Plankton

For the character, seeSheldon J. Plankton.

Phytoplankton include tiny one-celledeukaryoteswhich dophotosynthesis

Noctiluca scintillansis adinoflagellatewhich eats up other tiny plankton

Northernkrill,the favourite food of thebaleen whales

Planktonare driftingorganismsthat live in the surface layers of theocean.They live in the top layer of the ocean, called theepipelagic zone.They are not strong enough to swim against ocean currents. The term is in contrast tonekton,who can control their movements.There are three groups:

• Phytoplankton: which live at the surface of the ocean andphotosynthesise(use light to make sugars and othermolecules).
  • Eukaryotealgae:diatoms,coccolithophores,somedinoflagellates.
  • Bacteria:cyanobacteria.
• Zooplankton: smallprotozoansormetazoans:Ctenophores;jellyfish;rotifers;foraminifera;tinycrustaceaand otheranimals.Someeggsandlarvaeof larger animals such as fish, crustaceans, andannelids.Apart from the eggs, they all feed on other plankton.
• Some groups fall into both categories.Dinoflagellatescan be either photosynthetic producers orheterotrophconsumers; many species aremixotrophicdepending upon their circumstances. It is also hard to fitvirusesinto this scheme; yet they are present in great numbers.

Plankton are important in the ocean'sfood chain.They are the main source of food for almost allfishlarvae as they switch from their yolk sacs to catchingprey.Basking sharksandblue whalesfeed on them directly; other large fish feed on them indirectly, by eating fish of smaller size, such asherrings.

The distribution of plankton is governed more by nutrients than by temperature. Large tracts of ocean are blue and sterile. The reason is that these areas lack one or more crucial nutrients for the photosynthetic plankton, upon whom all the others depend. Broadly speaking, areas near land masses get nutrients by rivers and wind. The keynutrientlacking in thePacific oceanisiron,essential inmoleculessuch asferredoxins,iron-sulfurproteinswhich doelectrontransfer in a range ofmetabolicreactions.