Planktic foraminifera were collected with 150 µm BONGO nets from the upper 200 m water depth at 20 stations across the Mediterranean Sea between 2 May and 2 June 2013. The main aim is to characterize the species distribution and test the covariance between foraminiferal area density (ρA) and seawater carbonate chemistry in a biogeochemical gradient including ultraoligotrophic conditions. Average foraminifera abundances are 1.42 ± 1.43 ind. 10 m−3 (ranging from 0.11 to 5.20 ind. 10 m−3), including 12 morphospecies. Large differences in species assemblages and total abundances are observed between the different Mediterranean sub-basins, with an overall dominance of spinose, symbiont-bearing species indicating oligotrophic conditions. The highest values in absolute abundance are found in the Strait of Gibraltar and the Alboran Sea. The western basin is dominated by Globorotalia inflata and Globigerina bulloides at slightly lower standing stocks than in the eastern basin. In contrast, the planktic foraminiferal assemblage in the warmer, saltier, and more nutrient-limited eastern basin is dominated by Globigerinoides ruber (white). These new results, when combined with previous findings, suggest that temperature-induced surface water stratification and food availability are the main factors controlling foraminiferal distribution. In the oligotrophic and highly alkaline and supersaturated with respect to calcite and aragonite Mediterranean surface water, standing stocks and ρA of G. ruber (white) and G. bulloides are affected by both food availability and seawater carbonate chemistry. Rapid warming increased surface ocean stratification impacting food availability and changes in trophic conditions could be the causes of reduced foraminiferal abundance, diversity, and species-specific changes in planktic foraminiferal calcification.
Posts Tagged 'BRcommunity'
Low planktic foraminiferal diversity and abundance observed in a spring 2013 west–east Mediterranean Sea plankton tow transect (update)
Published 5 May 2017 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, field, Mediterranean, otherprocess, protists
Naturally acidified habitat selects for ocean acidification–tolerant mussels
Published 3 May 2017 Science ClosedTags: adaptation, Baltic, biological response, BRcommunity, calcification, chemistry, field, growth, mollusks, morphology, mortality, otherprocess, reproduction
Ocean acidification severely affects bivalves, especially their larval stages. Consequently, the fate of this ecologically and economically important group depends on the capacity and rate of evolutionary adaptation to altered ocean carbonate chemistry. We document successful settlement of wild mussel larvae (Mytilus edulis) in a periodically CO2-enriched habitat. The larval fitness of the population originating from the CO2-enriched habitat was compared to the response of a population from a nonenriched habitat in a common garden experiment. The high CO2–adapted population showed higher fitness under elevated PCO2 (partial pressure of CO2) than the non-adapted cohort, demonstrating, for the first time, an evolutionary response of a natural mussel population to ocean acidification. To assess the rate of adaptation, we performed a selection experiment over three generations. CO2 tolerance differed substantially between the families within the F1 generation, and survival was drastically decreased in the highest, yet realistic, PCO2 treatment. Selection of CO2-tolerant F1 animals resulted in higher calcification performance of F2 larvae during early shell formation but did not improve overall survival. Our results thus reveal significant short-term selective responses of traits directly affected by ocean acidification and long-term adaptation potential in a key bivalve species. Because immediate response to selection did not directly translate into increased fitness, multigenerational studies need to take into consideration the multivariate nature of selection acting in natural habitats. Combinations of short-term selection with long-term adaptation in populations from CO2-enriched versus nonenriched natural habitats represent promising approaches for estimating adaptive potential of organisms facing global change.
