croaker individuals and populations. The molecular response to acidification was analyzed by RNA-Seq. The differentially expressed genes (DEGs) between right and left sensory epithelia of the utricle in each CO2 treatment group were identified. In higher CO2 concentration groups, nervous system function and regulation of bone mineralization pathways were enriched with DEGs. The comparative transcriptome analyses provide valuable molecular information about how the inner ear system responds to an acidified environment.

The Multi-Generational Effect of Seawater Acidification on Larval Development, Reproduction, Ingestion Rate, and ATPase Activity of Tigriopus japonicus Mori, 1938

Ocean acidification threatens marine organisms continuously. To ascertain if adaptation of marine species to ocean acidification enhanced over multiple generations, we studied the transgenerational effects of ocean acidification on the development, reproduction, ingestion rate, and ATPase activity of a copepod Tigriopus japonicus Mori, 1938. In the first mode, individuals were exposed to either one of the pH levels (8.1 (control), 7.7, 7.3) for five successive generations. In the second mode, each successive generation was exposed to a lower pH level (pH levels: 8.1, 7.9, 7.7, 7.5, 7.3). After prolonged exposure to a constant seawater acidification level, the capacity to adapt to the stress increased. However, when exposed to seawater of descending pH, the detrimental effects gradually increased. Energy allocated to development and reproduction was reduced although the ingestion rate continued to improve in successive generations. Therefore, ongoing ocean acidification might lower the energy transfer of copepods to higher trophic levels.

Ocean acidification and warming modify stimulatory benthos effects on sediment functioning: An experimental study on two ecosystem engineers

Many macrofauna have a stimulatory effect on sediment functioning through their burrowing, feeding and irrigation activities. Here, we investigated the single and combined effect of ocean acidification and warming on the stimulatory effect of two key-species inhabiting sandy seabeds in the Southern Bight of the North Sea; the bivalve Abra alba and the polychaete Lanice conchilega. The species were separately incubated in natural sediment in the laboratory under ambient, low pH (pH: -0.3), warm (T: + 3°C) and mimicked climate change (pH: -0.3, T: +3°C) conditions. After six weeks of incubation, nutrient and oxygen exchange were measured at the sediment-water interface to estimate aerobic sediment metabolism and nitrogen cycling. Both species facilitate sediment community oxygen consumption, nitrification and denitrification under ambient conditions. The stimulatory effect of A. alba disappeared in a low pH environment and decreased over time in the warmer treatments along with increased mortality. In contrast, L. conchilega stimulated sediment biogeochemical cycling more when seawater becomes acidified (+ 8 to 41%, depending on the function) but warming had no effect. We explain these species-specific climate change effects by different behavioral and physiological coping strategies that cascade on to sediment biogeochemical cycling, especially through altered oxygenation the sediment matrix.

Effects of ocean acidification and eutrophication on the growth and photosynthetic performances of a green tide alga Ulva prolifera

With the impact of fossil fuel burning and industrialization, atmospheric CO2 concentration will reach about 1000 ppmv in 2100, and more and more CO2 will be absorbed by ocean, resulting in ocean acidification. The Chinese coastal waters are showing unexpectedly high levels of acidification due to a combination of global ocean acidification and severe regional eutrophication, which is caused by natural accumulation or human activities such as aquacultural tail water input, potentially affecting macroalgal blooms. However, little is known about the combined effects of ocean acidification and entrophication on the eco-physiology of bloom-forming macroalgae. This study investigated Ulva prolifera, a dominant species causing green tide in the South Yellow Sea, and explored its growth and physiological responses under the combination conditions of ocean acidification and enriched nutrients. In this study, U. prolifera thalli were cultured under two CO2 conditions (air and 1000 μatm) and two nutrient conditions (High Nutrient, HN, 135 μmol L-1 N and 8.5 μmol L-1 P; Normal Nutrient, NN, 27 μmol L-1 N and 1.7 μmol L-1 P). The results showed that eutrophication conditions obviously enhanced the relative growth rate and photosynthetic performance of U. prolifera. Elevated pCO2 had no significant effect on U. prolifera growth and photosynthetic performance under normal nutrient conditions. However, under eutrophication conditions elevated pCO2 inhibited U. prolifera growth. Moreover, eutrophication conditions markedly improved the contents of chlorophyll a, chlorophyll b and nitrate reductase activity and inhibited the soluble carbohydrate content, but elevated pCO2 had no significant effect on them under nutrient-replete conditions. In addition, elevated pCO2 significantly reduced the carotenoid content under eutrophication conditions and had no effect on it under normal nutrient conditions. These findings indicate that seawater eutrophication would greatly accelerate U. prolifera bloom, which may also be suppressed to a certain extent by ocean acidification in the future. The study can provide valuable information for predicting the future outbreaks of U. prolifera green tide in nearshore regions.

