Plankton is small plants or animals that may be microscopic in size. It floats or drifts in huge numbers in bodies of both fresh and salt water. There are two distinct types of plankton. The first is minute, often microscopic sized plants known as phytoplankton and animal organisms known as zooplankton. Within each plankton type there are many different variations or species. In fact, there are an estimated 5,000 different types of phytoplankton and thousands of zooplankton species. Many zooplankton are the eggs or larvae of larger marine animals that are classified as plankton during the early stages of their life cycle.
Where Does the Term Plankton Come From?
The term “plankton” is derived from the Greek “planktos” for wandering or drifting. Phyto, as in phytoplankton, is taken from the Latin “phyton” which means tree or plant. The “zoo” in zooplankton is taken from the Greek word “zoe” meaning life. Colonies of plankton are known as “blooms”.
What are the Two Primary Groups of Plankton?
Most plankton remains microscopic in size throughout its life cycle. Two examples of this type of plankton are bacterioplankton and virioplankton. However, many species of zooplankton known as ichthyoplankton are the eggs and larvae of larger marine creatures such as crustaceans and jellyfish. Ichthyoplankton feeds off phytoplankton and zooplankton. Of the two distinct plankton groupings, zooplankton comprises approximately 70 percent of the ocean’s plankton population.
What do plankton eat?
If plankton is at the bottom of the food chain, on what does plankton itself feed? This is a complex, multifaceted question due to the vast diversity of plankton species and sub-species. Plankton is not only divided into plant and animal forms. In both of those broad classifications, there are thousands and thousands of species and sub-species. Scientists have discovered more than 5,000 different species of phytoplankton alone. There are estimates that the number of zooplankton species might be in the tens of thousands.
Phytoplankton, as a plant, obtains its food in the same manner as other plant life. Its main source of nutrition is the sun. As a result of photosynthesis, all plant life has the ability to absorb sunlight and to transform the energy into food (carbohydrates). Phytoplankton never lacks for food as long as the sun shines. Plants have the ability to maximize their utilization of available sunlight. Even plant life living in areas where sunlight is restricted or reduced, such as in the depths of the sea, are capable of trapping the smallest amounts of available sunlight as food. This ability to transform sunlight into food, along with changes in the earth’s climate and increased pollution levels in the world’s oceans, have been credited with a tremendous growth in plankton blooms in some areas of the world. These enormous blooms can even be seen from space as huge swaths of color in the ocean. Because phytoplankton is so susceptible to changes in their environment, it provides an excellent research framework for scientists studying climatic change and the effects weather changes on the earth’s oceans and atmosphere.
Zooplankton is by far the most prolific of the two types of plankton. Besides the many small and often microscopic animals that make up a large part of the zooplankton population, there are many types of zooplankton that are the eggs and larvae of other sea creatures. These species of zooplankton grow and develop into much larger animals and fish. For many of these creatures, their main source of food is the phytoplankton. Some of the larger species of zooplankton are true predators and feed off other zooplankton.
The Role Of Phytoplankton on the Earth’s Biosphere
Phytoplankton is a vital part of earth’s biosphere. As a plant, it has the unique ability to absorb carbon dioxide and release oxygen into the atmosphere through the process of photosynthesis. Along with the rest of the planet’s plant life, phytoplankton is responsible for the constant replenishment of the oxygennecessary for life. In fact, phytoplankton is responsible for 50 percent of earth’s oxygen renewal. Phytoplankton is also an essential element in the ocean’s food chain. Many fish and other marine creature rely on it as a readily available and primary food source.
How do Plankton Reproduce?
The reproductive methods used by plankton can be divided into two main categories. Phytoplankton, usually microscopic, is a single-celled organism. In most cases, it reproduces by cloning itself. One single-celled phytoplankton organism will split into two identical phytoplankton plants. This method of reproduction is highly efficient as no male or female partners are required. In fact, reproduction can be so rapid that, were it not for the presence of inhibiting factors such as marine creatures feeding off the phytoplankton, their growth rate would be almost beyond the imagination. Indeed, some scientists have speculated that one of the Ten Plagues of Egypt, when the water turned red, was in fact, a population explosion of a particular, red-colored type of phytoplankton.
Some phytoplankton species combine within them both male and female elements. Others reproduce by shedding filaments which then grow into phytoplankton. In all cases, the offspring are clones of the parent.
Zooplankton, on the other hand, being animal, even though a simple one, has a wide variety of reproductive systems. As noted, some types of zooplankton are the eggs or larvae of larger sea creatures that will develop and reproduce as their parents did. However, many species of zooplankton are distinct species and have their own, often unique ways of reproducing. Nature has contrived many different ways to ensure that the female zooplankton egg is fertilized by the male zooplankton’s sperm. In some species, the male and female zooplankton will use external appendages to keep together during the egg and sperm uniting. Other zooplankton species will release eggs into the water. The eggs will float until they come into contact with sperm. Yet other species release eggs and sperm simultaneously into the water to encourage reproduction.
The main difference between the reproductive methods of phytoplankton and zooplankton lies in the simple fact that all zooplankton reproduction demands both a male and a female partner. The female contributes an egg and the male the sperm as in mammals and other living creatures.
What is the Lifespan of Plankton?
Because there are more than 5,000 species of phyloplankton and thousands of species of zooplankton. There is no specific lifespan that would apply to all species of plankton. With such a wide diversity of species and sub-species, many of which are actually the early stages of larger, more complex biological organisms, defining an accurate lifespan for plankton as a whole is not practical or realistic. However, scientific research, especially that conducted over the past 10 years, provides information that enables one to make a general estimate of life cycles and lifespans for the different plankton groupings.
If one looks at the zooplankton (animal) population, research has shown that the lifespan is, to a large extent, dependent upon the size of the organism. The larger the organism, the longer the lifespan of the species of plankton. By and large, zooplankton lifespans range from only a few months to much more than a year. Jellyfish, for example, are estimated by some scientists to have average lifespans of approximately a year. But some jellyfish species can live longer. Chaetognaths (arrow worms) are a major component of plankton in all parts of the world. They have an average life span of only 200 days.
A problem that one encounters in attempting to provide a reasonable estimate of the lifespan of plankton is how to relate to single-celled plankton. As most single-cell organisms tend to reproduce by division, it can be said that they never really die. Each new generation is the clone of the previous. It is thus single-celled immortality. But even here there is wide diversity in time periods. One-celled plankton divide as frequently as every few hours or they could divide every few days. Various one-celled plankton species have different dividing time periods.
The determination of the lifespan of plankton must also consider non-optimal conditions. The optimum conditions for the extension of life are rarely found in nature. One consideration alone, the fact that plankton is a major source of food for many marine creatures, limits the realistic lifespan, as opposed to the biological lifespan, of plankton. Thus a more practical term to employ in such a discussion might be “life expectancy” as opposed to “lifespan”