Posts Tagged 'BRcommunity'

Competitive interactions moderate the effects of elevated temperature and atmospheric CO2 on the health and functioning of oysters

Global increases in sea temperatures and atmospheric concentrations of CO2 may affect the health of calcifying shellfish. Little is known, however, about how competitive interactions within and between species may influence how species respond to multiple stressors. We experimentally assessed separate and combined effects of temperature (12 or 16°C) and atmospheric CO2 concentrations (400 and 1000 ppm) on the health and biological functioning of native (Ostrea edulis) and invasive (Crassostrea gigas) oysters held alone and in intraspecific or interspecific mixtures. We found evidence of reduced phagocytosis under elevated CO2 and, when combined with increased temperature, a reduction in the number of circulating haemocytes. Generally, C. gigas showed lower respiration rates relative to O. edulis when the species were in intraspecific or interspecific mixtures. In contrast, O. edulis showed a higher respiration rate relative to C. gigas when held in an interspecific mixture and exhibited lower clearance rates when held in intraspecific or interspecific mixtures. Overall, clearance rates of C. gigas were consistently greater than those of O. edulis. Collectively, our findings indicate that a species’ ability to adapt metabolic processes to environmental conditions can be modified by biotic context and may make some species (here, C. gigas) competitively superior and less vulnerable to future climatic scenarios at local scales. If these conclusions are generic, the relative role of species interactions, and other biotic parameters, in altering the outcomes of climate change will require much greater research emphasis.

Continue reading ‘Competitive interactions moderate the effects of elevated temperature and atmospheric CO2 on the health and functioning of oysters’

The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt (update)

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. Samples for phytoplankton enumeration were collected from the upper mixed layer (30 m) during two cruises, the first to the South Atlantic sector (January–February 2011; 60° W–15° E and 36–60° S) and the second in the South Indian sector (February–March 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 Subtropical, Polar, and Subantarctic fronts. The influence of environmental parameters, such as sea surface temperature (SST), salinity, carbonate chemistry (pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macronutrients (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, with the coccolithophore Emiliania huxleyi and diatoms Fragilariopsis nana, F. pseudonana, and Pseudo-nitzschia spp. as the most numerically dominant and widely distributed. A combination of SST, macronutrient concentrations, and pCO2 provided the best statistical descriptors of the biogeographic variability in biomineralizing species composition between stations. Emiliania huxleyi occurred in silicic acid-depleted waters between the Subantarctic Front and the Polar Front, a favorable environment for this species after spring diatom blooms remove silicic acid. Multivariate statistics identified a combination of carbonate chemistry and macronutrients, covarying with temperature, as the dominant drivers of biomineralizing nanoplankton in the GCB sector of the Southern Ocean.

Continue reading ‘The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt (update)’

Nutrient loading fosters seagrass productivity under ocean acidification

The effects of climate change are likely to be dependent on local settings. Nonetheless, the compounded effects of global and regional stressors remain poorly understood. Here, we used CO2 vents to assess how the effects of ocean acidification on the seagrass, Posidonia oceanica, and the associated epiphytic community can be modified by enhanced nutrient loading. P. oceanica at ambient and low pH sites was exposed to three nutrient levels for 16 months. The response of P. oceanica to experimental conditions was assessed by combining analyses of gene expression, plant growth, photosynthetic pigments and epiphyte loading. At low pH, nutrient addition fostered plant growth and the synthesis of photosynthetic pigments. Overexpression of nitrogen transporter genes following nutrient additions at low pH suggests enhanced nutrient uptake by the plant. In addition, enhanced nutrient levels reduced the expression of selected antioxidant genes in plants exposed to low pH and increased epiphyte cover at both ambient and low pH. Our results show that the effects of ocean acidification on P. oceanica depend upon local nutrient concentration. More generally, our findings suggest that taking into account local environmental settings will be crucial to advance our understanding of the effects of global stressors on marine systems.

Continue reading ‘Nutrient loading fosters seagrass productivity under ocean acidification’

The fatty acid content of plankton is changing in subtropical coastal waters as a result of OA: results from a mesocosm study


• First mesocosm experiment to investigate OA impacts on fatty acids profiles of plankton in subtropical coastal waters.
• Contents of total FA, PUFA, and MUFA of phytoplankton increased at late exponential phase under high pCO2 condition.
• Mesozooplankton grazing rate decreased, while DHA uptake rate increased under high pCO2 condition.


Ocean Acidification (OA) effects on marine plankton are most often considered in terms of inorganic carbon chemistry, but decreasing pH may influence other aspects of cellular metabolism. Here we present the effects of OA on the fatty acid (FA) content and composition of an artificial phytoplankton community (Phaeodactylum tricornutum, Thalassiosira weissflogii, and Emiliania huxleyi) in a fully replicated, ∼4 m3 mesocosm study in subtropical coastal waters (Wuyuan Bay, China, 24.52°N, 117.18°E) at present day (400 μatm) and elevated (1000 μatm) pCO2 concentrations. Phytoplankton growth occurred in three phases during the 33-day experiment: an initial exponential growth leading to senescence and a subsequent decline phase. Phytoplankton sampled from these mesocosms were fed to mesozooplankton collected by net haul from Wuyuan Bay. Concentrations of saturated fatty acids (SFA) in both phytoplankton and mesozooplankton remained high under acidified and non-acidified conditions. However, polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA) increased significantly more under elevated pCO2 during the late exponential phase (Day 13), indicating increased nutritional value for zooplankton and higher trophic levels. Indeed, uptake rates of the essential FA docosahexaenoic acid (C20:5n3, DHA) increased in mesozooplankton under acidified conditions. However, mesozooplankton grazing rates decreased overall with elevated pCO2. Our findings show that these selected phytoplankton species have a relatively high tolerance to acidification in terms of FA production, and local mesozooplankton in these subtropical coastal waters can maintain their FA composition under end of century ocean acidification conditions.

