Chapter 14: Primary Productivity Insert: Textbook cover photo Plankton, Plants and Algae Insert: Textbook cover photo

Chapter 14 Study Plan Plankton Drift with the Ocean Plankton Collection Methods Depend on the Organism’s Size Most Phytoplankton Are Photosynthetic Autotrophs Measuring Primary Productivity 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

Chapter 14 Six 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 fishes. Not all producers are drifters. Seaweeds and mangroves are also important contributors.

Plankton Drift with the Ocean 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. (RIGHT) 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.

Plankton Drift with the Ocean 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.

Plankton Drift with the Ocean Autotrophic plankton that generate glucose by photosynthesis, the primary producers, are generally called phytoplankton. Phytoplankton are critical to all life on Earth because of their great contribution to food webs and their generation of large amounts of atmospheric oxygen through photosynthesis. Planktonic autotrophs are thought to bind at least 50 trillion kilograms of carbon into carbohydrates each year, roughly 50% of the food made by photosynthesis on Earth!

Most Phytoplankton Are Photosynthetic Autotrophs Major types of phytoplankton? Picoplankton – this category encompasses most other plankton types, which are very small. 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.

Most Phytoplankton Are Photosynthetic Autotrophs Picoplankton: 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.

Most Phytoplankton Are Photosynthetic Autotrophs Diatoms Apart from cyanobacteria, the most productive photosynthetic organisms in the plankton are the diatoms. Diatoms have transparent silica frustules that allow for both protection and light penetration into the cell. Diatoms store energy as fatty acids and oils, compounds that are lighter than their equivalent volume of water and assist in flotation. When diatoms die, their valves fall to the seafloor to accumulate as layers of siliceous ooze. (RIGHT) Photographs of various diatoms.

Most Phytoplankton Are Photosynthetic Autotrophs Dinoflagellates The majority of dinoflagellates live free in the water. Most have two whiplike projections, called flagella. One flagellum drives the organism forward, while the other causes it to rotate in the water. A few common species of dinoflagellates are bioluminescent. Some species are responsible for Harmful Algal Blooms, sometimes referred to as a “red tide”.

Most Phytoplankton Are Photosynthetic Autotrophs Coccolithophores (TOP RIGHT) Coccolithophores are covered with disks of calcium carbonate (coccoliths) fixed to the outside of their cell walls. Coccoliths can build seabed deposits of calcareous ooze. (BOTTOM RIGHT) The coccoliths (not the organic cells themselves) act like mirrors suspended in the water and can reflect a significant amount of the incoming sunlight. The reflectance from the blooms can be picked up by satellites in space.

Production Equals Consumption at the Compensation Depth Autotrophs also respire as they photosynthesize - they use some of the carbohydrates and oxygen they produce. Carbohydrate production usually exceeds consumption, but not always. The compensation depth is the “break even” depth. (RIGHT) Compensation depth and its relationship to other aspects of productivity. Note the position of the bottom of the euphotic zone.

Phytoplankton Productivity Varies with Local Conditions Variation in oceanic primary productivity by season and latitude. In the tropics, an intense thermocline prevents nutrient-rich water from rising to the surface. Productivity is low throughout the year. In the northern temperate ocean, nutrients rising to the surface combine with spring and summer sunlight to stimulate a plankton bloom. 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.

Zooplankton Consume Primary Producers Heterotrophic plankton are collectively called zooplankton. The mass of zooplankton is typically about 10% that of phytoplankton. Most zooplankton spend their whole lives in the plankton community, so we call them holoplankton. (TOP RIGHT) Copepod. Some planktonic animals are the juvenile stages of crabs, barnacles, clams, sea stars, and other organisms that will later adopt a benthic or nektonic lifestyle. They are known as meroplankton. (BOTTOM RIGHT) Larval sea urchin.

Seaweeds And Land Plants Are Diverse and Effective Primary Producers Between 1% and 5% of the ocean’s primary productivity is carried out by the large marine multicellular algae we informally call seaweeds. Seaweeds are technically not plants. They are different enough from vascular plants to be classified as protistans. Seaweeds are nonvascular and do not need the bundles of conductive vessels that plants require to transport CO2, water, nutrients, and sunlight to make carbohydrates. Seaweeds occur in a great variety of sizes and shapes.

Seaweeds And Land Plants Are Diverse and Effective Primary Producers 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). Macrocystis. This fast- growing, alga is one of the common kelp forest species of western North America.

Seaweeds And Land Plants Are Diverse and Effective Primary Producers 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.

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. (TOP) Mangroves are found in sediment rich lagoons, bays and estuaries. Mangroves also have distinctive roots that provide anchorage, trap sediment and protect small organisms. (BOTTOM)

Seaweeds And Land Plants Are Diverse and Effective Primary Producers Distribution of kelp beds and mangrove communities worldwide.