Plankton

Plankton Definition Plankton - Any drifting organisms which can be animals, plants, archaea, or bacteria, that live in the pelagic zone of oceans, seas, or fresh water. Plankton are defined by their role in the environment. They provide a crucial source of food to more familiar aquatic organisms such as fish.

Plankton Definitions While some forms of plankton are capable of independent movement (diel vertical migration) their horizontal position in the water is determined by currents in the body of water they inhabit. Plankton are unable to resist ocean currents.

Types of Planktons Holoplankton organisms that spend their whole lives as plankton (e.g. most algae, copepods, salps, and some jellyfish). Meroplankton are those organisms that are only planktonic for part of their lives (usually the larval stage), and then graduate to either the nekton or a benthic (sea floor) existence. Examples of meroplankton include the larvae of sea urchins, starfish, crustaceans, marine worms, and most fish. Sea star (Meroplankton) Holoplankton

Functional Groups of Planktons Phytoplankton- plant plankton, autotrophic, prokaryotic or eukaryotic algae that live near the water surface where there is enough light to support photosynthesis. Among the more important groups are the diatoms, cyanobacteria, dinoflagellates and coccolithophores.

Functional Groups of Planktons Zooplankton- animal plankton, small protozoans or metazoans (e.g. crustaceans and other animals) that feed on other plankton and telonemia. Some of the eggs and larvae of larger animals, such as fish, crustaceans, and annelids, are included here.

Functional Groups of Planktons Bacterioplankton, bacteria and archaea, which play an important role in recycling organic material into the water (note that the prokaryotic phytoplankton are also bacterioplankton).

Common Types of Plankton Diatoms are the most common phytoplankton. They are one celled producers with a covering (called a frustule) of glass. Many species have flotation mechanisms (spines, internal oil droplets, colonies). Diatoms are important oxygen producers in marine ecosystems (usually the first step in the food chain). They are holoplanktonic. When conditions are bad they die, sink, the cell decomposes and the frustule breaks up and mixes with sand and mud. This combination of sediments and glass frustules makes a siliceous ooze called diatomaceous earth Asexual reproduction occurs with diatoms in good conditions in a unique way so that some get smaller and smaller until they are too small to function properly.

Common Types of Plankton Cont.. Certain species of diatoms produce harmful chemicals (most notably domoic acid) which can concentrate in animals who eat plankton (filter feeders). Large amounts of domoic acid consumed by mammals (such as seals, sea lions and humans) can cause erratic behavior and lead to death.

Plankton Size Group Size range (ESD) Examples Megaplankton > 2×10-2 m (20+ mm) metazoans; e.g. jellyfish; ctenophores; salps and pyrosomes (pelagic Tunicata); Cephalopoda metazoans; e.g. Pteropods; Chaetognaths; Euphausiacea (krill); Macroplankton 2×10-3→2×10-2 m (2-20 mm) Medusae; ctenophores; salps, doliolids and pyrosomes (pelagic Tunicata); Cephalopoda Mesoplankton 2×10-4→2×10-3 m (0.2 mm-2 mm) Medusae; Cladocera; Ostracoda; Chaetognaths; Pteropods; Tunicata; Heteropoda

Plankton Size Cont.. Group Size range (ESD) Examples Microplankton 2×10-5→2×10-4 m (20-200 µm) Large eukaryotic protists; most phytoplankton; Protozoa (Foraminifera); ciliates; Rotifera; juvenile metazoans - Crustacea (copepod nauplii) Nanoplankton 2×10-6→2×10-5 m (2-20 µm) Small eukaryotic protists; Small Diatoms; Small Flagellates; Pyrrophyta; Chrysophyta; Chlorophyta; Xanthophyta Picoplankton 2×10-7→2×10-6 m (0.2-2 µm) Small eukaryotic protists; bacteria; Chrysophyta

Plankton Size Cont.. Group Size range (ESD) Examples Femtoplankton < 2×10-7 m (< 0.2 µm) marine viruses

Distribution Plankton are found in oceans, seas and lakes. The first cause of amount and variability plankton varies horizontally, vertically and seasonally. This is caused by the availability of light in an area. A secondary cause of variability is the availability of nutrients. Large areas of tropical and sub-tropical oceans have a lot of light they have a low availability of nutrients such as nitrate, phosphate and silicate. This is a result of ocean-circulation and ocean layering or stratification of water column.

Importance of Plankton Phytoplankton fix carbon in sunlight by photosynthesis. Primary production (the amount of carbon produced by photosynthesis) occurs as a result of phytoplankton. Phytoplankton are at the bottom of the aquatic food web and produce all the energy for all other life in the water. Phytoplankton produce approximately 60% of the oxygen for the planet Earth.