Continue reading ‘The fatty acid content of plankton is changing in subtropical coastal waters as a result of OA: results from a mesocosm study’

Combined, short-term exposure to reduced seawater pH and elevated temperature induces community shifts in an intertidal meiobenthic assemblage

In future global change scenarios the surface ocean will experience continuous acidification and rising temperatures. While effects of both stressors on marine, benthic communities are fairly well studied, consequences of the interaction of both factors remain largely unknown. We performed a short-term microcosm experiment exposing a soft-bottom community from an intertidal flat in the Westerscheldt estuary to two levels of seawater pH (ambient pHT = 7.9, reduced pHT = 7.5) and temperature (10 °C ambient and 13 °C elevated temperature) in a crossed design. After 8 weeks, meiobenthic community structure and nematode staining ratios, as a proxy for mortality, were compared between treatments and structural changes were related to the prevailing abiotic conditions in the respective treatments (pore water pHT, sediment grain size, total organic matter content, total organic carbon and nitrogen content, phytopigment concentrations and carbonate concentration). Pore water pHT profiles were significantly altered by pH and temperature manipulations and the combination of elevated temperature and reduced pH intensified the already more acidic porewater below the oxic zone. Meiofauna community composition was significantly affected by the combination of reduced pH and elevated temperature resulting in increased densities of predatory Platyhelminthes, reduced densities of Copepoda and Nauplii and complete absence of Gastrotricha compared to the experimental control. Furthermore, nematode staining ratio was elevated when seawater pH was reduced pointing towards reduced degradation rates of dead nematode bodies. The observed synergistic interactions of pH and temperature on meiobenthic communities and abiotic sediment characteristics underline the importance of multistressor experiments when addressing impacts of global change on the marine environment.

Continue reading ‘Combined, short-term exposure to reduced seawater pH and elevated temperature induces community shifts in an intertidal meiobenthic assemblage’

Effects of the interaction of ocean acidification, solar radiation, and warming on biogenic dimethylated sulfur compounds cycling in the Changjiang River Estuary

Ocean acidification (OA) affects marine primary productivity and community structure, and therefore may influence the biogeochemical cycles of volatile biogenic dimethyl sulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) and photochemical oxidation product dimethyl sulfoxide (DMSO). A 23-day incubation experiment on board was conducted to investigate the short-term response of biogenic sulfur compounds production and cycling to OA in the Changjiang River Estuary and further understand its effects on biogenic sulfur compounds. Result showed that phytoplankton abundance and species presented remarkable differences under three different pH levels in the late stage of the experiment. A significant reduction in chlorophyll a (Chl-a), DMS, particulate DMSP (DMSPp), and dissolved DMSO (DMSOd) concentrations was identified under high CO2 levels. Moreover, minimal change was observed in the production of dissolved DMSP (DMSPd) and particulate DMSO (DMSOp) among treatments. The ratios of DMS, total DMSP (DMSPt), and total DMSO (DMSOt) to Chl-a were also not affected by a change in pH. In addition, DMS and DMSOd were highly related to mean bacterial abundance under three pH levels. Additional incubation experiments on light and temperature showed that the influence of pH on productions of dimethylated sulfur compounds also depended on solar radiation and temperature conditions. DMS photodegradation rate increased with decreasing pH under full-spectrum natural light and UVB light. Thus, OA may lead to decreasing DMS concentrations in the surface seawater. Light and temperature conditions also play an important role in the production and cycling of biogenic sulfur compounds.

Continue reading ‘Effects of the interaction of ocean acidification, solar radiation, and warming on biogenic dimethylated sulfur compounds cycling in the Changjiang River Estuary’

The impact of elevated CO2 on Prochlorococcus and microbial interactions with ‘helper’ bacterium Alteromonas

Prochlorococcus is a globally important marine cyanobacterium that lacks the gene catalase and relies on ‘helper’ bacteria such as Alteromonas to remove reactive oxygen species. Increasing atmospheric CO2 decreases the need for carbon concentrating mechanisms and photorespiration in phytoplankton, potentially altering their metabolism and microbial interactions even when carbon is not limiting growth. Here, Prochlorococcus (VOL4, MIT9312) was co-cultured with Alteromonas (strain EZ55) under ambient (400p.p.m.) and elevated CO2 (800p.p.m.). Under elevated CO2, Prochlorococcus had a significantly longer lag phase and greater apparent die-offs after transfers suggesting an increase in oxidative stress. Whole-transcriptome analysis of Prochlorococcus revealed decreased expression of the carbon fixation operon, including carboxysome subunits, corresponding with significantly fewer carboxysome structures observed by electron microscopy. Prochlorococcus co-culture responsive gene 1 had significantly increased expression in elevated CO2, potentially indicating a shift in the microbial interaction. Transcriptome analysis of Alteromonas in co-culture with Prochlorococcus revealed decreased expression of the catalase gene, known to be critical in relieving oxidative stress in Prochlorococcus by removing hydrogen peroxide. The decrease in catalase gene expression was corroborated by a significant ~6-fold decrease in removal rates of hydrogen peroxide from co-cultures. These data suggest Prochlorococcus may be more vulnerable to oxidative stress under elevated CO2 in part from a decrease in ecosystem services provided by heterotrophs like Alteromonas. This work highlights the importance of considering microbial interactions in the context of a changing ocean.

Continue reading ‘The impact of elevated CO2 on Prochlorococcus and microbial interactions with ‘helper’ bacterium Alteromonas’

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Ocean acidification in the IPCC AR5 WG II

OUP book