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The future for microplankton in the Baltic Sea – Effects of SWS and climate change
Published 2 May 2017 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, chemistry, community composition, field, laboratory, multiple factors, otherprocess, photosynthesis, phytoplankton, prokaryotes, protists, salinity, temperature, zooplankton
The Baltic Sea is located between 53°N to 66°N and from 10°E to 30°E and is the second largest brackish water body in the world. It consists of several basins where the Baltic Proper is the major water mass. Around 85 million people live in the catchment area of the Baltic Sea, which subjects it to a range of environmental pressures, such as increased nutrient inputs from human activities (eutrophication), shipping, over-fishing, acid rain and trace metals released from anti-fouling paint. All these stressors, combined with low alkalinity, variable salinity and limited water exchange, makes the Baltic Sea a very sensitive area that may be less resilient to future stressors such as climate change or increased shipping activities. Microplankton communities consist of small heterotrophic bacteria, picoplankton, phytoplankton, cyanobacteria and smaller grazers, such as ciliates and zooplankton. In the Baltic Proper, there is a succession of blooms, within the microplankton community, from diatoms and dinoflagellates in the early spring to cyanobacteria during summer and ending with a second diatom and dinoflagellate bloom in the autumn. The cyanobacteria of the Baltic Proper bloom every summer and are dominated by Aphanizomenon sp. and Nodularia spumigena. Dolichospermum spp. is present but is less abundant. The effects of climate change were tested on a natural microplankton community, as well as on isolated cyanobacteria species from the Baltic Sea. To simulate effects of climate change, the temperature was increased from 12°C to 16°C, salinity decreased from 6-7 to 3-4 and atmospheric pCO2-levels was increased from 380 ppm to 960 ppm. The biovolume of Aphanizomenon sp. and N. spumigena increased when temperature was increased by 4°C. When salinity was decreased by three units, both the growth and photosynthetic activity of N. spumigena were reduced while Aphanizomenon sp. was unaffected, and the growth of Dolichospermum sp. was increased. Furthermore, present-day salinities were beneficial, in terms of increased biovolumes, of diatoms, dinoflagellates and ciliates, compared to reduced future salinity. Increased atmospheric pCO2 had no effect on any of the species in the microplankton community. These results show that the future microplankton community may be positive, in terms of increased biovolume, for the cyanobacteria species Aphanizomenon sp. and Dolichospermum spp. An increase of cyanobacteria blooms may open up to the possibility to grow and/or harvest these species as a source of biofuel or fatty acids (FA). Dolichospermum sp. yielded higher total FA content per biovolume, compared to the other two cyanobacteria species in phosphorus-depleted medium and Aphanizomenon sp. in nitrogen-depleted medium. Natural nutrient levels in the Baltic Proper are low both in nitrogen and phosphorus, which indicates a possible future market for biofuel and FA technologies. Additionally, the effects of seawater scrubbing (SWS) were tested on a natural summer-bloom microplankton community. Three different concentrations of scrubber water were added; 1%, 3% and 10%. To elucidate effects of decreased pH alone, water acidified with H2SO4 was added in equal concentrations. The six treatments were compared to a control without acidifying substances. SWS or the corresponding pH treatments, did not have a direct effect on microplankton species composition and biovolume. However, the increased amount of Cu and Zn in the scrubber water, combined with significant decrease in pH and alkalinity already at the 1% scrubber water treatment calls for precaution when implementing scrubber units on the shipping fleet of the Baltic Sea. The accumulated effects of long-term repeated addition constantly throughout the year, i.e. in a shipping lane, are yet to be elucidated.
Structural and functional organization of fish assemblages in a Mediterranean shallow CO2 vent
Published 2 May 2017 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, field, fish, Mediterranean, morphology, otherprocess, vents
The “business-as-usual emission scenario” simulated by the IPCC (Intergovernmental Panel on Climate Change) suggests that atmospheric CO2 levels could approach 800 ppm by the end of the century. Corresponding biogeochemical models indicate that surface ocean water pH will drop from a pre-industrial value of about 8.2 to 7.8 within 2100 (Feely et al., 2010). This phenomenon known as “Ocean Acidification” (OA) is caused by the increasing CO2 emissions due to anthropic activities, with a current consequence decrease of about 0.1 unit of pH (Caldeira & Wickett 2003) that is having effects on seawater carbonate chemistry and on marine ecosystems. Many short-term laboratory experiments have shown the effects of OA on marine calcareous organisms (Doney et al., 2009), but also on not-calcifying ones. For instance, experiments on fish have revealed effects on physiological and behavioral aspects (Dixson et al., 2010; Munday et al., 2009), but many other aspects are still unknown (Ishimatsu et al., 2008). On the other hand, field experiments have been conducted in naturally acidified marine ecosystems, known as CO2 vents, which are currently investigated to study the long-term effects of OA on species, communities and ecological processes (Hall-Spencer et al. 2008).
Shallow CO₂ vents are widespread in Mediterranean (Dando et al., 1999) and represent a sort of natural mesocosms, where marked pH gradients are present at small spatial scales. The aim of this PhD project is to assess the effect of high pCO2/low pH on the structural and functional organization of fish assemblages in a Mediterranean shallow CO₂ vent (Aeolian Archipelago, NE Sicily). In particular, we compare the responses of a chronic exposed fish assemblage living near the primary vent (mean pH = 7.8; hereafter “Low pH”) with other two fish assemblages living at normal pH (mean pH = 8.2; hereafter “Control 1” and “Control 2”) in Vulcano and Lipari Islands. We hypothesized that the organization of fish assemblage at the low pH site is different from that in controls. To test our hypothesis we use several descriptors and different methodologies. First, we compared fish community structure by using Underwater Visual Census technique to assess species richness and abundance (frequency of occurrence). Then we carried out samplings to evaluate trophic organization of fish assemblages (we used stable isotopes of carbon and nitrogen to analyze food web and trophic levels), bioaccumulation and biomagnification of trace elements (concentration and bio-availability of several trace elements, also toxic ones, may increase due to direct input from the vent and to peculiar pH and Eh conditions), and the characteristics of carbonate structures like otoliths (to assess the effect of acidification on these structures by morphological analysis). Otoliths are also used as natural tags to study fish “site fidelity” of this particular site through microchemistry analysis of trace elements and isotopic composition.
