Chapter 15.3 Oceanic Productivity

Marine organisms are connected through food production and consumption. Producers in the ocean are phytoplankton, larger algae, and bacteria. Consumers are crabs, clams, sea stars, fish, dolphins, and whales.

Primary Productivity Primary productivity is organisms making food substances using photosynthesis or chemosynthesis. Photosynthesis is using light energy to make glucose molecules. Chemosynthesis is using chemical energy to make glucose molecules.

2 factors influence an areas photosynthetic productivity: the availability of nutrients and the amount of sunlight. Primary producers need nutrients like nitrogen, phosphorous, and iron. Most primary producers will live where there are plenty of nutrients and sunlight.

Productivity in Polar Oceans Polar regions like the Arctic Ocean will experience periods of continuous darkness for about 3 months and then 3 months of continuous light. Because of this algae called diatoms peak in May. This is because the sun rises high enough to provide good light to the water. This leads to more zooplankton (they eat diatoms) There is a lot of nutrients that rise from deeper levels, so the limiting factor in polar areas on photosynthetic productivity is sunlight.

Productivity in Tropical Oceans Productivity is low in tropical regions. Light will penetrate much deeper here than in polar regions. Productivity is low because there is not mixing between surface water and nutrient-rich deeper water. There are not enough nutrients in surface water and then not enough sunlight in deep waters.

Productivity in Temperate Oceans A combination of sunlight and nutrient supply will limit productivity here. Seasons also affect the productivity greatly. Winter – low productivity due to lack of sunlight. There is plenty of nutrients during this time. Spring – There is more sunlight and nutrients during this time. The nutrients to eventually run out so that is the limiting factor during spring. Summer – The thermocline still does not allow the water to mix so nutrients are still the limiting factor to productivity during this time. Fall – The thermocline breaks down during this time so nutrients are readily available but there is less sunlight.

Oceanic Feeding Relationships Oceanic producers are marine algae, plants, and bacteria. These make food available for the consumers.

Trophic Levels Zooplankton are herbivores so they eat algae. Larger herbivores each larger algae and marine plants. Herbivores are eaten by carnivores. Each of the feeding stages is called a trophic level.

Transfer Efficiency The transfer of energy between trophic levels is inefficient. Usually only about 2% of the light energy absorbed by algae is changed into food for the herbivores.

Food Chains and Food Webs A food chain is a sequence of organisms through which energy is transferred. Food web shows many different ways animals eat or are eaten.