Posts Tagged 'otherprocess'

Impacts of Zn and Cu enrichment under ocean acidification scenario on a phytoplankton community from tropical upwelling system

Highlights

• Phytoplankton showed higher resilience to increasing CO2.

• Few centric diatoms showed positive response to increasing CO2 supply.

• Addition of Zn under increasing CO2 inhibited cell division, but not biomass.

• The combined effects of increasing CO2 and Cu addition was insignificant on growth.

• Cu addition at high CO2 level promoted toxigenic pennate diatom growth.

Abstract

Increasing dissolution of CO2 in the surface ocean is rapidly decreasing its pH and changing carbon chemistry which is further affecting marine biota in several ways. Phytoplankton response studies under the combination of elevated CO2 and trace metals are rare. We have conducted two consecutive onboard incubation experiments (R. V. Sindhu Sadhana; August 2017) in the eastern Arabian Sea (SW coast of India) during an upwelling event. A nutrient enriched diatom bloom was initiated onboard and grown under ambient (≈400 μatm, A-CO2) and high CO2 levels (≈1000 μatm; H–CO2) with different zinc (Zn; 1 nM) and copper (Cu) concentrations (1 nM, 2 nM and 8 nM). Phytoplankton community composition and the dominant genera were different during these two experiments. CO2 enrichment alone did not show any significant growth stimulating impact on the experimental community except enhanced cell density in the first experiment. Addition of Zn at A-CO2 level revealed no noticeable responses; whereas, the same treatment under H–CO2 level significantly reduced cell number. Considerably high protein content under H–CO2+Zn treatment was possibly counteracting Zn toxicity which also caused slower growth rate. Cu addition did not show any noticeable impact on growth and biomass production except increased protein content as well as decreased carbohydrate: protein ratio. This can be attributed to relatively higher protein synthesis than carbohydrate to alleviate oxidative stress generated by Cu. The centric diatom Chaetoceros and toxin producing pennate diatom Pseudo-nitzschias howed no significant response to either CO2 or Zn enrichment. Large centric diatom Leptocylindrus and Skeletonema responded positively to Zn addition in both CO2 levels. The former species showed the most sensitive response at the highest Cu and H–CO2 treatment; whereas, the pennate diatoms Nitzschia and Pseudo-nitzschia (toxigenic diatom) showed higher resilience under elevated CO2 and Cu levels. This observation indicated that in future ocean, increasing CO2 concentrations and trace metal pollution may potentially alter phytoplankton community structure and may facilitate toxigenic diatom bloom in the coastal waters.

Continue reading ‘Impacts of Zn and Cu enrichment under ocean acidification scenario on a phytoplankton community from tropical upwelling system’

Clam feeding plasticity reduces herbivore vulnerability to ocean warming and acidification

Ocean warming and acidification affect species populations, but how interactions within communities are affected and how this translates into ecosystem functioning and resilience remain poorly understood. Here we demonstrate that experimental ocean warming and acidification significantly alters the interaction network among porewater nutrients, primary producers, herbivores and burrowing invertebrates in a seafloor sediment community, and is linked to behavioural plasticity in the clam Scrobicularia plana. Warming and acidification induced a shift in the clam’s feeding mode from predominantly suspension feeding under ambient conditions to deposit feeding with cascading effects on nutrient supply to primary producers. Surface-dwelling invertebrates were more tolerant to warming and acidification in the presence of S. plana, most probably due to the stimulatory effect of the clam on their microalgal food resources. This study demonstrates that predictions of population resilience to climate change require consideration of non-lethal effects such as behavioural changes of key species.

Continue reading ‘Clam feeding plasticity reduces herbivore vulnerability to ocean warming and acidification’

A meta-analysis of microcosm experiments shows that dimethyl sulfide (DMS) production in polar waters is insensitive to ocean acidification

Emissions of dimethylsulfide (DMS) from the polar oceans play a key role in atmospheric processes and climate. Therefore, it is important to increase our understanding of how DMS production in these regions may respond to climate change. The polar oceans are particularly vulnerable to ocean acidification (OA). However, our understanding of the polar DMS response is limited to two studies conducted in Arctic waters, where in both cases DMS concentrations decreased with increasing acidity. Here, we report on our findings from seven summertime shipboard microcosm experiments undertaken in a variety of locations in the Arctic Ocean and Southern Ocean. These experiments reveal no significant effects of short-term OA on the net production of DMS by planktonic communities. This is in contrast to similar experiments from temperate north-western European shelf waters where surface ocean communities responded to OA with significant increases in dissolved DMS concentrations. A meta-analysis of the findings from both temperate and polar waters (n=18 experiments) reveals clear regional differences in the DMS response to OA. Based on our findings, we hypothesize that the differences in DMS response between temperate and polar waters reflect the natural variability in carbonate chemistry to which the respective communities of each region may already be adapted. If so, future temperate oceans could be more sensitive to OA, resulting in an increase in DMS emissions to the atmosphere, whilst perhaps surprisingly DMS emissions from the polar oceans may remain relatively unchanged. By demonstrating that DMS emissions from geographically distinct regions may vary in their response to OA, our results may facilitate a better understanding of Earth’s future climate. Our study suggests that the way in which processes that generate DMS respond to OA may be regionally distinct, and this should be taken into account in predicting future DMS emissions and their influence on Earth’s climate.

Continue reading ‘A meta-analysis of microcosm experiments shows that dimethyl sulfide (DMS) production in polar waters is insensitive to ocean acidification’

Aragonite pteropod abundance and preservation records from the Maldives, equatorial Indian Ocean: inferences on past oceanic carbonate saturation and dissolution events

Highlights

• 1.2 Myr record of pteropod abundance/preservation variations from the Maldives

• Periods of enhanced ventilation during MIS 8, 3, 2 and MIS 14-13, 6-5 transitions

• MBDI marked by very poor preservation of pteropods during MIS 13 to 11

• Seawater carbonate chemistry plays a role in shell calcification.