This study provided a complete and exhaustive frame of fish assemblages structure and trophic organization at different pH levels. As scant data are available in the literature on this topic, the results of this research provide information about the ecological effects of long-term exposure to high CO2 levels on fish, a key biological component whose monitoring is relevant not only from the ecological side, but also for the economic one and for the implications on human health. Moreover, this study confirms the importance to use the naturally acidified environments to test ecological hypotheses on the effects of OA on communities and ecosystems.
Large-scale seaweed cultivation diverges water and sediment microbial communities in the coast of Nan’ao Island, South China Sea
Published 26 April 2017 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, field, mitigation, molecular biology, North Pacific, otherprocess, prokaryotes, sediment
Seaweed cultivation not only provides economy benefits, but also remediates the environment contaminated by mariculture of animals (e.g., fish, shrimps). However, the response of microbial communities to seaweed cultivation is poorly understood. In this study, we analyzed the diversity, composition, and structure of water and sediment microbial communities at a seaweed, Gracilaria lemaneiformis, cultivation zone and a control zone near Nan’ao Island, South China Sea by MiSeq sequencing of 16S rRNA gene amplicons. We found that large-scale cultivation of G. lemaneiformis increased dissolved oxygen (DO) and pH but decreased inorganic nutrients, possibly due to nutrient uptake, photosynthesis and other physiological processes of G. lemaneiformis. These environmental changes significantly (adonis, P < 0.05) shifted the microbial community composition and structure of both water column and sediment samples in the G. lemaneiformis cultivation zone, compared to the control zone. Also, certain microbial taxa associated with seaweed, such as Arenibacter, Croceitalea, Glaciecola, Leucothrix and Maribacter were enriched at the cultivation zone. In addition, we have proposed a conceptual model to summarize the results in this study and guide future studies on relationships among seaweed processes, microbial communities and their environments. Thus, this study not only provides new insights into our understanding the effect of G. lemaneiformis cultivation on microbial communities, but also guides future studies on coastal ecosystems.
Ice Acidification: A review of the effects of ocean acidification on sea ice microbial communities
Published 24 April 2017 Science ClosedTags: biological response, BRcommunity, prokaryotes, review
Sea ice algae are naturally exposed to a wider range of pH and CO2 concentrations than marine phytoplankton. While climate change and ocean acidification (OA) will impact pelagic communities, their effects on sea ice microbial communities remains unclear.
Sea ice contains several distinct microbial communities, which are exposed to differing environmental conditions depending on their depth within the ice. Bottom communities mostly experience relatively benign bulk ocean properties, while interior brine and surface communities experience much greater extremes.
Most OA studies have examined the impacts on single sea ice algae species in culture. Although some studies examined the effects of OA alone, most also examined the effects of OA and either light, nutrients or temperature. With few exceptions, increased CO2 concentration caused either no change or an increase in growth and/or photosynthesis. In situ studies of brine and surface algae also demonstrated a wide tolerance to increased and decreased pH and showed increased growth at higher CO2 concentrations. The short time period of most experiments (< 10 days) together with limited genetic diversity (i.e. use of only a single strain), however, has been identified as a limitation to the broader interpretation of results.
While there have been few studies on the effects of OA on marine bacterial communities in general, impacts appear to be minimal. In sea ice also, the few reports available suggest no negative impacts on growth or community richness.
Sea ice ecosystems are ephemeral, melting and re-forming each year. Thus, for some part of each year organisms inhabiting the ice must also survive outside of the ice, either as part of the phytoplankton or as resting spores on the bottom. During these times, they will be exposed to the full range of co-stressors that pelagic organisms experience. Their ability to continue to make a major contribution to sea ice productivity will depend not only on their ability to survive in the ice but also on their ability to survive the increasing seawater temperatures, changing distribution of nutrients and declining pH forecast for the water column over the next centuries.
