Giant tortoises, the elephants or hippos of the Galapagos ecosystem?

By Susana Madera

Quito, Jul 9 (EFE).- An international team of scientists is trying to decide whether Galapagos giant tortoises are the elephants or hippopotamuses of their environment.

Considered ecosystem engineers, the giant tortoises influence the habitat on the Ecuadorian islands.

Their penchant for relaxing in pools of water spreads terrestrial nutrients in aquatic zones much like a hippo does in its native African habitat.

A grazing hippo can eat 40 kilograms of grass in a night and when the animal moves to the water to cool off during the day, it defecates partially-digested vegetation into the water, which acts a fertilizer, Diego Ellis Soto, a researcher with the giant tortoise movement ecology project (PEMTG) told Efe.

“We think the Galapagos tortoises are doing something very similar,” he added, pointing to how the massive influx of natural fertilizers from the mud carried on the animals’ shells benefits plant and insect life in the pools they frequent, and can even change the oxygen levels in the water.

“The tortoises could be considered a mixture between hippopotamuses and elephants because they are critical for the aquatic ecosystems like the pools but also are very important for the terrestrial ecosystem in the Galapagos, given that they eat more than 60 species of plants, spread seeds and help germination, similar to the elephants in Africa.”

The study of the animals, which can weigh up to 300kg and are endemic to the Ecuadorian Pacific archipelago, began on the island of Santa Cruz, where scientists located a pool of water packed with up to 60 tortoises at a time.

It was the equivalent of one tortoise per square meter.

“We thought that in some extreme cases the biomass of the tortoises would be greater than that of the water in the pool,” he added, specifying that these natural ponds vary in size from one square kilometer to just nine square meters.