Posts Tagged 'community composition'

Combined effects of ocean acidification and increased light intensity on natural phytoplankton communities from two Southern Ocean water masses

The composition of phytoplankton communities plays a major role in the efficiency of the biological carbon pump and energy transfer to higher trophic levels. Phytoplankton community composition can be significantly affected by changes in environmental conditions. We investigated the effect of increased pCO2 and light intensity on natural communities from two Southern Ocean water masses, the Subtropical Frontal Zone (STFZ) and Subantarctic Surface Waters (SASW). The community in both experiments shifted to predominately dinoflagellates under high pCO2 and high light and the community composition was significantly different between both treatments at the end of the incubation. In the STFZ assemblage, the combination of increased light and pCO2 had a small positive effect on diatom, coccolithophores and picoeukaryote abundance at the beginning of the experiment while higher pCO2 alone had no or a negative effect. In the SASW assemblage, the combination of increased light and pCO2 had a negative effect on diatom abundance while lower pH/higher pCO2 alone resulted in an increase in diatom counts compared to the control. Coccolithophores grew only in the control treatment. Our results show that there are taxon-specific and locality specific differences in natural phytoplankton community responses to increased light and pCO2 within low nutrient regions.

Continue reading ‘Combined effects of ocean acidification and increased light intensity on natural phytoplankton communities from two Southern Ocean water masses’

Elevated pCO2 alters marine heterotrophic bacterial community composition and metabolic potential in response to a pulse of phytoplankton organic matter

Factors that affect the respiration of organic carbon by marine bacteria can alter the extent to which the oceans act as a sink of atmospheric carbon dioxide. We designed seawater dilution experiments to assess the effect of pCO2 enrichment on heterotrophic bacterial community composition and metabolic potential in response to a pulse of phytoplankton‐derived organic carbon. Experiments included treatments of elevated (1000 ppm) and low (250 ppm) pCO2, amended with 10 μmol L‐1 dissolved organic carbon from Emiliana huxleyi lysates, and were conducted using surface‐seawater collected from the South Pacific Subtropical Gyre. To assess differences in community composition and metabolic potential, shotgun metagenomic libraries were sequenced from low and elevated pCO2 treatments collected at the start of the experiment and following exponential growth. Our results indicate bacterial communities changed markedly in response to the organic matter pulse over time and was significantly affected by pCO2 enrichment. Elevated pCO2 also had disproportionate effects on the abundance of sequences related to proton pumps, carbohydrate metabolism, modifications of the phospholipid bilayer, resistance to toxic compounds and conjugative transfer. These results contribute to a growing understanding of the effects of elevated pCO2 on bacteria‐mediated carbon cycling during phytoplankton bloom conditions in the marine environment.

Continue reading ‘Elevated pCO2 alters marine heterotrophic bacterial community composition and metabolic potential in response to a pulse of phytoplankton organic matter’

Toxic algal bloom induced by ocean acidification disrupts the pelagic food web

Ocean acidification, the change in seawater carbonate chemistry due to the uptake of anthropogenic CO2, affects the physiology of marine organisms in multiple ways1. Diverse competitive and trophic interactions transform the metabolic responses to changes in community composition, seasonal succession and potentially geographical distribution of species. The health of ocean ecosystems depends on whether basic biotic functions are maintained, ecosystem engineers and keystone species are retained, and the spread of nuisance species is avoided2. Here, we show in a field experiment that the toxic microalga Vicicitus globosus has a selective advantage under ocean acidification, increasing its abundance in natural plankton communities at CO2 levels higher than 600 µatm and developing blooms above 800 µatm CO2. The mass development of V. globosus has had a dramatic impact on the plankton community, preventing the development of the micro- and mesozooplankton communities, thereby disrupting trophic transfer of primary produced organic matter. This has prolonged the residence of particulate matter in the water column and caused a strong decline in export flux. Considering its wide geographical distribution and confirmed role in fish kills3, the proliferation of V. globosus under the IPCC4 CO2 emission representative concentration pathway (RCP4.5 to RCP8.5) scenarios may pose an emergent threat to coastal communities, aquaculture and fisheries.

Continue reading ‘Toxic algal bloom induced by ocean acidification disrupts the pelagic food web’

Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages

Increasing atmospheric carbon dioxide and its dissolution in seawater have reduced ocean pH and carbonate ion concentrations, with potential implications on calcifying organisms. To assess the response of large Caribbean benthic foraminifera to low carbonate saturation conditions, we analyzed benthic foraminifers’ abundance and relative distribution in surface sediments in proximity to low-carbonate-saturation submarine springs and at adjacent control sites. Our results show that the total abundance of large benthic foraminifera was significantly lower at the low-pH submarine springs than at control sites, although responses were species specific. The relative abundance of high-magnesium, porcelaneous foraminifera was higher than that of hyaline foraminifera at the low-pH springs due to the abundant Archaias angulatus, a chlorophyte-bearing foraminifer, which secretes a large and robust test that is more resilient to dissolution at low-calcite saturation. The different assemblages found at the submarine springs indicate that calcareous symbiont-barren foraminifera are more sensitive to the effects of ocean acidification than agglutinated and symbiont-bearing foraminifera, suggesting that future ocean acidification will likely impact natural benthic foraminifera populations.

