Posts Tagged 'biological response'



Declines over the last two decades of five intertidal invertebrate species in the western North Atlantic

Climate change has already altered the environmental conditions of the world’s oceans. Here we report declines in gastropod abundances and recruitment of mussels (Mytilus edulis) and barnacles (Semibalanus balanoides) over the last two decades that are correlated with changes in temperature and ocean conditions. Mussel recruitment is declining by 15.7% per year, barnacle recruitment by 5.0% per year, and abundances of three common gastropods are declining by an average of 3.1% per year (Testudinalia testudinalisLittorina littorea, and Nucella lapillus). The declines in mussels and the common periwinkle (L. littorea) are correlated with warming sea temperatures and the declines in T. testudinalis and N. lapillus are correlated with aragonite saturation state, which affects rates of shell calcification. These species are common on shores throughout the North Atlantic and their loss is likely to lead to simplification of an important food web on rocky shores.

Continue reading ‘Declines over the last two decades of five intertidal invertebrate species in the western North Atlantic’

Short-term effects of increased CO2, nitrate and temperature on photosynthetic activity in Ulva rigida (Chlorophyta) estimated by different pulse amplitude modulated fluorometers and oxygen evolution

Short-term effects of pCO2 (700 – 380 ppm; HC-LC) and nitrate content (50-5 βM; HN-LC) on photosynthesis, estimated by different pulse amplitude modulated (PAMs) fluorometers and by oxygen evolution, were investigated in Ulva rigida (Chlorophyta) under solar radiation (ex-situ) and in the laboratory under artificial light (in-situ). After 6-days of incubation at ambient temperature (AT), algae were subjected to a 4 oC-temperature increase (AT+4oC) for 3 d. Both in-situ and ex-situ, maximal electron transport rate (ETRmax) and in situ gross photosynthesis (GP) measured by O2 evolution presented the highest values under HCHN, and the lowest under HCLN, across all measuring systems. Maximal quantum yield (Fv/Fm), and ETRmax of PSII (ETR(II)max) and of PSI (ETR(I)max), decreased under HCLN under AT+4°C. Ex situ ETR was higher than in situ ETR. At noon, Fv/Fm decreased (indicating photoinhibition), whereas ETR(II)max and maximal non-photochemical quenching (NPQmax) increased. ETR(II)max decreased under AT+4oC in contrast to Fv/Fm, photosynthetic efficiency (αETR) and saturated irradiance (EK). Thus, U. rigida exhibited a decrease in photosynthetic production under acidification, LN levels and AT+4oC. These results emphasize the importance of studying the interactive effects between environmental parameters using in-situ vs. ex-situ conditions when aiming to evaluate the impact of global change on marine macroalgae.

Continue reading ‘Short-term effects of increased CO2, nitrate and temperature on photosynthetic activity in Ulva rigida (Chlorophyta) estimated by different pulse amplitude modulated fluorometers and oxygen evolution’

Diel vertical migration into anoxic and high-pCO2 waters: acoustic and net-based krill observations in the Humboldt Current

A select group of marine organisms can enter the Oxygen Minimum Zones (OMZs) and even anoxic waters, while performing diel vertical migration (DVM). DVM of the euphausiid Euphausia eximia off northern Chile in the spring of 2015 was documented based on acoustic measurements using an echo sounder along with net samplings. Dissolved oxygen (DO) concentrations were obtained using a vertical profiler, and water samples were collected to obtain in situ nitrite (NO2) concentrations as well as pHT, total alkalinity (AT), and therefore carbon dioxide partial pressure (pCO2) was estimated. Krill were found to migrate up to the surface (0–50 m) during the night and returned to ca. 200–300 m depth during the day, spending between 11 and 14 h at these layers. At the surface, DO and NO2 concentrations were 208 and 0.14 μM respectively, while pHT was 8.04 and 405 μatm pCO2. In contrast, at the deeper layers (200–300 m), DO and NO2 were < 3 and 6.3 μM respectively, with pHT 7.53 and 1490 μatm pCO2. The pHT and high pCO2 values at depths represent the conditions predicted for open ocean waters in a worst-case global warming scenario by 2150. The acoustic scatter suggested that > 60% of the krill swarms enter the OMZ and anoxic waters during the daytime. These frequent migrations suggest that krill can tolerate such extreme conditions associated with anoxic and high-pCO2 waters. The inferences drawn from the observation of these migrations might have strong implications for the current oceanic carbon pump models, highlighting the need for understanding the molecular and physiological adaptations allowing these migrations.

