Carbon dynamics and community production in the Mississippi River plume

Dissolved inorganic carbon (DIC), total alkalinity (TAlk), pH, and dissolved oxygen (DO) were determined in the Mississippi River plume during five cruises conducted in the spring, summer, and fall. In contrast to many other large rivers, both DIC and TAlk were higher in river water than in seawater. Substantial losses of DIC, relative to TAlk, occurred within the plume, particularly at intermediate salinities. DIC removal was accompanied by high DO, high pH, and nutrient depletion, and was attributed to high phytoplankton production. As a result, the carbonate saturation in the plume became much higher than in ocean and river waters. A mixing model was used to determine DIC removal. We provide evidence that the use of a two-end-member (river and ocean) mixing model was valid during late summer and fall (low discharge period). However, for other periods we used salinity and TAlk to delineate a mixing model that included two river end members and an ocean end member. Net community production rates in the plume, estimated using a box model, peaked in the summer and were among the highest reported to date for large river plumes. In the summer and fall, biological production in the river plume consumed a majority of the available nutrients, whereas during the spring only a small fraction of the available nutrients were consumed in the plume. Biological production was the dominant process influencing pH and carbonate saturation state along the river-ocean gradient, whereas physicochemical dynamics of mixing played an important role in controlling the TAlk and DIC distributions of this large river plume.

Changes in carbon uptake mechanisms in two green marine algae by reduced seawater pH

Acidification of the oceans, as a consequence of anthropogenic CO₂ emissions has reduced the pH at the surface of oceans by 0.1 unit compared to pre-industrial values. The reduction of seawater pH changes the relative proportion of the inorganic carbon (C_i) species which could potentially affect the modes of C_i assimilation by marine microalgae. In this study the effects of changes in external pH on the modes of C_i uptake over the pH range 5.0 to 7.5 were determined mass spectrometrically in Stichococcus minor Naegeli and S. cylindricus Butcher et Umbauk. Both species were found to tolerate a broad range of pH from pH 5.0 to 9.5 but the optimum for growth of both species was 8.2. Both species were also found to grow over a range of salinities and are best described as brackish water species rather than marine species, since they grow over wide ranges of salinity and pH. Neither species expresses external carbonic anhydrase (CA) activity. In both species, cells grown at pH 5.0, where the bulk of dissolved inorganic carbon (DIC) is in the form of CO₂, active HCO₃⁻ and CO₂ uptake were absent and cells appear to take up CO₂ by diffusion. However, active HCO₃⁻ uptake was present in cells of both species grown at pH 6.0, 7.0 and 7.5 but active CO₂ uptake was not detectable. Cells of both species, when grown at pH 8.2, display both active CO₂ uptake and active HCO₃⁻ uptake.

Invasive algal mats degrade coral reef physical habitat quality

Invasive species alter the ecology of marine ecosystems through a variety of mechanisms or combination of mechanisms. This study documented critical physical parameters altered by the invasive red macroalga Gracilaria salicorniain situ, including: reduced irradiance, increased sedimentation, and marked variation in diurnal dissolved oxygen and pH cycles in Kāne‘ohe Bay, O‘ahu, Hawai‘i. Paired studies showed that algal mats reduced irradiance by 99% and doubled sediment accumulation. Several mats developed hypoxia and hyperoxia in the extreme minima and maxima, though there was no statistical difference detected in the mean or the variability of dissolved oxygen between different 30 min time points of 24 h cycles between algal mat-open reef pairs. The algal mat significantly acidified the water under the algal mat by decreasing pH by 0.10–0.13 pH units below open reef pH. A minimum of pH 7.47 occurred between 14 and 19 h after sunrise. Our combined results suggest that mats of G. salicornia can alter various physical parameters on a fine scale and time course not commonly detected. These changes in parameters give insight into the underlying basis for negative impact, and suggest new ways in which the presence of invasive species leads to decline of coral reef ecosystems.

Coral Reefs are a tell tale sign for climate change

Coral Reefs are at the forefront of climate change and at least two of the three main impacts you will have noticed: coral bleaching and storm damage, both of which derive from increased sea temperatures. The third major change to coral reefs however is a little less obvious, and that is the acidification of the ocean. Acidification happens when the sea absorbs increasing levels of CO2 from the atmosphere. At its most simple, the more CO2 in the atmosphere, the more the sea absorbs and the current levels are 50 times higher than normal (Cadeira, 2006). The result? Less carbonate is available for biological systems such as coral reefs, which will weaken the reef system. Weak reefs mean less resiliency to pollution, storm damage, disease, a shift in biodiversity (an abundance of parrot fish for example who love to chomp on the reefs) and damage by humans.

Trouble in paradise: Ocean acidification this way comes

Sustainability of tropical corals in question, but some species developing survival mechanisms

Double, double toil and trouble;

Fire burn, and caldron bubble.

—Shakespeare, Macbeth

Mo’orea, it’s called–this island in French Polynesia that’s been dubbed the most beautiful island in the world.

Here Tahitian breezes dance across crystal blue waters and beneath the tropical seas lies a necklace of coral reefs that encircles Mo’orea like a string of brightly colored jewels.

Extensive reefs of a coral named Porites and other species form atolls, or reefs that ring Mo’orea’s lagoons.

Porites are colonial corals, also known as Scleractinians, found in shallow tropical waters throughout the Indo-Pacific and Caribbean regions.

Think tropical reef and your mind’s eye is likely seeing Porites.

These corals and other calcifying marine life, such as coralline algae, are also the world’s primary reef-builders.  And therein lies the trouble.

The seas in which these calcifying species dwell are turning acidic, their pH slowly dropping as Earth’s oceans acidify in response to increased carbon dioxide in the atmosphere.