Importance of Plankton Cont.. Zooplankton are initially the sole prey item for almost all fish larvae as they use up their yolk sacs and switch to external feeding for nutrition. Fish species rely on the density and distribution of zooplankton to coincide with first-feeding larvae for good survival of larvae, which can otherwise starve. Natural factors (e.g. variations in oceanic currents) and man-made factors (e.g. dams on rivers) can strongly affect zooplankton density and distribution, which can in turn strongly affect the larval survival, and therefore breeding success and stock strength, of fish species.

Common Phytoplankton Diatoms Dinoflagellates

Bioluminescence Some species of dinoflagellates will produce a blue/green light, after dark, when they are disturbed. This probably functions to scare predators away in the natural environment. There are always a few of these dinoflagellates in the water but their small size keeps their tiny spark of light from being visible on most nights. But, if these species are blooming, and very concentrated in the seawater, every movement of the water produces a glow - waves appear to light up as they break at night and fish leave glowing trails in the water as they swim at night. This phenomenon is seen all over the world.

Zooplankton Zooplankton are tiny animals found in all ocean zones, particularly the pelagic and littoral zones in the ocean, but also in ponds, lakes, and rivers. They are a key component of marine ecosystems. The most common plankton are protists, nanoplanktonic flagellates, cnidarians, ctenophores, rotifers, chaetognatha, veliger larvae, copepods, cladocera, euphausids, krill and tunicates.

Nanoplanktonic Flagellates Nanoplanktonic flagellates that help keep bacteria populations under control. They are characterized by either a long tail used for swimming (flagellates) or by hair-like structures called cilia (ciliates). Some dinoflagellates have a net-like structure called a protoplasmic net—used to capture and eat prey that are typically larger in size than bacteria. Some dinoflagellate species are also responsible for harmful fish kills and the infamous red tides. Ciliates are capable of catching bacteria, other protists and phytoplankton.

Cnidarians These contain the colonial siphonophores and the scyphozoans—also known as the true jellyfish. Both of these animals are predators and have stinging tentacles. They are not found often in fresh water and in the ocean they inhabit the layers closer to the surface. Comb jellies or ctenophores were previously classified under Cnidaria but have recently been distinguished from other jellyfish because they lack the characteristic stinging cells of other jellyfish known as nematocysts. Comb jellies effectively keep copepod zooplankton levels in check through

Cnidarians

Phylum Rotifera Most of the rotifers are non-motile (not able to move) but about 100 species are holoplanktonic. Rotifers eat bacteria, detritus, other rotifers, algae or protozoa. Rotifers are highly efficient reproducers. They are able to reproduce asexually (without a mate) when environmental conditions are good, and sexually when environmental conditions are stressful.

Rotifer

Marine Gastropods Larvae of benthic mollusks usually found in coastal waters, such as marine gastropods including heteropods or pteropods.

Krill They are found all over the world. They can be 3 cm large and are an important source of food for many types of whales. In cold waters, krill often feed on diatoms, a type of phytoplankton. In warmer water they prefer to eat other animals

Tunicates (Sea Squirts) Some tunicates are planktonic, such as the holoplanktonic classes Appendicularia and Thaliasia. Both are filter feeders; Appendicularia consumes small food particles using a mucous filter. Other types of tunicates are benthic and are only planktonic during their larval stages.

Copepods Most macrozooplankton are copepods found in marine and freshwater ecosystems. Copepods swim using an antenna and frontal structures on their bodies. They eat phytoplankton and detritus, and occasionally other zooplankton smaller in size.

Adaptations They have structural adaptations to be able to float in the water column. Adaptations include: flat bodies, lateral spines, oil droplets, floats filled with gases, sheaths made of gel-like substances, and ion replacement. The flat body and spines allow some species of plankton to resist sinking by increasing the surface area of their bodies while minimizing the volume. All other adaptations keep plankton from sinking quickly to the bottom. Zooplankton have also adapted mechanisms to deter fish (their heaviest predator) including: transparent bodies, bright colors, bad tastes, red coloring in deeper water, and cyclomorphosis. Cyclomorphosis occurs when predators release chemicals in the water that signal zooplankton, such as rotifers or cladocerans, to increase their spines and protective shields.

Night Swimming Many types of zooplankton migrate deeper into the water during the day and come up at night. The migration of species appears to be dependent on location rather than particular species types. All plankton migrate differently based on factors like age, sex and the season. The amount of light is probably the major factor in the extent of migratory behavior. It seems that zooplankton move around most in low light and least in higher light situations. It’s possible that zooplankton migrate to lower levels during the day so they are less visible to predators relying on vision. At night, zooplankton can sneak up to the surface and snack on phytoplankton relatively safely. The lower metabolism occurring in colder waters during the day may also be a factor in the migration of zooplankton. This way, zooplankton can save energy by feeding in the cooler, night waters. The fact that different species of zooplankton have varying migration times may be the result of a partitioning of resources.