Posts Tagged 'North Atlantic'



Physiological effects of climate change on the American lobster, Homarus americanus

Increases in anthropogenic input of carbon dioxide into the atmosphere have caused widespread patterns of ocean warming and ocean acidification. Both processes will likely have major impacts on commercial fisheries and aquaculture, with acidification posing a particular threat to many marine calcifying invertebrates. In the State of Maine, commercial fisheries landings and a growing aquaculture industry have a combined value in excess of $600 million, 75% of which is sustained by marine calcifiers. Moreover, the American lobster (Homarus americanus) supports the most economically valuable fishery in the Gulf of Maine and Atlantic Canada. Previous research has documented a strong link between lobster biology and ocean temperature, but it is unclear how H. americanuswill respond to a rapidly changing environment. Additionally, previous efforts have focused primarily on the direct effects of a changing climate on lobsters (i.e., changes in growth, survival, and calcification), with little emphasis placed on the potential for sublethal effects to impact the population.

In this dissertation, I explore the effects of increasing ocean temperatures and acidification on H. americanus to understand how environmental changes can alter the health and physiology in multiple life stages of marine calcifying invertebrates. In Chapter 1, I introduce the global patterns and effects of climate change on marine calcifiers and review the current state of knowledge of my study species. In Chapter 2, I discuss how exposure to warming conditions impacts larval development, with a focus on potential trade-offs between enhanced growth and developmental instability. In Chapter 3, I continue to explore the sublethal impacts of warming on larval lobsters by examining changes in gene expression patterns in postlarvae exposed to varying temperatures during development. Chapter 4 explores how short-term exposure to acidified conditions impacts subadult (50 – 65 mm carapace length) lobster thermal physiology, hemolymph chemistry, and stress levels, a relatively understudied yet crucial life history stage. Finally, Chapter 5 summarizes the overarching themes of the dissertation, and concludes by providing suggestions for future research efforts.

Continue reading ‘Physiological effects of climate change on the American lobster, Homarus americanus’

Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows

The net ecosystem productivity (NEP) of two contrasting seagrass meadows within one of the largest seagrass ecosystems in the world, Florida Bay, was assessed using direct measurements over consecutive diel cycles. We report significant differences between NEP determined by dissolved inorganic carbon (NEPDIC) and by dissolved oxygen (NEPDO), likely driven by differences in air-water gas exchange and contrasting responses to variations in light intensity. In this first direct determination of NEPDIC in seagrasses, we found that both seagrass ecosystems were net heterotrophic, on average, despite large differences in seagrass net aboveground primary productivity. Net ecosystem calcification (NEC) was also negative, indicating that both sites were net dissolving of carbonate minerals. We suggest that a combination of carbonate dissolution and respiration in sediments exceeded seagrass primary production and calcification, supporting our negative NEP and NEC measurements. Furthermore, a simple budget analysis indicates that these two seagrass meadows have contrasting impacts on pH buffering of adjacent systems, due to variations in the TA : DIC export ratio. The results of this study highlight the need for better temporal resolution, as well as accurate carbonate chemistry accounting in future seagrass metabolism studies.

Continue reading ‘Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows’

Impacts of ocean acidification on carboxylated carbon nanotube effects induced in the clam species Ruditapes philippinarum

Although the increased production of nanoparticles (NPs) has raised extensive concerns about the potential toxic effects on aquatic organisms, as well as the increasing evidences which documented the impact of ocean acidification (OA) on the physiology and fitness of marine invertebrates, limited number of studies reported their combined toxic effects. For these reasons, in the present study, we investigated the physiological and biochemical responses of one of the most economically important bivalve species in the World, the Manila clam Ruditapes philippinarum, after the exposure to an environmnetally relevant concentration of carboxylated carbon nanotubes and predicted OA conditions. The results showed that the organisms were not only susceptible to NPs but also to seawater acidification. Different responses between low pH and NPs for most tested biomarkers were observed, both in terms of physiological (respiration rate) and biochemical responses (metabolic capacity, oxitative status and neurotoxicity). Acidified pH significantly decreased the respiration rate and metabolism and increased the energy reserves consumption. Moreover, increase of the oxidative damage was also detected under this condition confirming that the mechanism of enhanced toxicity in the organisms should be attributed to lower aggregation state with more suspended NPs in acidified seawater, indicating that seawater acidification significantly influenced the impact of the used NPs in the exposed organisms.

