When Christopher Columbus and his crew were sailing across the Atlantic, they were amazed to find a mass of vegetation. It looked like a carpet of little yellow grapes so they called it sargazo. In fact the Sargassum weed is a brown algae and the ‘grapes’ are the air bladders that keep it afloat. It may look like the attached marine plants found in coastal waters, but it’s found in the middle of the North Atlantic Gyre. The area is called the Sargasso Sea.

At the centre of the ocean gyres the water is clear blue and there’s nothing to bring nutrients to the surface, so how does Sargassum weed survive? The most likely answer is that as the Gulf Stream meanders, little rings of nutrient-rich coastal water break away and drift into the Sargasso Sea, supporting the algal growth.

Sargassum weed provides a habitat for many creatures more often found near coasts, including shrimps, crabs, worms and fish, so it’s no wonder that Columbus thought his ship must be nearing an island. Some life-forms have evolved along with the weed and taken on its colour for camouflage. The sargassum fish (Histrio histrio) uses its fins to crawl through the plant forest.

Flotsam and jetsam can circuit the north Atlantic for a long time but eventually it collects in the Sargasso Sea where it provides shelter for juvenile fish such as tuna that use it to hide from sea birds. Natural and man-made debris is used in this way in many of the world’s oceans and it follows that where you find small fish you find predators. Wahoos and dorado have developed a strong interest in floating flotsam.