Interactive effects of temperature, food and skeletal mineralogy mediate biological responses to ocean acidification in a widely distributed bryozoan
Published 21 April 2017 Science ClosedTags: biological response, BRcommunity, bryozoa, dissolution, laboratory, morphology, multiple factors, nutrients, physiology, temperature
Marine invertebrates with skeletons made of high-magnesium calcite may be especially susceptible to ocean acidification (OA) due to the elevated solubility of this form of calcium carbonate. However, skeletal composition can vary plastically within some species, and it is largely unknown how concurrent changes in multiple oceanographic parameters will interact to affect skeletal mineralogy, growth and vulnerability to future OA. We explored these interactive effects by culturing genetic clones of the bryozoan Jellyella tuberculata (formerly Membranipora tuberculata) under factorial combinations of dissolved carbon dioxide (CO2), temperature and food concentrations. High CO2 and cold temperature induced degeneration of zooids in colonies. However, colonies still maintained high growth efficiencies under these adverse conditions, indicating a compensatory trade-off whereby colonies degenerate more zooids under stress, redirecting energy to the growth and maintenance of new zooids. Low-food concentration and elevated temperatures also had interactive effects on skeletal mineralogy, resulting in skeletal calcite with higher concentrations of magnesium, which readily dissolved under high CO2. For taxa that weakly regulate skeletal magnesium concentration, skeletal dissolution may be a more widespread phenomenon than is currently documented and is a growing concern as oceans continue to warm and acidify.
Variable response to warming and ocean acidification by bacterial processes in different plankton communities
Published 20 April 2017 Science ClosedTags: abundance, biological response, BRcommunity, community composition, laboratory, multiple factors, otherprocess, physiology, prokaryotes, South Pacific, temperature
Extracellular bacterial enzymes play an important role in the degradation of organic matter in the surface ocean but are sensitive to changes in pH and temperature. This study tested the individual and combined effects of lower pH (-0.3) and warming (+3°C) projected for the year 2100 on bacterial abundance, process rates and diversity in plankton communities of differing composition from 4 locations east of New Zealand. Variation was observed in magnitude and temporal response between the different communities during 5 to 6 day incubations. Leucine aminopeptidase activity showed the strongest response, with an increase in potential activity under low pH alone and in combination with elevated temperature in 3 of 4 incubations. Temperature had a greater effect on bacterial cell numbers and protein synthesis, with stronger responses in the elevated temperature and combined treatments. However, the most common interactive effect between temperature and pH was antagonistic, with lower bacterial secondary production in the combined treatment relative to elevated temperature, and lower leucine aminopeptidase activity in the combined treatment relative to low pH. These results highlight the variability of responses to and interactions of environmental drivers, and the importance of considering these in experimental studies and prognostic models of microbial responses to climate change.
Ocean acidification effects on mesozooplankton community development: Results from a long-term mesocosm experiment
Published 19 April 2017 Science ClosedTags: abundance, BRcommunity, cnidaria, community composition, crustaceans, field, laboratory, mesocosms, morphology, North Atlantic, otherprocess, physiology, reproduction, respiration, zooplankton
Ocean acidification may affect zooplankton directly by decreasing in pH, as well as indirectly via trophic pathways, where changes in carbon availability or pH effects on primary producers may cascade up the food web thereby altering ecosystem functioning and community composition. Here, we present results from a mesocosm experiment carried out during 113 days in the Gullmar Fjord, Skagerrak coast of Sweden, studying plankton responses to predicted end-of-century pCO2 levels. We did not observe any pCO2 effect on the diversity of the mesozooplankton community, but a positive pCO2 effect on the total mesozooplankton abundance. Furthermore, we observed species-specific sensitivities to pCO2 in the two major groups in this experiment, copepods and hydromedusae. Also stage-specific pCO2 sensitivities were detected in copepods, with copepodites being the most responsive stage. Focusing on the most abundant species, Pseudocalanus acuspes, we observed that copepodites were significantly more abundant in the high-pCO2 treatment during most of the experiment, probably fuelled by phytoplankton community responses to high-pCO2 conditions. Physiological and reproductive output was analysed on P. acuspes females through two additional laboratory experiments, showing no pCO2 effect on females’ condition nor on egg hatching. Overall, our results suggest that the Gullmar Fjord mesozooplankton community structure is not expected to change much under realistic end-of-century OA scenarios as used here. However, the positive pCO2 effect detected on mesozooplankton abundance could potentially affect biomass transfer to higher trophic levels in the future.
