Posts Tagged 'abundance'

Variability in the phytoplankton community of Kavaratti reef ecosystem (northern Indian Ocean) during peak and waning periods of El Niño 2016

El Niño, an interannual climate event characterized by elevated oceanic temperature, is a prime threat for coral reef ecosystems worldwide, owing to their thermal threshold sensitivity. Phytoplankton plays a crucial role in the sustenance of reef trophodynamics. The cell size of the phytoplankton forms the “master morphological trait” with implications for growth, resource acquisition, and adaptability to nutrients. In the context of a strong El Niño prediction for 2015–2016, the present study was undertaken to evaluate the variations in the size-structured phytoplankton of Kavaratti reef waters, a major coral atoll along the southeast coast of India. The present study witnessed a remarkable change in the physicochemical environment of the reef water and massive coral bleaching with the progression of El Niño 2015–2016 from its peak to waning phase. The fluctuations observed in sea surface temperature, pH, and nutrient concentration of the reef water with the El Niño progression resulted in a remarkable shift in phytoplankton size structure, abundance, and community composition of the reef waters. Though low nutrient concentration of the waning phase resulted in lower phytoplankton biomass and abundance, the diazotroph Trichodesmium erythraeum predominated the reef waters, owing to its capability of the atmospheric nitrogen fixation and dissolved organic phosphate utilization.

Continue reading ‘Variability in the phytoplankton community of Kavaratti reef ecosystem (northern Indian Ocean) during peak and waning periods of El Niño 2016’

Simulated ocean acidification reveals winners and losers in coastal phytoplankton

The oceans absorb ~25% of the annual anthropogenic CO2 emissions. This causes a shift in the marine carbonate chemistry termed ocean acidification (OA). OA is expected to influence metabolic processes in phytoplankton species but it is unclear how the combination of individual physiological changes alters the structure of entire phytoplankton communities. To investigate this, we deployed ten pelagic mesocosms (volume ~50 m3) for 113 days at the west coast of Sweden and simulated OA (pCO2 = 760 μatm) in five of them while the other five served as controls (380 μatm). We found: (1) Bulk chlorophyll a concentration and 10 out of 16 investigated phytoplankton groups were significantly and mostly positively affected by elevated CO2 concentrations. However, CO2 effects on abundance or biomass were generally subtle and present only during certain succession stages. (2) Some of the CO2-affected phytoplankton groups seemed to respond directly to altered carbonate chemistry (e.g. diatoms) while others (e.g. Synechococcus) were more likely to be indirectly affected through CO2 sensitive competitors or grazers. (3) Picoeukaryotic phytoplankton (0.2–2 μm) showed the clearest and relatively strong positive CO2 responses during several succession stages. We attribute this not only to a CO2 fertilization of their photosynthetic apparatus but also to an increased nutrient competitiveness under acidified (i.e. low pH) conditions. The stimulating influence of high CO2/low pH on picoeukaryote abundance observed in this experiment is strikingly consistent with results from previous studies, suggesting that picoeukaryotes are among the winners in a future ocean.

Continue reading ‘Simulated ocean acidification reveals winners and losers in coastal phytoplankton’

Effects of elevated CO2 and temperature on phytoplankton community biomass, species composition and photosynthesis during an autumn bloom in the Western English Channel

The combined effects of elevated pCO2 and temperature were investigated during an autumn phytoplankton bloom in the Western English Channel (WEC). A full factorial 36-day microcosm experiment was conducted under year 2100 predicted temperature (+4.5 °C) and pCO2 levels (800 μatm). The starting phytoplankton community biomass was 110.2 (±5.7 sd) mg carbon (C) m−3 and was dominated by dinoflagellates (~ 50 %) with smaller contributions from nanophytoplankton (~ 13 %), cryptophytes (~ 11 %)and diatoms (~ 9 %). Over the experimental period total biomass was significantly increased by elevated pCO2 (20-fold increase) and elevated temperature (15-fold increase). In contrast, the combined influence of these two factors had little effect on biomass relative to the ambient control. The phytoplankton community structure shifted from dinoflagellates to nanophytoplankton at the end of the experiment in all treatments. Under elevated pCO2 nanophytoplankton contributed 90% of community biomass and was dominated by Phaeocystis spp., while under elevated temperature nanophytoplankton contributed 85 % of the community biomass and was dominated by smaller nano-flagellates. Under ambient conditions larger nano-flagellates dominated while the smallest nanophytoplankton contribution was observed under combined elevated pCO2 and temperature (~ 40 %). Dinoflagellate biomass declined significantly under the individual influences of elevated pCO2, temperature and ambient conditions. Under the combined effects of elevated pCO2 and temperature, dinoflagellate biomass almost doubled from the starting biomass and there was a 30-fold increase in the harmful algal bloom (HAB) species, Prorocentrum cordatum. Chlorophyll a normalised maximum photosynthetic rates (PBm) increased > 6-fold under elevated pCO2 and > 3-fold under elevated temperature while no effect on PBm was observed when pCO2 and temperature were elevated simultaneously. The results suggest that future increases in temperature and pCO2 do not appear to influence coastal phytoplankton productivity during autumn in the WEC which would have a negative feedback on atmospheric CO2.

