Life in the Ocean

Published 07 Dec 2016


What is picoplankton and why is it important in the ecology of the ocean?


Planktons with cells that range from 0.2 and 2.0 µm are called picoplanktons. There are two types of picoplanktons depending on their feeding preferences: the photosynthetic picoplankton and the heterotrophic picoplankton. The former is the plankton that dominates the central oligotrophic regions. These regions have scarce supply of nutrients. There are three major groups under this type: cyanobacteria (Synechococcus), cyanobacteria (Prochlorococcus), and picoplanktonic eukaryotes.

This plankton is important since, aside from the “biological pump” that distributes nutrients in the depths, it synthesizes the available nutrients to provide nutrients to other organisms in the area. The latter type of plankton, as its name suggests, is the type of plankton that do not perform photosynthesis. It can be either prokaryotes or eukaryotes. Heterotrophic picoplanktons can be found on both seawater and freshwater environments. These picoplanktons are important in the carbon cycle since they feed on organic matter (i.e. waste products, carcasses of dead creatures) descended into the depths. These creatures help in maintaining the cleanliness in the ocean floor.


Salinity and osmotic balance are closely related. Discuss how organisms compensate for changes in salinity when they move from the ocean to an estuary, as occurs with various species of shrimp and fish during their life cycle.


The blue crabs, shrimp, and lobsters, also called decapod crustaceans, are some of the species in which salinity is part of their life cycle. Salinity is important in the regulation of internal ion concentration of the crustaceans, decapods and fishes. In the case of the blue crabs, most of the time, the adults are found in the estuarine environment where there is a relatively low-salinity water. After mating, the female blue crab journeys into the deeper parts of the ocean to release the fertilized eggs.

The grass shrimp, Palaemonetes vulgaris, also live in the low-salinity water of the estuaries. The changes in the salinity levels across the estuaries into the ocean depths are compensated by changes in the ion concentration of the species. In this way, the organisms are able to survive and complete their life cycle. During their larval stage, high salinity inhibits growth of some types of pathogenic organisms and invasive species thus shrimps and other crustaceans and fishes usually lay their eggs in high-salinity waters, e.g. ocean. The organisms then return to the low-salinity waters when they mature or reach optimum stage for survival and completion of the life cycle.


How does the fossilization process take place in marine organisms? Go to the web sites indicated at the end of Supplemental Activity 3 of Chapter 21 in The Endless Voyage Study Guide, and answer the question in a brief manner (not a report).


Fossil preservation of organisms depends upon three key factors: type of animal, environment, and events after death. In arid, acidic and tropical environments, bones are usually decomposed at faster rates while in the marine environment, there are factors (i.e. salinity) that serve as preservatives of the remains thus allowing preservation of the organisms’ details after it dies, called fossil. Fossilization in marine organisms is accomplished through rapid sedimentation and absence of process interruption. When the organism dies, its remains are quickly covered by sand or mud and some organic matter that descends from the ocean surface to the abyss.

This will bury the remains and in effect, it will be protected from disturbances for thousands or even millions of years. The remains will not be available for scavengers which are present in the open environments inland. It will also be protected from erosion and washing away as well as decomposing bacteria. The sedimentation process will continue and after sometime, the surrounding sediments will harden into rocks, layers of rocks formed from sediments and remains of the organism. Organism’s details maybe omitted in the process depending on the type of rock and mineral deposits that buried it. The most common types are calcite and aragonite (both form of calcium carbonate), quartz and silica.


  • Thornton-Devictor, S. (2004). Transitions to the Deep: Adaptations in Decapod Crustaceans for Life Along the 31º30N Atlantic Transect. Retrieved April 22, 2007, from
  • Oram, J.J. (2005). Patterns of Temperature, Salinity, and Suspended Particulate Material in San Francisco Estuary: Water Year 2005 in the Context of Previous Water Years. Retrieved April 23, 2007, from
  • Dinosaur Fossilization (n.d.). Retrieved April 23, 2007, from
  • How Fossils Form (n.d.). Retrieved April 23, 2007, from
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