New Mathematical Model Helps Biologists Understand How Coral Dies in Warming Waters

[HighlandReefer]

http://www.sciencedaily.com/releases...0329203228.htm

ScienceDaily (Mar. 29, 2010) — Cornell University researchers have found a new tool to help marine biologists better grasp the processes under the sea: They have created mathematical models to unveil the bacterial community dynamics behind afflictions that bleach and kill coral.

Warming waters are triggering coral bleaching and disease in the Caribbean, Indian Ocean and Great Barrier Reef off the Australian coast. Now new mathematical models explain for the first time how beneficial bacteria on coral suddenly give way to pathogens when waters warm.

"Before this study, we just had observations but little understanding of the mechanism" for what causes coral disease and bleaching, said Laura Jones, Cornell senior research associate in ecology and evolutionary biology. Justin Mao-Jones '08, conducted the research as an undergraduate in the School of Operations Research and Information Engineering, is the paper's lead author.

The model reveals how a healthy normal microbial community in the coral surface mucus layer protects corals from disease by preventing invasion and overgrowth by pathogenic bacteria. But when corals are stressed, for example by elevated temperatures (a heat spell), the community of microbes suddenly switches. Species associated with a healthy coral organism -- "resident species" -- decline as pathogens associated with coral disease take their place.

The researchers used models to simulate bacterial community dynamics within the surface coral mucus, under normal conditions, and under the warming conditions that lead to a sudden shift from beneficial bacteria to pathogens on the coral's surface.

"There's a critical threshold where the system jumps to a pathogen-dominated state," said Jones.

They also found that the models replicated a pattern others have observed: once the disease-causing microbes establish themselves, they persist even if the water cools down enough to favor the beneficial bacteria. The coral is then often too damaged to recover, and the reefs begin to die.

Preventing oceans from warming will require people to curb climate change, and may be unavoidable in the short term, said Jones. But reducing poor water quality, which stresses the coral and makes the oceans more hospitable to pathogens, could perhaps ward off the sudden shift to pathogens dominating the coral surface, she added.

Other co-authors included Stephen Ellner, a Cornell professor of ecology and evolutionary biology and the paper's senior author; and Kim Ritchie, a marine biologist at the MOTE Marine Laboratory.

An Emerging Infectious Diseases grant from the National Science Foundation (NSF EF-0326705) funded the study.

[HighlandReefer]

http://www.sciencedaily.com/releases...0304101433.htm

Dissolved Organic Matter In Water Column May Influence Coral Health
ScienceDaily (Mar. 7, 2008) — Bacterial communities endemic to healthy corals could change depending on the amount and type of natural and man-made dissolved organic matter in seawater, report researchers from The University of Texas at Austin Marine Science Institute and Mote Marine Laboratory in Sarasota, Florida.

Healthy corals naturally exude a surrounding mucous layer in which a complex population of bacteria exists. Recent studies have indicated that some coral diseases may be linked to community shifts in this bacterial population.

In experiments with a common reef building coral in the Florida Keys, Chris Shank of the University of Texas Marine Science Institute and Kim Ritchie of Mote Marine Laboratory found an obvious shift in the composition of the coral bacterial community resulting from changes in the pool of surrounding dissolved organic matter.

Dissolved organic matter in the water column near Florida Keys coral reefs comes from a variety of natural sources, including coastal mangroves, seagrasses, and plankton, as well as man-made sources, including sewage effluent. The composition of dissolved organic matter surrounding Florida Keys coral reefs has likely changed in recent decades due to growing coastal populations.

"When coastal ecosystems are physically altered, the natural flow of dissolved organic material to nearby coral ecosystems is disrupted with potentially harmful consequences for the corals," said Shank, assistant professor of marine science.

Shank and Ritchie, manager of the Marine Microbiology Program at Mote, placed Montastraea faveolata coral fragments in aquaria filled with water collected from either Florida Bay or from an offshore bluewater site.

Dissolved organic matter concentrations are much greater in Florida Bay than in offshore waters and typically have different chemical characteristics. Water collected from these distinct locations used for the coral incubation experiments represented the variable nature of dissolved organic matter experienced by corals in the middle and lower Florida Keys.

They found that the microbial community of healthy corals shifts measurably when exposed to water from Florida Bay, suggesting the microbes that normally play a role in coral immunity may be out-competed by potentially problematic bacteria. In combination with increased water temperatures, this is an example of the type of compounded stressors known to cause health problems in corals, or "reef deterioration."

The scientists' research is part of their larger effort to investigate the link between alterations to the south Florida ecosystem and Florida Keys coral ecosystems. Coral reefs there, as with coral reefs around the world, are increasingly threatened by rising water temperatures, advancing ocean acidification and rapidly rising coastal populations.

Corals are especially susceptible to coastal alterations because they commonly exist in shallow waters at the interface of land and sea.

Shank and Ritchie are planning a series of experiments to more closely evaluate the chemical nature of the water column dissolved organic matter surrounding the corals in the Florida Keys and identify shifts in potentially harmful bacterial populations.

The scientists reported their results March 4 at the Ocean Sciences Meeting in Orlando, Florida.

[Randy Holmes-Farley]

Very interesting. Thanks for posting it.

The changes in bacteria with organic carbon dosing may also be worth considering in this light.

[cwegescheide]

Are you suggesting a tanker full of Vodka dosing the keys?

[HighlandReefer]

Originally Posted by cwegescheide

Are you suggesting a tanker full of Vodka dosing the keys?

I purposely posted both articles together, since I found it interesting that changes in water parameters can cause shifts in bacterial populations found in the mucal layer of coral and in some cases the bacterial population shifts are detrimental. They are finding this can occur with changes to higher temperatures, changes in the kind of organic matter and in changes of concentrations of heavy metals like copper. As Randy has stated above, this could apply to carbon dosing and changes made in sources of carbon dosing. This includes vitamins, amino acids & possibly foods we add to our tanks. I would assume that it would depend on bacterial populations present in a tank. At least in the ocean there can be thousands of species of bacteria in one liter.

With this knowledge, it makes one ponder about what we feed, dose as carbon sources and add as heavy metal supplements (like copper, lead, zinc....etc) and if we should make dramatic changes suddenly without care.

At least with organic changes in the water column it seems to be reversible if corrected in a reasonable amount of time.

I will look forward to their findings when they begin braking the organic carbon sources down and compare them individually.