Continue reading ‘Diel vertical migration into anoxic and high-pCO2 waters: acoustic and net-based krill observations in the Humboldt Current’

Ocean acidification impacts on zooplankton

Rising atmospheric CO2 alters the ocean biochemistry in the process known as ocean acidification (OA). It influences biodiversity at different levels, including zooplankton, which is a key component of aquatic communities and plays a pivotal role in the structure and functioning of marine planktonic food webs as a major link between pelagic primary producers and planktivorous. The effect of OA on the fitness of individual zooplanktonic species has been reported by many studies mostly developed under laboratory conditions. In this context, this chapter reviews the OA effects on zooplankton and describes the potential of natural shallow-water CO2 vents as in situ laboratories. The impact on zooplankton assemblages is shown from a study in the North Atlantic (Azores islands) and the suitability of this area for future studies on marine organisms and ecosystems. Sites with naturally elevated CO2 conditions are described, including which variables and limitations must be considered. Results shown are highly relevant to improve our predictions of the responses of zooplankton to climate change stressors including OA. Future studies including long-term multigenerational exposure to multiple stressors (e.g. increased pCO2 and food shortage) are a priority to understand the adaptation capacity of common species and how the zooplankton communities will shift.

Continue reading ‘Ocean acidification impacts on zooplankton’

Early development and metabolic rate of the sea louse Caligus rogercresseyi under different scenarios of temperature and pCO2

Highlights

  • The temperature has a significant effect on the hatching time of C. royercresseyi.

  • Combination of pCO2 and temperature has a significant effect on survival in C. rogercresseyi.

  • The combination of pCO2 and temperature had no impact on the size of nauplius I, nauplius II and copepodid stage.

  • Only the temperature has a significant effect on oxygen consumption rate of C. royercresseyi.

Abstract

Anthropogenic CO2 emissions have led to ocean acidification and a rise in the temperature. The present study evaluates the effects of temperature (10, 15 and 20 °C) and pCO2 (400 and 1200 μatm) on the early development and oxygen consumption rate (OCR) of the sea louse Caligus rogercresseyi. Only temperature has an effect on the hatching and development times of nauplius I. But both factors affected the development time of nauplius II (<temperature = longer development time). Copepodid survival time was also affected by temperature and pCO2, at 10 °C and 400 μatm, survival was 30 and 44% longer than at 15 and 20 °C. OCRs were impacted by temperature but not by pCO2. In all treatments, OCR was lower for nauplius II than for the copepodid. Our results show the need to further evaluate the effects of a combination of environmental drivers on the performance of C. rogercresseyi, in a changing and uncertain future.

Continue reading ‘Early development and metabolic rate of the sea louse Caligus rogercresseyi under different scenarios of temperature and pCO2’

Effects of temperature and pH on the egg production and hatching success of a common Korean copepod

The recent accelerated ocean acidification and global warming caused by increased atmospheric carbon dioxide may have an impact on the physiology and ecology of marine animals. This study was conducted to determine the egg production rate (EPR) and hatching success (EHS) of Acartia ohtsukai in response to the combined effects of an increase in temperature and a lower pH. Acartiaohtsukai with fresh surface seawater were collected in the northwestern Yeoja Bay of Korea in September 2017. The temperature and pH conditions applied included two different pH levels (representing the present: 7.9 and the future: 7.6) and three temperature values (26 °C, 28 °C, and 30 °C). In the pH 7.9, EPR significantly increased with increased temperature, but in pH 7.6, it significantly decreased as the temperature increased. EHS was lower in pH 7.6 than in pH 7.9. These results suggest that changes in the marine environment due to global warming and ocean acidification may affect Acartia populations and cause overall fluctuations in copepods of the genus Acartia.

Continue reading ‘Effects of temperature and pH on the egg production and hatching success of a common Korean copepod’

Changing carbon-to-nitrogen ratios of organic-matter export under ocean acidification

Ocean acidification (OA) will affect marine biotas from the organism to the ecosystem level. Yet, the consequences for the biological carbon pump and thereby the oceanic sink for atmospheric CO2 are still unclear. Here we show that OA considerably alters the C/N ratio of organic-matter export (C/Nexport), a key factor determining efficiency of the biological pump. By synthesizing sediment-trap data from in situ mesocosm studies in different marine biomes, we find distinct but highly variable impacts of OA on C/Nexport, reaching up to a 20% increase/decrease under partial pressure of CO2 (pCO2) conditions projected for 2100. These changes are driven by pCO2 effects on a variety of plankton taxa and corresponding shifts in food-web structure. Notably, our findings suggest a pivotal role of heterotrophic processes in controlling the response of C/Nexport to OA, thus contradicting the paradigm of primary producers as the principal driver of biogeochemical responses to ocean change.

