About Tripneustes depressus A.Agassiz, 1863
Tripneustes depressus A.Agassiz, 1863 is the largest sea urchin species found in the Galápagos Islands. It has a mean diameter of 11.5 cm (4.5 in), with an average growth rate of 0.5 mm (0.02 in) per month. There is very little morphological difference between T. depressus, Tripneustes gratilla, and Tripneustes ventricosus. The three are suspected to be the same species, and genetic analysis supports this argument. T. ventricosus is found in the Caribbean; it may have become separated from T. depressus when the land bridge between North and South America closed. T. gratilla has a broad range across the tropical Indo-Pacific, spanning from East Africa to Hawaii. T. depressus is distributed in the tropical eastern Pacific Ocean. It occurs in Mexico, along the western coast of Central America, in Panama, in Ecuador, and around the Galápagos Islands. This species can be found in both intertidal and subtidal zones. Its abundance varies greatly across the Galápagos, and overall, it was approximately ten times more common in 2012 than it was four decades earlier. The diet of T. depressus consists largely of algae, and may also include fragments of seagrass. Red filamentous algae is its main dietary component, but pieces of sponge and other invertebrates have also been found in its stomach contents. It may actually be a generalist feeder rather than a strict herbivore, as it sometimes turns cannibalistic during periods of food scarcity.