Continue reading ‘Impacts of ocean acidification on carboxylated carbon nanotube effects induced in the clam species Ruditapes philippinarum’

Ecological and socioeconomic strategies to sustain Caribbean coral reefs in a high-CO2 world

The Caribbean and Western Atlantic region hosts one of the world’s most diverse geopolitical regions and a unique marine biota distinct from tropical seas in the Pacific and Indian Oceans. While this region varies in human population density, GDP and wealth, coral reefs, and their associated ecosystem services, are central to people’s livelihoods. Unfortunately, the region’s reefs have experienced extensive degradation over the last several decades. This degradation has been attributed to a combination of disease, overfishing, and multiple pressures from other human activities. Furthermore, the Caribbean region has experienced rapid ocean warming and acidification as a result of climate change that will continue and accelerate throughout the 21st century. It is evident that these changes will pose increasing threats to Caribbean reefs unless imminent actions are taken at the local, regional and global scale. Active management is required to sustain Caribbean reefs and increase their resilience to recover from acute stress events. Here, we propose local and regional solutions to halt and reverse Caribbean coral reef degradation under ongoing ocean warming and acidification. Because the Caribbean has already experienced high coral reef degradation, we suggest that this region may be suitable for more aggressive interventions than might be suitable for other regions. Solutions with direct ecological benefits highlighted here build on existing knowledge of factors that can contribute to reef restoration and increased resilience in the Caribbean: (1) management of water quality, (2) reduction of unsustainable fishing practices, (3) application of ecological engineering, and (4) implementing marine spatial planning. Complementary socioeconomic and governance solutions include: (1) increasing communication and leveraging resources through the establishment of a regional reef secretariat, (2) incorporating reef health and sustainability goals into the blue economy plans for the region, and (3) initiating a reef labelling program to incentivize corporate partnerships for reef restoration and protection to sustain overall reef health in the region.

Continue reading ‘Ecological and socioeconomic strategies to sustain Caribbean coral reefs in a high-CO2 world’

Impact de l’acidification et du réchauffement sur les communautés planctoniques de l’estuaire du Saint-Laurent et la production de diméthylsulfure (in French)

Anthropogenic carbon dioxide (CO2) emissions have increased since the industrial revolution, leading to modifications in atmospheric CO2 content and an increase in oceanic CO2 partial pressures (pCO2). The uptake of CO2 by the oceans has resulted in a lowering of surface water pH, corresponding to an increase in the acidity of the oceans by ~30 % compared with pre-industrial times. Furthermore, climate change resulting from the accumulation of anthropogenic CO2 in the atmosphere is responsible for the observed warming of sea surface temperatures since the mid 20th century. The fate of planktonic communities in the face of these changes in the marine environment over the next century remains uncertain. Even less understood are the possible interactions of acidification and warming on the production of dimethylsulfide (DMS), a sulfur-containing gas produced by planktonic communities and involved in climate regulation. The aim of this thesis is to determine the impact of heightened pCO2 on the development of the phytoplanktonic blooms in the Lower St. Lawrence Estuary (LSLE), and their production of DMS, as well as to evaluate how concomitant warming could modulate the effects of acidification. Two intricate experiments were carried out during this study. First, a microcosm experiment (~20 L) was conducted in the summer of 2013 to assess the effects of pCO2 on the development of the LSLE spring diatom bloom, paying special attention to the microbial processes governing the production of DMS. Second, a multifactorial mesocosm experiment (~2600 L) was carried out in the fall of 2014 to investigate the combined effects of pCO2 and temperature on the development of the fall bloom in the LSLE and the production of DMS. Results from our microcosm experiment show that the blooming phytoplankton community of the LSLE during spring is resistant to pCO2 increases superior to the expected values for 2100. This resistance likely reflects its adaptation to the estuarine setting, an environment known for rapid and intense fluctuations of pCO2. This first experiment has also highlighted a reduction of the average concentrations of DMS by 15 and 40 % in planktonic assemblages respectively subjected to pCO2 of ~1850 μatm and ~2700 μatm compared to the control (~775 μatm). Parallel incubations have shown, using 35S-DMSPd, that the negative effect of acidification on DMS mostly stemmed from a decrease in the conversion efficiency of DMSP to DMS by bacteria. The second experiment has also highlighted a strong resistance of the diatom Skeletonema costatum to a wide range of pH (~8.0–7.2), and corresponding pCO2 (~90–3000 μatm). In this study, a warming of 5 °C accelerated the development and decline of the bloom, but did not affect the integrated primary production over the duration of the experiment. As in the first experiment, heightened pCO2 resulted in a decrease of average concentrations of DMS of ~66 % in the most acidified mesocosms compared to the least acidified mesocosms at in situ temperature (10 °C). However, the negative effect of an increase in pCO2 on the net production of DMS could be mitigated by a warming of surface waters. Indeed, my results reveal that the net production of DMS was higher at 15 °C compared to 10 °C over the whole pCO2 gradient in our mesocosm study. These novel results suggest that warming of surface waters could mitigate, at least partly, the negative effect of acidification on DMS net production in the LSLE and perhaps in the world’s oceans.

