Meroplankton

Meroplankton is a term used to describe a wide variety of planktonic organisms, which spend a portion of their lives in the benthic region of the ocean. These organisms do not remain as plankton permanently, rather, they are planktonic components in transition, which eventually become larger organisms. After a period of time in the plankton, meroplankton either graduate to the nekton or adopt a benthic (often sessile) lifestyle on the seafloor. Meroplankton consists of larval stages of organisms such as sea urchins, starfish, crustaceans and dinoflagellates and diatoms. Meroplankton forms an algal medium that is found between the loosely mixed sediments and water. This layer can be re-suspended in the water column by turbulent mixing. Success of meroplankton populations depends on many factors, such as adult fecundity, fertilization success, growth and larval stage duration, behaviour, dispersal, and settlement. Mortality depends on many factors, such as predation, competition, disease, parasites, and physiological stresses. Survival and mortality of meroplankton has a direct effect on adult population numbers of many species. Many of the common, well-known animals found on the Great Barrier Reef spend time as free-swimming meroplankton, bearing little or no resemblance to the adult they will become. The differences between the appearance of larval and adult stages led to much confusion in the past when larval forms were often believed to be completely different species from the adults. Larvae spend varying amounts of time in the plankton, from minutes to over a year. However, just how long these tiny animals can be considered truly planktonic is under some debate.