Posts Tagged 'growth'

Carbon and nitrogen accumulation and interspecific competition in two algae species, Pyropia haitanensis and Ulva lactuca, under ocean acidification conditions

If the atmospheric CO2 continues to increase as predicted, Pyropia haitanensis would experience the coupled effects of ocean acidification (OA) and interference from the epiphyte alga Ulva lactuca. In the current study, we evaluated the carbon (C) and nitrogen (N) accumulation in P. haitanensis and U. lactuca under OA conditions, as well as the interspecific competition between these two algae. We found that, under mono-culture conditions, OA significantly enhanced the growth of both P. haitanensis and U. lactuca and markedly increased the soluble carbohydrate (SC) content and C/N ratios in P. haitanensis, but reduced its soluble proteins (SP) content. In U. lactuca, OA reduced its SP content, but increased C/N ratios, while its SC content was not significantly affected. Under biculture conditions, the rapid growth of U. lactuca and its comparatively more efficient use of nutrients resulted in insufficient available N sources for P. haitanensis. Biculture with U. lactuca increased SC but declined SP content. This also resulted in some membrane injuries that were indicated by increased malondialdehyde (MDA) content and depressed growth in P. haitanensis. Biculture with U. lactuca was disadvantageous for carbon and nitrogen accumulation in P. haitanensis. The results demonstrated that under conditions of OA, the negative effects caused by the epiphyte U. lactuca were more pronounced. If the CO2 levels rise as predicted, Ulva algae would severely interfere with maricultivation of P. haitanensis.

Continue reading ‘Carbon and nitrogen accumulation and interspecific competition in two algae species, Pyropia haitanensis and Ulva lactuca, under ocean acidification conditions’

Direct and indirect effects of elevated CO2 are revealed through shifts in phytoplankton, copepod development, and fatty acid accumulation

Change in the nutritional quality of phytoplankton is a key mechanism through which ocean acidification can affect the function of marine ecosystems. Copepods play an important role transferring energy from phytoplankton to higher trophic levels, including fatty acids (FA)—essential macronutrients synthesized by primary producers that can limit zooplankton and fisheries production. We investigated the direct effects of pCO2 on phytoplankton and copepods in the laboratory, as well as the trophic transfer of effects of pCO2 on food quality. The marine cryptophyte Rhodomonas salina was cultured at 400, 800, and 1200 μatm pCO2 and fed to adult Acartia hudsonica acclimated to the same pCO2 levels. We examined changes in phytoplankton growth rate, cell size, carbon content, and FA content, and copepod FA content, grazing, respiration, egg production, hatching, and naupliar development. This single-factor experiment was repeated at 12°C and at 17°C. At 17°C, the FA content of R. salina responded non-linearly to elevated pCO2 with the greatest FA content at intermediate levels, which was mirrored in A. hudsonica; however, differences in ingestion rate indicate that copepods accumulated FA less efficiently at elevated pCO2. A. hudsonica nauplii developed faster at elevated pCO2 at 12°C in the absence of strong food quality effects, but not at 17°C when food quality varied among treatments. Our results demonstrate that changes to the nutritional quality of phytoplankton are not directly translated to their grazers, and that studies that include trophic links are key to unraveling how ocean acidification will drive changes in marine food webs.

Continue reading ‘Direct and indirect effects of elevated CO2 are revealed through shifts in phytoplankton, copepod development, and fatty acid accumulation’

Particulate inorganic to organic carbon production as a predictor for coccolithophorid sensitivity to ongoing ocean acidification

Ocean acidification (OA) can induce shifts in plankton community composition, with coccolithophores being mostly negatively impacted. This is likely to change particulate inorganic and organic carbon (PIC and POC, respectively) production, with impacts on the biological carbon pump. Hence, assessing and, most importantly, understanding species‐specific sensitivities of coccolithophores is paramount. In a multispecies comparison, spanning more than two orders of magnitude in terms of POC and PIC production rates, among Calcidiscus leptoporus, Coccolithus pelagicus subsp. braarudii, Emiliania huxleyi, Gephyrocapsa oceanica, and Scyphosphaera apsteinii, we found that cellular PIC : POC was a good predictor for a species’ OA sensitivity. This is likely related to the need for cellular pH homeostasis, which is challenged by the process of calcification producing protons internally, especially when seawater pH decreases in an OA scenario. With higher PIC : POC, species and strains being more sensitive to OA coccolithophores may shift toward less calcified varieties in the future.

Continue reading ‘Particulate inorganic to organic carbon production as a predictor for coccolithophorid sensitivity to ongoing ocean acidification’

Insensitivities of a subtropical productive coastal plankton community and trophic transfer to ocean acidification: results from a microcosm study

Highlights
• Lower apparent growth was observed under elevated CO2 of 1000 μatm.

• Primary production and trophic transfer were unaffected by high CO2.

• Fatty acid profiles of phyto-/zooplankton were unaffected by ocean acidification.

Abstract
Ocean acidification (OA) has potential to affect marine phytoplankton in ways that are partly understood, but there is less knowledge about how it may alter the coupling to secondary producers. We investigated the effects of OA on phytoplankton primary production, and its trophic transfer to zooplankton in a subtropical eutrophic water (Wuyuan Bay, China) under present day (400 μatm) and projected end-of-century (1000 μatm) pCO2 levels. Net primary production was unaffected, although OA did lead to small decreases in growth rates. OA had no measurable effect on micro-/mesozooplankton grazing rates. Elevated pCO2 had no effect on phytoplankton fatty acid (FA) concentrations during exponential phase, but saturated FAs increased relative to the control during declining phase. FA profiles of mesozooplankton were unaffected. Our findings show that short-term exposure of plankton communities in eutrophic subtropical waters to projected end-of-century OA conditions has little effect on primary productivity and trophic linkage to mesozooplankton.

