Their new study is the first to describe the IME over the scale of an entire ocean and discusses the role of both natural and human island populations on phytoplankton growth.
The team measured just how much phytoplankton grew around small islands and atolls in two ways. They used satellite imagery over a decade and direct ship-based surveys to verify that their image estimates were correct.
The IME was found to be near-ubiquitous, with 91 percent of the coral ecosystems studied demonstrating the phenomenon, some showing as much as 86 percent more phytoplankton biomass compared to neighboring ocean areas.
In other words, phytoplankton coral island hotspots surrounded by barren oceans landscapes were nearly everywhere the team looked.
The higher rate of phytoplankton growth around the coral islands is caused by nutrients that result from decomposing reef animals, upwellings of nutrient-rich colder waters toward the surface, the mixing effects of waves and currents, and sedimentation from land erosion. There are also human-derived runoffs from agriculture, urban development and wastewater inputs, which all add nutrients to coastal waters.
Who cares about the IME or Darwin’s Paradox?
Microscopic phytoplankton play an outsize role in ocean life.
By converting the sun’s energy into plant growth, they are an essential component in our oceans and drive the structure of food webs and ultimately global fisheries yields. More phytoplankton also means more energy-rich resources for important reef building organisms that determine the architecture of tropical coral reefs, which provide protection for neighboring coastlines.
Increased levels of phytoplankton are, however, not always good news. Extreme levels of nutrient enrichment from runoff related to agriculture and other human activities have been shown to increase phytoplankton biomass to levels that can cause sea population structures to change entirely. High levels of nutrients have also led to mass mortalities of more sensitive, yet important species along with the suppression of reef growth.
By better understanding the role of the IME and its impacts on fisheries as well as the negative effects of high human-derived nutrient enrichment, island nations can focus marine conservation efforts on ensuring they do not overload local reef systems past such tipping points.
The future of coral islands
Climate change is predicted to raise ocean temperatures, which will lower lower ocean productivity by changing the way our oceans cycle and mix around the planet. The IME will therefore be an ever important phenomenon to understand as we develop plans to support coral reef ecosystems in the future to avoid stresses from warmer waters.
To sustainably exploit tropical fisheries and continue to rely on coral reefs to protect nearshore human populations, research should focus on understanding the processes that make coral islands and atolls hotspots of productivity. We must dive deeper into questions Darwin was asking some 180 years ago while applying them to today’s global oceans and predicted future change.
Andrew Frederick Johnson, Postdoctoral Researcher of Marine Biology at Scripps Insitution of Oceanography, University of California, San Diego
This article was originally published on The Conversation. Read the original article.
Featured Photo Credit: Zafer Kizilkaya, CC BY-SA
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