About Meyenaster gelatinosus (Meyen, 1834)
Meyenaster gelatinosus is a white starfish that typically has six arms, with a mean radius ranging from 150 to 210 mm (5.9 to 8.3 in). This species is native to the southeastern Pacific Ocean, where it occurs along the coasts of Chile. It is abundant in subtidal kelp forests, and can also be found on sand and gravel bottoms, and among seagrasses. It most often lives in areas with strong water surge, and is not found in calm, quiet locations. In Chilean kelp forests, M. gelatinosus is one of the dominant predators, alongside other species including the starfishes Stichaster striatus, Luidia magellanica and Heliaster helianthus, the fish Pinguipes chilensis, Semicossyphus darwini and Cheilodactylus variegatus, and the Chilean abalone (Concholepas concholepas), a gastropod mollusc. When M. gelatinosus traps the multi-armed H. helianthus, it everts its stomach over several of the prey's arms. The prey sheds these arms through autotomy in response to the predation; while M. gelatinosus feeds on the shed arms, H. helianthus escapes. One study conducted in Chile found that up to 76% of the H. helianthus population had regenerating arms from this interaction. A study in Tongoy Bay, located in north-central Chile, found that M. gelatinosus acts as a generalist predator in sand and gravel habitats, but shows a strong preference for the Peruvian scallop (Argopecten purpuratus) when in seagrass meadows. During this study, Peruvian scallop populations declined dramatically after heavy commercial harvesting over a short period. This decline led the starfish to increase its preference for scallops in both habitats, but forced the starfish to broaden its diet in seagrass areas, replacing the missing scallops with small epifauna. M. gelatinosus can feed on Peruvian scallops of all sizes, ranging from 4 to 14 cm (2 to 6 in) in diameter, but it specifically preys on larger scallop specimens. Local fishermen are aware that they compete with this starfish for access to scallops. In another separate study, the main prey recorded for M. gelatinosus was the Chilean sea urchin (Loxechinus albus). M. gelatinosus often carefully selects and pursues this urchin prey. The Chilean sea urchin responds to a foraging M. gelatinosus from at least one metre away by fleeing. This escape response is effective in areas with strong wave action, because the surging water sweeps the sea urchin away from the predator. The Chilean sea urchin can distinguish between foraging and non-foraging M. gelatinosus, and only takes evasive action when encountering a foraging individual. Sea urchins have even been observed touching non-foraging M. gelatinosus.
