Posts Tagged 'laboratory'

The effects of climate change on the heart rates & growth of sea slugs in the Gulf of Maine

In the next 80 years, sea surface temperatures are expected to increase by 1.5o to 2oC and ocean pH is expected to drop by 0.06 to 0.32 units, with exacerbated effects seen in coastal waters. Temperature increase has already forced organisms to shift their range polewards and ocean acidification has negatively affected calcifying organisms. Interactive effects, only more recently studied, vary depending on phylum and life cycle stage. This study examined both the upper thermal tolerance and interactive effect of temperature and acidification on the heart rate of five cold-water species of nudibranchs (Aeolidia papillosa, Cuthona gymnota, Dendronotus frondosus, Flabellina verrucosa, and Onchidoris bilamellata) and one species of sacoglossan (Placida dendritica) from the Gulf of Maine. Thermal tolerance was determined by recording heart rate for each organism starting at 4oC and increasing the temperature by increments of 4oC until the organism’s heartbeat slowed or ceased. For interactive effects, pH levels used were pH 8 (control) and pH 7 at temperatures: 4o, 8o (control), 12o, and 16oC. Upper thermal tolerance limits ranged from 16o to 20oC for the nudibranchs and 24oC for the sacoglossan. The combined effects of increasing temperature and lower pH were neutral, negatively additive, and antagonistic. Only F. verrucosa exhibited an interactive effect, with higher temperature and lower pH leading to decreased heart rate. Although no interactive effect was demonstrated in C. xgymnota, D. frondosus, and O. bilamellata, lower pH slowed heart rates across all temperatures. Subsequently, the relationship between temperature and growth rates was examined in D. frondosus and F. verrucosa. The nudibranchs were reared for eight weeks at 4o, 10o, or 16oC and growth was measured weekly. The ideal temperature for growth appeared to be 10oC, whereas 16oC was lethal. Additionally, an unsuccessful attempt was made to culture A. papillosa, but the number of embryos per egg capsule and larval growth rates were examined. Size of adult sea slug positively impacted the number of embryos per egg capsule, with embryos increasing in length by 50% over the first week and 10% over subsequent weeks. With an interactive effect only seen in one species and upper temperatures being lethal if held constant for a month, temperature appears to be the greatest threat to survival. What is happening to these sea slugs in the GOM is likely happening to other snails and marine invertebrates throughout the ocean. Knowing how organisms will react to the projected changes can help inform future policies and practices.

Continue reading ‘The effects of climate change on the heart rates & growth of sea slugs in the Gulf of Maine’

Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)

Highlights

  • Marine fishes will be exposed to multiple stressors under climate change.
  • Hypoxia and high pCO2 are both expected to cause shifts in energy metabolism.
  • No signs of energetic shifts were observed at transcriptomic or enzymatic levels.
  • Multiple stressor transcriptomes are not predictable based on responses to single stressors.
  • Blue rockfish may be relatively tolerant to intensified upwelling conditions.

Abstract

Global climate change is predicted to increase the co-occurrence of high pCO2 and hypoxia in upwelling zones worldwide. Yet, few studies have examined the effects of these stressors on economically and ecologically important fishes. Here, we investigated short-term responses of juvenile blue rockfish (Sebastes mystinus) to independent and combined high pCO2 and hypoxia at the molecular level, using changes in gene expression and metabolic enzymatic activity to investigate potential shifts in energy metabolism. Fish were experimentally exposed to conditions associated with intensified upwelling under climate change: high pCO2 (1200 μatm, pH~7.6), hypoxia (4.0 mg O2/L), and a combined high pCO2/hypoxia treatment for 12 h, 24 h or two weeks. Muscle transcriptome profiles varied significantly among the three treatments, with limited overlap among genes responsive to both the single and combined stressors. Under elevated pCO2, blue rockfish increased expression of genes encoding proteins involved in the electron transport chain and muscle contraction. Under hypoxia, blue rockfish up-regulated genes involved in oxygen and ion transport and down-regulated transcriptional machinery. Under combined high pCO2 and hypoxia, blue rockfish induced a unique set of ionoregulatory and hypoxia-responsive genes not expressed under the single stressors. Thus, high pCO2 and hypoxia exposure appears to induce a non-additive transcriptomic response that cannot be predicted from single stressor exposures alone, further highlighting the need for multiple stressor studies at the molecular level. Overall, lack of a major shift in cellular energetics indicates that blue rockfish may be relatively resistant to intensified upwelling conditions in the short term.