Mollusk Response Under Ocean Acidification in Shallow Marine Settings of Sicily (Central Mediterranean)

Anthropogenic CO2 is a major driver of change in most marine ecosystems, as the consequent ocean acidification is threatening marine calcifying organisms. In this respect, long-term analyses on ocean acidification effects on marine ecosystems acclimated to high pCO2, as found around CO2 vents, are needed. Here we tackle mollusk assemblages from acidified shallow marine settings off the Aeolian archipelago (Central Mediterranean). The detected gradient manifests along a 34 m long transect (9.6 m and 11.4 m water depth), mostly in a Posidonia oceanica matte from normal (site 1) to high levels (site 3) of pCO2 (405 μatm, pH 8.1 and 715 μatm, pH 7.8; respectively). The strongest acidified condition at the vent crater (site 4, pCO2 1110 μatm, pH 7.7). At the vent site gaseous emissions are characterized by ~99% in volume of CO2 and ~0.6% of H2S. However, water dissolved H2S was below detection limit and the sulphate content along the transect does not show significant variations with respect to normal seawater values. Preliminary paleoecologic surveys on diversity structure (diversity profiles) and taphonomic degradation (NMDS, z scored % values) were conducted on mollusk remains collected along the natural pH gradient (sites 1-4). Along the P. oceanica matte (sites 1-3), overall mollusk taxon diversity (alpha and beta) decreased, mollusk in site 3 were mostly juveniles and had higher overall taphonomic damages than those retrieved at normal pH conditions. Within the vent crater only fewer and highly taphonomically altered gastropod specimens were retrieved on the pebbly seafloor, suggesting a very short residence time of shell material and rapid dissolution. Even if vents are not exact predictors of the anthropogenic-designed future of marine settings, due to their limited spatial and temporal extent, they can act as natural laboratories where to evaluate the output of ecosystem processes under rising pCO2 and the effects on the creation of the future fossil record.

Deoxygenation enhances photosynthetic performance and increases N2 fixation in the marine cyanobacterium Trichodesmium under elevated pCO2.

Effects of changed levels of dissolved O2 and CO2 on marine primary producers are of general concern with respect to ecological effects of ongoing ocean deoxygenation and acidification as well as upwelled seawaters. We investigated the response of the diazotroph Trichodesmium erythraeum IMS 101 after it had acclimated to lowered pO2 (~60 μM O2) and/or elevated pCO2 levels (HC, ~32 μM CO2) for about 20 generations. Our results showed that reduced O2 levels decreased dark respiration significantly, and increased the net photosynthetic rate by 66 and 89% under the ambient (AC, ~13 μM CO2) and the HC, respectively. The reduced pO2 enhanced the N2 fixation rate by ~139% under AC and only by 44% under HC, respectively. The N2 fixation quotient, the ratio of N2 fixed per O2 evolved, increased by 143% when pO2 decreased by 75% under the elevated pCO2. Meanwhile, particulate organic carbon and nitrogen quota increased simultaneously under reduced O2 levels, regardless of the pCO2 treatments. Nevertheless, changed levels of O2 and CO2 did not bring about significant changes in the specific growth rate of the diazotroph. Such inconsistency was attributed to the daytime positive and nighttime negative effects of both lowered pO2 and elevated pCO2 on the energy supply for growth. Our results suggest that Trichodesmium decrease its dark respiration by 5% and increase its N2-fixation by 49% and N2-fixation quotient by 30% under future ocean deoxygenation and acidification with 16% decline of pO2 and 138% rise of pCO2 by the end of this century.

Thanks mum. Maternal effects in response to ocean acidification of sea urchin larvae at different ecologically relevant temperatures

Juvenile stages of marine species might be more vulnerable than adults to climate change, however larval vulnerability to predictable environmental changes can be mitigated by parental anticipatory buffer effects occurring during gametogenesis. In this study, ocean acidification effect were investigated on larval growth of two sea urchins, Arbacia lixula and Paracentrotus lividus, at different temperature levels. Results showed that altered pH and temperature affected larval development in both species, with significant length reductions of spicules and significant increases in abnormal larvae. Detrimental effects of reduced pH and high temperature were however dependent on the mother. Furthermore, the responses of A. lixula larvae from the ambient site (pH ∼ 8.0) were compared with those of larvae obtained from mothers collected from a natural CO2 vent (pH ∼ 7.7) in Ischia. Comparisons highlighted a transgenerational response, as the CO2 vent larvae proved to be more resilient to reduced pH, although more sensitive to increased temperature.

