Lesson: Primary Production

Transcription

1 Lesson: Primary Production By Keith Meldahl Corresponding to Chapter 14: Primary Producers Microscopic phytoplankton -- tiny single-celled plants that float at the ocean s surface, are the ultimate food source for most life in the sea. This picture shows some of phytoplankton as well as zooplankton -- small animals that eat phytoplankton.

2 Summary of Important Concepts Primary producers, also called autotrophs, are organisms that use photosynthesis to capture the Sun s energy and use it to synthesize glucose. Through photosynthesis, primary producers generate food for all other forms of marine life: a process called primary production. Primary producers include phytoplankton, algae, and marine plants. Organisms that cannot synthesize glucose are called heterotrophs. They must consume autotrophs or other heterotrophs for food. All marine animals are heterotrophs. Feeding relationships between organisms resemble webs, with different organisms feeding at different trophic levels, depending on what is available as a food source. Primary production varies from place to place in the oceans, and varies with the seasons, mostly as a function of the availability of light and chemical nutrients.

3 Summary of Important Concepts, continued The most important primary producers in the oceans are the phytoplankton: single-celled photosynthesizing organisms that float and drift near the ocean surface, in the euphotic zone; the region of enough sunlight for photosynthesis. Zooplankton are animal consumers of phytoplankton or other zooplankton. Some zooplankton spend their entire lives floating and drifting. Other zooplankton are animals that spend only the early stages of life this way, and later either settle to the sea floor or become active swimmers. Multicellular algae and plants are important primary producers in many coastal areas.

4 Capture and Flow of Energy Most of the energy used by marine organisms to make food comes from the sun. Photosynthesis is the process used by most producers to convert the sun s energy to food energy. Organisms that are capable of photosynthesis are called primary producers. Photosynthesis is represented by this chemical equation: 6 CO H 2 O --> C 6 H 12 O O 2 In photosynthesis, 6 molecules of carbon dioxide (CO 2 ) and 6 molecules of water (H 2 O) are converted, using the Sun s energy, to 1 molecule of glucose (C 6 H 12 O 6 ), with 6 molecules of oxygen (O 2 ) given off as a waste product. The glucose molecule represents carbohydrates: the basic building block of living things. Thus photosynthesis makes two things essential for all life: FOOD and OXYGEN!

5 Capture and Flow of Energy The flow of energy through living systems. Energy flows from the Sun to producers, who capture it and use it to grow and reproduce, forming food for consumers.

6 The Cycling of Matter The cycling of matter through living systems. Unlike energy, which flows one-way from producers to consumers, the materials that make up living things are recycled back and forth.

7 Feeding (Trophic) Relationships What terms are used to describe feeding relationships? Autotrophs organisms that make their own food, and are also the ultimate food source for all other life. Also called primary producers or simply producers. Producers include all plants and phytoplankton, and some bacteria. Heterotrophs - organisms that must consume other organisms for energy. Heterotrophs include all animals, as well as fungi and most bacteria. Trophic pyramid - a model that describes who eats whom Primary consumers - these organisms eat producers Secondary Consumers - these organisms eat primary consumers Top consumers - the top of the tropic pyramid

8 Feeding (Trophic) Relationships Feeding relationships of different autotrophs and heterotrophs can be illustrated by a trophic pyramid. In most trophic pyramids there is roughly a 10-fold decrease in biomass (the total abundance of organisms at each level) going from one trophic level up to the next.

9 Feeding (Trophic) Relationships Another way to illustrate feeding relationships is a food web. This food web shows the main trophic relationships in a typical marine community, from primary producers (bottom) to top consumers (top).

10 Primary Productivity Primary productivity is the synthesis of organic material from inorganic substances. Most primary productivity occurs through photosynthesis, which as we have seen, involves the synthesis of glucose from water, carbon dioxide, and the Sun s energy. Glucose is a carbon-based molecule. (Recall its chemical formula is C 6 H 12 O 6 ). As such, we can measure primary productivity in grams of carbon bound into organic material per square meter of ocean surface per year, or: gc/m 2 /yr

11 Primary Productivity This figure illustrates the concept of measuring oceanic productivity in gc/ m 2 /yr. The diatom illustrated is one of several kinds of important phytoplankton -- singled-celled photosynthesizing primary producers

12 Primary Productivity Recent studies suggest that average ocean primary productivity is between 75 gc/ m 2 /yr and 150 gc/ m 2 /yr.however the amount of productivity varies widely, as shown in this figure. Some marine communities, such as coral reefs and kelp beds are exceptionally productive.

