How we Capture the Change of the Gili Islands

“I’ve seen changes every time I dive, but I don’t have any photos to compare” and “The reef was so healthy, I wish I had taken more pictures”. These are two of the most common responses we get when we ask people about the past condition of the coral reef around the Gilis.

We have heard numerous stories about how pristine the reef was, and how the land itself looked so different before the rapid growth of investors came to build. How has this affected the marine life of these islands?

If you change the way you look at things, the things you look at change

One afternoon, the Gili Shark Conservation team came up with a way to record these changes and track how it affects the surrounding environment. We decided to make a time-series of images of the same coral to see if there is any change over time.

We were inspired by the Chasing Coral team who were successful in taking underwater time-lapse  photos of coral over a period of three years, and captured the progression of the global coral bleaching event in 2016. (the picture that belongs to this paragraph is taken by the team of Chasing Coral). The reefs around the Gili Islands were incredibly affected by this bleaching event. Since then, however, there have been some signs of recovery around the Gili Islands, but there has been no photo evidence to be able to track this improvement!

Underwater and Aerial Time-Series Images

We realized that over the past few years, the changes around the Gilis have happened not only underwater, but also on land. Could we track the changes of the land in the same way we will track the corals, and how could we do this effectively? We came up with the idea of taking drone footage to make time-series aerial images from several spots in Gili Air. The idea is the same, to see changes. However, these aerial images will let us see more, like shoreline and land-use changes, as well as coral reef changes.

We live in a very visual world, information is more easily transferred with graphics or images. In this case, if we want to present a case that there are declining live coral coverage around Gili Islands, it is better to present it on images rather than essays or tables full of numbers.

Method

Our underwater images are taken at the south side of Meno Slope, because every Friday we go there for our weekly Dive Against Debris. We take images of four samples: two hard corals, one soft coral, and one rubble. For the aerial images, we chose a site for all four sides of Gili Air – south, east, north, and west – in hopes that our samples are representing the entire system. The images are taken once a week during mid-day to get uniform lighting of the landscape.

The results so far

We started taking the time-lapse photos in late February 2018. During this 2 month period, we have already seen apparent changes. Since our sampling frequency is on weekly basis, we are able to observe monthly and seasonally phenomenon/event such as sand accretion in transition period between rainy and dry season.

We record the temperature and the salinity with every photo taken, and so we have been able to track how the change of temperature has affected our coral samples. In mid-April, there was a two-degree (Celsius) temperature increase and during that time,  our hard coral sample has been greatly affected. Take a look at the hard coral on the right side of the image. In February, the sample was completely healthy, but by April, it was completely covered by algae. Aerial images in April also suggested that calm wave conditions during the transition to dry season have brought a massive volume of sand inside west Gili Air Harbor (left side of the image). So far, it has been interesting to see changes and be able to track them side by side in order to compare.

We know that we cannot make any conclusion from this project by short-term data set. We are planning to gather the dataset for as long as we can. So ten years from now when someone asks “what did Gili Islands look like back then?” we can give them both stories and images in an evolving time series!