Impacts of Coastal Acidification on Louisiana Plankton

Anthropogenic input of carbon dioxide (CO2) has an increasingly acidifying effect on the world’s oceans with the potential to impact biogeochemical cycles and food web dynamics. Coastal Louisiana is an area highly vulnerable to changing climate, but the unique local water chemistry created by input from the Mississippi and Atchafalaya Rivers makes the manifestation of elevated CO2 and its biological implications difficult to predict. Louisiana estuaries are highly productive and support a large commercial market for the eastern oyster, Crassostrea virginica. This study explores the use of experimental microcosms to expose natural phytoplankton assemblages and larval oysters to elevated pCO2. Spring and fall phytoplankton were collected from two biogeochemically distinct Louisiana estuaries and cultured in lab for 16 weeks while bubbling with CO2 enriched air corresponding to current (400 ppm) and future (1000 ppm) pCO2 levels. Spring phytoplankton assemblages increased in diatoms over the first 8 weeks, but after 14 weeks of incubation transitioned to cyanobacterial dominance regardless of pCO2 level, likely due to a nutrient imbalance. Fall phytoplankton assemblages also increased in diatoms over the first 8 weeks, but after 14 weeks returned to their original community structure, showing evidence of adaptation to elevated pCO2 exposure. Over the course of a 6-day pilot study, resilience was also observed during early larval oyster development, as D-stage C. virginica survived and grew at the same rate in control and elevated pCO2 cultures. In Louisiana, spring and fall phytoplankton blooms in conjunction with water temperature are critical in dictating the timing of oyster spawning. When low pH is compounded with seasonal salinity, temperature, and nutrient variations, it has the potential to influence the phytoplankton community during a critical oyster spawning time, creating a mismatch. Coastal acidification could affect the success of larval oysters by changing the availability and quality of its food source, phytoplankton

Impacts of elevated pCO\u3csub\u3e2\u3c/sub\u3e on estuarine phytoplankton biomass and community structure in two biogeochemically distinct systems in Louisiana, USA

© 2018 Ocean acidification has the potential to impact the ocean\u27s biogeochemical cycles and food web dynamics, with phytoplankton in the distinctive position to profoundly influence both, as individual phytoplankton species play unique roles in energy flow and element cycling. Previous studies have focused on short-term exposure of monocultures to low pH, but do not reflect the competitive dynamics within natural phytoplankton communities. This study explores the use of experimental microcosms to expose phytoplankton assemblages to elevated pCO2 for an extended period of time. Phytoplankton communities were collected from two biogeochemically distinct Louisiana estuaries, Caillou Lake (CL) and Barataria Bay (BB), and cultured in lab for 16 weeks while bubbling CO2 enriched air corresponding to current (400 ppm) and future (1000 ppm) pCO2 levels. Results suggest that elevated pCO2 does not implicitly catalyze an increase in phytoplankton biomass (chlorophyll a). While pigment data showcased a parabolic trend and microscopic observations revealed a loss in species diversity within each major taxonomic class. By the end of the 16-week incubation, 10 out of the 12 cultures had a community structure analogous to that of the startup phytoplankton assemblage collected from the field. Natural phytoplankton assemblages exposed to elevated pCO2 experienced multiple transitional states over the course of a 16-week incubation, indicating that there is no deterministic successional pathway dictated by coastal acidification but community adaptation was observed

Image_4_Production of Calcium-Binding Proteins in Crassostrea virginica in Response to Increased Environmental CO2 Concentration.PDF

<p>Biomineralization is a complexed process by organisms producing protective and supportive structures. Employed by mollusks, biomineralization enables creation of external shells for protection against environmental stressors. The shell deposition mechanism is initiated in the early stages of development and is dependent upon the concentration and availability of calcium carbonate ions. Changes in concentrations of the critical ions required for shell formation can result in malformation of shells. As pCO₂ concentrations in the atmosphere continue to increase, the oceans are becoming more acidified. This process, known as ocean acidification (OA), has demonstrated adverse effects on shell formation in calcifying organisms across taxa. Although OA is known to inhibit the shell deposition in mollusks, the impact of OA on the gene regulation of calcium deposition remains unknown. Here we show the responses of four calcium-binding protein genes, caltractin (cetn), calmodulin (calm), calreticulin (calr), and calnexin (canx), to CO₂-derived OA using a Crassostrea virginica mantle cell (CvMC) culture model and a larval C. virginica model. These four genes were cloned from C. virginica and the three-dimensional structures of the proteins encoded by these four genes were fully characterized using homolog modeling methods. Although an acidified environment by increased atmospheric pCO₂ (1,000 ppm) did not result in significant effects on CvMC proliferation and apoptosis, lower environmental pH induced upregulations of all four calcium-binding protein genes in CvMCs. Similarly, increased pCO₂ did not affect the growth of larval C. virginica in the early stages of development. However, elevated pCO₂ concentrations enhanced the expression of these calcium-binding protein genes at the protein level. The four calcium-binding protein genes demonstrated responsive expression profiles to an acidified environment at both cellular and individual levels. Further investigation of these genes may provide insight into the molecular regulation of mollusk biomineralization under OA stress.</p