13 Factors That Limit Productivity Primary productivity requires FOUR basic components: Water Carbon dioxide Inorganic nutrients Sunlight Since water and carbon dioxide are in good supply in the ocean, the factors that usually limit primary productivity are availability of inorganic nutrients and availability of sunlight. The next slide illustrates some examples of the effects of nutrient availability and sunlight availability on primary production.

14 Factors That Limit Productivity This figure shows us that productivity is very low in the tropical oceans all year long. How can this be? There is abundant sunlight in the tropics! But in fact, that s the problem. The Sun heats the ocean surface, creating a strong thermocline, with warm water on top of cold water. The cold water down below contains many nutrients, but these cannot get up to the surface because of the thernocline. Thus tropical oceans tend to have low primary production.

15 Factors That Limit Productivity This figure also shows us that productivity is very high in the north polar areas during a short period of time in the height of the northern hemisphere summer. In the polar regions, the water is cold from the surface on downward. There is no thermocline, and therefore the water is well-mixed with plenty of nutrients. However there is only abundant sunlight during the summer, and so productivity peaks in the summer, and is practically non-existent the rest of the year.

16 Plankton Plankton are organisms that float and drift with the ocean currents. Plankton consist of many species, some of which are autotrophs and some of which are heterotrophs. Scientists collect and study plankton using fine mesh nets called plankton nets.

17 Plankton PLANKTON means any organism that floats and drifts in the ocean. Planktonic organisms can be divided into: Phytoplankton -- plankton that photosynthesize. Zooplankton -- heterotrophs that consume phytoplankton or other zooplankton.

18 Phytoplankton MAJOR TYPES OF PHYTOPLANKTON: Diatoms - widely distributed single-celled phytoplankton; contain a rigid internal shell (frustule) made of silica. Dinoflagellates - widely distributed single-celled phytoplankton; use a flagella to move; many forms are bioluminescent. Coccolithophores and silicoflagellates Nanoplankton and picoplankton - this category encompasses most other types of plankton, which are very small.

19 Phytoplankton Because they require sunlight, phytoplankton are limited to the euphotic zone: the uppermost 70 meters (230 feet) or so of the water column. This is the region in which enough sunlight penetrates to have photosynthesis.

20 Zooplankton are heterotrophs that float and drift, and consume either phytoplankton or other zooplankton. These krill are a very abundant type of zooplankton. Zooplankton Zooplankton can be divided into two categories: Holoplankton -- organisms that spend their entire lives as zooplankton. Examples include krill and copepods. Meroplankton -- organisms that are zooplankton temporarily, during the larval life stage. Later in their development they become either active swimmers, or settle to live on the sea bed.

21 Larger Marine Producers: Algae Most primary productivity in the oceans comes from phytoplankton. However in coastal areas large, multicellular algae are also important producers. Algae producers are commonly called seaweeds. Seaweeds can be classified based on the type of pigments they use in photosynthesis. These pigments give different seaweeds different colors. 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 as an accessory pigment. Rhodophytes get their red color from the accessory pigment called phycobilius.

22 Larger Marine Producers: Algae The kelp in this figure is an example of a Phaeophyte. Kelp attaches to the bottom by a strong holdfast, and reaches lengths well in excess of 100 feet. It is a common algae in shallow coastal waters along the Pacific Coast of North America. Rhodophytes -- the red algae -- can be encrusting (growing as sheets or layers) or standing erect. This group contains most of the world s species of seaweeds. Rhodophytes can grow in dimmer light, and thus at greater depths, than other types of seaweeds.

23 Larger Marine Producers: Marine Angiosperms Angiosperms are advanced vascular plants that reproduce with flowers and seed. Most angiosperms are found on land but a few species are found in the ocean. Sea grasses are found on many coasts. Unlike plants on land, their pollen is distributed by flowing water, rather than by wind or insects. Mangroves are found in sediment rich lagoons, bays and estuaries along tropical and subtropical coasts.

24 Larger Marine Producers This figure shows the distribution of two common communities of larger marine producers: kelp beds and mangroves.