Interannual stability of organic to inorganic carbon production on a coral atoll

Ocean acidification has the potential to adversely affect marine calcifying organisms, with substantial ocean ecosystem impacts projected over the 21st century. Characterizing the in situ sensitivity of calcifying ecosystems to natural variability in carbonate chemistry may improve our understanding of the long-term impacts of ocean acidification. We explore the potential for intensive temporal sampling to isolate the influence of carbonate chemistry on community calcification rates of a coral reef and compare the ratio of organic to inorganic carbon production to previous studies at the same location. Even with intensive temporal sampling, community calcification displays only a weak dependence on carbonate chemistry variability. However, across three years of sampling, the ratio of organic to inorganic carbon production is highly consistent. Although further work is required to quantify the spatial variability associated with such ratios, this suggests that these measurements have the potential to indicate the response of coral reefs to ongoing disturbance, ocean acidification, and climate change.

Continue reading ‘Interannual stability of organic to inorganic carbon production on a coral atoll’

Influence of ambient water intrusion on coral reef acidification in the Chuuk lagoon, located in the coral-rich western Pacific Ocean

Weekly carbonate chemistry condition data recorded between 2008 and 2014 in the Chuuk lagoon (7.3°N and 151.5°E) of the Federated States of Micronesia, located in the western Pacific Ocean, were analyzed. The results showed that, during periods of weak intrusion of ambient seawater from the surrounding open ocean, two internal biological processes (calcification and respiration) reinforced each other and together lowered the pH of the reef water for extended periods, ranging from a few to several months. The analysis indicated that reduced intrusion of ambient water is associated with periods of low wind speeds. Such conditions increase the residence time of reef water, thus promoting acidification by respiration and calcification. This phenomenon likely affects many other areas of the coral-rich western Pacific Ocean, which contains 50% of global coral reefs and in which the degree of ambient water intrusion into the atolls has been shown to be closely associated with the El Niño–Southern Oscillation-induced wind speed change.

Continue reading ‘Influence of ambient water intrusion on coral reef acidification in the Chuuk lagoon, located in the coral-rich western Pacific Ocean’

Photosynthesis and calcification in two Halimeda species from Phuket, Thailand

Calcification rates, as well as rates of photosynthetic inorganic carbon (Ci) uptake and relative electron transport (rETR), were measured by alkalinity titrations and pulse-amplitude-modulated (PAM) fluorometry in a simple experimental set up for Halimeda macroloba and Halimeda borneensis from Tangkhen Bay, Phuket, Thailand. While calcification was saturated at bulk seawater concentrations of ~0.3 and ~0.2 mm CO32-, respectively, for the two species, photosynthetic Ci uptake was saturated at ~1.0 and 0.6 mm HCO3-, respectively. Thus, the normal seawater concentrations of these two Ci forms (0.3 mm CO32- and 1.7 mm HCO3-) were viewed as saturating for both processes. rETR increased towards the end of the incubations as a function of irradiance despite the decrease in Ci uptake. This implies that part of the photosynthetic electron flow was diverted to processes other than CO2 reduction under Ci-limiting conditions, and shows that fluorometry is not a good way to estimate photosynthetic efficiencies under such conditions. Based on the responses to pH and Ci reported here, we estimate that the predicted range of ocean acidification for 2100 will still allow for positive rates of calcification in these two Halimeda species.

Continue reading ‘Photosynthesis and calcification in two Halimeda species from Phuket, Thailand’

Response of marine copepods to a changing tropical environment: winners, losers and implications

Background. Climate change concurrent with anthropogenic disturbances can initiate serial changes that reverberate up the food chain with repercussions for fisheries. To date, there is no information available concerning the combined effects of global warming and human impacts on tropical marine food webs. While temperate copepods respond differently to warming and environmental stressors, the extent to which tropical copepods can adapt to rising temperature of already warm waters remains unknown. We hypothesize that sea warming and other anthropogenic disturbances over the long term will have the greatest impact on the copepod community in nearshore waters where their effects are accentuated, and therefore vulnerable and resilient species could be identified.

Methods. Zooplankton samples were collected during two time periods (1985–86 and 2014–15) interposed by marked anthropogenic disturbances, and at the same five stations located progressively from inshore to offshore in Klang Strait, Malaysia, following the asymmetrical before-after-control-impact (BACI) design. Copepods were identified to species, and results were interpreted by univariate (ANOVA) and multivariate (PERMANOVA, PCO) analyses of the computed species abundance and diversity measures.

