Posts Tagged 'community composition'

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’

DISCO – Drivers and impacts of coastal ocean acidification

Ocean acidification, mainly attributed to the increasing anthropogenic CO2 in the atmosphere, is characterised by a lowering pH together with a shift in the sea water carbonate chemistry toward lower concentration of carbonate ions. On the coasts, where the environmental variability is high due to natural and human impacts, ocean acidification mainly affects the frequency, magnitude, and duration of lower pH and lower calcium carbonate saturation events. Coastal ecosystems are adapted to environmental variability such as frequent changes in salinity, temperature, pH, oxygen levels and organic matter content. However, the effects of an increase of the range of this variability on coastal species, and especially on calcifiers, are still not clear. In this context, this thesis explores the impacts of coastal ocean acidification combined with other environmental stressors on benthic foraminifera.

In the Skagerrak-Baltic Sea region, foraminifera faunas varied along a strong gradient in terms of salinity, pH, and dissolved oxygen concentration, and species were adapted to local environmental stressors. However, the specimens of Ammonia spp. and Elphidium spp. observed in the south Baltic Sea were partially to completely dissolved, probably due to a combination of different stressors affecting the required energy for biomineralisation.

In a culture study, the coastal species Ammonia spp. and E. crispum were found to be resistant to dissolution under varying salinity and pH, which reflects the environmental variations in their natural habitats. However, their resistance to lower pH is decreased when cultured in brackish water conditions, and living decalcified specimens were also observed under a salinity of 5. This underlines the importance of a high salinity in the calcification process of foraminifera.

At the entrance of the Baltic Sea, environmental changes during the last 200 years were reconstructed using foraminiferal faunas. Four periods were identified with varying oxygen levels, salinity, organic matter content, and pollution with lower pH. This highlights that foraminiferal faunas were able to adapt to multiple environmental stressors.

This thesis concludes that, even if coastal species of foraminifera can tolerate extremely varying conditions in their environment on the short term, it is likely that tolerance thresholds will be passed for benthic ecosystems under the future increase in anthropogenic impacts such as coastal ocean acidification.

Further studies of micro-organisms such as foraminifera will be necessary to improve our understanding of past environmental changes and to put present and future changes into a larger context.

Continue reading ‘DISCO – Drivers and impacts of coastal ocean acidification’

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’

Eukaryotic metabarcoding pipelines for biodiversity assessment of marine benthic communities affected by ocean acidification

The development of high-throughput sequencing technologies has provided ecologists with an efficient approach to assess biodiversity in benthic communities, particularly with the recent advances in metabarcoding technologies using universal primers. However, analyzing such high-throughput data is posing important computational challenges, requiring specialized bioinformatics solutions at different stages during the processing pipeline, such as assembly of paired-end reads, chimera removal, correction of sequencing errors, and clustering of obtained sequences into Molecular Operational Taxonomic Units (MOTUs). The inferred MOTUs can then be used to estimate species diversity, composition, and richness. Although a number of methods have been developed and commonly used to cluster the sequences into MOTUs, relatively little guidance is available on their relative performance. We focused our study in the benthic community from a natural CO2 vent present in the Canary Islands, as it can be used as a natural laboratory in which to investigate the impacts of chronic ocean acidification. Here, we propose a pipeline for studying this community using a fragment of the mitochondrial cytochrome c oxidase I (COI) sequence. We compared two DNA extraction methods, two clustering methods and validated a robust method to eliminate false positives. We found that we can obtain optimal results purifying DNA from 0.3 g of sample. Using the step-by-step aggregation algorithm implemented in SWARM for clustering yields similar results as using the Bayesian clustering method of CROP, in much less time. We introduced the new algorithm MINT (Multiple Intersection of N Tags), in order to eliminate false positives due to random errors produced before or after the sequencing. Our results show that a fully-automated analysis pipeline can be used for assessing biodiversity of marine benthic communities using COI as a metabarcoding marker in an objective, accurate and affordable manner.

Continue reading ‘Eukaryotic metabarcoding pipelines for biodiversity assessment of marine benthic communities affected by ocean acidification’

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

Highlights

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.

Abstract

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’

Assessing the consequences of environmental impacts: variation in species responses has unpredictable functional effects

Many biological processes underpin ecosystem functioning and health. Determining changes in these processes following disturbance is crucial in assessing the wider impacts on ecosystem function and ultimately ecosystem services. Whilst the focus is often on whether disturbance drives changes in ecosystem function through mortality, sub-lethal effects on the physiology and behaviour of organisms may also have cascading effects on ecosystem processes, functions and services. In this mesocosm study, we investigated the effects of a severe short-term exposure (8 d) to a simulated environmental impact—a leak of a subsea geological CO2 capture and storage reservoir—on key biological processes (bioturbation), an ecosystem function (nutrient cycling) and on the functional group composition for 7 common benthic invertebrate species. We statistically allocated species to functional effect groups based on their measured functional effect relative to other species. Following exposure, we observed behavioural responses driving changes in bioturbation for several species and altered nutrient cycling. Responses were species specific and resulted in shifts in functional effect group composition for some key nutrients (nitrate and silicate). We show that the allocation of species to functional groups by measuring specified ecosystem processes and functions can change following environmental perturbations. This implies that whilst biodiversity and ecosystem functioning are intricately linked, maintaining species identities and abundances after environmental perturbation is no guarantee to maintaining ecosystem functions, as species alter their rate and mode of activity following an environmental stress.

Continue reading ‘Assessing the consequences of environmental impacts: variation in species responses has unpredictable functional effects’


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Ocean acidification in the IPCC AR5 WG II

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