Image_1_Production of Calcium-Binding Proteins in Crassostrea virginica in Response to Increased Environmental CO2 Concentration.PDF

<p>Biomineralization is a complexed process by organisms producing protective and supportive structures. Employed by mollusks, biomineralization enables creation of external shells for protection against environmental stressors. The shell deposition mechanism is initiated in the early stages of development and is dependent upon the concentration and availability of calcium carbonate ions. Changes in concentrations of the critical ions required for shell formation can result in malformation of shells. As pCO₂ concentrations in the atmosphere continue to increase, the oceans are becoming more acidified. This process, known as ocean acidification (OA), has demonstrated adverse effects on shell formation in calcifying organisms across taxa. Although OA is known to inhibit the shell deposition in mollusks, the impact of OA on the gene regulation of calcium deposition remains unknown. Here we show the responses of four calcium-binding protein genes, caltractin (cetn), calmodulin (calm), calreticulin (calr), and calnexin (canx), to CO₂-derived OA using a Crassostrea virginica mantle cell (CvMC) culture model and a larval C. virginica model. These four genes were cloned from C. virginica and the three-dimensional structures of the proteins encoded by these four genes were fully characterized using homolog modeling methods. Although an acidified environment by increased atmospheric pCO₂ (1,000 ppm) did not result in significant effects on CvMC proliferation and apoptosis, lower environmental pH induced upregulations of all four calcium-binding protein genes in CvMCs. Similarly, increased pCO₂ did not affect the growth of larval C. virginica in the early stages of development. However, elevated pCO₂ concentrations enhanced the expression of these calcium-binding protein genes at the protein level. The four calcium-binding protein genes demonstrated responsive expression profiles to an acidified environment at both cellular and individual levels. Further investigation of these genes may provide insight into the molecular regulation of mollusk biomineralization under OA stress.</p

Production of Calcium-Binding Proteins in Crassostrea virginica in Response to Increased Environmental CO2 Concentration

Biomineralization is a complexed process by organisms producing protective and supportive structures. Employed by mollusks, biomineralization enables creation of external shells for protection against environmental stressors. The shell deposition mechanism is initiated in the early stages of development and is dependent upon the concentration and availability of calcium carbonate ions. Changes in concentrations of the critical ions required for shell formation can result in malformation of shells. As pCO2 concentrations in the atmosphere continue to increase, the oceans are becoming more acidified. This process, known as ocean acidification (OA), has demonstrated adverse effects on shell formation in calcifying organisms across taxa. Although OA is known to inhibit the shell deposition in mollusks, the impact of OA on the gene regulation of calcium deposition remains unknown. Here we show the responses of four calcium-binding protein genes, caltractin (cetn), calmodulin (calm), calreticulin (calr), and calnexin (canx), to CO2-derived OA using a Crassostrea virginica mantle cell (CvMC) culture model and a larval C. virginica model. These four genes were cloned from C. virginica and the three-dimensional structures of the proteins encoded by these four genes were fully characterized using homolog modeling methods. Although an acidified environment by increased atmospheric pCO2 (1,000 ppm) did not result in significant effects on CvMC proliferation and apoptosis, lower environmental pH induced upregulations of all four calcium-binding protein genes in CvMCs. Similarly, increased pCO2 did not affect the growth of larval C. virginica in the early stages of development. However, elevated pCO2 concentrations enhanced the expression of these calcium-binding protein genes at the protein level. The four calcium-binding protein genes demonstrated responsive expression profiles to an acidified environment at both cellular and individual levels. Further investigation of these genes may provide insight into the molecular regulation of mollusk biomineralization under OA stress