Continue reading ‘Changing carbon-to-nitrogen ratios of organic-matter export under ocean acidification’

Lack of oxidative damage on temperate juvenile catsharks after a long-term ocean acidification exposure

Ocean acidification is a consequence of chemical changes driven mainly by a continuous uptake of carbon dioxide, resulting in pH decrease. This phenomenon represents an additional threat to marine life, with expected effects ranging from changes in behavioral responses and calcification rates to the potential promotion of oxidative stress. To unravel the impacts of ocean acidification on the antioxidant system of sharks, we performed a long-term exposure (9 months, since early embryogenesis) to high CO2 conditions (pCO2 ~ 900 μatm) on a temperate shark (Scyliorhinus canicula). The following biomarkers were measured: enzymatic antioxidant defense (superoxide dismutase, catalase and glutathione peroxidase), protein repair and removal (heat shock proteins and ubiquitin), and oxidative damage on lipids (malondialdehyde) and DNA (8-hydroxy-2′-deoxyguanosine). Changes in the antioxidant enzyme defense were restricted to an increase in catalase activity in the muscle, an enzyme that plays a major role in oxidative stress mitigation. On the other hand, no evidence of oxidative damage was found, indicating that the observed increase in catalase activity may be enough to neutralize the effects of potentially higher reactive oxygen species. These results further indicate that these sharks’ antioxidant system can successfully cope with the levels of carbon dioxide projected for the end of the century. Nonetheless, the interaction between ocean acidification and the rise in temperature expected to occur in a near future may disturb their antioxidant capacity, requiring further investigation.

Continue reading ‘Lack of oxidative damage on temperate juvenile catsharks after a long-term ocean acidification exposure’

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

Highlights

  • It is possible to keep adult COTS in modified conditions for several months with minimal losses.

  • The natural peak of reproduction for COTS in New Caledonia is around the end of the calendar year.

  • A +2 °C warming exposure of 3–4 months have detrimental effects on quality and quantity of COTS eggs along with fertilisation success.

  • During sub-optimal spawning season, COTS fertilisation success drops by 3-fold for animals exposed to elevated temperature.

Abstract

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.

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

A new “business as usual” climate scenario and the stress response of the Caribbean coral Montastraea cavernosa

The climate change related decline of shallow (<30 m) coral reef ecosystems has been driven by the mortality of scleractinian corals caused primarily by the phenomenon known as “coral bleaching.” But despite pervasive phase shifts and macroalgal dominance on many coral reefs, some coral species have persisted. One of those species is Montastraea cavernosa which has been categorized as resilient to a range of biotic and abiotic stressors. In order to understand the mechanism(s) of resistance in this coral, we present the results of a thermal stress and ocean acidification (OA) experiment on M. cavernosa, both its brown and orange color morphs, representing conditions predicted by the Representative Concentration Pathway (RCP) 6.0 scenario in the year 2100. We assessed the community response of the prokaryotic microbiome, the photophysiological response of the endosymbiotic Symbiodiniaceae and the molecular responses of critical pathways in the host by quantifying transcript abundances of genes encoding fluorescent proteins, heat shock proteins, antioxidant enzymes and regulators of apoptosis. After a 12 d acclimatization experiment, no visible bleaching was observed in any treatment, and the excitation pressure on photosystem II of the symbiotic Symbiodiniaceae showed no effects of the independent or interactive effects of thermal stress and OA, while only minor, but significant, changes in the prokaryotic microbiome were observed when exposed to RCP 6.0 predicted OA conditions. At the end of the experiment, the host heat shock protein 90 showed an increase in transcript abundance under the combined effects of thermal stress and OA compared to high temperatures alone, but these treatment groups were not significantly different from treatments under normal temperatures. While Bax, an activator of apoptosis, was significantly higher under thermal stress alone compared to control samples. Taken together, M. cavernosa, exhibits ecological stability over time and this may be based on its physiological persistence, resistance and resilience when experimentally exposed to the ecologically realistic RCP 6.0 climate model predictions.

Continue reading ‘A new “business as usual” climate scenario and the stress response of the Caribbean coral Montastraea cavernosa’


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