Stony Coral Tissue Loss Disease – Investigating Possible Pathogens and Transmission Mechanisms
MERMAID - Metagenomic Examinations of Reefs; Microbial Assessments Including Disease
Reef Metagenomics
Stony Coral Tissue Loss Disease
Antibiotic-Resistance Gene (ARG) Baselines
Coral disease was first documented on Florida reefs in the 1970s. Since then, outbreaks of diseases have increased, and disease is now one major reason why coral reefs worldwide are in decline. Although what causes most coral diseases is not known, the few with known causes have been linked to microorganisms, highlighting the need for studies of microbes associated with diseased corals.
What Is Stony Coral Tissue Loss Disease (SCTLD)?
In 2014, a new coral disease known as stony coral tissue loss disease, or SCTLD, appeared off the coast of Miami, Florida. This highly devastating disease is characterized by rapidly progressing lesions that can result in full coral colony mortality in a matter of weeks if corals don’t receive treatment. More than 20 different species of stony corals (those with hard skeletons) are known to be susceptible to this disease, including numerous species listed as threatened under the U.S. Endangered Species Act and important reef-builders. Today, the disease has spread throughout the entire Florida Reef Tract and across the Caribbean, leaving a trail of devastation in its wake -- on some reefs, some of the most vulnerable coral species have lost more than 95% of their pre-SCTLD populations.
What Causes SCTLD?
Although the causative agent(s) of SCTLD remains unknown, scientists suspect microbes are involved. One complication is that corals, even healthy ones, naturally host complex and highly diverse microbial communities. This creates complicating “background noise” when trying to pinpoint a microbial cause of a disease. To overcome this complication, we have developed a different method to narrow down the “suspect pool” of possible causes of SCTLD.
Scientists have demonstrated that SCTLD can spread from infected corals to healthy corals placed in the same water (“waterborne transmission”), indicating that the causative agent is shed by the infected corals into the surrounding environment. By placing SCTLD-infected corals in mesocosms (small experimental environments) containing sterilized seawater (seawater treated to remove most microorganisms), any microbes later found in this water will be those that have been shed by the infected coral, including SCTLD’s causative agent(s).
We also do not know how much of the causative agent(s) a healthy coral must be exposed to before they become sick – this is called the infectious dose. To overcome this unknown, our method uses tangential flow filtration, or TFF, a method of filtering which essentially removes the water from the mesocosms, leaving behind a highly concentrated version of the microbial community that we can analyze.
Because different types of microorganisms (for example, bacteria, viruses, etc) generally have different sizes, following TFF-concentration, our method next utilizes size fractionation – passing the TFF-concentrated coral mesocosm microbial communities through a sequential series of filters with different size openings (“pores”) to separate out these different-sized microbial groups.
As an extension of our method, to help determine which microbial group is responsible for SCTLD, we have also tested attaching these filters to healthy coral fragments and monitoring for the appearance of SCTLD symptoms.
How Has SCTLD Spread?
In addition to the identity of the causative agent(s), other unknowns surrounding SCTLD include how the disease has managed to spread so rapidly and so sporadically. In the Caribbean, for example, SCTLD outbreaks often popped up in seemingly random locations, suggesting the disease was not spreading via movement of natural water currents. Instead, these outbreaks often occurred near major ports, suggesting that ships may serve as vectors for the disease. However, the mechanisms by which this may occur remain unclear. One possibility is that SCTLD pathogen(s) may enter new areas attached to ships as biofilms (complex communities of microorganisms that form on submerged surfaces). Our work with Project MERMAID. revealed that biofilms formed on stainless steel in association with SCTLD-infected corals carried microbial signatures of the disease.
Coral Microbial Ecology
Measuring Coral Growth to Help Restore Reefs
Coral Disease
Coral disease was first documented on Florida reefs in the 1970s. Since then, outbreaks of diseases have increased, and disease is now one major reason why coral reefs worldwide are in decline. Although what causes most coral diseases is not known, the few with known causes have been linked to microorganisms, highlighting the need for studies of microbes associated with diseased corals.
What Is Stony Coral Tissue Loss Disease (SCTLD)?
In 2014, a new coral disease known as stony coral tissue loss disease, or SCTLD, appeared off the coast of Miami, Florida. This highly devastating disease is characterized by rapidly progressing lesions that can result in full coral colony mortality in a matter of weeks if corals don’t receive treatment. More than 20 different species of stony corals (those with hard skeletons) are known to be susceptible to this disease, including numerous species listed as threatened under the U.S. Endangered Species Act and important reef-builders. Today, the disease has spread throughout the entire Florida Reef Tract and across the Caribbean, leaving a trail of devastation in its wake -- on some reefs, some of the most vulnerable coral species have lost more than 95% of their pre-SCTLD populations.
What Causes SCTLD?
Although the causative agent(s) of SCTLD remains unknown, scientists suspect microbes are involved. One complication is that corals, even healthy ones, naturally host complex and highly diverse microbial communities. This creates complicating “background noise” when trying to pinpoint a microbial cause of a disease. To overcome this complication, we have developed a different method to narrow down the “suspect pool” of possible causes of SCTLD.
Scientists have demonstrated that SCTLD can spread from infected corals to healthy corals placed in the same water (“waterborne transmission”), indicating that the causative agent is shed by the infected corals into the surrounding environment. By placing SCTLD-infected corals in mesocosms (small experimental environments) containing sterilized seawater (seawater treated to remove most microorganisms), any microbes later found in this water will be those that have been shed by the infected coral, including SCTLD’s causative agent(s).
We also do not know how much of the causative agent(s) a healthy coral must be exposed to before they become sick – this is called the infectious dose. To overcome this unknown, our method uses tangential flow filtration, or TFF, a method of filtering which essentially removes the water from the mesocosms, leaving behind a highly concentrated version of the microbial community that we can analyze.
Because different types of microorganisms (for example, bacteria, viruses, etc) generally have different sizes, following TFF-concentration, our method next utilizes size fractionation – passing the TFF-concentrated coral mesocosm microbial communities through a sequential series of filters with different size openings (“pores”) to separate out these different-sized microbial groups.
As an extension of our method, to help determine which microbial group is responsible for SCTLD, we have also tested attaching these filters to healthy coral fragments and monitoring for the appearance of SCTLD symptoms.
How Has SCTLD Spread?
In addition to the identity of the causative agent(s), other unknowns surrounding SCTLD include how the disease has managed to spread so rapidly and so sporadically. In the Caribbean, for example, SCTLD outbreaks often popped up in seemingly random locations, suggesting the disease was not spreading via movement of natural water currents. Instead, these outbreaks often occurred near major ports, suggesting that ships may serve as vectors for the disease. However, the mechanisms by which this may occur remain unclear. One possibility is that SCTLD pathogen(s) may enter new areas attached to ships as biofilms (complex communities of microorganisms that form on submerged surfaces). Our work with Project MERMAID. revealed that biofilms formed on stainless steel in association with SCTLD-infected corals carried microbial signatures of the disease.