Continue reading ‘Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages’

Effect of elevated pCO2 on trace gas production during an ocean acidification mesocosm experiment (update)

A mesocosm experiment was conducted in Wuyuan Bay (Xiamen), China, to investigate the effects of elevated pCO2 on the phytoplankton species Phaeodactylum tricornutum (P. tricornutum), Thalassiosira weissflogii (T. weissflogii) and Emiliania huxleyi (E. huxleyi) and their production ability of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), as well as four halocarbon compounds, bromodichloromethane (CHBrCl2), methyl bromide (CH3Br), dibromomethane (CH2Br2) and iodomethane (CH3I). Over a period of 5 weeks, P. tricornuntum outcompeted T. weissflogii and E. huxleyi, comprising more than 99% of the final biomass. During the logarithmic growth phase (phase I), mean DMS concentration in high pCO2 mesocosms (1000µatm) was 28% lower than that in low pCO2 mesocosms (400µatm). Elevated pCO2 led to a delay in DMSP-consuming bacteria concentrations attached to T. weissflogii and P. tricornutum and finally resulted in the delay of DMS concentration in the high pCO2 treatment. Unlike DMS, the elevated pCO2 did not affect DMSP production ability of T. weissflogii or P. tricornuntum throughout the 5-week culture. A positive relationship was detected between CH3I and T. weissflogii and P. tricornuntum during the experiment, and there was a 40% reduction in mean CH3I concentration in the high pCO2 mesocosms. CHBrCl2, CH3Br, and CH2Br2 concentrations did not increase with elevated chlorophyll a (Chl a) concentrations compared with DMS(P) and CH3I, and there were no major peaks both in the high pCO2 or low pCO2 mesocosms. In addition, no effect of elevated pCO2 was identified for any of the three bromocarbons.

Continue reading ‘Effect of elevated pCO2 on trace gas production during an ocean acidification mesocosm experiment (update)’

Rhodoliths holobionts in a changing ocean: host-microbes interactions mediate coralline algae resilience under ocean acidification

Life in the ocean will increasingly have to contend with a complex matrix of concurrent shifts in environmental properties that impact their physiology and control their life histories. Rhodoliths are coralline red algae (Corallinales, Rhodophyta) that are photosynthesizers, calcifiers, and ecosystem engineers and therefore represent important targets for ocean acidification (OA) research. Here, we exposed live rhodoliths to near-future OA conditions to investigate responses in their photosynthetic capacity, calcium carbonate production, and associated microbiome using carbon uptake, decalcification assays, and whole genome shotgun sequencing metagenomic analysis, respectively. The results from our live rhodolith assays were compared to similar manipulations on dead rhodolith (calcareous skeleton) biofilms and water column microbial communities, thereby enabling the assessment of host-microbiome interaction under climate-driven environmental perturbations.

Continue reading ‘Rhodoliths holobionts in a changing ocean: host-microbes interactions mediate coralline algae resilience under ocean acidification’

Longstanding signals of marine community structuring by winter storm wave-base

Coastal marine communities face both physical oceanographic changes and altered ecological relationships due to indirect human activities, such as climate-related changes, and direct human activities, such as extraction of wave energy as a renewable resource. Often single physical oceanographic changes and altered ecological relationships are investigated, rather than multiple potential drivers. Here we investigated the links between the structure of offshore benthic bivalve communities to multiple physical drivers including wave-base, and more traditional drivers of marine soft sediment community structure (e.g. temperature, pH, dissolved oxygen, salinity, and nutrients). Our benthic bivalve community data (both modern and historical) were collected from bulk sediment box-core samples taken over a depth range of 20-70 m on the continental shelf of Newport, Oregon, USA. Environmental data were collected through CTD casts at sampling locations and through NOAA Buoy Station 46094. We used a non-linear hierarchical regression approach to look for a systematic response in the benthos. Subtidal bivalve communities structured themselves along a depth gradient with a distinct shift in species’ rank abundance at 50 m, and this shift was most strongly associated with storm wave-base. This distinct wave-driven community structure was present in both modern-day bivalve communities and century-scale historical communities, suggesting both the importance of waves and the long-standing nature of their impacts on biological communities in this system. These results emphasize potential consequences of changing wave-base on this shelf, which could occur indirectly through changing storm regimes due to anthropogenic climate change or directly through large-scale wave energy harvest.

Continue reading ‘Longstanding signals of marine community structuring by winter storm wave-base’


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Ocean acidification in the IPCC AR5 WG II

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