Individual dinoflagellate cysts species of surface sediment samples from the Mediterranean Sea

To determine the relationship between the spatial dinoflagellate cyst distribution and oceanic environmental conditions, 34 surface sediments from the Eastern and Western Mediterranean Sea have been investigated for their dinoflagellate cyst content. Multivariate ordination analyses identified sea-surface temperature, chlorophyll-a , nitrate concentration, salinity, and bottom oxygen concentration as the main factors affecting dinoflagellate cyst distribution in the region. Based on the relative abundance data, two associations can be distinguished that can be linked with major oceanographic settings. (1) An offshore eastern Mediterranean regime where surface sediments are characterized by oligotrophic, warm, saline surface water, and high oxygen bottom water concentrations (Impagidinium species, Nematosphaeropsis labyrinthus, Pyxidinopsis reticulata and Operculodinium israelianum). Based on the absolute abundance, temperature is positively related to the cyst accumulation of Operculodinium israelianum. Temperature does not form a causal factor influencing the accumulation rate of the other species in this association. Impagidinium species and Nematosphaeropsis labyrinthus show a positive relationship between cyst accumulation and nitrate availability in the upper waters. (2) Species of association 2 have highest relative abundances in the Western Mediterranean Sea, Strait of Sicily/NW Ionian Sea, and/or the distal ends of the Po/Nile/Rhône River plumes. At these stations, surface waters are characterized by (relative to the other regime) higher productivity associated with lower sea-surface temperature, salinity, and lower bottom water oxygen concentrations (Selenopemphix nephroides, Echinidinium spp., Selenopemphix quanta, Quinquecuspis concreta, Brigantedinium spp. and Lingulodinium machaerophorum). Based on both the absolute and relative abundances, Selenopemphix nephroides is suggested to be a suitable indicator to trace changes in the trophic state of the upper waters. The distribution of Lingulodinium machaerophorum is related to the presence of river-influenced surface waters, notably the Nile River. We suggest that this species might form a suitable marker to trace past variations in river discharge, notably from the Nile.

Impact of CO2 enrichment on organic matter dynamics during nutrient induced coastal phytoplankton blooms

A mesocosm experiment was conducted to investigate the impact of rising fCO2 on the build-up and decline of organic matter during coastal phytoplankton blooms. Five mesocosms (~38 m³ each) were deployed in the Baltic Sea during spring (2009) and enriched with CO2 to yield a gradient of 355-862 µatm. Mesocosms were nutrient fertilized initially to induce phytoplankton bloom development. Changes in particulate and dissolved organic matter concentrations, including dissolved high-molecular weight (>1 kDa) combined carbohydrates, dissolved free and combined amino acids as well as transparent exopolymer particles (TEP), were monitored over 21 days together with bacterial abundance, and hydrolytic extracellular enzyme activities. Overall, organic matter followed well-known bloom dynamics in all CO2 treatments alike. At high fCO2, higher dPOC:dPON during bloom rise, and higher TEP concentrations during bloom peak, suggested preferential accumulation of carbon-rich components. TEP concentration at bloom peak was significantly related to subsequent sedimentation of particulate organic matter. Bacterial abundance increased during the bloom and was highest at high fCO2. We conclude that increasing fCO2 supports production and exudation of carbon-rich components, enhancing particle aggregation and settling, but also providing substrate and attachment sites for bacteria. More labile organic carbon and higher bacterial abundance can increase rates of oxygen consumption and may intensify the already high risk of oxygen depletion in coastal seas in the future.

Lack of evidence for elevated CO2-induced bottom-up effects on marine copepods: a dinoflagellate-calanoid prey-predator pair

Rising levels of atmospheric CO2 are responsible for a change in the carbonate chemistry of seawater with associated pH drops (acidification) projected to reach 0.4 units from 1950 to 2100. We investigated possible indirect effects of seawater acidification on the feeding, fecundity, and hatching success of the calanoid copepod Acartia grani, mediated by potential CO2-induced changes in the nutritional characteristics of their prey. We used as prey the autotrophic dinoflagellate Heterocapsa sp., cultured at three distinct pH levels (control: 8.17, medium: 7.96, and low: 7.75) by bubbling pure CO2 via a computer automated system. Acartia grani adults collected from a laboratory culture were acclimatized for 3 d at food suspensions of Heterocapsa from each pH treatment (ca. 500 cells/ml; 300 ?g C/l). Feeding and egg production rates of the preconditioned females did not differ significantly among the three Heterocapsa diets. Egg hatching success, monitored once per day for the 72 h, did not reveal significant difference among treatments. These results are in agreement with the lack of difference in the cellular stoichiometry (C : N, C : P, and N : P ratios) and fatty acid concentration and composition encountered between the three tested Heterocapsa treatments. Our findings disagree with those of other studies using distinct types of prey, suggesting that this kind of indirect influence of acidification on copepods may be largely associated with interspecific differences among prey items with regard to their sensitivity to elevated CO2 levels.

The response of Antarctic sea ice algae to changes in pH and CO2

Ocean acidification substantially alters ocean carbon chemistry and hence pH but the effects on sea ice formation and the CO2 concentration in the enclosed brine channels are unknown. Microbial communities inhabiting sea ice ecosystems currently contribute 10-50% of the annual primary production of polar seas, supporting overwintering zooplankton species, especially Antarctic krill, and seeding spring phytoplankton blooms. Ocean acidification is occurring in all surface waters but the strongest effects will be experienced in polar ecosystems with significant effects on all trophic levels. Brine algae collected from McMurdo Sound (Antarctica) sea ice was incubated in situ under various carbonate chemistry conditions. The carbon chemistry was manipulated with acid, bicarbonate and bases to produce a pCO2 and pH range from 238 to 6066 µatm and 7.19 to 8.66, respectively. Elevated pCO2 positively affected the growth rate of the brine algal community, dominated by the unique ice dinoflagellate, Polarella glacialis. Growth rates were significantly reduced when pH dropped below 7.6. However, when the pH was held constant and the pCO2 increased, growth rates of the brine algae increased by more than 20% and showed no decline at pCO2 values more than five times current ambient levels. We suggest that projected increases in seawater pCO2, associated with OA, will not adversely impact brine algal communities.