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420 - On the trail of the coral-killing starfish
December 2012
Acanthaster planci is the principle natural enemy of reef-building corals. Outbreaks of this coral-feeding starfish occur periodically, due to reasons that remain unclear. It decimates entire reefs in the space of just a few years, as has been the case in French Polynesia since 2004. A new study conducted by IRD researchers and their partners( 1) describes this population explosion around Moorea, the “sister island of Tahiti”( 2). The rate of living coral cover in ocean depths and lagoons alike has dropped from 50% (healthy reef) to under 5% in 2009. The ecosystem will need at least a decade to be restored to its original state.
418 - Pearl culture, the black gold of French Polynesia?
December 2012
The second greatest economic resource of French Polynesia after tourism, black pearl culture has been facing a major crisis since the first decade of this century. Overproduction, falling prices, reduced activity that had boosted many remote atolls... In response, IRD researchers and their partners( 1) are helping to maintain and sustain the sector.
In particular, scientists have been studying the Ahe atoll lagoon (north of Tahiti) since 2008. Specifically, they coordinated studies on the plankton resources available to feed oysters and on water flow in the lagoon.
These projects contribute to decision-making tools intended for oyster farmers, for the sustainable exploitation of the "Tahitian treasure".
405 - The new face of El Niño
May 2012
El Niño is changing. This climatic troublemaker is increasingly appearing in a form known as Modoki, Japanese for 'similar but different'. The heart of the phenomenon is moved from the eastern tropical Pacific towards the centre of the Pacific basin. New research conducted by the IRD and its partners from the Legos( 1) laboratory details the biological aspects of Modoki in the equatorial zone. Such events reduce the levels of phytoplankton in the central Pacific area: Satellite images analysed between 1997 and 2010 show the ocean to be less green during the events of 2002-2007 and 2009-2010. This colouring demonstrates reduced levels of surface marine algae, synonymous with a low level of biological activity.
Another study conducted with Peruvian( 2) researchers and those from the Locean( 3) laboratory has revealed that Modoki, inversely to its larger cousin, might be responsible for upwelling( 4) the length of the South-American coastline. A high resolution oceanic model, linked to satellite and historic data from Imarpe( 5), indicates that recent episodes have seen an increase in this rising cold water, rich in nutrients. The predicted increase in frequency of Modoki( 6) events could thus influence fishing in the zone.
Potential new threat for coral reefs and the health of communities in the tropics
July 2008
Coral reef fish harbour an unexpectedly high biodiversity of parasites
July 2007
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