Chapter 14 Plankton, Algae, and Plants

1. Oceanography An Invitation to Marine Science, 7th Tom Garrison Chapter 14 Plankton, Algae, and Plants

2. Chapter 14 Study Plan • Plankton Drift with the Ocean • Plankton Collection Methods Depend on the Organism’s Size • Phytoplankton Are Autotrophs • Primary Productivity May Be Measured Using Radioactive “Tags” • Lack of Nutrients and Light Can Limit Primary Productivity • Production Equals Consumption at the Compensation Depth • Phytoplankton Productivity Varies with Local Conditions • Zooplankton Consume Primary Producers • Seaweeds and Marine Plants Are Diverse and Effective Primary Producers

3. Chapter 14 Main Concepts • Plankton drift or swim weakly, going where the ocean goes, unable to move consistently against waves or current flow. • Plankton is an artificial category; a category not based on a phylogenetic (evolutionary) relationship but rather on a shared lifestyle. • Phytoplankton are autotrophic—that is, they make their own food, usually by photosynthesis. Plankton productivity depends on largely on light and nutrient availability. • The ocean’s most productive phytoplankters are very small cyanobacteria working in a “microbial loop.” • Zooplankton – drifting animals – consume phytoplankton species (diatoms, dinoflagellates, coccolithophores), forming a food web that eventually supports larger animals like fish. • Not all producers are drifters. Seaweeds and mangroves are also important contributors.

4. Phytoplankton Are Autotrophs • What are the major types of phytoplankton? • Diatoms – the dominant and most productive of the photosynthetic plankton • Dinoflagellates – widely distributed single-celled phytoplankton; use flagella to move • Coccolithophores – small single-celled autotrophs • Picoplankton – this category encompasses most other plankton types, which are very small.

5. Plankton Drift with the Ocean (left) Representative plankton and nekton of the pelagic zone in the region of the subtropical Atlantic Ocean. Note the relative magnification of organisms in the plankton community. (right) Key. This stylized representation shows organisms to be much more crowded than they are in real life.

6. Plankton Collection Methods Depend on the Organism’s Size Pelagic organisms live suspended in seawater. They can be divided into two broad groups based on their lifestyle: The plankton drift or swim weakly, going where the ocean goes, unable to move consistently against waves or current flow. The nekton are pelagic organisms that actively swim. The standard plankton net is made of fine mesh and has a mouth up to 1 meter (3.3 feet) in diameter. The net is towed behind a ship for a set distance. The number of organisms present in the water can be estimated if the trapped organisms are counted and the volume of sampled water is known

7. Plankton Are Autotrophs The “official” food chain of larger planktonic organisms (green) contrasts with the “black market economy” of the microbial loop (red). Larger planktonic organisms are unable to separate the astonishingly small cyanobacteria and microscopic consumers from the water and so cannot utilize them as food.

8. Microbial loop vs “Official” food chain Microciliates microflagellates Zooplankton Cyanobacteria Phytoplankton Dissolved organic material; inorganic nutrients Fishes Decomposition, wastes Copepod Wastes, decomposition Diatom Dinoflagellate Prochlorococcus Synechococcus Stepped Art Fig. 14-5, p. 383

9. Primary Productivity May Be Measured Using Radioactive “Tags” The light-dark bottle technique for estimating marine primary productivity. Clear and opaque bottles are filled with water from the area to be studied. Pairs of bottles are lowered to depths at which 100%, 50%, 25%, 10%, 5%, and 1% of surface illumination is present, and photosynthesis and respiration are allowed to occur. Carbohydrate production by autotrophs in the bottles is measured by radioactively tagged bicarbonate ions added to each bottle. The difference in the quantity of carbohydrates in each pair of bottles over time gives an indication of the productivity at each depth, a depth at which carbohydrate production equals consumption.

10. Production Equals Consumption at the Compensation Depth What is the balance between respiration and photosynthesis at different depths? The compensation depth is the “break even” depth. Remember, many factors affect compensation depth; it is not fixed and will vary between locations and at different times of day. (right) Compensation depth and its relationship to other aspects of productivity. Note the position of the bottom of the euphotic zone.

11. Phytoplankton Productivity Differs with Latitude and Varies with the Seasons Variation in oceanic primary productivity by season and latitude. The area under each green curve (phytoplankton biomass) represents total productivity. (a) In the tropics, an intense thermocline prevents nutrient-rich water from rising to the surface. Productivity is low throughout the year. (b) In the northern temperate ocean, nutrients rising to the surface combine with spring and summer sunlight to stimulate a plankton bloom. (c) In the northern polar ocean, a high and thin productivity spike occurs when the sun reaches high enough above the horizon to allow light to penetrate the ocean surface.

12. Seaweeds And Land Plants Differ in Structure (a) The thallus (body) of a typical multi-cellular alga. These organisms can grow at a rate of 50 centimeters (20 inches) per day and reach a length of 40 meters (132 feet).

13. Seaweeds Are Classified by Their Photosynthetic Pigments • Some oceanic autotrophs are attached (remember, plankton are drifters). Attached autotrophs are forms of protists we commonly call algae, or seaweed. Seaweeds can be classified based on the type of pigments they have. • Chlorophytes are green due to the presence of chlorophyll and the lack of accessory pigments. • Phaeophytes are brown. They contain chlorophyll and the secondary pigment fucoxanthin. • Rhodophytes These seaweeds get their red color from the accessory pigments called phycobilins.

14. Seaweeds Are Classified by Their Photosynthetic Pigments Distribution of kelp beds and mangrove communities worldwide.

15. Marine Angiosperms Are Flowering Plants • Angiosperms are advanced vascular plants that reproduce with flowers and seed. Most angiosperms are found on land but a few species are found in ocean environments. • Sea grasses are found on the coasts. Their seeds are distributed by water. Sea grasses are very productive as compared to phytoplankton. • Mangroves are found in sediment rich lagoons, bays and estuaries. Mangroves also have distinctive roots that provide anchorage, trap sediment and protect small organisms.

16. Chapter 14 in Perspective In this chapter you learned that organisms that drift in the ocean are known collectively as plankton. Bacteria and cyanobacteria, along with larger single-celled plantlike organisms like diatoms and dinoflagellates, are collectively called phytoplankton and are responsible for most of the ocean’s primary productivity. (The larger marine producers we call seaweeds, and relatively simple organisms that depend on chemosynthesis account for most of the rest.) Phytoplankton – and zooplankton, the small, drifting or weakly swimming animals that consume them – are the first links in most oceanic food webs. Plankton are most common along the coasts, in the upper sunlit layers of the temperate zone, in areas of equatorial upwelling, and in the southern sub-polar ocean. Planktonic cyanobacteria are often present in astonishingly high numbers, especially in areas such as the tropics that lack adequate nutrients for the larger phytoplankters. Many physical and biological factors influence marine primary productivity, the most important being the availability of light and inorganic nutrients. Worldwide oceanic productivity almost certainly exceeds land productivity, but a much smaller mass of producers is responsible for productivity in the ocean than on land—marine producers are considerably more efficient in assembling glucose molecules. The larger producers informally known as seaweeds are classified by color (that is, pigment composition) into three large groups: green, brown, and red algae. Some forms of brown algae, which we call kelp, grow in great underwater forests. Note that not all large marine autotrophs are algae; some are plants – sea grasses and mangroves. In the next chapter you will learn more about the world of marine heterotrophs – animals. Freed from the need to make their own food, animals have evolved astonishing adaptations for grazing, predation, and parasitism.