Chapter 3 Phytoplankton Most primary production in the sea is accomplished by phytoplankton–unicellular, photosynthetic organisms. Hence, marine primary producers are fundamentally different from terrestrial producers.

Phytoplankton Groups Most common phytoplankton are from 3 divisions in two kingdoms, – Monera – and Protista.

Phytoplankton Groups

Cyanobacteria –Cyanobacteria have been producing oxygen in the sea for more than three billion years. Today they are everywhere, from intertidal rocks and estuaries to coral reefs and the open sea. Species capable of nitrogen fixation commonly form symbiotic associations with a variety of marine organisms.

Phytoplankton Groups Fig. 3.3 A transmission electron micrograph of a marine cyanobacterium, Synechoccus. (Courtesy of C. Osilin)

Phytoplankton Groups Chrysophyta –Division Chrysophyta is represented in the sea by nanoplanktonic coccolithophores and silicoflagellates and diatoms that can be macroscopic.

Phytoplankton Groups Fig. 3.6 SEM of three coccolithophore cells, each showing clearly their dense coverings of coccoliths. ( Courtesy of F. Reid) Chrysophyta

Phytoplankton Groups Chrysophyta –Diatoms, often the most important members of cold-water phytoplankton communities, occur in a large variety of shapes, sizes, and locations.

Phytoplankton Groups Fig An SEM view of Thalassiosira, a coastal diatom, clearly showing the epitheca, hypotheca, and a connecting girdle of cell wall material. ( Courtesy of G. Fryxell ) Chrysophyta

Phytoplankton Groups Fig Several common types of temperate-water planktonic diatoms. (Courtesy of F. Reid & K. Lang. ) Chrysophyta

Phytoplankton Groups Dinophyta –Dinophytes dominate warm-water phytoplankton communities and are unique in their abilities to create light via bioluminescence and powerful toxins that become deadly via the phenomenon of biological magnification.

Phytoplankton Groups Fig SEMs of some common marine dinophytes (Courtesy of E. Venrick & F. Reid) Dinophyta

Phytoplankton Groups Other Phytoplankton –With improving technology, our understanding of and nano-, pico-, and ultraplanktonic species is increasing each year. –These include additional classes of Chrysophyta and members of the division Chlorophyta

Adaptations for a Planktonic Existence Phytoplankton confront a persistent dilemma in that they must remain in the photic zone, yet nutrients occur in much greater concentrations near the seafloor. Most of their adaptations are responses to their need to linger near the surface while accumulating nutrients that are in extremely short supply.

Adaptations for a Planktonic Existence Size –An extremely small cell diameter provides most phytoplankton with a relatively high surface area-to-volume ratio. This attribute increases frictional resistance to sinking and enables efficient uptake of very dilute nutrients.

Adaptations for a Planktonic Existence Size

Adaptations for a Planktonic Existence Size Fig With increasing size (a, b) the ratio of surface area to volume decreases, unless the larger structure (c) remains subdivided.

Adaptations for a Planktonic Existence Sinking Fig Sinking patterns of the elongate diatom, Rhizosolenia (top), and the spiral chain-forming diatom, Asterionella (bottom)

Adaptations for a Planktonic Existence Adjustments to Unfavorable Environmental Conditions Fig Inactive resistant stages of two species of Chaetoceros.

Primary Production in the Sea Measurement of Primary Production –Estimation of gross and net primary production is necessary for understanding production potentials of and the quantity of organics available to marine communities. –Such estimates have been made for nearly 100 years, starting with light-and-dark-bottle techniques and culminating with modern remote sensing via satellites.

Primary Production in the Sea Measurement of Primary Production Fig The results of a hypothetical light- and dark-bottle experiment.

Primary Production in the Sea Fig This phytoplankton bloom along the California coast, was imaged by SeaWiFS on August, 2003 for true color (left) and for chlorophyll a concentrations.

Primary Production in the Sea Factors that Affect Primary Production –Grazing. Small herbivorous grazers routinely occur at such high concentrations that phytoplankton communities may be destroyed over a period of just a few weeks.

Primary Production in the Sea Fig Generalized population changes of a prey species and its predator, oscillating between unlimited (solid) and limited (dashed) phases of population growth. Factors that Affect Primary Production  Grazing.

Primary Production in the Sea Fig Fate of sunlight as it enters sea water. The violet and red ends of the visible spectrum are absorbed first. Factors that Affect Primary Production  Light in Water.

Primary Production in the Sea Factors that Affect Primary Production –Light in water. Light is necessary for all photosynthetic organisms, yet it occurs at sufficient intensity only in the relatively shallow photic zone. Consequently, accessory photosynthetic pigments (such as fucoxanthin) are more important in marine producers than terrestrial plants.

Primary Production in the Sea Factors that Affect Primary Production Fig Patterns of light absorption for three photosynthetic pigments: phycoerythrin, fucoxanthin, and chlorophyll a. (Adapted from Saffo, 1987.)  Light in Water.

Primary Production in the Sea Factors that Affect Primary Production Fig Distribution of dissolved silicate, nitrate, and phosphate in the Atlantic and Pacific oceans. (Adapted from Sverdrup, Johnson, and Fleming 1942.)  Nutrient Distribution.

Primary Production in the Sea Factors that Affect Primary Production –Nutrient Regeneration. Marine producers rely on a number of mechanisms of nutrient regeneration, such as turbulent mixing, convective mixing, and upwelling.

Primary Production in the Sea  Nutrient regeneration Fig Seasonal growth and decline of thermoclines in tropical (top), temperate (center), and polar (bottom) ocean waters.

Primary Production in the Sea Factors that Affect Primary Production –Nutrient Regeneration. Fig Coastal upwelling in the Northern Hemisphere.