Continue reading ‘Impact de l’acidification et du réchauffement sur les communautés planctoniques de l’estuaire du Saint-Laurent et la production de diméthylsulfure (in French)’

Seasonal DNA methylation variation in the flat tree oyster Isognomon Alatus from a mangrove ecosystem in North Biscayne Bay, Florida

Epigenetic analyses constitute an emerging approach for better understanding of the mechanisms underlying environmental responses and their role during acclimatization and adaptation across diverse ecosystems. The expansion of environmental epigenetic studies to a broader range of ecologically and environmentally relevant organisms will enhance the capability to forecast ecological and evolutionary processes, as well as to facilitate a retrospective assessment of stress exposures in biomonitor organisms through “epigenetic footprinting” analyses. With such purpose, the present study monitored spatial and temporal variation in abiotic parameters (temperature, salinity, pH, and horizontal visibility) over a 2-y period in a mangrove ecosystem located in North Biscayne Bay (North Miami, FL). The obtained data were subsequently compared with epigenetic modifications (global genome-wide DNA methylation levels) in the flat tree oyster Isognomon alatus, used as a sentinel model organism across experimental sites. The obtained results revealed a certain level of seasonality in temporal DNA methylation patterns, which seem to be primarily associated with changes in temperature and horizontal visibility. These results constitute the first long-term study combining spatial and temporal epigenetic analyses in a marine organism in its natural environment, laying the initial groundwork to assess the biomonitoring potential of environmental epigenetic analyses.

Continue reading ‘Seasonal DNA methylation variation in the flat tree oyster Isognomon Alatus from a mangrove ecosystem in North Biscayne Bay, Florida’

Reduced Symbiodiniaceae diversity in Palythoa tuberculosa at a heavily acidified coral reef

Symbiodiniaceae diversity in hosts is known to change with the environment and particularly with temperature and light intensity. However, higher levels of pCO2, as could be expected under future ocean acidification scenarios, have been documented to show little to no effect in influencing the diversity of Symbiodiniaceae in hosts in previous studies. In this study, we examined hypervariable psbAncr sequences to identify the Cladocopium (former Symbiodinium ‘Clade C’) diversity within the zooxanthellate zoantharian Palythoa tuberculosa at an acidified reef in southern Japan. Palythoa tuberculosa were collected from a reef at the volcanic island of Iwotorishima in southern Japan; specimens from a high pCO2 site and from a nearby control (normal pCO2) site (Inoue et al. in Nat Clim Change 3:683–687, 2013). We observed a statistically significant reduction in Cladocopium diversity at the high pCO2 site with only one Cladocopium lineage present, compared to at the control site with two lineages present. Our results demonstrate that higher pCO2 can potentially negatively influence the diversity of host Symbiodiniaceae within anthozoan hosts, an important implication in the face of ongoing ocean acidification and climate change.

Continue reading ‘Reduced Symbiodiniaceae diversity in Palythoa tuberculosa at a heavily acidified coral reef’


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Ocean acidification in the IPCC AR5 WG II

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