Meroplankton are a wide variety of aquatic organisms which have both planktonic and benthic stages in their life cycles. Much of the meroplankton consists of larval stages of larger organism. Meroplankton can be contrasted with holoplankton, which are planktonic organisms that stay in the pelagic zone as plankton throughout their entire life cycle. After a period of time in the plankton, many meroplankton graduate to the nekton or adopt a benthic (often sessile) lifestyle on the seafloor. The larval stages of benthic invertebrates make up a significant proportion of planktonic communities. The planktonic larval stage is particularly crucial to many benthic invertebrate in order to disperse their young. Depending on the particular species and the environmental conditions, larval or juvenile-stage meroplankton may remain in the pelagic zone for durations ranging from hour to months. Not all meroplankton are larvae or juvenile stages of larger organisms. Many dinoflagellates are meroplanktonic, undergoing a seasonal cycle of encystment and dormancy in the benthic zone followed by excystment and reproduction in the pelagic zone before returning to the benthic zone once more. There also exist meroplanktonic diatoms; these have a seasonal resting phase below the photic zone and can be found commonly amongst the benthos of lakes and coastal zones. Spatial distribution Meroplankton species composition depends on spatial distribution and reproductive habits of adults in a given area. Biotic and abiotic factors such as tidal and lunar cycles and availability of food determine adult spawning schedules, in turn, determining subsequent meroplankton populations. Behavioural factors, such as predator avoidance are also important. Freshwater inputs play a key role in meroplankton species composition in estuarine environments. Effects of tides contribute greatly to meroplankton species distribution. One study conducted in a Patagonian Fjord found that species composition of the meroplankton community depended on the seasonally varying input levels from the Baker river as well as vertical and horizontal stratification of the water column. Events such as wind driven upwelling and downwelling also affect meroplankton species distribution. Most species are swept in the direction of the flow of water, either off shore during an upwelling or near shore during a downwelling. Some species, such as bivalve larvae, have the ability to maintain their nearshore position during these events. The distribution of meroplankton is also highly seasonal. Many meroplankton have short residence times in the pelagic zone which follow seasonal reproduction patterns. The timing of meroplankton population rises can