Feeding behavior of the urchin-eating urchin Salmacis sphaeroides

概要

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On the shallow sandy bottom in the innermost part of the Gulf of Thailand, the regular sea urchin Salmacis sphaeroides feeds on two spatangoid urchins: Brissus latecarinatus, one of the locally dominant infaunal macrobenthic animals, and Lovenia elongata. Aggregations of Salmacis were frequently seen on the soft bottom during a survey of the macrobenthos in the Gulf, and Brissus individuals lacking spines were found beneath the aggregations. Brissus species, which are infaunal, were attacked by Salmacis, although the reason for their presence on top of the sandy bottom remains unknown. Salmacis were seen feeding first on the spines of Brissus, exposing the test. Occasionally, Salmacis carrying empty, broken tests of Brissus were observed, indicating that the Brissus organs were also eaten by Salmacis. The fact that Salmacis ate several kinds of food items such as water hyacinths originated from the nearby river system, sea pens, jellyfish, and other urchins indicates that this species is an omnivore. Cannibalism was also found both in the field and laboratory. The feeding strategy of Salmacis has evolved to incorporate diverse food items, but Brissus is undoubtedly an important food source because of its high abundance.