Direct observations of clustering (schooling and swarming) behaviour in mysids (Crustacea: Mysidacea)

A new scheme is presented for the classification of mysid aggregations according to the mechanisms stimulating their formation and mamtenance.Previous classifications were inadequate in simply and effectively describing the social behavlour of 6 species of mysids commonly found in the sublittoral zone off the east coast of Tasmania.All the species observed exhibit clustering behaviour whlch under the present scheme is defined as: individuals of all stages (although generally segregated) are distributed in integrated aggregations at least during daylight in response to internal biological mechanisms.Cluster form is flexible and subject to both intrinsic and extrinsic factors.Clusters display features of swarming, schooling and shoaling behaviour and a high level of integration between individuals.Evidence for the intrinsic nature of clustering behaviour in mysids is discussed and extrinsic factors are described as periodically influencing the fornl of the aggregative behaviour.The functions of clustering include increased reproductive potential, antipredation, and maintenance of position in the environment; however, the latter is the most important factor influencing variation in clustering behaviour.Maintenance of position varies with substrate attraction and hydrographic conditions, and the adaptive significance of the different forms of clustering behaviour employed by species in the present study is discussed.