Differential effects of ocean acidification and warming on biological functioning of a predator and prey species may alter future trophic interactions

Independently, ocean warming (OW) and acidification (OA) from increased anthropogenic atmospheric carbon dioxide are argued to be two of the greatest threats to marine organisms. Increasingly, their interaction (ocean acidification and warming, OAW) is shown to have wide-ranging consequences to biological functioning, population and community structure, species interactions and ecosystem service provision. Here, using a multi-trophic experiment, we tested the effects of future OAW scenarios on two widespread intertidal species, the blue mussel Mytilus edulis and its predator Nucella lapillus. Results indicate negative consequences of OAW on the growth, feeding and metabolic rate of M. edulis and heightened predation risk. In contrast, Nucella growth and metabolism was unaffected and feeding increased under OAW but declined under OW suggesting OA may offset warming consequences. Should this differential response between the two species to OAW, and specifically greater physiological costs to the prey than its predator come to fruition in the nature, fundamental change in ecosystem structure and functioning could be expected as trophic interactions become disrupted.

The effects of ocean acidification on fishes - history and future outlook.

The effects of increased levels of carbon dioxide (CO2 ) on the Earth's temperature have been known since the end of the 19th century. It was long believed that the oceans' buffering capacity would counteract any effects of dissolved CO2 in marine environments, but during recent decades, many studies have reported detrimental effects of ocean acidification on aquatic organisms. The most prominent effects can be found within the field of behavioural ecology, e.g., complete reversal of predator avoidance behaviour in CO2 -exposed coral reef fish. Some of the studies have been very influential, receiving hundreds of citations over recent years. The results have also been conveyed to policymakers and publicized in prominent media outlets for the general public. Those extreme effects of ocean acidification on fish behaviour have, however, spurred controversy, given that more than a century of research suggests that there are few or no negative effects of elevated CO2 on fish physiology. This is due to sophisticated acid-base regulatory mechanisms that should enable their resilience to near-future increases in CO2 . In addition, an extreme "decline effect" has recently been shown in the literature regarding ocean acidification and fish behaviour, and independent research groups have been unable to replicate some of the most profound effects. Here, the author presents a brief historical overview on the effects of elevated CO2 and ocean acidification on fishes. This historical recap is warranted because earlier work, prior to a recent (c. 10year) explosion in interest, is often overlooked in today's ocean acidification studies, despite its value to the field. Based on the historical data and the current knowledge status, the author suggests future strategies with the aim to improve research rigour and clarify the understanding of the effects of ocean acidification on fishes.

Accelerated light carbon sequestration following late Paleocene-early Eocene carbon cycle perturbations

Carbon releases into the climate system produce global warming and ocean acidification events that can be reversed eventually by carbon sequestration. However, the underlying controls on the timescales of carbon removal, and their dependence on the amplitude of the initial perturbation, are poorly understood. Here, we assess a series of late Paleocene-early Eocene (LPEE) carbon cycle perturbations (∼56-52 Ma) of different amplitudes to constrain carbon removal timescales. Carbon isotope excursions (CIEs) and sedimentation patterns for the largest event, the Paleocene-Eocene Thermal Maximum (PETM), allow identification of a light carbon injection that appeared ∼85 kyr after the PETM onset. This CIE may have been triggered by orbital forcing of long (∼400 kyr) and short (∼100 kyr) eccentricity maxima. The various LPEE light carbon injections were followed by exponential carbon removal trends with half-life (t1/2) estimates of ∼6-26 kyr. These values are smaller than background estimates for the modern carbon cycle (t1/2>100 kyr), which reveals accelerated light carbon sequestration. We find that one estimated t1/2 period coincided temporally with ocean acidification recovery in different locations with contrasting paleo-water depths. This pattern indicates enhanced chemical weathering following LPEE CIEs; however, chemical weathering timescales are an order of magnitude longer than the observed t1/2 estimates. This reveals that several carbon processes were optimized during LPEE CIE recovery. Similar t1/2 estimates are obtained for light carbon injections of different sizes, which suggests that carbon removal was optimized to conditions induced by the initial perturbation. Temperature controls on oxygen solubility may have accelerated the oceanic biological pump in proportion to each LPEE carbon injection. This process may have caused accelerated carbon sequestration during LPEE CIE recovery and produced the short carbon removal timescales identified by t1/2 estimates of LPEE carbon cycle perturbations.