Continue reading ‘Effects of elevated CO2 and temperature on phytoplankton community biomass, species composition and photosynthesis during an autumn bloom in the Western English Channel’

Species interactions can shift the response of a maerl bed community to ocean acidification and warming (update)

Predicted ocean acidification and warming are likely to have major implications for marine organisms, especially marine calcifiers. However, little information is available on the response of marine benthic communities as a whole to predicted changes. Here, we experimentally examined the combined effects of temperature and partial pressure of carbon dioxide (pCO2) increases on the response of maerl bed assemblages, composed of living and dead thalli of the free-living coralline alga Lithothamnion corallioides, epiphytic fleshy algae, and grazer species. Two 3-month experiments were performed in the winter and summer seasons in mesocosms with four different combinations of pCO2 (ambient and high pCO2) and temperature (ambient and +3 °C). The response of maerl assemblages was assessed using metabolic measurements at the species and assemblage scales. This study suggests that seasonal variability represents an important driver influencing the magnitude and the direction of species and community response to climate change. Gross primary production and respiration of assemblages was enhanced by high pCO2 conditions in the summer. This positive effect was attributed to the increase in epiphyte biomass, which benefited from higher CO2 concentrations for growth and primary production. Conversely, high pCO2 drastically decreased the calcification rates in assemblages. This response can be attributed to the decline in calcification rates of living L. corallioides due to acidification and increased dissolution of dead L. corallioides. Future changes in pCO2 and temperature are likely to promote the development of non-calcifying algae to the detriment of the engineer species L. corallioides. The development of fleshy algae may be modulated by the ability of grazers to regulate epiphyte growth. However, our results suggest that predicted changes will negatively affect the metabolism of grazers and potentially their ability to control epiphyte abundance. We show here that the effects of pCO2 and temperature on maerl bed communities were weakened when these factors were combined. This underlines the importance of examining multi-factorial approaches and community-level processes, which integrate species interactions, to better understand the impact of global change on marine ecosystems.

Continue reading ‘Species interactions can shift the response of a maerl bed community to ocean acidification and warming (update)’

Individual and interactive effects of warming and CO2 on Pseudo-nitzschia subcurvata and Phaeocystis antarctica, two dominant phytoplankton from the Ross Sea, Antarctica (update)

We investigated the effects of temperature and CO2 variation on the growth and elemental composition of cultures of the diatom Pseudo-nitzschia subcurvata and the prymnesiophyte Phaeocystis antarctica, two ecologically dominant phytoplankton species isolated from the Ross Sea, Antarctica. To obtain thermal functional response curves, cultures were grown across a range of temperatures from 0 to 14 °C. In addition, a co-culturing experiment examined the relative abundance of both species at 0 and 6 °C. CO2 functional response curves were conducted from 100 to 1730 ppm at 2 and 8 °C to test for interactive effects between the two variables. The growth of both phytoplankton was significantly affected by temperature increase, but with different trends. Growth rates of P. subcurvata increased with temperature from 0 °C to maximum levels at 8 °C, while the growth rates of P. antarctica only increased from 0 to 2 °C. The maximum thermal limits of P. subcurvata and P. antarctica where growth stopped completely were 14 and 10 °C, respectively. Although P. subcurvata outgrew P. antarctica at both temperatures in the co-incubation experiment, this happened much faster at 6 than at 0 °C. For P. subcurvata, there was a significant interactive effect in which the warmer temperature decreased the CO2 half-saturation constant for growth, but this was not the case for P. antarctica. The growth rates of both species increased with CO2 increases up to 425 ppm, and in contrast to significant effects of temperature, the effects of CO2 increase on their elemental composition were minimal. Our results suggest that future warming may be more favorable to the diatom than to the prymnesiophyte, while CO2 increases may not be a major factor in future competitive interactions between Pseudo-nitzschia subcurvata and Phaeocystis antarctica in the Ross Sea.

