Fangataufa is an isolated, ring-shaped island of coral in the Tuamotu Archipelago of French Polynesia. In the 1960s, this Pacific Ocean atoll was subjected to atmospheric nuclear testing, which offered a unique opportunity for an unthinkable and otherwise impossible field experiment: how do animal communities restart themselves after a catastrophic event, like a nuclear blast, wipes them out entirely? Researchers who’ve been studying mollusks on these reefs for 30 years reveal that the communities do rebuild themselves over time, but their composition before nuclear experiments is very different from what developed afterwards. The findings were published in Proceedings of the Royal Society B this week. 

Ecologists want to know if communities are structured by internal or external forces following specific assembly rules or by random processes. A good way to study something like this is to compare communities from before and after a catastrophe. In nature, pioneer species recolonize in the aftermath of landslides and volcanic eruptions, for example, and community restructuring follows. 

Pierre Legendre from Université de Montréal and Bernard Salvat from Université de Perpignan conducted ecological monitoring on the Fangataufa atoll (pictured to the right) to understand the evolution of impacted animal communities. Heat from a series of four nuclear tests between 1966 and 1970 annihilated previous reef communities, and the mollusks were either partly or entirely wiped out.

The duo compared observations across 30 years’ worth of surveying, which involved collecting every long-lived mollusk (from clams to limpets, herbivores and carnivores alike) that were present in study quadrants cleverly marked out by rope ladders. And new communities were compared with those surveyed before the nuclear tests. For the most part, all the reefs developed a community composition quite different from that before the blasts. 

On reef flats and edges, the new communities were the result of chance – the randomly-determined colonization by mollusk larvae floating in from the open ocean. Here, differences in community composition seem to be the result of neutral processes like random settlement. 

Meanwhile, something different happened in the supralittoral (or splash) zones right at the high tide line: only some species could survive in those harsh conditions, so those same species were the ones that re-colonized the area, though some were less abundant than before. Here, environmental conditions, or filtering, controlled the development of the new communities.

Images: Alain Feulvarch / Flickr CC BY 2.0 (top), NASA / Wikimedia (middle)