Tropical coral reef coral patterns in Indonesian shallow water areas close to underwater volcanic vents at Minahasa Seashore, and Mahengetang and Gunung Api Islands
Published 19 April 2017 Science ClosedTags: abundance, biological response, BRcommunity, community composition, corals, field, otherprocess, South Pacific, vents
Coral community patterns on some Indonesian reefs influenced by CO2 from underwater volcanic vents and nutrients from eutrophication pressures were examined. The overall aim of the study was to provide an insight into the significance of future ocean acidification compared to eutrophication pressures on tropical coral communities. Coral cover and seawater characteristics at acidified sites (with varied levels of eutrophication), i.e., moderate acidification (pH: 7.87 ± 0.04), low acidification (pH: 8.01 ± 0.04) and reference (pH: 8.2 ± 0.02), were observed at reefs associated with Minahasa Seashore, and Mahengetang and Gunung Api Islands. Results showed that coral community patterns varied among locations and acidified sites, e.g., domination of families such as Alcyoniidae, Acroporidae, Poritidae and Heliporidae, and with different levels of abiotic cover. Surprisingly, pH was not detected as the major determining factor. This finding probably relates to tropical seawater temperatures being high enough to still allow for aragonite deposition even at pH values down to 7.8. Nutrients (phosphate and dissolved inorganic nitrogen) were shown to be the main determining factors that influenced community patterns on the observed coral reefs. Overall, the results indicate that tropical coral reef community patterns will continue to vary as pH decreases to the predicted oceanic value of pH 7.8 over the next 100 years, and bio-geo-ecological characteristics and anthropogenic pressures will be the major factors determining Indonesian tropical coral community structure, compared to pH.
The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt
Published 18 April 2017 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, field, Indian, otherprocess, phytoplankton, South Atlantic
The Great Calcite Belt (GCB) of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region, provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Water samples for phytoplankton enumeration were collected from the upper 30 m during two cruises, the first to the South Atlantic sector (Jan–Feb 2011; 60 °W–15 °E and 36–60 °S) and the second in the South Indian sector (Feb–Mar 2012; 40–120 °E and 36–60 °S). The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Sub-Tropical, Polar, and Sub-Antarctic Fronts. The influence of environmental parameters, such as sea-surface temperature (SST), salinity, carbonate chemistry (i.e., pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macro-nutrients (i.e., nitrate + nitrite, phosphate, silicic acid, ammonia), and mixed layer average irradiance, on species composition across the GCB, was assessed statistically. Nanophytoplankton (cells 2–20 μm) were the numerically abundant size group of biomineralizing phytoplankton across the GCB, the coccolithophore Emiliania huxleyi and the diatoms Fragilariopsis nana, F. pseudonana and Pseudonitzschia sp. were the most dominant and widely distributed species. A combination of SST, macro-nutrient concentrations and pCO2 were the best statistical descriptors of biogeographic variability of biomineralizing species composition between stations. Emiliania huxleyi occurred in the silicic acid-depleted waters between the Sub-Antarctic Front and the Polar Front, indicating a favorable environment for this coccolithophore in the GCB after spring diatom blooms remove silicic acid to limiting levels. After full consideration of variability in carbonate chemistry and temperature on the distribution of nanoplankton in the GCB, we find that temperature remains the dominant driver of biogeography in a large proportion of the modern Southern Ocean.
Altered epiphyte community and sea urchin diet in Posidonia oceanica meadows in the vicinity of submarine volcanic CO2 vents
Published 13 April 2017 Science ClosedTags: abundance, algae, annelids, biological response, BRcommunity, community composition, echinoderms, field, Mediterranean, otherprocess, phanerogams, vents
Ocean acidification (OA) predicted for 2100 is expected to shift seagrass epiphyte communities towards the dominance of more tolerant non-calcifying taxa. However, little is known about the indirect effects of such changes on food provision to key seagrass consumers. We found that epiphyte communities of the seagrass Posidonia oceanica in two naturally acidified sites (i.e. north and south sides of a volcanic CO2 vent) and in a control site away from the vent at the Ischia Island (NW Mediterranean Sea) significantly differed in composition and abundance. Such differences involved a higher abundance of non-calcareous crustose brown algae and a decline of calcifying polychaetes in both acidified sites. A lower epiphytic abundance of crustose coralline algae occurred only in the south side of the vents, thus suggesting that OA may alter epiphyte assemblages in different ways due to interaction with local factors such as differential fish herbivory or hydrodynamics. The OA effects on food items (seagrass, epiphytes, and algae) indirectly propagated into food provision to the sea urchin Paracentrotus lividus, as reflected by a reduced P. oceanica exploitation (i.e. less seagrass and calcareous epiphytes in the diet) in favour of non-calcareous green algae in both vent sites. In contrast, we detected no difference close and outside the vents neither in the composition of sea urchin diet nor in the total abundance of calcareous versus non-calcareous taxa. More research, under realistic scenarios of predicted pH reduction (i.e. ≤ 0.32 units of pH by 2100), is still necessary to better understand cascading effects of this altered urchin exploitation of food resources under acidified conditions on ecosystem diversity and function.
