1.
Planktonic organisms can swim, but they can’t make significant headway against the currents in which they drift.
2.
Plankton is an artificial category; a category not based on a phylogenetic
(evolutionary) relationship but rather on a shared lifestyle.
3.
Even the finest nets allow picoplankton to escape. These exceptionally small organisms must be collected using exceedingly fine filters.
4.
Measurements of physical ocean conditions such as dissolved carbon dioxide and oxygen content, pH, temperature, and light intensity at the time and place of sampling are of special importance in interpreting plankton samples.
5.
Coccolithophores are the most abundant nanoplankters, and the larger diatoms and dinoflagellates are classified as microplankton. Superabundant marine viruses are categorized as femtoplankters.
6.
An autotroph is an organism capable of making its own food from inorganic nutrients.
7.
Not all plankters are autotrophic. Heterotrophs depend on autotrophs for nutrition.
8.
The most important phytoplankters are the minute cyanobacteria, the larger diatoms and dinoflagellates, and the prolific coccolithophores.
9.
Picoplankters such as cyanobacteria and archaea are of great interest because of their vanishingly small size, biochemical efficiency, and apparent immense contribution to world productivity.
10.
The “microbial loop” is a complete microecosystem—a community operating on the smallest possible scale—that manufactures and consumes particulate and dissolved carbon in amounts almost beyond comprehension. Organisms of the loop are not available to fishes and other larger consumers because the small animals on which they prey are unable to separate these exceptionally small creatures from the surrounding water.
11.
Diatoms and dinoflagellates are both single-celled autotrophic eukaryotes.
Diatoms have glass shells (valves) pierced with tiny pores and are more efficient photosynthesizers than dinoflagellates. Dinoflagellates evolved earlier than diatoms and have a covering made of a form of cellulose. Their photosynthetic efficiency is, on average, not as great as that of diatoms’. Dinoflagellates are occasionally responsible for harmful algal blooms known as “red tides.”
12.
Primary producers assemble carbon atoms from carbon dioxide into 6-carbon chains in the carbohydrate glucose. Primary productivity is expressed as amount of carbon fixed (bound into glucose) in the water column per square meter of surface per day ( gC/m 2 /day ).
13.
Researchers can count the atoms of carbon made into carbohydrates by “tagging” them using radioactive carbon atoms. This method is more accurate than the
“light/dark bottle” method also described in the text.
14.
Lack of light and lack of nutrients are especially limiting to phytoplankton productivity.
15.
Lack of iron is often limiting in the open ocean.
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16.
The most successful producers at the limit of the photic zone are cyanobacteria possessing pigments able to absorb the blue light present at these depths, and couple the energy of the light into bonds within the glucose molecule. Below the realm of photosynthesis exists a population of picoplanktonic chemosynthetic cyanobacteria now being investigated.
17.
At a certain depth, the production of carbohydrates and oxygen by photosynthesis through a day’s time will exactly equal the consumption of carbohydrates and oxygen by respiration. This break-even depth is called the compensation depth.
18.
Because they are not autotrophic (they don’t make food by photosynthesis or chemosynthesis), zooplankton have no compensation depth.
19.
Productivity in the tropics is generally low because of nutrient deficiency, and the north polar ocean suffers from slow nutrient turnover and low illumination, so the overall productivity prize goes to the temperate and southern subpolar zones.
20.
Water circulating in the great tropical gyres has abundant sunlight and CO
2
but is generally deficient in surface nutrients because the strong thermocline discourages the vertical mixing necessary to bring nutrients up from the depths.
The tropical oceans away from land are therefore often considered oceanic deserts nearly devoid of visible plankton.
21.
Plankton productivity is high in the temperate zone’s spring and summer months when upwelling near coasts has returned some nutrients to the surface and sunlight is readily available.
22.
Zooplankton are heterotrophs – organisms unable to synthesize food for their own use. Heterotrophs are dependent on autotrophs (primary producers; phytoplankton) for food.
23.
Holoplanktonic organisms spend their whole life cycle in the plankton community. Meroplankton spend only part of their lives (usually their juvenile stages) as plankton.
24.
The decomposition of falling biological debris and the activity of zooplankton can create a low-oxygen zone below the well-lighted surface zone. Oxygen depleted by the animals there is not replaced by phytoplankton.
25.
Algae is a collective term for autotrophs possessing chlorophyll and capable of photosynthesis but lacking vessels to conduct sap. Not all algae are seaweeds – diatoms and dinoflagellates are unicellular algae.
26.
Marine multicellular algae are classified in three divisions based on their pigments.
Accessory pigments in autotrophs greatly enhance photosynthesis because they absorb the dim blue light at depth and transfer its energy to the adjacent chlorophyll molecules. Red alga absorb blue light, and can live at the greatest depths.
27.
Angiosperms are vascular plants. Examples are sea grasses and mangroves.
28.
Seaweeds are the source of an important commercial product called algin. Its long, intertwining molecules are used to stiffen fabrics, make adhesives, suspend water and oil together in salad dressings, prevent the formation of gritty crystals in ice cream, clarify beer and wine, and manufacture shoe stains, soaps, and shaving cream.
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