Ocean deoxygenation could be silently killing coral reefs, scientists say
The cause of this bleaching event was climate change, which brought unusually warm waters to the Great Barrier Reef in February, and disrupted the delicate, symbiotic relationship between the corals and their life-sustaining algae. In general, when sea temperatures rise, corals become stressed and expel algae from their tissues. Without this algae, the corals turn ghostly white and slowly starve. [...]"
Coral reef survival under accelerating ocean deoxygenation
"Global warming and local eutrophication simultaneously lower oxygen (O2) saturation and increase biological O2 demands to cause deoxygenation. Tropical shallow waters, and their coral reefs, are particularly vulnerable to extreme low O2 (hypoxia) events. These events can drive mass mortality of reef biota; however, they currently remain unaccounted for when considering coral reef persistence under local environmental alterations and global climatic change. [...]"
Source: Nature Climate Change
Authors: David J. Hughes et al.
Denitrification Aligns with N2 Fixation in Red Sea Corals
"Denitrification may potentially alleviate excess nitrogen (N) availability in coral holobionts to maintain a favourable N to phosphorous ratio in the coral tissue. However, little is known about the abundance and activity of denitrifiers in the coral holobiont. The present study used the nirS marker gene as a proxy for denitrification potential along with measurements of denitrification rates in a comparative coral taxonomic framework from the Red Sea: Acropora hemprichii, Millepora dichotoma, and Pleuractis granulosa. [...]"
Source: Scientific Reports
Authors: Arjen Tilstra et al.
Extinction of cold-water corals on the Namibian shelf due to low oxygen contents
"They were also able to link this event with a shift in the Benguela upwelling system, and an associated intensification of the oxygen minimum zone in this region. The team has now published their findings in the journal Geology.
Known as 'ecosystem engineers', cold-water corals play an important role in the species diversity of the deep sea. The coral species Lophelia pertusa is significantly involved in reef formation. [...]"
Coral Mortality Event in the Flower Garden Banks of the Gulf of Mexico in July 2016: Local Hypoxia due to Cross-Shelf Transport of Coastal Flood Water
"Remotely sensed and in situ data, in tandem with numerical modeling, are used to explore the causes of an episode of localized but severe mortality of corals, sponges, and other invertebrates at the Flower Garden Banks (FGB) National Marine Sanctuary in July 2016. [...]"
Source: Continental Shelf Research
Authors: Matthieu Le Hénaff et al.
Photosynthesis by marine algae produces sound, contributing to the daytime soundscape on coral reefs
"We have observed that marine macroalgae produce sound during photosynthesis. The resultant soundscapes correlate with benthic macroalgal cover across shallow Hawaiian coral reefs during the day, despite the presence of other biological noise. Likely ubiquitous but previously overlooked, this source of ambient biological noise in the coastal ocean is driven by local supersaturation of oxygen near the surface of macroalgal filaments, and the resultant formation and release of oxygen-containing bubbles into the water column. During release, relaxation of the bubble to a spherical shape creates a monopole sound source that ‘rings’ at the Minnaert frequency. [...]"
Source: PLOS ONE
Authors: Simon E. Freeman et al.
Reef-building corals thrive within hot-acidified and deoxygenated waters
"Coral reefs are deteriorating under climate change as oceans continue to warm and acidify and thermal anomalies grow in frequency and intensity. In vitro experiments are widely used to forecast reef-building coral health into the future, but often fail to account for the complex ecological and biogeochemical interactions that govern reefs. Consequently, observations from coral communities under naturally occurring extremes have become central for improved predictions of future reef form and function. Here, we present a semi-enclosed lagoon system in New Caledonia characterised by diel fluctuations of hot-deoxygenated water coupled with tidally driven persistently low pH, relative to neighbouring reefs. Coral communities within the lagoon system exhibited high richness (number of species = 20) and cover (24–35% across lagoon sites). [...]"
Source: Scientific Reports
Authors: Emma F. Camp