Effects of in situ CO2 enrichment on Posidonia oceanica epiphytic community composition and mineralogy
Published 13 April 2017 Science ClosedTags: abundance, algae, biological response, BRcommunity, community composition, field, otherprocess, phanerogams, physiology, protists
Alterations in seagrass epiphytic communities are expected under future ocean acidification conditions, yet this hypothesis has been little tested in situ. A Free Ocean Carbon Dioxide Enrichment system was used to lower pH by a ~0.3 unit offset within a partially enclosed portion (1.7 m3) of a Posidonia oceanica meadow (11 m depth) between June 21 and November 3, 2014. Leaf epiphytic community composition (% cover) and bulk epiphytic mineralogy were compared every 4 weeks within three treatments, located in the same meadow: a pH-manipulated (experimental enclosure) and a control enclosure, as well as a nearby ambient area. Percent coverage of invertebrate calcifiers and crustose coralline algae (CCA) did not appear to be affected by the lowered pH. Furthermore, fleshy algae did not proliferate at lowered pH. Only Foraminifera, which covered less than 3% of leaf surfaces, declined in manner consistent with ocean acidification predictions. Bulk epiphytic magnesium carbonate composition was similar between treatments and percentage of magnesium appeared to increase from summer to autumn. CCA did not exhibit any visible skeleton dissolution or mineral alteration at lowered pH and carbonate saturation state. Negative impacts from ocean acidification on P. oceanica epiphytic communities were smaller than expected. Epiphytic calcifiers were possibly protected from the pH treatment due to host plant photosynthesis inside the enclosure where water flow is slowed. The more positive outcome than expected suggests that calcareous members of epiphytic communities may find refuge in some conditions and be resilient to environmentally relevant changes in carbonate chemistry.
Spatial patterns of phytoplankton composition and upper-ocean biogeochemistry do not follow carbonate chemistry gradients in north-west European Shelf seas
Published 12 April 2017 Science ClosedTags: biological response, BRcommunity, chemistry, field, North Atlantic, phytoplankton
A key difficulty in ocean acidification (OA) research is to predict its impact after physiological, phenotypic and genotypic adaptation has had time to take place. Observational datasets can be a useful tool in addressing this issue. During a cruise in June-July 2011, measurements of upper-ocean biogeochemical variables, climatically active gases and plankton community composition were collected from northwestern European seas. We used various multivariate statistical techniques to assess the relative influences of carbonate chemistry and other environmental factors on these response variables. We found that the spatial patterns in plankton communities were driven more by nutrient availability and physical variables than by carbonate chemistry. The best subset of variables able to account for phytoplankton community structure was the euphotic zone depth, silicic acid availability, mixed layer average irradiance and nitrate concentration (59% of variance explained). The spatial variations in phytoplankton and coccolithophores species composition were both found to be more strongly associated with nutrients and physical variables than carbonate chemistry, with the latter only explaining 14% and 9% of the variance, respectively. The plankton community composition and contribution of calcifying organisms was not observed to change under lower calcite saturation state (B) conditions, although no regions of undersaturation (B < 1) were encountered during the cruise. Carbonate chemistry played a more prominent, but still secondary, role in determining dinoflagellate and diatom assemblage composition (20% and 13% of total variance explained, respectively). Nutrient and physical variables also explained more of the spatial variations of most climatically-active gases and selected biogeochemical response variables, although some also appeared to be influenced by carbonate chemistry. This observational study has demonstrated that ocean acidification research needs to be set in context with other environmental forcing variables to fully appreciate the primary, or indeed secondary, role that increasing fCO2 has on biological communities and associated biogeochemical rates.
Potential sources of variability in mesocosm experiments on the response of phytoplankton to ocean acidification (update)
Published 11 April 2017 Media coverage ClosedTags: abundance, biological response, BRcommunity, community composition, communitymodeling, mesocosms, methods, modeling, morphology, otherprocess, phytoplankton
Mesocosm experiments on phytoplankton dynamics under high CO2 concentrations mimic the response of marine primary producers to future ocean acidification. However, potential acidification effects can be hindered by the high standard deviation typically found in the replicates of the same CO2 treatment level. In experiments with multiple unresolved factors and a sub-optimal number of replicates, post-processing statistical inference tools might fail to detect an effect that is present. We propose that in such cases, data-based model analyses might be suitable tools to unearth potential responses to the treatment and identify the uncertainties that could produce the observed variability. As test cases, we used data from two independent mesocosm experiments. Both experiments showed high standard deviations and, according to statistical inference tools, biomass appeared insensitive to changing CO2 conditions. Conversely, our simulations showed earlier and more intense phytoplankton blooms in modeled replicates at high CO2 concentrations and suggested that uncertainties in average cell size, phytoplankton biomass losses, and initial nutrient concentration potentially outweigh acidification effects by triggering strong variability during the bloom phase. We also estimated the thresholds below which uncertainties do not escalate to high variability. This information might help in designing future mesocosm experiments and interpreting controversial results on the effect of acidification or other pressures on ecosystem functions.
