Plankton is derived from the Greek language and means ‘wandering’. When we think of organisms in the ocean that wander—can’t control their motion against the current—we usually think of animals such as jellyfish. Jellyfish are zooplankton; zoo is Greek for animal. But that’s only part of the story… Plankton can be divided into many groups, but the most common divisor is between zooplankton and phytoplankton. Phytoplankton are tiny, aquatic plants usually so small they must be viewed with a microscope.Phyto is Greek for a plant.
Plankton can further be categorized to account for the tiniest living constituents in the ocean, bacteria and viruses. Bacterio- and virioplankton belong to the group encompassing the smallest planktonic organisms, the picoplankton (1 picometer = 10-12 meters). Bacteria and viruses may be enumerated in a number of ways, and some examples are as follows. Both can be visualized under a microscope using fluorescence: samples are treated with biological stains, and when they are illuminated with light of a specific wavelength, the stained components emit light of a longer wavelength (fluorescence). The fluorescence is visible when a microscope is fitted with a set of filters specific for the stain. ·
Bacteria rods visualized with multiple stains These images were collected at different magnifications. Viruses = the smallest green dots (The big, round green dots are bacteria.) Photo by Molecular Probes Inc. Photo by Dr. Jed Fuhrman
Bacterio-andVirioplankton Bacteria colonies can be counted when they are grown on media (agar). A drawback to this method is most marine bacteria cannot be grown in the laboratory; however, culturing bacteria can be useful to answer some research questions. Bacteria colonies grown on marine agar, which is a culture medium for microorganisms derived from seaweed. Some colonies are circled.
Phytoplankton have a marvelous diversity of forms. They can be classified according to a number of characteristics (for example, by morphology); in coastal waters, they are often divided into 2 groups: diatoms and dinoflagellates. Diatoms have glass cell walls (called frustules), which the cells form by taking up dissolved silicate from seawater.
Some diatom species have ‘setae’, which are spine-like projections. The projections increase the cell’s surface area, thus increasing the cell’s drag and reducing its sinking rate into deeper, darker waters that have less sunlight. Individual cells may also form long chains to reduce sinking rates.
Dinoflagellates Dino is Greek for whirling; flagellum is Latin for a whip. Dinoflagellates can ‘swim’ through the water—and stay in nutrient-rich patches—using a pair of whip-like flagella.
Dinoflagellates are capable of capturing energy in 1 of 3 ways: Autotrophs perform photosynthesis to capture the sun’s energy and transform it to food. In this regard, dinoflagellates are plant-like. (auto- is G for self; troph is Greek for nourishment) Heterotrophs cannot perform photosynthesis and must obtain organic carbon, by eating other organisms or decayed marine biota, to provide nutrition. In this regard, dinoflagellates are animal-like. (hetero- is G for other; troph is Greek for nourishment) Mixotrophs can both perform photosynthesis and take up dissolved organic matter. Thus, in this regard, dinoflagellates are both plant-like and animal-like. (mixo- is Greek for mix;troph is Greek for nourishment)
Dinoflagellates may also be classified by their outer coatings: In this image, you can clearly see the transverse grooves (cingulums) for the flagella. Armored dinoflagellates have an outer, protective coating made of cellulose.
Again, in this image, you can clearly see the transverse grooves (cingulums) for the flagella. Naked dinoflagellates have no outer coating made of cellulose.
Phytoplankton Of the 5000species of phytoplankton, about 300 species can occur in ‘blooms’ with concentrations high enough to color the water, including the so-called ‘red tides’ and ‘brown tides’. At least 90 of the bloom-forming species are harmful to humans or animals. When filter feeders, such as oysters, are present during toxic algal blooms, they may concentrate algal toxins in their tissues, and, in turn, when people eat the shellfish, they can contract illnesses affecting the nervous or gastrointestinal system. Also, when the bloom ends, phytoplankton cells die, then they sink to bottom waters and are decomposed by bacteria. These aerobic bacteria use oxygen in the water; sometimes the oxygen level is reduced so much that shellfish and other bottom-dwelling organisms suffocate. Numbers from Bowers et al. 2000
Sarah creek is home to an oyster farm run by the non-profit Chesapeake Bay Foundation*. As a result of the bloom, approximately 650,000oysters died. The secchi disk is ~15 cm in diameter; the shadow in the water is from a davit on the boat carrying the science party. Photos by Dr. Rob Brumbaugh * http://www.cbf.org In September 2003, a toxic dinoflagellate bloom (Gymnodinium sp.)occurred in Sarah Creek, which flows into the York River, a tributary to Chesapeake Bay. Algal concentrations were great enough to color the water.
Plankton (Greek for ‘wandering’) can be divided into 2 groups: PhytoplanktonZooplankton (phyto- G, ‘a plant’) (zoo- G, ‘an animal’) can be divided into 2 groups • armored • “naked” DiatomsDinoflagellates* • glass-like shells • move using • some have setae (projections whip-like flagella that prevent sinking and grazing) can be divided into 3 groups autotrophsmixotrophsheterotrophs (auto- G, ‘self’) (mixo- G, ‘mix’) (hetero- G, ‘other’) (troph G, ‘nourishment’) *Dino- G, whirling; flagellum Latin, a whip
Bibliography Bowers, H.A., Tengs T., Glasgow H.B. Jr., Burkholder J.M., Rublee P.A., and Oldach D.W. 2000. Development of real-time PCR assays for rapid detection of Pfiesteria piscicida and related dinoflagellates. Applied and Environmental Microbiology 66: 4641-4648. Carlton, J.T. 1985. Transoceanic and interoceanic dispersal of coastal marine organisms: the biology of ballast water. Oceanography and Marine Biology Annual Review 23: 313-371. Hallegraeff, G.M. 1993. A review of harmful algal blooms and their apparent global increase. Phycologia 32: 79-99.