20 research outputs found
Ocean acidification challenges copepod phenotypic plasticity
Ocean acidification is challenging phenotypic plasticity of
individuals and populations. Calanoid copepods (zooplankton) are shown to be
fairly plastic against altered pH conditions, and laboratory studies indicate
that transgenerational effects are one mechanism behind this plasticity. We
studied phenotypic plasticity of the copepod Acartia sp. in the
course of a pelagic, large-volume mesocosm study that was conducted to
investigate ecosystem and biogeochemical responses to ocean acidification. We
measured copepod egg production rate, egg-hatching success, adult female size
and adult female antioxidant capacity (ORAC) as a function of acidification
(fCO2 ∼ 365–1231 µatm) and as a function of
quantity and quality of their diet. We used an egg transplant experiment to
reveal whether transgenerational effects can alleviate the possible negative
effects of ocean acidification on offspring development. We found significant
negative effects of ocean acidification on adult female size. In addition, we
found signs of a possible threshold at high fCO2, above which adaptive
maternal effects cannot alleviate the negative effects of acidification on
egg-hatching and nauplii development. We did not find support for the
hypothesis that insufficient food quantity (total particulate carbon
< 55 µm) or quality (C : N) weakens the
transgenerational effects. However, females with high-ORAC-produced eggs with
high hatching success. Overall, these results indicate that Acartia
sp. could be affected by projected near-future CO2 levels
An experimental investigation of phytoplankton nutrient limitation in two contrasting low arctic lakes
We investigated whether phytoplankton communities in two lakes in SW Greenland were phosphorus or nitrogen limited. The study lakes have contrasting water chemistry (mean conductivities differ ten fold) and are located near Kangerlussuaq, SW Greenland (similar to 67 degrees N, 51 degrees W). A microcosm nutrient enrichment experiment was performed in June 2003 to determine whether nitrate or phosphate addition stimulated phytoplankton growth. Samples were analysed for species composition, biomass, and alkaline phosphatase activity (APA). Initially, both lakes had extremely low total phosphorus but high total nitrogen concentrations and high APA, suggesting that the phytoplankton were phosphorus limited prior to the start of the experiment. The phytoplankton composition and biomass (mainly Ochromonas spp.) responded to phosphate but not to nitrate addition. In both lakes, chlorophyll a increased significantly when phosphate was added. Furthermore, APA was significantly lower in the two lakes when phosphate was added compared to the control and the nitrogen addition treatment. The dominance of mixotrophic pbytoplankton and high DOC values suggest that these lakes may be regulated by microbial loop processes
Negligible effects of ocean acidification on <i>Eurytemora affinis</i> (Copepoda) offspring production
Ocean acidification is caused by increasing amounts of carbon dioxide
dissolving in the oceans leading to lower seawater pH. We studied the
effects of lowered pH on the calanoid copepod <i>Eurytemora affinis</i> during a mesocosm experiment
conducted in a coastal area of the Baltic Sea. We measured copepod
reproductive success as a function of pH, chlorophyll <i>a</i> concentration, diatom
and dinoflagellate biomass, carbon to nitrogen (C : N) ratio of suspended
particulate organic matter, as well as copepod fatty acid composition. The
laboratory-based experiment was repeated four times during 4 consecutive
weeks, with water and copepods sampled from pelagic mesocosms enriched with
different CO<sub>2</sub> concentrations. In addition, oxygen radical
absorbance capacity (ORAC) of animals from the mesocosms was measured weekly
to test whether the copepod's defence against oxidative
stress was affected by pH. We found no effect of pH on offspring production.
Phytoplankton biomass, as indicated by chlorophyll <i>a</i> concentration and
dinoflagellate biomass, had a positive effect. The concentration of
polyunsaturated fatty acids in the females was reflected in the eggs and
had a positive effect on offspring production, whereas monounsaturated fatty
acids of the females were reflected in their eggs but had no significant
effect. ORAC was not affected by pH. From these experiments we conclude that
<i>E. affinis</i> seems robust against direct exposure to ocean acidification on a
physiological level, for the variables covered in the study. <i>E. affinis</i> may not have
faced acute pH stress in the treatments as the species naturally face large
pH fluctuations
A Less Saline Baltic Sea Promotes Cyanobacterial Growth, Hampers Intracellular Microcystin Production, and Leads to Strain-Specific Differences in Allelopathy
A light-induced shortcut in the planktonic microbial loop
Mixotrophs combine photosynthesis with phagotrophy to cover their demands in energy and essential nutrients. This gives them a competitive advantage under oligotropihc conditions, where nutrients and bacteria concentrations are low. As the advantage for the mixotroph depends on light, the competition between mixo- and heterotrophic bacterivores should be regulated by light. To test this hypothesis, we incubated natural plankton from the ultra-oligotrophic Eastern Mediterranean in a set of mesocosms maintained at 4 light levels spanning a 10-fold light gradient. Picoplankton (heterotrophic bacteria (HB), pico-sized cyanobacteria, and small-sized flagellates) showed the fastest and most marked response to light, with pronounced predator-prey cycles, in the high-light treatments. Albeit cell specific activity of heterotrophic bacteria was constant across the light gradient, bacterial abundances exhibited an inverse relationship with light. This pattern was explained by light-induced top-down control of HB by bacterivorous phototrophic eukaryotes (PE), which was evidenced by a significant inverse relationship between HB net growth rate and PE abundances. Our results show that light mediates the impact of mixotrophic bacterivores. As mixo- and heterotrophs differ in the way they remineralize nutrients, these results have far-reaching implications for how nutrient cycling is affected by light
Nutrient limitation of periphyton growth in arctic lakes in south-west Greenland
This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, distribution,
and reproduction in any medium, provided the original
author(s) and the source are credited.Many arctic lakes are oligotrophic systems
where phototrophic growth is controlled by nutrient supply.