A data–model synthesis to explain variability in calcification observed during a CO2 perturbation mesocosm experiment (update)
Published 11 April 2017 Science ClosedTags: biological response, BRcommunity, calcification, mesocosms, methods, modeling, phytoplankton
The effect of ocean acidification on growth and calcification of the marine algae Emiliania huxleyi was investigated in a series of mesocosm experiments where enclosed water volumes that comprised a natural plankton community were exposed to different carbon dioxide (CO2) concentrations. Calcification rates observed during those experiments were found to be highly variable, even among replicate mesocosms that were subject to similar CO2 perturbations. Here, data from an ocean acidification mesocosm experiment are reanalysed with an optimality-based dynamical plankton model. According to our model approach, cellular calcite formation is sensitive to variations in CO2 at the organism level. We investigate the temporal changes and variability in observations, with a focus on resolving observed differences in total alkalinity and particulate inorganic carbon (PIC). We explore how much of the variability in the data can be explained by variations of the initial conditions and by the level of CO2 perturbation. Nine mesocosms of one experiment were sorted into three groups of high, medium, and low calcification rates and analysed separately. The spread of the three optimised ensemble model solutions captures most of the observed variability. Our results show that small variations in initial abundance of coccolithophores and the prevailing physiological acclimation states generate differences in calcification that are larger than those induced by ocean acidification. Accordingly, large deviations between optimal mass flux estimates of carbon and of nitrogen are identified even between mesocosms that were subject to similar ocean acidification conditions. With our model-based data analysis we document how an ocean acidification response signal in calcification can be disentangled from the observed variability in PIC.
Assessing phytoplankton community structure in relation to hydrographic parameters and seasonal variation (Pre and Post Monsoon)
Published 3 April 2017 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, field, Indian, otherprocess, phytoplankton
The present study is conducted to assess hydrographical parameters, phytoplankton composition and the relationship between physicochemical parameters and phytoplankton assemblages along Chabahar coastal waters, South coast of Iran. Based on the collected samples from four stations, all the hydrographical parameters such as sea surface temperature, salinity, pH, DO and nitrate, inorganic phosphate, silicate, and phytoplankton assemblages were studied for five months (from April 2014 to August 2014). A total of 165 phytoplankton groups/taxa were observed in which the Dinophyceae formed the dominant group in all seasons. During the pre-monsoon season, Dinophyceae (56.5%) was the most abundant phytoplankton group followed by Bacillariophyceae (40.8%), Cyanophyceae (1.7 %) and Dictyochophyceae (0.8%). Meanwhile, in the post-monsoon season, Dinophyceae was dominant (49.5%), followed by Bacillariophyceae (46.7%), Cyanophyceae (1.8%), and Dictyochophyceae (1.8%). The highest phytoplankton density was in mid-May (19584953± 345182 cell per litter) and the lowest was in late July (163928± 1790 cells per liter). Salinity, nitrate, phosphate, silicate showed significant variation (p<0.05) among seasons while pH, seawater temperature, dissolve oxygen did not show significant differences in all stations over the study periods (p<0.05). Phytoplankton density correlated positively with water temperature and salinity. Results showed an increased concentration in phytoplankton density during Pre-monsoon season followed by Post-monsoon and monsoon season.
Moving ocean acidification research beyond a simple science: investigating ecological change and their stabilizers
Published 3 April 2017 Science ClosedTags: adaptation, algae, biological response, BRcommunity, methods, otherprocess, performance, primary production, review
The response of complex ecological communities to ocean acidification reflects interactions among species that propagate or dampen ecological change. Yet, most studies have been based on short-term experiments with limited numbers of interacting species. Both limitations tend to exaggerate measured effects and when combined with our predisposition for investigating change, we reduce insight into pathways of stability, acclimation and adaptation. Here, we review accepted and emerging insights into processes that drive ecological change (top-down and bottom-up) and the stabilizing processes by which ecological complexity may dampen change. With an emphasis on kelp forest examples, we show that boosted primary productivity from enriched CO2 creates competitive imbalances that drive habitat change, but we also recognise intensifying herbivory on these habitats dampens this change. Foraging herbivores thrive on CO2 enriched plants and over successive generations their populations expand. When we consider such population level responses, we open new questions regarding density-effects (e.g. competition, susceptibility to predation and disease), as well as the bottom-up benefits to predators. Nevertheless, research on predators has lagged behind because their wide-ranging behaviour typically imposes logistical difficulties for observational and experimental research. We know that ocean warming imposes elevated metabolic costs on their foraging whilst acidification hampers navigation of their larvae towards suitable habitat and impairs their hunting and avoidance of predators as adults. Connecting such top-down with bottom-up responses is fundamental for progress, and is also contingent on understanding the mechanisms that dampen change. These stabilizers have the potential to keep pace with abiotic change and thereby influence the drivers of acclimation and adaption. Certainly, we acknowledge that investigating change is often simpler and associated bold messages appeal to citation impact. Yet, if we are to anticipate the ability of complex ecological communities to persist in changing environments, then understanding the shifting balance between the propagation of resource enrichment and its consumption across trophic levels is central to this challenge.
