Early development, settlement, growth, and spatial distribution of the sea cucumber Cucumaria frondosa (Echinodermata: Holothuroidea)

Cucumaria frondosa was studied in the field and in the laboratory to elucidate its development, growth, substrate selection, and migration patterns. In 1992 and 1993, spawnings in the laboratory and in the lower St. Lawrence Estuary occurred in mid-June. Males spawned first, followed shortly by females. The fertilized eggs and resulting embryos were buoyant. They developed into pentactula 9 d after fertilization. In the laboratory, embryonic development was fastest at 12 degrees C, pH 8, and salinity 26 psu (practical salinity unit). The first contact of embryos with the substrate, made with the tentacles, occurred ca. 48 d after fertilization. Following a search period of 3-40 h, settlement was achieved using the ambulacral podia. Laboratory and field observations showed that gravel or rock were favored by larvae during settlement. After reaching ca. 2.8 mm in length, ca 4-5 months later, young sea cucumbers moved to sheltered, illuminated areas of rocky substrate, and migrated from protected to exposed areas after they exceeded ca 35 mm in length. Overall, the growth rates were maximal during the spring and summer phytoplanktonic blooms with rising temperature. Field observations showed a size-dependent migration from photic to aphotic depths (greater than or equal to 40 m depth), when the animals reached sexual maturity.