Posts Tagged 'zooplankton'

Upwelling modulation of functional traits of a dominant planktonic grazer during “warm-acid” El Niño 2015 in a year-round upwelling area of Humboldt Current

Climate change is expected to exacerbate upwelling intensity and natural acidification in Eastern Boundaries Upwelling Systems (EBUS). Conducted between January-September 2015 in a nearshore site of the northern Humboldt Current System directly exposed to year-round upwelling episodes, this study was aimed at assessing the relationship between upwelling mediated pH-changes and functional traits of the numerically dominant planktonic copepod-grazer Acartia tonsa (Copepoda). Environmental temperature, salinity, oxygen, pH, alkalinity, chlorophyll-a (Chl), copepod adult size, egg production (EP), and egg size and growth were assessed through 28 random oceanographic surveys. Agglomerative clustering and multidimensional scaling identified three main di-similitude nodes within temporal variability of abiotic and biotic variables: A) “upwelling”, B) “non-upwelling”, and C) “warm-acid” conditions. Nodes A and B represented typical features within the upwelling phenology, characterized by the transition from low temperature, oxygen, pH and Chl during upwelling to higher levels during non-upwelling conditions. However, well-oxygenated, saline and “warm-acid” node C seemed to be atypical for local climatology, suggesting the occurrence of a low frequency oceanographic perturbation. Multivariate (LDA and ANCOVA) analyses revealed upwelling through temperature, oxygen and pH were the main factors affecting variations in adult size and EP, and highlighted growth rates were significantly lower under node C. Likely buffering upwelling pH-reductions, phytoplankton biomass maintained copepod reproduction despite prevailing low temperature, oxygen and pH levels in the upwelling setting. Helping to better explain why this species is among the most recurrent ones in these variable yet productive upwelling areas, current findings also provide opportune cues on plankton responses under warm-acid conditions, which are expected to occur in productive EBUS as a consequence of climate perturbations.

Continue reading ‘Upwelling modulation of functional traits of a dominant planktonic grazer during “warm-acid” El Niño 2015 in a year-round upwelling area of Humboldt Current’

Respuesta transgeneracional a la acidificación marina del copépodo Acartia Tonsa Dana, 1849 (in Spanish)

La acidificación oceánica producida por el aumento de la concentración de dióxido de carbono en el océano representa una amenaza para los ecosistemas marinos, porque provoca una disminución del pH y una alteración en la química del agua de mar. El copépodo calanoide marino Acartia tonsa Dana, 1849 es una especie ecológica y socioeconómicamente importante. Este trabajo se centra en cómo afecta el pH ácido al copépodo A. tonsa, determinando la tasa de supervivencia, reproducción y desarrollo a diferentes tratamientos de pH, e intenta averiguar si se produce una respuesta transgeneracional para contrarrestar los efectos de la acidificación oceánica.

Continue reading ‘Respuesta transgeneracional a la acidificación marina del copépodo Acartia Tonsa Dana, 1849 (in Spanish)’

El Niño-related thermal stress coupled with upwelling-related ocean acidification negatively impacts cellular to population-level responses in pteropods along the California Current System with implications for increased bioenergetic costs

Understanding the interactive effects of multiple stressors on pelagic mollusks associated with global climate change is especially important in highly productive coastal ecosystems of the upwelling regime, such as the California Current System (CCS). Due to temporal overlap between a marine heatwave, an El Niño event, and springtime intensification of the upwelling, pteropods of the CCS were exposed to co-occurring increased temperature, low Ωar and pH, and deoxygenation. The variability in the natural gradients during NOAA’s WCOA 2016 cruise provided a unique opportunity for synoptic study of chemical and biological interactions. We investigated the effects of in situ multiple drivers and their interactions across cellular, physiological, and population levels. Oxidative stress biomarkers were used to assess pteropods’ cellular status and antioxidant defenses. Low aragonite saturation state (Ωar) is associated with significant activation of oxidative stress biomarkers, as indicated by increased levels of lipid peroxidation (LPX), but the antioxidative activity defense might be insufficient against cellular stress. Thermal stress in combination with low Ωar additively increases the level of LPX toxicity, while food availability can mediate the negative effect. On the physiological level, we found synergistic interaction between low Ωar and deoxygenation and thermal stress (Ωar:T, O2:T). On the population level, temperature was the main driver of abundance distribution, with low Ωar being a strong driver of secondary importance. The additive effects of thermal stress and low Ωar on abundance suggest a negative effect of El Niño at the population level. Our study clearly demonstrates Ωar and temperature are master variables in explaining biological responses, cautioning the use of a single parameter in the statistical analyses. High quantities of polyunsaturated fatty acids are susceptible to oxidative stress because of LPX, resulting in the loss of lipid reserves and structural damage to cell membranes, a potential mechanism explaining extreme pteropod sensitivity to low Ωar. Accumulation of oxidative damage requires metabolic compensation, implying energetic trade-offs under combined thermal and low Ωar and pH stress. Oxidative stress biomarkers can be used as early-warning signal of multiple stressors on the cellular level, thereby providing important new insights into factors that set limits to species’ tolerance to in situ multiple drivers.