Effects of CO2 concentration on a late summer surface sea ice community
Published 27 March 2017 Science ClosedTags: Antarctic, biological response, BRcommunity, field, growth, otherprocess, prokaryotes
Annual fast ice at Scott Base (Antarctica) in late summer contained a high biomass surface community of mixed phytoflagellates, dominated by the dinoflagellate, Polarella glacialis. At this time of the year, ice temperatures rise close to melting point and salinities drop to less than 20. At the same time, pH levels can rise above 9 and nutrients can become limiting. In January 2014, the sea ice microbial community from the top 30 cm of the ice was exposed to a gradient of pH and CO2 (5 treatments) that ranged from 8.87 to 7.12 and 5–215 µmol CO2 kg−1, respectively, and incubated in situ. While growth rates were reduced at the highest and lowest pH, the differences were not significant. Likewise, there were no significant differences in maximum quantum yield of PSII (Fv/Fm) or relative maximum electron transfer rates (rETRmax) among treatments. In a parallel experiment, a CO2 gradient of 26–230 µmol CO2 kg−1 (5 treatments) was tested, keeping pH constant. In this experiment, growth rates increased by approximately 40% with increasing CO2, although differences among treatments were not significant.. As in the previous experiment, there was no significant response in Fv/Fm or rETRmax. A synchronous grazing dilution experiment found grazing rates to be inconclusive These results suggest that the summer sea ice brine communities were not limited by in situ CO2 concentrations and were not adversely affected by pH values down to 7.1.
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Influence of ocean acidification and deep water upwelling on oligotrophic plankton communities in the subtropical North Atlantic: Insights from an in situ mesocosm study
Published 15 March 2017 Science ClosedTags: abundance, biogeochemistry, biological response, BRcommunity, chemistry, community composition, crustaceans, field, fish, mesocosms, methods, mollusks, multiple factors, nitrogen fixation, North Atlantic, nutrients, otherprocess, physiology, phytoplankton, primary production, prokaryotes, protists, virus, zooplankton
Oceanic uptake of anthropogenic carbon dioxide (CO2) causes pronounced shifts in marine carbonate chemistry and a decrease in seawater pH. Increasing evidence indicates that these changes – summarized by the term ocean acidification (OA) – can significantly affect marine food webs and biogeochemical cycles. However, current scientific knowledge is largely based on laboratory experiments with single species and artificial boundary conditions, whereas studies of natural plankton communities are still relatively rare. Moreover, the few existing community-level studies were mostly conducted in rather eutrophic environments, while less attention has been paid to oligotrophic systems such as the subtropical ocean gyres.
Here we report from a recent in situ mesocosm experiment off the coast of Gran Canaria in the eastern subtropical North Atlantic, where we investigated the influence of OA on the ecology and biogeochemistry of plankton communities in oligotrophic waters under close-to-natural conditions. This paper is the first in this Research Topic of Frontiers in Marine Biogeochemistry and provides (1) a detailed overview of the experimental design and important events during our mesocosm campaign, and (2) first insights into the ecological responses of plankton communities to simulated OA over the course of the 62-day experiment.
One particular scientific objective of our mesocosm experiment was to investigate how OA impacts might differ between oligotrophic conditions and phases of high biological productivity, which regularly occur in response to upwelling of nutrient-rich deep water in the study region. Therefore, we specifically developed a deep water collection system that allowed us to obtain ~85 m3 of seawater from ~650 m depth. Thereby, we replaced ~20% of each mesocosm’s volume with deep water, and thus successfully simulated a deep water upwelling event that induced a pronounced plankton bloom.
Our study revealed significant effects of OA on the entire food web, leading to a restructuring of plankton communities that emerged during the oligotrophic phase, and was further amplified during the bloom that developed in response to deep water addition. Such CO2-related shifts in plankton community composition could have consequences for ecosystem productivity, biomass transfer to higher trophic levels, and biogeochemical element cycling of oligotrophic ocean regions.
