COLONISATION OF THE WATER COLUMN BY OSTRACODS: WHEN, HOW AND WHY?

Ostracods are a major group of small aquatic arthropods and are by far the most prolific group of arthropods in the fossil record, ranging over some 500 million years from at least the Ordovician Period onward. They are important contributors to all kinds of aquatic ecosystems, occurring in marine, brackish and freshwater. Ostracods are an important component of modern marine zooplankton from the ocean ‘Mixed Layer’ to abyssal depths. Often very abundant in sub-thermocline ocean waters, most ostracod zooplankton are detritus feeders on falling organic particles (‘marine snow’). Ostracods were early zooplankton colonists, making the ecological shift from the benthos during the Silurian, and leaving behind an unparalleled fossil record of their environmental distribution, and crucially of their soft anatomy. Coupled with detailed work on the physiology of Recent ostracods, there is an extensive dataset from which to assess the ‘when’ (temporally), ‘how’ (carapace design, physiology and functional anatomy), and ‘why’ (environmental and biological feedback mechanisms) ostracods colonized the water column, a major event in the ecological radiation of the group and a model for the study of benthic to zooplanktonic ecological shifts.