In 1883, the world shuddered as the loudest known sound in human history echoed from its epicenter in Indonesia. The noise generated by Krakatoa, a volcanic island in the Sunda Strait, was heard over 3,000 kilometers aways both to the east and west; the resulting tsuanamis produced waves over 30 meters in height and killed 36 thousand people. The eruption altered weather globally. The volcanic dust suspended in the atmosphere halted a proportion of the solar radiation able to reach the Earth–in the year that followed global temperatures were reduced by as much as 1.2 degrees Celsius, not reverting back to normal until 1888.
From this volcanic destruction (two thirds of Krakatoa sank into the sea due to the blast), the island of Anak Krakatau-‘child of Krakatau’-was born, rising from Krakatoa’s crater less then 80 years ago. This newly emerged island presents a unique opportunity to witness to the early stages of ecosystem development.
Eruptions on Anak Krakatau have been active recently, leading some to speculate whether or not another epic volcanic event is on the horizon. Interestingly, fringing coral reefs have since formed on Anak Krakatau and nearby areas. The recovery of the island’s terrestrial ecosystems has been subject to much attention and research. However, the marine communities have largely been unstudied until the last decade. In a work published this year in Coral Reefs, Dr. Starger and colleagues examined the genetic diversity in two reef-building corals, organisms within a marine ecosystem that was totally obliterated by the eruption in 1883. Using microsatellites–short, repeating sequences of DNA–the researchers found that the genetic diversity in Pocillopora damicornis and Seriatopora hystrix, has largely recovered due to initial larval migration from other upstream sources. Further analyses indicate that the coral populations within the Krakatau region may be self-recruiting at this point, and may even be providing larvae to other regions.
So these species of corals have recovered after an sudden, violent eruption. What can we glean from this? Coral reefs worldwide are in trouble, experiencing rapid decline, with mass mortality events projected. In the face of such degradation, more data are needed for conservation, particularly in order to design effective marine protected areas (MPAs). Connectivity is paramount in placing reserves. Coral reefs can serve as larval sources, able to provide offspring to other areas, or sinks, which cannot. The researchers show the repopulation of a destroyed marine ecosystem in the Java Sea from other sources, eventually becoming self-seeding. This larval transport, especially in corals, may not permanently sustain reef populations over time, but can help to initally repopulate areas, for example, after a giant volcano pops its top. Understanding the source-sink dynamics of these hugely-diverse ecosystems will likely be imperative in conservation planning. Recovery of reef environments after disasters is dependent on healthy, nearby larval sources, giving importance to identifying and protecting these areas in networks of MPAs.
C. J. Starger, P. H. Barber, Ambariyanto, & A. C. Baker (2010). The recovery of coral genetic diversity in the Sunda Strait following the 1883 eruption of Krakatau Coral Reefs, 29, 547-565 : 10.1007/s00338-010-0609-2