Islands support ocean life in many ways – recent research explains why

Schematic showing factors involved in the Island Mass Effect.

Writing in Nature Communications, the authors describe the extent to which the Island Mass Effect happens and also identify some of the key drivers in this ‘positive feed-back effect’, which acts as a life-supporting mechanism.

Researchers measured a massive increase in phytoplankton in the waters surrounding 35 small islands and atolls in the Pacific Ocean. They recorded up to 86% more phytoplankton in these waters than is found in open oceans. At the base of the food chain, the presence of a greater number of these microscopic organisms has an effect right up the food chain to the top predators like tuna, who feed on the fish and animals supported by the phytoplankton.

Once the growth begins, it becomes a self-fuelling cycle, a little bit of life brings more. The physical presence of the islands themselves creates circulation patterns and the positive feed-back effect begins, with fish being attracted to the phytoplankton, and larger fish and birds to the fish. Their droppings add ‘fertiliser’ to the water, encouraging production of yet more phytoplankton, which in turn supports more life.

Human activity also feeds into the cycle. Run-off from agricultural fertiliser from land and other human activity also feed into the system- whether beneficial or not.

Another important element identified by the researchers is the presence of lagoons contained within the atoll’s reefs. Their shallow protected waters attract large numbers of birds and their basins are washed out daily by the tide, distributing nutrients into the shallow waters at their rim, and driving further phytoplankton growth.

Jamison M. Gove, Margaret A. McManus, Anna B. Neuheimer, Jeffrey J. Polovina, Jeffrey C. Drazen, Craig R. Smith, Mark A. Merrifield, Alan M. Friedlander, Julia S. Ehses, Charles W. Young, Amanda K. Dillon, Gareth J. Williams. Near-island biological hotspots in barren ocean basins.Nature Communications, 2016; 7: 10581 DOI: 10.1038/ncomms10581