Islands near Java that were sterilized when Krakatoa exploded in 1883, killing an estimated 36,000 people. Scientists have monitored the islands for 140 years, documenting how plants and animals gradually recolonized the barren volcanic rock.
A natural laboratory from ash
On August 27, 1883, the volcano Krakatoa produced one of the loudest sounds in recorded history, a series of explosions heard nearly 5,000 kilometers away. The eruption destroyed two-thirds of the island and buried the remaining fragments—Rakata, Sertung, and Panjang—in a layer of superheated ash and pumice up to 30 meters deep. The event was a complete biological reset; every plant, animal, and seed was obliterated.
This sterilization created a unique opportunity for science: a chance to observe primary succession from a known starting point. Nine months after the eruption, the first visitor found only a single, tiny spider spinning a web. In 1886, botanist Melchior Treub landed on Rakata and documented the first plant colonists. He found no trees or shrubs. Instead, the life-starved rock was coated in a thin film of blue-green algae (cyanobacteria), which fixed nitrogen and created a substrate for other life. Treub also identified 11 species of ferns and a few flowering plants, all of which likely arrived as microscopic, wind-borne spores or sea-rafted seeds.
The initial phase of recolonization was slow and sorted by dispersal method. Wind and water were the only vectors. Within a decade, the interior of the islands was covered not by forest, but by a dense savanna of grasses like Imperata cylindrica. The coastlines saw the establishment of hardy trees like the Australian pine (Casuarina equisetifolia), a nitrogen-fixing species whose seeds could survive long journeys in saltwater.
The arrival of animals
The development of a true forest required a new set of colonists: animals. The first animal arrivals, after the initial spider, were insects and a species of monitor lizard found in 1889, which is a capable swimmer. The real change began with the arrival of birds and fruit bats from the nearby islands of Java and Sumatra, located about 40 kilometers away. These animals acted as mobile seed dispersers, carrying the seeds of forest trees in their digestive tracts.
Fig trees (Ficus species) were particularly important. Their arrival, facilitated by birds, led to more colonization. The period between 1908 and 1921 showed a peak in animal immigration, as the developing woodland created new habitats. As the forest canopy began to close between 1921 and 1933, the sun-loving grasses of the earlier savanna stage were shaded out, leading to the local extinction of the species that depended on them.
Today, the islands support a mixed tropical forest, although it is still considered species-poor compared to the mainland. The forest on Rakata is dominated by trees such as Neonauclea calycina. The entire process demonstrates how ecosystems are assembled piece by piece, with each new arrival potentially changing the environment for all subsequent colonists. This long-running study has become a foundational example of island biogeography and ecological succession.
💡Fun Facts
The 1883 eruption was so loud it was clearly heard in Perth, Australia (3,110 km away) and on Rodrigues island near Mauritius (4,800 km away).
The first animal discovered on the sterilized island months after the eruption was a single spider.
A new volcano, Anak Krakatau ("Child of Krakatoa"), began to grow from the caldera in 1927 and has erupted dozens of times, creating a new, younger laboratory for succession.
The 1883 blast ejected so much ash into the stratosphere that it lowered global temperatures and caused vividly colored sunsets around the world for several years.
Accessible 24/7 by boat, but landings are subject to weather and volcanic activity.
Admission
A permit from the conservation authority (BKSDA) is required to enter the park area, typically arranged by a tour operator.
Accessibility
Access is by boat only, often from Carita or Anyer on Java. Landings can be on rocky or sandy shores. Terrain on the islands is rugged and undeveloped.
Krakatoa recolonization plotsSunda Strait, Indonesia