In the poor waters of the tropical Pacific, islands are sources of nutrients for microscopic photosynthetic algae, or phytoplankton, in the surrounding waters. The result is an enrichment of phytoplankton - a "bloom" - close to the islands, which supports the higher trophic levels, including the fish that are essential to the survival of the islanders. This fertilising effect, known as the 'island effect', is reflected in an increase in chlorophyll concentration (an indicator of phytoplankton biomass), which can be identified by satellite observations of water colour. The researchers developed an algorithm that automatically identifies the area enriched by islands from a map of chlorophyll concentration and applied it to a database of all the Pacific islands. The algorithm detects seasonal enrichment for 99 % of the islands, representing 3 % of the tropical Pacific's surface area, whereas the islands represent only 0.4 %. The researchers quantified the local and basin-wide increases in chlorophyll and primary production by comparing island-enriched waters with neighbouring waters. They also discovered, for the first time, significant impacts on the structure of the phytoplankton community and its biodiversity, visible in anomalies in the water colour signal. These results suggest that, in addition to strong local biogeochemical impacts, islands can have even greater ecological impacts.
To find out more
Messié, M., Petrenko, A., Doglioli, A.M. et al. Basin-scale biogeochemical and ecological impacts of islands in the tropical Pacific Ocean. Nat. Geosci (2022).
Contact
Monique Messié
MBARI
+1 831 775 1836
monique@mbari.org
Anne Petrenko
MIO/PYTHEAS
04 86 09 06 06
anne.petrenko@mio.osupytheas.fr