口永良部島におけるニシキベラThalassoma cupidoの成長に伴う食性と採餌行動の変化

ニシキベラの成長に伴う食性と採餌行動の変化を、南西諸島の口永良部島の磯水域で調査した。小型魚は主に小型甲殻類(ヨコエビ類、カイアシ類、介形類、等脚類、タナイス類、クマ類)を、これらの小型の餌生物が豊富な微小藻場で摂餌していた。一方、大型になるに従い、worm類(多毛類、ホシムシ類)、貝類(巻貝類、ピザラ異類、二枚貝類)、大型甲殻類(カニ類、シャコ類、エビ類、ヤドカリ類)を含む、より大型の餌を摂餌していた。これらの、より大型の餌生物の生息宿度は微小藻場では比較的低いため、大型になるに従い採餌の範囲を拡大すると共に、より大型の餌生物が生息する石灰藻場やブダイ類のかじり跡へと採餌場所を移行させた。

Ontogenetic changes in diet and foraging behavior of Thalassoma cupido were studied on the shallow reefs at Kuchierabu-jima Island, southern Japan. Small fish mainly took small crustaceans (gammarids, copepods, ostracods, isopods, tanaids and cumaceans) from algal mats, where the small prey species lived in a large numbers. While larger fish consumed correspondingly larger prey, including worms (polychaetes, sipunculids), shells (gastropods, chitons and pelecypods), and large crustaceans (crabs, stmatopods, shrimps and hermit crabs). Because the density of larger prey species was relatively low in the initial habitats foraged, larger fish shifted their foraging attention to coraline algal mats and sites scraped by scarid fish, where the larger prey species were present, as well as foraging over larger areas.