Phytoplankton are microscopic algae that are the primary producers in coastal and marine ecosystems. They use sunlight to convert carbon dioxide and water into glucose and oxygen through photosynthesis.

Upwelling is the process by which nutrient-rich water from the deep ocean is brought to the surface. This process is driven by winds and ocean currents, and it is essential for the productivity of coastal and marine ecosystems.

Sea otters are a keystone species in coastal and marine ecosystems because they prey on sea urchins. Sea urchins graze on kelp, and if sea otter populations decline, sea urchin populations can increase, leading to a decline in kelp forests. Kelp forests provide habitat and food for a variety of other species, so the decline of kelp forests can have a cascading effect on the entire ecosystem.

Coral recruitment is the process by which new coral colonies are formed. This occurs when coral larvae settle on a hard substrate and begin to grow. Coral recruitment is essential for the maintenance and growth of coral reefs.

Climate change, overfishing, and pollution are all major threats to coastal and marine ecosystems. Climate change is causing ocean temperatures to rise, which is leading to coral bleaching and the loss of coral reefs. Overfishing is reducing the populations of fish and other marine animals. Pollution is entering coastal and marine ecosystems from a variety of sources, including sewage, agricultural runoff, and industrial waste.

Trophic transfer is the process by which nutrients are transferred from one organism to another through a food chain. This occurs when an organism consumes another organism and absorbs the nutrients that were stored in the consumed organism's body.

Coral and zooxanthellae have a mutualistic relationship. Coral provide zooxanthellae with a protected environment and access to sunlight, while zooxanthellae provide coral with food through photosynthesis.

Decomposition is the process by which nutrients are released from dead organisms into the environment. This process is carried out by decomposers, which are organisms that break down organic matter into simpler compounds.

Sea turtles and remoras have a commensal relationship. Remoras attach themselves to sea turtles and feed on the scraps of food that the sea turtles leave behind. The sea turtles benefit from the remoras because the remoras help to clean their skin and remove parasites.

Oligotrophication is the process by which nutrients are lost from coastal and marine ecosystems. This can occur through a variety of processes, including nutrient uptake by plants and animals, denitrification, and nitrogen fixation.

Sea lice, mistletoe, and dodder are all examples of parasites. Sea lice attach themselves to salmon and feed on their blood. Mistletoe attaches itself to trees and steals their nutrients. Dodder attaches itself to plants and steals their water and nutrients.

Nitrogen fixation is the process by which nutrients are converted from inorganic forms to organic forms. This process is carried out by nitrogen-fixing bacteria, which convert atmospheric nitrogen into ammonia.

Sharks and seals have a predator-prey relationship. Sharks prey on seals, and seals are a major food source for sharks.

Weathering is the process by which nutrients are released from rocks and minerals into the environment. This process can be caused by a variety of factors, including wind, water, and temperature changes.

Barnacles and mussels have a competitive relationship. Both species attach themselves to rocks and other hard surfaces, and they compete for space and food.