Continue reading ‘Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)’

Changes in the metabolic potential of the sponge microbiome under ocean acidification

Anthropogenic CO2 emissions are causing ocean acidification, which can affect the physiology of marine organisms. Here we assess the possible effects of ocean acidification on the metabolic potential of sponge symbionts, inferred by metagenomic analyses of the microbiomes of two sponge species sampled at a shallow volcanic CO2 seep and a nearby control reef. When comparing microbial functions between the seep and control sites, the microbiome of the sponge Stylissa flabelliformis (which is more abundant at the control site) exhibits at the seep reduced potential for uptake of exogenous carbohydrates and amino acids, and for degradation of host-derived creatine, creatinine and taurine. The microbiome of Coelocarteria singaporensis (which is more abundant at the seep) exhibits reduced potential for carbohydrate import at the seep, but greater capacity for archaeal carbon fixation via the 3-hydroxypropionate/4-hydroxybutyrate pathway, as well as archaeal and bacterial urea production and ammonia assimilation from arginine and creatine catabolism. Together these metabolic features might contribute to enhanced tolerance of the sponge symbionts, and possibly their host, to ocean acidification.

Continue reading ‘Changes in the metabolic potential of the sponge microbiome under ocean acidification’

Variation in the effects of ocean acidification on shell growth and strength in two intertidal gastropods

Many marine organisms rely on calcified hard parts to resist predation, and ocean acidification (OA) affects calcification negatively. However, calcification-related consequences may manifest in variable and/or cryptic ways across species. For example, shell strength is a primary defense for resisting shell-crushing predation, yet the consequences of OA on such biomechanical properties cannot be assessed visually. We exposed 2 species of intertidal gastropods common to the west coast of North America (the black turban snail Tegula funebralis and the striped dogwhelk Nucella ostrina) to OA (pH decreased by ~0.5 units) and predation cues for 6 mo, then measured both shell growth and strength. Shell growth in T. funebralis was significantly depressed under OA and in the presence of predation cues (declines of 83 and 63%, respectively). Shells produced by OA-exposed T. funebralis were also 50% weaker. In contrast, shell growth of N. ostrina was unaffected by OA, yet its shells were still 10% weaker. These findings highlight the potential for both different and easily overlooked responses of organisms to seawater acidification. Moreover, such results raise the possibility of ensuing shifts in consumption rates and rankings of prey items by shell-crushing predators, leading to shifts in the balance of species interactions in temperate shoreline communities.

Continue reading ‘Variation in the effects of ocean acidification on shell growth and strength in two intertidal gastropods’

Ocean acidification reduces net calcification and wound healing in the tropical crustose coralline alga, Porolithon onkodes (Corallinales, Rhodophyta)

Highlights

  • Wounding did not affect net calcification or tissue mortality in Porolithon onkodes.
  • In contrast, elevated pCO2 reduced net calcification and living tissue.
  • Elevated pCO2 also reduced tissue regeneration within wounds.
  • Reduced wound healing under elevated pCO2 could affect the ecology of coralline algae.

Abstract

Reef dwelling algae employ a variety of physical and chemical defenses against herbivory, and the response to wounding is extremely important in algal communities. Wound healing mechanisms in crustose coralline algae (CCA) are related to skeletal growth and net calcification rate. Ocean acidification (OA) is known to affect rates of net calcification in a number of calcifying organisms, including CCA. Reduced rates of net calcification in CCA are likely to alter wound healing, and thus affect the consequences of herbivore-CCA interactions on coral reefs. The response of the tropical CCA Porolithon onkodes to OA and artificial wounding was quantified in a 51-day laboratory experiment. Eight artificially wounded (cut to a mean depth of 182 μm) and eight non-wounded samples of P. onkodes were randomly placed into each of four treatments (n = 64 samples total). Each treatment was maintained at a different pCO2 level representative of either ambient conditions or end-of-the-century, predicted conditions (IPCC, 2014); 429.31 ± 20.84 (ambient), 636.54 ± 27.29 (RCP4.5), 827.33 ± 38.51 (RCP6.0), and 1179.39 ± 88.85 μatm (RCP8.5; mean ± standard error). Elevated pCO2 significantly reduced rates of net calcification in both wounded and non-wounded samples of P. onkodes (slopes = −6.4 × 10−4 and −5.5 × 10−4 mg cm−2 d−1 per μatm pCO2, respectively over 51 days). There also was a significant reduction in the rate of vertical regeneration of thallus tissue within the wounds as pCO2 increased (slope = −1.5 × 10−3 μm d−1 per μatm pCO2 over 51 days). This study provides evidence that elevated pCO2 could reduce the ability of this important alga to recover from wounding. Because wounding by herbivores plays an important role in determining CCA community structure, we propose reduced wound healing as a mechanism by which OA might affect the structure and functional roles of CCA communities on coral reefs.