No effect of ocean acidification on growth, photosynthesis, or dissolved organic carbon release by three temperate seaweeds with different dissolved inorganic carbon uptake strategies

AbstractIn a future ocean, dissolved organic carbon (DOC) release by seaweed has been considered a pathway for organic carbon that is not incorporated into growth under carbon dioxide (CO2) enrichment/ocean acidification (OA). To understand the influence of OA on seaweed DOC release, a 21-day experiment compared the physiological responses of three seaweed species, two which operate CO2 concentrating mechanisms (CCMs), Ecklonia radiata (C. Agardh) J. Agardh and Lenormandia marginata (Hooker F. and Harvey) and one that only uses CO2 (non-CCM), Plocamium cirrhosum (Turner) M.J. Wynne. These two groups (CCM and non-CCM) are predicted to respond differently to OA dependent on their affinities for Ci (defined as CO2 + bicarbonate, HCO3−). Future ocean CO2 treatment did not drive changes to seaweed physiology—growth, Ci uptake, DOC production, photosynthesis, respiration, pigments, % tissue carbon, nitrogen, and C:N ratios—for any species, regardless of Ci uptake method. Our results further showed that Ci uptake method did not influence DOC release rates under OA. Our results show no benefit of elevated CO2 concentrations on the physiologies of the three species under OA and suggest that in a future ocean, photosynthetic CO2 fixation rates of these seaweeds will not increase with Ci concentration.

Combined effects of climate change stressors and predators with contrasting feeding-digestion strategies on a mussel species

We investigated the combined effects of Ocean Warming (OW), Acidification (OA) and predator cues (Non-Consumptive Effects; NCEs) of two predators with contrasting feeding-digestion strategies on the mussel Perumytilus purpuratus. We considered starfish-NCEs (partially external digestion) and snail-NCEs (internal digestion). Mussels were exposed for 13 weeks to cross-factored OA (~500 and ~1400 μatm, pCO2) and OW (~15 and ~20 °C) conditions, in the presence/absence of NCEs from one or both predators. Mussels exposed to both NCEs exhibited smaller length and buoyant weight growth than those under control or snail-NCEs conditions. Mussels exposed to starfish-NCEs exhibited smaller wet mass than control mussels. OW and starfish-NCEs in isolation or combined with snail-NCEs increased mussel oxygen consumption. Byssal biogenesis was affected by the three-factors interaction. Clearance rates were affected by the OW × OA interaction. We suggest that mainly starfish-NCEs, in isolation or interacting with OA or/and OW, can threat mussel traits and the associated community.

Restoration and coral adaptation delay, but do not prevent, climate-driven reef framework erosion of an inshore site in the Florida Keys

For reef framework to persist, calcium carbonate production by corals and other calcifiers needs to outpace loss due to physical, chemical, and biological erosion. This balance is both delicate and dynamic and is currently threatened by the effects of ocean warming and acidification. Although the protection and recovery of ecosystem functions are at the center of most restoration and conservation programs, decision makers are limited by the lack of predictive tools to forecast habitat persistence under different emission scenarios. To address this, we developed a modelling approach, based on carbonate budgets, that ties species-specific responses to site-specific global change using the latest generation of climate models projections (CMIP6). We applied this model to Cheeca Rocks, an outlier in the Florida Keys in terms of high coral cover, and explored the outcomes of restoration targets scheduled in the coming 20 years at this site by the Mission: Iconic Reefs restoration initiative. Additionally, we examined the potential effects of coral thermal adaptation by increasing the bleaching threshold by 0.25, 0.5, 1 and 2˚C. Regardless of coral adaptative capacity or restoration, net carbonate production at Cheeca Rocks declines heavily once the threshold for the onset of annual severe bleaching is reached. The switch from net accretion to net erosion, however, is significantly delayed by mitigation and adaptation. The maintenance of framework accretion until 2100 and beyond is possible under a decreased emission scenario coupled with thermal adaptation above 0.5˚C. Although restoration initiatives increase reef accretion estimates, Cheeca Rocks will only be able to keep pace with future sea-level rise in a world where anthropogenic CO2 emissions are reduced. Present results, however, attest to the potential of restoration interventions combined with increases in coral thermal tolerance to delay the onset of mass bleaching mortalities, possibly in time for a low-carbon economy to be implemented and complementary mitigation measures to become effective.