Microbes: The world of the unseen

text and photo by Steven Quistad

While diving around Wake Atoll your eyes are immediately drawn to the spectacular architecture constructed by thousands of years of coral growth. The reef supports a vibrant fish community consisting of almost every color and shape combination imaginable. Upon examination with the naked eye you could easily conclude that was most of the story; coral, fish, algae, and a few invertebrates, that describes the major players on a coral reef. However, that is only part of the story, the most abundant organisms on a coral reef are not those that can be seen with a mask, but those that require a powerful microscope.  Microbes (viruses, bacteria, protists and archaea) play a pivotal role in both healthy and diseased coral reef environments.

To put the shear number of microbes in perspective, imagine swimming down to the reef with a milk jug and scooping up a gallon of water. Within that milk jug you would have captured anywhere between 100,000,000-10,000,000,000 individual bacteria and a magnitude more of viruses! When you take into account the millions of gallons of seawater surrounding an atoll like Wake, you are talking about A LOT of microbes. These microbes are responsible for cycling nutrients, serve as food for larger organisms, and can sometimes act as pathogens to other members of the reef.

At Wake, we collected water samples to measure how nutrients are cycled, collected microbial DNA to indentify what microbes are present, and created microscope slides to count how many bacteria and viruses there are. On a relatively healthy reef such as Wake there tends to be a fewer number of microbes present, while on an unhealthy reef there are generally more microbes.  When microbes become too abundant they can kill the coral by suffocation or disease, potentially leading to a collapse of the entire coral reef ecosystem. An overabundance of microbes can be result from various human impacts such as overfishing or agricultural nutrient runoff.

Microbes serve as dynamic members of the coral reef community. They are essential parts of a healthy reef community,  but if they become too abundant they can ultimately lead to the reef's demise. Through the data we have collected at Wake, in combination with data from other cruises and future expeditions, we are beginning to establish a microbial baseline of what the microbial community of a healthy coral reef looks like. This baseline can be used to monitor the status of other reefs around the world and possibly to predict their future prosperity or collapse.

To count viruses and bacteria we stain them with a chemical called SYBR Gold, which binds to their DNA. We then expose the microbes to a specific wavelength of light, which causes them to glow. The tiny pinpricks are viruses while the larger glowing ovals are bacteria.