Continue reading ‘Ocean acidification reduces net calcification and wound healing in the tropical crustose coralline alga, Porolithon onkodes (Corallinales, Rhodophyta)’

Combined effects of ocean acidification and temperature on larval and juvenile growth, development and swimming performance of European sea bass (Dicentrarchus labrax)

Ocean acidification and ocean warming (OAW) are simultaneously occurring and could pose ecological challenges to marine life, particularly early life stages of fish that, although they are internal calcifiers, may have poorly developed acid-base regulation. This study assessed the effect of projected OAW on key fitness traits (growth, development and swimming ability) in European sea bass (Dicentrarchus labrax) larvae and juveniles. Starting at 2 days post-hatch (dph), larvae were exposed to one of three levels of PCO2 (650, 1150, 1700 μatm; pH 8.0, 7.8, 7.6) at either a cold (15°C) or warm (20°C) temperature. Growth rate, development stage and critical swimming speed (Ucrit) were repeatedly measured as sea bass grew from 0.6 to ~10.0 (cold) or ~14.0 (warm) cm body length. Exposure to different levels of PCO2 had no significant effect on growth, development or Ucrit of larvae and juveniles. At the warmer temperature, larvae displayed faster growth and deeper bodies. Notochord flexion occurred at 0.8 and 1.2 cm and metamorphosis was completed at an age of ~45 and ~60 days post-hatch for sea bass in the warm and cold treatments, respectively. Swimming performance increased rapidly with larval development but better swimmers were observed in the cold treatment, reflecting a potential trade-off between fast grow and swimming ability. A comparison of the results of this and other studies on marine fish indicates that the effects of OAW on the growth, development and swimming ability of early life stages are species-specific and that generalizing the impacts of climate-driven warming or ocean acidification is not warranted.

Continue reading ‘Combined effects of ocean acidification and temperature on larval and juvenile growth, development and swimming performance of European sea bass (Dicentrarchus labrax)’

Flow-driven micro-scale pH variability affects the physiology of corals and coralline algae under ocean acidification

Natural variability in pH in the diffusive boundary layer (DBL), the discrete layer of seawater between bulk seawater and the outer surface of organisms, could be an important factor determining the response of corals and coralline algae to ocean acidification (OA). Here, two corals with different morphologies and one coralline alga were maintained under two different regimes of flow velocities, pH, and light intensities in a 12 flumes experimental system for a period of 27 weeks. We used a combination of geochemical proxies, physiological and micro-probe measurements to assess how these treatments affected the conditions in the DBL and the response of organisms to OA. Overall, low flow velocity did not ameliorate the negative effect of low pH and therefore did not provide a refugia from OA. Flow velocity had species-specific effects with positive effects on calcification for two species. pH in the calcifying fluid (pHcf) was reduced by low flow in both corals at low light only. pHcf was significantly impacted by pH in the DBL for the two species capable of significantly modifying pH in the DBL. The dissolved inorganic carbon in the calcifying fluid (DICcf) was highest under low pH for the corals and low flow for the coralline, while the saturation state in the calcifying fluid and its proxy (FWHM) were generally not affected by the treatments. This study therefore demonstrates that the effects of OA will manifest most severely in a combination of lower light and lower flow habitats for sub-tropical coralline algae. These effects will also be greatest in lower flow habitats for some corals. Together with existing literature, these findings reinforce that the effects of OA are highly context dependent, and will differ greatly between habitats, and depending on species composition.

Continue reading ‘Flow-driven micro-scale pH variability affects the physiology of corals and coralline algae under ocean acidification’


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Ocean acidification in the IPCC AR5 WG II

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