Recent anthropogenic nutrient loading is associated with
biological and/or physico-chemical change in several lakes
across the arctic. Shifts in nutrient limitation (nitrogen (N),
phosphorus (P), or N ? P) and associated effects on the
growth and composition of algal communities are commonly
reported. The Kangerlussuaq region of south-west
Greenland forms a major lake district which is considered
to receive little direct anthropogenic disturbance. However,
long-range transport of pollutant N is now reaching
Greenland, and it was hypothesised that a precipitation
gradient from the inland ice sheet margin to the coast might
also deliver increased N deposition. In situ nutrient bioassays
were deployed in three lakes across the region: ice
sheet margin, inland (close to Kangerlussuaq) and the coast
(near Sisimiut), to determine nutrient limitation of lakes
and investigate any effects of nutrients on periphyton
growth and community composition. Nutrient limitation
differed amongst lakes: N limitation (ice sheet margin), N
and P limitation (inland) and N ? P co-limitation (coast).
Factors including variation in N supply, ice phenology,
seasonal algal succession, community structure and
physical limnology are explored as mechanisms to explain
differences amongst lakes. Nutrient limitation of arctic
lakes and associated ecological impacts are highly variable,
even across small geographic areas. In this highly sensitive
region, future environmental change scenarios carry a
strong risk of significantly altering nutrient limitation; in
turn, potentially severely impacting lake structure and
function
Ocean acidification causes no detectable effect on swimming activity and body size in a common copepod
Ocean acidification and desalination : climate-driven change in a Baltic Sea summer microplanktonic community
Helcom scenario modelling suggests that the Baltic Sea, one of the largest brackish-water bodies in the world, could expect increased precipitation (decreased salinity) and increased concentration of atmospheric CO2 over the next 100 years. These changes are expected to affect the microplanktonic food web, and thereby nutrient and carbon cycling, in a complex and possibly synergistic manner. In the Baltic Proper, the extensive summer blooms dominated by the filamentous cyanobacteria Aphanizomenon sp., Dolichospermum spp. and the toxic Nodularia spumigena contribute up to 30% of the yearly new nitrogen and carbon exported to the sediment. In a 12 days outdoor microcosm experiment, we tested the combined effects of decreased salinity (from 6 to 3) and elevated CO2 concentrations (380 and 960 µatm) on a natural summer microplanktonic community, focusing on diazotrophic filamentous cyanobacteria. Elevated pCO2 had no significant effects on the natural microplanktonic community except for higher biovolume of Dolichospermum spp. and lower biomass of heterotrophic bacteria. At the end of the experimental period, heterotrophic bacterial abundance was correlated to the biovolume of N. spumigena. Lower salinity significantly affected cyanobacteria together with biovolumes of dinoflagellates, diatoms, ciliates and heterotrophic bacteria, with higher biovolume of Dolichospermum spp. and lower biovolume of N. spumigena, dinoflagellates, diatoms, ciliates and heterotrophic bacteria in reduced salinity. Although the salinity effects on diatoms were apparent, they could not clearly be separated from the influence of inorganic nutrients. We found a clear diurnal cycle in photosynthetic activity and pH, but without significant treatment effects. The same diurnal pattern was also observed in situ (pCO2, pH). Thus, considering the Baltic Proper, we do not expect any dramatic effects of increased pCO2 in combination with decreased salinity on the microplanktonic food web. However, long-term effects of the experimental treatments need to be further studied, and indirect effects of the lower salinity treatments could not be ruled out. Our study adds one piece to the complicated puzzle to reveal the combined effects of increased pCO2 and reduced salinity levels on the Baltic microplanktonic community.publishedVersio
Seasonal and regional controls of phytoplankton production along a climate gradient in south-west greenland during ice-cover and ice-free conditions
Across a small geographic area (< 180 km), the region of South West Greenland covers a
natural climate gradient. Variation in temperature and precipitation result in marked
differences in limnology at three discrete locations: ice sheet margin, inland and the coast.
Replicate lakes from each location were sampled for physical (temperature, light), chemical
(dissolved oxygen, pH, conductivity, nutrients) and biological (chlorophyll a (Chl a),
photosynthetic pigments) variables on three occasions within a 12 month period: July - August 2010, April - May 2011 and June - July 2011 spanning ice cover. Variation in ice
phenology was linked to the climate gradient; however phytoplankton production and
community composition did not differ regionally. Large-scale seasonal fluctuations in
temperature and nutrient availability were the strongest predictors of phytoplankton
production, with a shift from nitrate to phosphorus controlled production between ice cover
and ice free conditions. Underlying seasonal drivers, variables predicting production were
unique to each location: ice sheet margin (soluble reactive phosphorus), inland (temperature)
and coast (silicate) and reflect local differences in nutrient availability. Results from the
current study have important consequences when controls over phytoplankton production in Arctic lakes are inferred from a limited number of sites, but up-scaled to represent pan-Arctic trends