In early June, 2013 a large phytoplankton bloom created jewel-toned stains in a sweeping arc off the shores of Scotland’s Hebrides archipelago. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite captured this true-color image of the massive bloom on June 10.
Phytoplankton – small, microscopic, plant-like organisms – live in these waters year-round, but usually go unnoticed because their population remains small. When sunlight increases, and when upwellings and currents bring nutrients to phytoplankton’s watery “dinner table”, then the organisms can reproduce explosively, and create huge blooms. Even though each organism lives only days, the bloom can remain visible in the ocean for many weeks.
These chlorophyll-rich microalgae form the basis of the marine food chain. One avid consumer of phytoplankton is the basking shark. Second only to the whale shark in size, this giant shark is equipped with gill-rakers which act much like sieves to gather plankton from the waters as the gentle beast slowly swims. Because phytoplankton is buoyant, blooms often rise near the surface; because basking sharks follow the plankton, they, too, often are found just under the surface, and can be easily viewed from boats or low-flying aircraft.
In recent weeks, numerous sightings of basking sharks have been reported in the waters off the Hebrides. With divers reporting visibility of only one meter, due to the thickness of the bloom, there should be plenty of food to host a sizable population of these phytoplankton-seeking sharks.