Results. Copepod total abundance was not significantly different among stations but higher after disturbance than before disturbance. However, changes in the abundance of particular species and the community structure between time periods were dramatic. Coastal large-bodied calanoid species (e.g., Acartia spinicauda, Calanopia thompsoni, Pseudodiaptomus bowmani and Tortanus forcipatus) were the most vulnerable group to disturbance. This however favored the opportunistic species (e.g., Oithona simplex, O. attenuata, Hemicyclops sp., Pseudomacrochiron sp. and Microsetella norvegica). Small-bodied copepods (e.g., Paracalanus sp., Parvocalanus crassirostris and Euterpina acutifrons) were unaffected. Centropages tenuiremis was likely an introduced species. There was no significant loss in species richness of copepods despite the dramatic changes in community structure.

Discussion. Sea warming and other human-induced effects such as eutrophication, acidification and coastal habitat degradation are likely the main factors that have altered copepod community structure. The large-bodied estuarine and coastal calanoid copepods are surmised to be vulnerable to eutrophication and hypoxia, while both resilient and opportunistic species are largely unaffected by, or adaptable to, degraded coastal environments and observed sea surface temperature (SST) rise. It is forecasted that SST rise with unmitigated anthropogenic impacts will further reduce large-bodied copepod species the favoured food for fish larvae with dire consequences for coastal fish production.

Continue reading ‘Response of marine copepods to a changing tropical environment: winners, losers and implications’

Micropaleontology and isotope stratigraphy of the upper Aptian to lower Cenomanian (~114-98 Ma) in ODP site 763, Exmouth Plateau, NW Australia

The biostratigraphy and isotope stratigraphy of the upper Aptian to lower Cenomanian interval including oceanic anoxic events OAE1b, 1c and 1d are investigated in ODP Site 763, drilled on the Exmouth Plateau offshore northwest Australia. Benthic foraminifera suggest that Site 763 was situated in outer neritic to upper bathyal water depths (~150-600 m). OAEs of the Atlantic basin and Tethys are typically associated with organic carbon-rich black shales and δ13C excursions. However, OAEs at this high latitude site correlate with ocean acidification and/or pyrite formation under anoxic conditions rather than black shales. Ocean acidification may be responsible for sporadic low abundances of planktic foraminifera compared to radiolarians and benthic foraminifera associated with increased volcanogenic CO2 production during the formation of the Southern and Central Kerguelen Plateaus. Sea surface temperature may have cooled to 11°C in the late Aptian but increased gradually during the Albian. The Aptian/Albian boundary is placed at a negative carbon isotope excursion associated with the lowest occurrence of Microhedbergella renilaevis, typically found within the Niveau Kilian black shale of OAE1b. Third-order sea level cycles, particularly in the middle Albian, produced cyclic changes in the abundance of inoceramid prisms that increased during inferred times of falling sea level. The late Albian OAE1c and OAE1d coincide with horizons of intense pyritization and the absence of all biocomponents suggesting the development of euxinia. Warm Tethyan waters reached the Exmouth Plateau during the latest Albian based on the presence of thermocline dwelling keeled planktic foraminifera including Planomalina buxtorfi.

Continue reading ‘Micropaleontology and isotope stratigraphy of the upper Aptian to lower Cenomanian (~114-98 Ma) in ODP site 763, Exmouth Plateau, NW Australia’

Souring seas: ocean acidification monitoring at Oregon’s Marine Reserves

The mystery began in 2007 at Whiskey Creek Shellfish Hatchery in Netarts Bay, Oregon. An inexplicable oyster larvae die-off spurred efforts to figure out the problem. The identified culprit? Ocean acidification.

Ocean acidification is the lesser known cousin of climate change. It is a change in water chemistry driven by rising atmospheric carbon dioxide. Seawater absorbs carbon dioxide, which affects chemical reactions in the ocean — including pH levels. With rising levels of carbon dioxide in the atmosphere, more and more of this gas is being absorbed by our oceans, lowering pH levels and making the ocean more acidic. Oregon, and the rest of the West Coast, are especially vulnerable to these changes, and are taking proactive steps in research and policy to better understand acidification impacts (visit the West Coast Ocean Acidification and Hypoxia Science Panel for more information).

Continue reading ‘Souring seas: ocean acidification monitoring at Oregon’s Marine Reserves’

Ocean acidification – the limits of adaptation

World’s longest laboratory experiment with the single-celled calcifying alga Emiliania huxleyi reveals that evolutionary adaptation to acidification is restricted

July 11, 2016 / Kiel. The most abundant single-celled calcifying alga of the world’s oceans, Emiliania huxleyi is basically able to adapt to ocean acidification through evolution. However, the longest evolution experiment that has been conducted with this organism so far shows, that the potential for adaptation is not as large as initially expected. The growth rate under elevated carbon dioxide concentrations has not improved significantly after four years. Calcification was even lower than in today’s cells from Emiliania huxleyi. The study shows that the effects of evolution in phytoplankton are more complex than previously thought.

Continue reading ‘Ocean acidification – the limits of adaptation’

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