Continue reading ‘Insensitivities of a subtropical productive coastal plankton community and trophic transfer to ocean acidification: results from a microcosm study’

Physiological and biochemical responses of Thalassiosira weissflogii (diatom) to seawater acidification and alkalization

Increasing atmospheric pCO2 leads to seawater acidification, which has attracted considerable attention due to its potential impact on the marine biological carbon pump and function of marine ecosystems. Alternatively, phytoplankton cells living in coastal waters might experience increased pH/decreased pCO2 (seawater alkalization) caused by metabolic activities of other photoautotrophs, or after microalgal blooms. Here we grew Thalassiosira weissflogii (diatom) at seven pCO2 levels, including habitat-related lowered levels (25, 50, 100, and 200 µatm) as well as present-day (400 µatm) and elevated (800 and 1600 µatm) levels. Effects of seawater acidification and alkalization on growth, photosynthesis, dark respiration, cell geometry, and biogenic silica content of T. weissflogii were investigated. Elevated pCO2 and associated seawater acidification had no detectable effects. However, the lowered pCO2 levels (25 ∼ 100 µatm), which might be experienced by coastal diatoms in post-bloom scenarios, significantly limited growth and photosynthesis of this species. In addition, seawater alkalization resulted in more silicified cells with higher dark respiration rates. Thus, a negative correlation of biogenic silica content and growth rate was evident over the pCO2 range tested here. Taken together, seawater alkalization, rather than acidification, could have stronger effects on the ballasting efficiency and carbon export of T. weissflogii.

Continue reading ‘Physiological and biochemical responses of Thalassiosira weissflogii (diatom) to seawater acidification and alkalization’

A comparison of species specific sensitivities to changing light and carbonate chemistry in calcifying marine phytoplankton

Coccolithophores are unicellular marine phytoplankton and important contributors to global carbon cycling. Most work on coccolithophore sensitivity to climate change has been on the small, abundant bloom-forming species Emiliania huxleyi and Gephyrocapsa oceanica. However, large coccolithophore species can be major contributors to coccolithophore community production even in low abundances. Here we fit an analytical equation, accounting for simultaneous changes in CO2 and light intensity, to rates of photosynthesis, calcification and growth in Scyphosphaera apsteinii. Comparison of responses to G. oceanica and E. huxleyi revealed S. apsteinii is a low-light adapted species and, in contrast, becomes more sensitive to changing environmental conditions when exposed to unfavourable CO2 or light. Additionally, all three species decreased their light requirement for optimal growth as CO2 levels increased. Our analysis suggests that this is driven by a drop in maximum rates and, in G. oceanica, increased substrate uptake efficiency. Increasing light intensity resulted in a higher proportion of muroliths (plate-shaped) to lopadoliths (vase shaped) and liths became richer in calcium carbonate as calcification rates increased. Light and CO2 driven changes in response sensitivity and maximum rates are likely to considerably alter coccolithophore community structure and productivity under future climate conditions.

Continue reading ‘A comparison of species specific sensitivities to changing light and carbonate chemistry in calcifying marine phytoplankton’

Elevated CO2 alters behavior, growth, and lipid composition of Pacific cod larvae

Highlights

• Ocean acidification has been shown to induce a range of effects on early life stages of commercially important marine fishes.

• Elevated CO2 levels strengthened behavioral phototaxis in larval Pacific cod.

• High CO2 reduced growth and energy storage during the first 2 weeks of life, but this effect was reversed by 5 weeks of age.

Abstract

High-latitude seas, which support a number of commercially important fisheries, are predicted to be most immediately impacted by ongoing ocean acidification (OA). Elevated CO2 levels have been shown to induce a range of impacts on the physiology and behavior of marine fish larvae. However, these responses have yet to be characterized for most fishery species, including Pacific cod (Gadus macrocephalus). Based on laboratory experiments, we present a multi-faceted analysis of the sensitivity of Pacific cod larvae to elevated CO2. Fish behavior in a horizontal light gradient was used to evaluate the sensitivity of behavioral phototaxis in 4–5 week old cod larvae. Fish at elevated CO2 levels (∼1500 and 2250 μatm) exhibited a stronger phototaxis (moved more quickly to regions of higher light levels) than fish at ambient CO2 levels (∼600 μatm). In an independent experiment, we examined the effects of elevated CO2 levels on growth of larval Pacific cod over the first 5 weeks of life under two different feeding treatments. Fish exposed to elevated CO2 levels (∼1700 μatm) were smaller and had lower lipid levels at 2 weeks of age than fish at low (ambient) CO2 levels (∼500 μatm). However, by 5 weeks of age, this effect had reversed: fish reared at elevated CO2 levels were slightly (but not significantly) larger and had higher total lipid levels and storage lipids than fish reared at low CO2. Fatty acid composition differed significantly between fish reared at high and low CO2 levels (p < 0.01) after 2 weeks of feeding, but this effect diminished by week 5. Effects of CO2 on FA composition of the larvae differed between the two diets, an effect possibly related more to dietary equilibrium and differential lipid class storage than a fundamental effect of CO2 on fatty acid metabolism. These experiments point to a stage-specific sensitivity of Pacific cod to the effects of OA. Further understanding of these effects will be required to predict the impacts on production of Pacific cod fisheries.

Continue reading ‘Elevated CO2 alters behavior, growth, and lipid composition of Pacific cod larvae’


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Ocean acidification in the IPCC AR5 WG II

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