Tripneustes gratilla, commonly known as the collector sea urchin or Pacific sea urchin, is a species of echinoid belonging to the family Toxopneustidae and the order Temnopleuroida. It is distributed in various regions of the Indo-Pacific Ocean, from the east coast of Africa, Southeast Asia, Australia, Japan, to the Pacific islands and the west coast of Central America. It inhabits coral reefs and shallow rocky bottoms, generally up to 35 meters deep.
This sea urchin is distinguished by its collecting behavior, as it gathers small pieces of the bottom, such as shells, detritus, algae and small stones, placing them on its body to mimic the environment and protect itself from predators. This habit makes it a master of camouflage in its natural habitat.
Morphologically, Tripneustes gratilla has a globular shape with a diameter varying between 10 and 15 cm. Its coloration is generally dark, typically bluish or purple, with white spines. The pedicels are also white, with a dark or black base. Some variants have completely orange spines, while others show orange tips or completely white spines. Compared to Tripneustes ventricosus, which is found in the western Atlantic, both species are morphologically similar, although the latter has more uniform coloration.
Tripneustes gratilla is herbivorous, feeding mainly on filamentous algae and macroalgae, especially the genera Thalassodendron and Syringodium, although it occasionally consumes detritus and decaying organic material. Its ability to consume large quantities of algae plays a crucial role in regulating algal growth in coral reefs, preventing overpopulation and helping to maintain ecological balance.
Reproductively, this sea urchin is externally fertilized, releasing sperm and eggs into the water during the warmer months of the year, usually between spring and summer. The larvae are planktonic and develop in the water column before settling on the seafloor, where they metamorphose into juvenile urchins.
An interesting fact about Tripneustes gratilla is its value in fisheries and aquaculture, as its gonads are considered a delicacy in several countries. In addition, its ability to control algal growth makes it a key species for maintaining coral reef health. However, in areas where it lacks natural predators, its proliferation can become a problem.
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