Continue reading ‘Individual and interactive effects of warming and CO2 on Pseudo-nitzschia subcurvata and Phaeocystis antarctica, two dominant phytoplankton from the Ross Sea, Antarctica (update)’

The effects of multiple stressors on the distribution of coastal benthic foraminifera: a case study from the Skagerrak-Baltic Sea region


Foraminifera in the Skagerrak-Baltic region are adapted to the large environmental conditions.
• Living dissolved Ammonia spp. and Elphidium spp. were found in the south Baltic Sea.
• The combination of multiple factors influences the energy available for biogenic calcification.
• Benthic ecosystems will be affected by an increase in the environmental variability.


Coastal ecosystems are subjected to both large natural variability and increasing anthropogenic impact on environmental parameters such as changes in salinity, temperature, and pH. This study documents the distribution of living benthic foraminifera under the influence of multiple environmental stressors in the Skagerrak-Baltic Sea region. Sediment core tops were studied at five sites along a transect from the Skagerrak to the Baltic Sea, with strong environmental gradients, especially in terms of salinity, pH, calcium carbonate saturation and dissolved oxygen concentration in the bottom water and pore water. We found that living foraminiferal densities and species richness were higher at the Skagerrak station, where the general living conditions were relatively beneficial for Foraminifera, with higher salinity and Ωcalc in the water column and higher pH and oxygen concentration in the bottom and pore water. The most common species reported at each station reflect the differences in the environmental conditions between the stations. The dominant species were Cassidulina laevigata and Hyalinea balthica in the Skagerrak, Stainforthia fusiformis, Nonionella aff. stella and Nonionoides turgida in the Kattegat and N. aff. stella and Nonionellina labradorica in the Öresund. The most adverse conditions, such as low salinity, low Ωcalc, low dissolved oxygen concentrations and low pH, were noted at the Baltic Sea stations, where the calcareous tests of the dominant living taxa Ammonia spp. and Elphidium spp. were partially to completely dissolved, probably due to a combination of different stressors affecting the required energy for biomineralization. Even though Foraminifera are able to live in extremely varying environmental conditions, the present results suggest that the benthic coastal ecosystems in the studied region, which are apparently affected by an increase in the range of environmental variability, will probably be even more influenced by a future increase in anthropogenic impacts, including coastal ocean acidification and deoxygenation.

Continue reading ‘The effects of multiple stressors on the distribution of coastal benthic foraminifera: a case study from the Skagerrak-Baltic Sea region’

Ocean acidification impacts primary and bacterial production in Antarctic coastal waters during austral summer


• Elevated CO2 decreased primary productivity and gross primary production.
• Elevated CO2 decreased bacterial productivity but increased bacterial production.
• Increased bacterial production was associated with reduced grazing pressure.
• Elevated CO2 decreased net community production when nitrate was available.
• Under nitrate limitation net community production responses to CO2 were suppressed.


Polar waters may be highly impacted by ocean acidification (OA) due to increased solubility of CO2 at colder water temperatures. Three experiments examining the influence of OA on primary and bacterial production were conducted during austral summer at Davis Station, East Antarctica (68°35′ S, 77°58′ E). For each experiment, six minicosm tanks (650 L) were filled with 200 μm filtered coastal seawater containing natural communities of Antarctic marine microbes. Assemblages were incubated for 10 to 12 days at CO2 concentrations ranging from pre-industrial to post-2300. Primary and bacterial production rates were determined using NaH14CO3 and 14C-leucine, respectively. Net community production (NCP) was also determined using dissolved oxygen. In all experiments, maximum photosynthetic rates (Pmax, mg C mg chl a− 1 h− 1) decreased with elevated CO2, clearly reducing rates of total gross primary production (mg C L− 1 h− 1). Rates of cell-specific bacterial productivity (μg C cell− 1 h− 1) also decreased under elevated CO2, yet total bacterial production (μg C L− 1 h− 1) and cell abundances increased with CO2 over Days 0–4. Initial increases in bacterial production and abundance were associated with fewer heterotrophic nanoflagellates and therefore less grazing pressure. The main changes in primary and bacterial productivity generally occurred at CO2 concentrations > 2 × present day (> 780 ppm), with the same responses occurring regardless of seasonally changing environmental conditions and microbial assemblages. However, NCP varied both within and among experiments, largely due to changing nitrate + nitrite (NOx) availability. At NOx concentrations < 1.5 μM photosynthesis to respiration ratios showed that populations switched from net autotrophy to heterotrophy and CO2 responses were suppressed. Overall, OA may reduce production in Antarctic coastal waters, thereby reducing food availability to higher trophic levels and reducing draw-down of atmospheric CO2, thus forming a positive feedback to climate change. NOX limitation may suppress this OA response but cause a similar decline.

Continue reading ‘Ocean acidification impacts primary and bacterial production in Antarctic coastal waters during austral summer’

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Ocean acidification in the IPCC AR5 WG II

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