• Glacial periods, MIS 16, 14, 6, 4, 2 are marked by larger and pristine shells.

Abstract

During the International Ocean Discovery Program (IODP) Expedition 359, a long continuous carbonate-rich sequence was recovered from the Inner Sea of Maldives. We investigated pteropod proxies (absolute abundance of pteropods species, total pteropods, epipelagic to mesopelagic ratio, fragmentation ratio, Limacina Dissolution Index (LDX), mean shell size variations of L. inflata) from Sites U1467 (water depth: 487 m) and U1468 (water depth: 521 m) to understand both surface and sub-surface paleoceanographic changes in the equatorial Indian Ocean and to improve our understanding of the factors responsible for pteropod preservation on longer timescales. A total of 15 species of pteropods were identified, and their downcore variations were documented from the core top to 707.49 mbsf in U1467 and from 447.4 to 846.92 mbsf in U1468. At the Site U1467, pteropod shells show high abundances/preservation up to a depth of 45 mbsf (~1.2 Ma), which is consistent with the presence of aragonite content in sediments (with the top 50 m bearing high aragonite content). Beyond 45 mbsf, only fragmented pteropod shells were seen down to 50 mbsf (corresponding to 1.5 Ma) followed by a total absence of pteropod shells and fragments from 50 mbsf (~1.5 Ma) to the end of the core at 846.92 mbsf (~24 Ma). A decrease in the SO42ˉconcentration and alkalinity in the interstitial fluid geochemistry is seen at these depths. The presence of dolomite content below 50 mbsf also indicates the alteration of aragonite into dolomite. Analyses of the carbonate preservation proxies reveal that the pteropods exhibit considerable fluctuation in abundance/preservation during the last 1.2 Myr. A good to moderate preservation (LDX: 2 to 3) is seen which correlates well with the fragmentation ratio but with an inverse relation with calcification rate. The proxies for in-life pteropod shell dissolution (average size of L. inflata and LDX) indicate that glacial periods (MIS 16, 14, 6, 4 and 2) have shown no signs of dissolution pointing better calcification under aragonite-saturated water column which is in good correlation with reduced atmospheric CO₂ concentration. Epipelagic/mesopelagic ratio indicates that the water column exhibited enhanced ventilation and mixing during glacial to interglacial periods, but intervals of intense stratification, a sign of poor ventilation or weakened circulation, was prevalent beyond MIS 14. The longest interval of poorest preservation was marked during MIS 11 and 13, which corresponds to the ‘Mid-Brunhes Dissolution Interval (MBDI).’ On a longer time scale, the abundances/preservation of pteropods in the Maldives seems to be controlled by changes in the seawater chemistry associated with monsoon productivity, water column ventilation, and atmospheric CO2 concentration.

Continue reading ‘Aragonite pteropod abundance and preservation records from the Maldives, equatorial Indian Ocean: inferences on past oceanic carbonate saturation and dissolution events’

Experimental acidification increases susceptibility of Mercenaria mercenaria to infection by Vibrio species

Highlights

• Clams in high pCO2/low pH were more susceptible to infection by pathogenic Vibrios.

• Growth and abundance of Vibrio spp. were greater under high pCO2/low pH.

• Clams reared under high pCO2/low pH seemed to have a broad tolerance range for pH.

• Long-term effect of acidification and susceptibility to vibriosis is understudied.

Abstract

Ocean acidification alters seawater carbonate chemistry, which can have detrimental impacts for calcifying organisms such as bivalves. This study investigated the physiological cost of resilience to acidification in Mercenaria mercenaria, with a focus on overall immune performance following exposure to Vibrio spp. Larval and juvenile clams reared in seawater with high pCO2 (∼1200 ppm) displayed an enhanced susceptibility to bacterial pathogens. Higher susceptibility to infection in clams grown under acidified conditions was derived from a lower immunity to infection more so than an increase in growth of bacteria under high pCO2. A reciprocal transplant of juvenile clams demonstrated the highest mortality amongst animals transplanted from low pCO2/high pH to high pCO2/low pH conditions and then exposed to bacterial pathogens. Collectively, these results suggest that increased pCO2 will result in immunocompromised larvae and juveniles, which could have complex and pernicious effects on hard clam populations.

Continue reading ‘Experimental acidification increases susceptibility of Mercenaria mercenaria to infection by Vibrio species’

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.

Continue reading ‘The effects of aragonite saturation state on hatchery-reared larvae of the greenshell mussel Perna canaliculus’

Standing genetic variation fuels rapid adaptation to ocean acidification

Global climate change has intensified the need to assess the capacity for natural populations to adapt to abrupt shifts in the environment. Reductions in seawater pH constitute a conspicuous global change stressor that is affecting marine ecosystems globally. Here, we quantify the phenotypic and genetic modifications associated with rapid adaptation to reduced seawater pH in the Mediterranean mussel, Mytilus galloprovincialis. We reared a genetically diverse larval population in two pH treatments (pHT 8.1 and 7.4) and tracked changes in the shell-size distribution and genetic variation through settlement. Additionally, we identified differences in the signatures of selection on shell growth in each pH environment. Both phenotypic and genetic data show that standing variation can facilitate adaptation to declines in seawater pH. This work provides insight into the processes underpinning rapid evolution, and demonstrates the importance of maintaining variation within natural populations to bolster species’ adaptive capacity as global change progresses.

Continue reading ‘Standing genetic variation fuels rapid adaptation to ocean acidification’


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Ocean acidification in the IPCC AR5 WG II

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