The Wallace Line is the perfect underwater destination; calm training sites for beginners, exciting offshore reefs for those more advanced, and extreme drift diving reserved for experts only.
The three Gilis lie a few miles off the Northwestern coast of Lombok and lie on the famous Wallace Line. These islands, together with Bali, Lombok, Sumbawa, Flores and Wetar make up the Lesser Sunda Islands. The land here formed in the Pliocene, 15 million years ago, when the Australian plate collided with the Asian plate. However, the bedrock of the surrounding seafloor is much, much older. The rocks here are pre-tertiary in origin and so, in some places, the ecosystems are as much as 250 million years old. This means the aquatic fauna and flora has had time to diverge and radiate into so many taxa as to fill the countless niches that often characterize a long established eco-system. Local geology therefore links biology to geography. We can say the Lesser Sunda Islands (a geological province) are in Wallacea, a phylogeographical province.
This area, also known as the Wallace line, is named after a British naturalist, Alfred Russel Wallace. Wallace, who worked closely with Charles Darwin, did a lot of early work on evolution and speciation during the reign of Queen Victoria. On one of his expeditions to South-East Asia, he noticed the marine life in Australasia was quite different to the marine life in the Orient.
After a little more travel, and a little more thought, Wallace drew a line between Bali and Lombok, which extended out past the Philippines. He remarked that East of this line lived all of the animals normally associated with Australia. West of this line lived all the animals of Oriental extraction. Wallace believed that few animals could cross the deep, fast flowing waters of the Lombok strait, and so over evolutionary time, two different populations began to emerge. This line passes almost straight through the Gili’s. What this actually means for a diver here- and indeed anywhere else in Wallacea- is that he sees an unusual and exceptional mixture of animals and plants from both populations, who would never otherwise have met. Indonesian waters have some of the highest measured biodiversity on the planet.
But why is the ecosystem here so unique? Beyond the atoll reefs, which shelter new divers from anything intimidating, are strong and relentless currents. The global ocean conveyor belt created this phenomenon by bringing a constant, renewed and large supply of nutrient-rich water. The Indonesian throughflow is an important part of this conveyor-belt metaphor. Strong, fast currents of cool, fresh water flow through a bottleneck from the Pacific Ocean to the warmer, saltier waters of Indian Ocean. As much water as three times the global oceanic freshwater input flows north-to-south through the Lombok strait every year. However, predicting currents is not quite so simple. Although the formidable movement of water through this region as a whole has been roughly consistent for thousands of years, on smaller local scales it is the wind that determines the direction and force of surface currents. Where local winds compete with global ocean thermohaline circulation, vicious and turbulent thermoclines and haloclines can result which makes for some of the most excitement an experienced diver could imagine.
All of this adds up to a divers paradise, the perfect place to learn the basics in clear, warm waters, on a white sandy bottom before you venture further offshore for some more adventurous fun or even a tech diving course.