Antarctic Thesaurus
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zooplankton
The name zooplankton is derived from the Greek work planktos meaning to wander and refers to the small size and weak swimming movements of organisms in this category. These characteristics seem to predispose them to floating at the mercy of the ocean currents...
It is not entirely true that zooplankton are at the mercy of the ocean currents. Many organisms in this catergory undergo vertical migrations over the course of every 24 hour period (diel vertical migration). The most common pattern is to migrate deeper in the water column during daytime and ascend towards the surface at night. The most likely explanation for this behaviour is to escape predators feeding in the upper lighted layers during daytime and exploit the food sources which are most abundant near the surface when it is too dark for successful capture by visual predators. However, vertical migration may also remove organisms from faster moving currents near the surface into deeper slower currents that may even be travelling in the reverse direction. Thus some degree of control over distribution is possible by varying the time spent at specific depths.
As well as being small and migrating vertically, they have adopted a range of other protective strategies, e.g. being transparent and agregating into schools or swarms.
Guide to Zooplankton of south eastern Australia Ritz, Swadling, Hosie, Cazassus University of Tasmania, 2003 p.1
A pteropod, or sea butterfly, is known as a zooplankton.
A zooplankton is comonly known as a drifting creature, unable to move much of its own accord. However, marine scientist, Steve Nicol, describes the zooplankton as actually pretty meaningless word for distinguishing between species. It's like defining all planktons as 'any things caught in a plankton net' (Nicol, 2008)