Revisiting the Deep Reef 12 months on

Image: Deep Reef team member and marine biologist Norbert taking images of an existing survey quatrat at 40m



November 2013: While the Shallow Reef team was busy surveying the reefs of the Caribbean region the Deep Reef team returned to the Coral Sea and revisited several locations from 2012's Great Barrier Reef and Coral Sea campaign. An important part of the 2012 expeditions to the Great Barrier Reef and Coral Sea was to establish a long-term monitoring program. This means that we did not just document deep reef communities at a single point in time, but monitored them over a period of time (12 months in this case) which helps scientists track any condition changes more easily. As such, large monitoring quadrats and temperature logging stations were set up at different sites, and last month the team revisited four of these deep reefs to collect data and document any changes that have occurred during the year since we were last there.


Holmes Reef

We teamed up with Mike Ball Dive Expeditions and conducted the surveying work from their boat. The first reef we visited was Holmes Reef in the Coral Sea, which was also one of the very first reefs we surveyed last year. Directly after jumping in on the reef site, it was clear that the shallow reef had suffered quite substantial storm damage since our last visit – unfortunately this also meant that one of our shallow quadrats got heavily damaged and had become almost unrecognizable. However, once we descended down along a steep wall on this site, we quickly found our quadrat on the deep reef (40m), which looked practically untouched. This demonstrates further that storm damage will vary at different depths on the reef.

As time is limited when we are diving the deep reef (40m and deeper), we quickly began photographing the quadrats. Each of the four marine biologists has a job to do - one diver takes the large overview photos documenting the entire quadrat in a single photo, two other divers document the quadrats on a finer scale by moving around and photographing a smaller square-metre quadrat within the large monitoring plots, and the fourth diver recovers the temperature loggers on these sites and replaces them with new ones.


Bougainville Reef

We had the opportunity to visit a reef in the Coral Sea that we had not surveyed in 2012: Bougainville Reef. This reef is stunning, a dramatic reefscape littered with caves and crevices. Here we collected a large amount of coral tissue samples for our DNA connectivity analyses, as it is a crucial location within the Coral Sea (located between Osprey Reef in the North and Holmes Reef in the South).

While deploying the ROV at Bougainville Reef, we found extensive light-dependent coral communities at depths of over 100 m. This is very interesting, as most sites that we have visited in the Coral Sea have tropical corals becoming extremely sparse below 80m (because corals are so light sensitive). Using the special zoom camera that we have on the ROV, we were able to identify many of the coral species by looking at their skeletal structure. This is a reef that the team are very interested to come back to survey in more detail in the future.


Osprey Reef

Next stop was Osprey Reef where we spent several days working, revisiting three different sites that we'd set up last year. Even with the latest in GPS technology it can sometimes be incredibly difficult to find deployed gear (quadrats and data-loggers) that has been left underwater for a year. We were fortunate that the Mike Ball Dive crew had already dived these sites a couple of weeks back and marked the monitoring quadrats with buoys, this meant that we could go straight to work when we arrived. Besides photographing the quadrats, we also collected some additional specimens to fill in particular gaps that we identified in last year’s mesophotic collection.


Deep reef temperature fluctuations

The temperature loggers we recovered showed some very interesting patterns with the deep reef exhibiting very distinct temperature patterns when compared to the shallow reef. Generally temperatures are very similar between shallow and deep reefs, however temperatures can fluctuate greatly in the deep and can be up to 4-5°C lower than the temperatures being experienced in the shallow. These drops in temperature are due to cold-water influxes from below the deep thermocline, which are pushed up against the steep walls of these reefs by currents and tides. These colder currents are of great interest to science as they likely play an important role in the ecology and physiology of these deep reef corals.


New time-lapse cameras

We also managed to deploy two time-lapse cameras again on the deep reef, which are set up to take a photo of the reef every 20 minutes over the next couple of months. These cameras are the ingenious work of Dr. Paul Muir, who built and equipped them with a large battery pack, timers, lights, and a wiper to keep the camera lens clear.  These underwater cameras may provide us with unique insights into processes such as sedimentation and reproduction on the deep reef, and have become an important tool in the deep reef monitoring work we do.


As technology progresses it is an exciting thing to be able to study an area that science knows so little about. The whole Catlin Seaview Survey team is looking forward to learning more about the mysterious deep reef.