MEPS 123:33-44 (1995)  -  doi:10.3354/meps123033

Direct observations of groups of mysids in shallow coastal waters of western Japan and southern Korea

Ohtsuka S, Inagaki H, Onbe T, Gushima K, Yoon YH

Groups (swarms, schools or aggregations) of mysids occurring in shallow coastal waters of western Japan and southern Korea were directly observed by SCUBA and skin divers during the day. Formation of groups was seen in 16 species belonging to the family Mysidae. These groups were often polyspecific, composed of 1 dominant species accounting for 50 to 100% of the number of individuals in the group and 0 to 5 guest species. Nipponomysis spp., Prionomysis aspera and Tenagomysis sp. formed flat, carpet-like or discoid swarms over sandy bottoms. Anisomysis aikawai, A. ijimai, A. mixta, A. pelewensis, Anisomysis spp., Lycomysis bispina, Nipponomysis sp., Paracanthomysis hispida, Siriella sp., and an unidentified leptomysid aggregated in shapes of ovals, spheres and columns. L. bispina and P. hispida were associated with algal beds. Other swarms were located near isolated rocks over sandy bottoms, near the edges of corals or along the seashore. Swarms were classified into 2 types in terms of mobility: stationary and migratory; however, the mobility of the swarms was changeable with season and with sexual maturity. Most swarms were made up of various developmental stages, but some swarms of A. aikawai and A. ijimai consisted only of juveniles. Densities of mysids in a swarm ranged from 13 to 571 ind. l-1. Sex ratios (male/female) of immature and mature males and females within a group varied between 0.22 and 2.40. Possible adaptive values of mysid groupings are discussed on the basis of present and previous findings: (1) antipredation, (2) maintenance of favorable position, and (3) feeding.

Mysid . Swarm . School . Aggregation . Group

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