Continue reading ‘El Niño-related thermal stress coupled with upwelling-related ocean acidification negatively impacts cellular to population-level responses in pteropods along the California Current System with implications for increased bioenergetic costs’

Climate change effects on copepod physiology and trophic transfer

Increased anthropogenic carbon dioxide (CO2) emissions have led to an increasingly acidified ocean and higher average global sea surface temperatures. This alteration of abiotic conditions is directly affecting aquatic organisms through physiological stress and indirectly through reductions in trophic transfer efficiency. Less efficient trophic transfer at the base of the food web would reduce the overall energy available to support higher trophic levels and could be detrimental to the dependent ecosystem. Estuarine ecosystems are subject to harmful algal blooms (HABs). They are also characterized by low species diversity, which lowers ecosystem resilience to environmental perturbations. This results in a system where changes in phytoplankton and their consumers can dramatically impact the health of the local community. Increased temperature and pCO2 are predicted to change nutritional adequacy and/or toxicity of some HAB species and their copepod consumers. Interactions between Karlodinium veneficum, a HAB species present in the Delaware Inland Bays, and its consumer Acartia tonsa, a locally-dominant copepod, were used to assess direct changes to physiology and/or indirect changes to trophic transfer. Acartia tonsa, toxic prey K. veneficum, and non-toxic prey Storeatula major were grown in multi-generational laboratory cultures at both ambient conditions (25 °C/400 ppm pCO2) and those predicted for year 2100 (29 °C/ 1000 ppm pCO2). Physiological changes were assessed using grazing, respirometry, egg production, and egg hatching success. Grazing experiments indicated there was not a direct toxic effect of the prey on A. tonsa. Respiration rates did not change significantly at higher temperature and pCO2 values, indicating physiological compensation. Egg production did not significantly differ between treatments, but a significant reduction in egg hatching success was found when A. tonsa were fed exclusively K. veneficum. Significant reduction of egg production and hatching also occurred as a result of higher temperature and pCO2. Significant reductions in efficiency of carbon transfer from prey to consumer offspring were found when A. tonsa ingested K. veneficum, and when A. tonsa ingested S. major at elevated temperature and pCO2. In summary, A. tonsa acclimated to the elevated pCO2 and temperature conditions, but changes in resource partitioning led to a lowered transfer of carbon to their offspring. Ingestion of K. veneficum also led to a lowered trophic transfer efficiency, irrespective of temperature and pCO2 level. This indicates that both HABs and increased temperature and pCO2 from climate change have the potential to alter ecosystem dynamics by reducing trophic transfer efficiency at the base of the food chain.

Continue reading ‘Climate change effects on copepod physiology and trophic transfer’

Response of pelagic calcifiers (Foraminifera, Thecosomata) to ocean acidification during oligotrophic and simulated up-welling conditions in the subtropical North Atlantic off Gran Canaria

Planktonic Foraminifera and thecosome pteropods are major producers of calcite and aragonite in the ocean and play an important role for pelagic carbonate flux. The responses of planktonic foraminifers to ocean acidification (OA) are variable among the species tested and so far do not allow for reliable conclusion. Thecosome pteropods respond with reduced calcification and shell dissolution to OA and are considered at high risk especially at high latitudes. The present investigation was part of a large-scale in situ mesocosm experiment in the oligotrophic waters of the eastern subtropical North Atlantic. Over 62 days, we measured the abundance and vertical flux of pelagic foraminifers and thecosome pteropods as part of a natural plankton community over a range of OA scenarios. A bloom phase was initiated by the introduction of deep-water collected from approx. 650 m depth simulating a natural up-welling event. Foraminifers occurred throughout the entire experiment in both the water column and the sediment traps. Pteropods were present only in small numbers and disappeared after the first two weeks of the experiment. No significant CO2 related effects were observed for foraminifers, but cumulative sedimentary flux was reduced at the highest CO2 concentrations. This flux reduction was most likely accompanying an observed flux reduction of particulate organic matter (POM) so that less foraminifers were intercepted and transported downward.

