With the expedition having just wound up, now is the perfect time to talk about the Paralenz dive cameras, their integral role in data collection for the camera drop project. Even though the cameras were designed with divers in mind, their compact size and impressive depth rating makes them an incredible tool for research. During the expedition, Paralenz cameras were used to survey fish communities living on deeper reefs, known as mesophotic reefs. The aims of the project were to investigate how fish community composition and structure differs with depth.

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The Paralenz rig just after a successful drop

Mesophotic reefs extend from 30m depth to as deep as 150m, in areas of high water clarity. Compared to shallow water reefs they are hugely understudied, due to their inaccessibility. Furthermore, current research is not evenly spread geographically, with most studies focusing on Caribbean reefs. What research there is points to mesophotic reefs as a highly important zone for various reasons. Firstly, some studies indicate that mesophotic reefs may be buffered from the threats facing shallow reefs, such as thermal bleaching and urbanisation. If deeper reefs are safer from these threats, then they could potentially act as a source for fish and coral larvae to repopulate degraded reefs. In addition, some studies have found mesophotic reefs to be important habitats for some juvenile fish and fish facing commercial exploitation. These 2 points have lead to the idea of deeper reefs acting as a refuge. However, recent research has suggested the previous points may not be true for all mesophotic reefs. Some mesophotic reefs are in worse condition than shallower reefs in the vicinity. In addition, there is doubt over how connected shallow and deep reefs actually are, meaning deeper reefs may not be able to repopulate shallower areas. It is imperative to study mesophotic reefs over a wide geographical range to determine their status relative to shallower refs and this is where Paralenz comes in to help.

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A crisp drop just below 30m
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A drop at 77.8m. Despite the depth, several fish species are clearly visible, such as dusky chromis and zebra angelfish

A major reason why mesophotic reefs are relatively understudied is due to their depth. Mesophotic reefs are largely beyond the reach of recreational SCUBA limits and advanced SCUBA techniques must be used instead – this is costly and not time efficient. Drop camera systems are a useful tool in surveying deeper reefs. A camera system can be lowered to the desired depth and left to record before retrieval. For this study, a stereo-video camera rig was built for use with Paralenz cameras. By using a stereo system, it is also possible to measure the lengths of individual fish. Using the Paralenz cameras had several major advantages. Firstly, their incredible depth rating meant fish communities could be surveyed over a range of depth. In addition, their compact size and user-friendly interface meant it was easy to conduct a large number of drops over a relatively small-time frame. Compared to other available cameras (and housings), Paralenz is also a cost-effective option. The in-built depth gauge and thermometers are a huge help as well. The overlay option means we don’t have to fix a dive computer in view of the cameras and obstruct the view. Lastly, the video quality of the Paralenz is excellent. The high resolution coupled with the depth colour correction means the picture is excellent even at 100m depth, making fish identification relatively straightforward.

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The deepest drop of the study, pictured at 145.9m. Although the rig reached a maximum depth of 146.4m, it never reached the bottom. Some fish are visible in the footage.

Looking forward from here, it is exciting to see how much further mesophotic reef study can go with a Paralenz drop camera rig. Although the data collection for this study was successful, there is plenty of room for further study. The more data that is collected, the better our understanding of deeper reefs will become, and Paralenz cameras could be a great tool in achieving that.

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