Continue reading ‘Response of pelagic calcifiers (Foraminifera, Thecosomata) to ocean acidification during oligotrophic and simulated up-welling conditions in the subtropical North Atlantic off Gran Canaria’

Environmental controls on pteropod biogeography along the Western Antarctic Peninsula

Pteropods are abundant zooplankton in the Western Antarctic Peninsula (WAP) and important grazers of phytoplankton and prey for higher trophic levels. We analyzed long‐term (1993–2017) trends in summer (January–February) abundance of WAP pteropods in relation to environmental controls (sea ice, sea surface temperature, climate indices, phytoplankton biomass and productivity, and carbonate chemistry) and interspecies dynamics using general linear models. There was no overall directional trend in abundance of thecosomes, Limacina helicina antarctica and Clio pyramidata, throughout the entire WAP, although L. antarctica abundance increased in the slope region and C. pyramidata abundance increased in the South. High L. antarctica abundance was strongly tied to a negative Multivariate El Niño Southern Oscillation Index the previous year. C. pyramidata abundance was best explained by early sea ice retreat 1‐yr prior. Abundance of the gymnosome species, Clione antarctica and Spongiobranchaea australis, increased over the time series, particularly in the slope region. Gymnosome abundance was positively influenced by abundance of their prey, L. antarctica, during the same season, and late sea ice advance 2‐yr prior. These trends indicate a shorter ice season promotes longer periods of open water in spring/summer favoring all pteropod species. Weak relationships were found between pteropod abundance and carbonate chemistry, and no long‐term trend in carbonate parameters was detected. These factors indicate ocean acidification is not presently influencing WAP pteropod abundance. Pteropods are responsive to the considerable environmental variability on both temporal and spatial scales—key for predicting future effects of climate change on regional carbon cycling and plankton trophic interactions.

Continue reading ‘Environmental controls on pteropod biogeography along the Western Antarctic Peninsula’

Microzooplankton grazing responds to simulated ocean acidification indirectly through changes in prey cellular characteristics

Microzooplankton (MZP) grazing is a factor that regulates oceanic primary production and is a controlling mechanism for marine biogeochemical cycling. Despite the prominent ecological role of MZP, few studies have explored their responses to ocean acidification (OA). Studies to date generally indicate that MZP are affected indirectly by OA through changes in phytoplankton prey composition and biomass concentration. Here, we conducted a series of experiments testing whether OA-induced changes in cellular characteristics of individual prey species can cause changes in MZP grazing. Two tintinnid ciliates (Eutintinnus sp. and Schmidingerella sp.) and a heterotrophic dinoflagellate (Oxyrrhis marina) were offered phytoplankton prey (Emiliania huxleyi) cultured under 3 pCO2 concentrations. Using linear mixed effects models, we found that Eutintinnus sp. and O. marina exhibited a step-wise increase in ingestion rates on E. huxleyi cells cultured under elevated pCO2. Schmidingerella sp. ingestion showed a non-linear response, whereby cells cultured under high pCO2 were ingested at higher rates than cells from moderate pCO2. The percentages of all 3 MZP populations observed feeding were higher on E. huxleyi cells cultured under elevated pCO2, with Eutintinnus sp. showing a step-wise increase. We postulate that this response is caused by the observed increased coccosphere volume in E. huxleyi cells cultured under elevated pCO2. If changes in phytoplankton cell volume are widespread under OA, this could be an important mechanism by which MZP grazing behavior shifts and planktonic food web dynamics are altered in the future ocean.

Continue reading ‘Microzooplankton grazing responds to simulated ocean acidification indirectly through changes in prey cellular characteristics’

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Ocean acidification in the IPCC AR5 WG II

OUP book